TinyRC.com - Blogs http://tinyrc.com/forums/blog.php This is a discussion forum powered by vBulletin. To find out about vBulletin, go to http://www.vbulletin.com/ . en Sun, 05 Feb 2012 13:55:00 GMT vBulletin 360 http://tinyrc.com/forums/images/misc/rss.jpg TinyRC.com - Blogs http://tinyrc.com/forums/blog.php Box Stock Mini-Z Tuning http://tinyrc.com/forums/blog.php?b=290 Tue, 31 Jan 2012 23:42:29 GMT Box Stock is a Mini-Z racing class getting popular nowadays because of its low entry cost for serious racing action -- anyone can go out and buy an... Box Stock is a Mini-Z racing class getting popular nowadays because of its low entry cost for serious racing action -- anyone can go out and buy an MR-02EX for $180, put in some AAA's and off you go! It also appeals to veteran racers because of the potential for even-performance racing: in theory, no one racer will have the advantage of the part-of-the-day cutting-edge upgrade, everyone will gravitate to the same gear ratio, same motor, same everything.

But of course, this is my technical blog we're talking about. ;) There are things we can do to a "Box Stock" car to make the car more enjoyable and predictable to drive, and therefore better. In keeping with the spirit of most Box Stock rulesets, I'm not talking about tweaking motors to make them faster or making the spec tires stickier via special truing tricks. These tweaks are simply going to turn a decent Box Stock car -- in my case, a FOB (fresh out of box) MR-03W-MM -- into a smooth-driving, beginner-friendly car suitable for battling other FOB Mini-Z's in one of the closest racing classes I've ever partaken in. :) I apologize for the lack of pictures in this post btw, but at least these tips aren't really requiring of detailed diagrams.


Step 1: Wheels and tires.

Depending on the track, tire tape and truing wheels and tires may be allowed to get the cars operating within a comfortable performance bubble (decent steering and no traction rolling). Almost no track owner I know of complains about taping the tires -- it's a simple matter of helping keep the cars right-side up. When truing is allowed on top of taping, I recommend cutting the tires down to something smaller but reasonable, say like 23.5mm. Truing too small is unnecessary (this isn't Mod racing) but not truing at all sometimes leaves the car too high = traction rolling. My Box Stock car runs at RC Kenon with a spec tire package, so I have trued the front PN Slick 25's to 23mm. My PN Radial 8's in the rear are not trued, just left as is. No traction problems even after several weeks thanks to the weak stock 70t motor.


Step 2: Run in the motor and bushings.

Sometimes Box Stock classes will allow for bearings to replace the stock bushings, and in those cases, that's fine. But sometimes they don't -- and in those cases that's still fine because the stock Kyosho bushings are surprisingly smooth once run in correctly. :) The procedure isn't rocket science -- pop those bushings into your stock wheels with mounted tires, and spin spin spin! I don't like to use polish with plastic bushings just because I might not be able to wash it all out, leading to eventual wear and slop. Just hone out the bushings a little bit with a natural break-in process. In the rear, I recommend gently running in the rear axle bushings and the motor on the bench: put the car on a stand and hold full throttle for 10-15 minutes or so. This break-in process helps the car run smooth and fast the very first time it hits the track.


Step 3: Check other sources of binding.

With Kyosho's build qualities, typically the only other source of binding is on the older MR-02 chassis, at the front kingpin suspension. Try to work the suspension up and down to free it up, but if that doesn't work then polishing the kingpins in a dremel will be the final solution. I also recommend flipping the spring perches such that they rest against the top of the chassis' "arms" -- a much smarter setup than stock, where the perches slid up and down the kingpins. Luckily, the MR-03 comes with very smooth kingpins and suffers no such issue.


Step 4: Lower the front.

Tuning theory as covered by myself and many others teaches that a little rake towards the front increases steering, and with no rear traction issues to worry about, a little more steering means faster. The MR-03 front suspension comes with one shim above the knuckles and one shim below -- move both shims below the knuckles to drop the front end about 0.3mm. At the same time (not applicable for all bodies), MR-03 chassis kits and readysets should come with an extra pair of shims: rules allowing, I like to lower the front clip with these (good for another ~0.6mm I believe) to add just a little more rake to the setup. For the MR-02 or 02EX chassis, it's possible to lower the front ride height by removing the preload shims on the front springs. You may or may not be able to get away with gluing them to the underside of the knuckle to use as lowering spacers. :D


Step 5: Add a little damping.

Some tracks will not allow this, but I would push for it as it makes all Box Stock Mini-Z's ten times more enjoyable to drive. With the exception of the unfortunate RML (Rear Mount -- Low) chassis configuration, all MR-02's and 03's come with a top spring in a crude tube damper assembly. Shove a significant quantity of thick diff grease (think Kyosho 30,000wt thick!) into this top shock, and you will have sufficient damping to significantly smooth out the rear end of your Box Stock car, making it a lot more predictable in corner entries as well as high speed corners. This makes the biggest difference for experienced drivers I think as we can see the chatter and intrinsically want it gone -- but for any driver of any skill level, eliminating the chatter makes the car more obedient to commands and IMO generally improves the racing action.

If you want to take this trick to its logical conclusion, then you can achieve roll damping too to complement the bump damping you just implemented. Pop the metal ball out of the end of your top shock, and find the thickest, heaviest industrial grease that you can get your hands on. Slather this grease around the inside of the plastic ball joint before popping the metal ball back in, then roll the ball around a bit to distribute the grease. Attach the shock back to your stock motor pod and notice that there's now a tiny bit of damping action when you roll the pod. Even that tiny bit of damping will reduce the chatter you get from these cars and improve corner speed just a tiny bit. ;)


With these little tweaks, my Box Stock MR-03 GT-R is not the fastest in a straight line, nor does it have the most turn-in steering compared to its competitors, but it is without a doubt the smoothest-driving car in the field and allows its driver to push it hard. At a recent club race at RC Kenon we held a hot lap challenge for the Box Stock class cars, and while most of the hot laps being laid down were in the 10.6xx and 10.7xx range, I was able to push my little GT-R to a single 10.0xx hot lap, turning in early, maintaining corner speed and not being afraid to lay on the throttle VERY early. That's really all it took, just five very slight changes to the car, fully allowed at Kenon, that took off more than half a second from the car's lap potential.

My final point in writing this post is that Box Stock class is a fine class for beginners, in that no tuning is expected, but at the same time it's the best environment to introduce the concept of competitive tuning -- here are the very limited areas that you can modify on your car, go play! -- without being overwhelming. Not only does doing so prime casual hobbyists for more involved and technically challenging racing, but it also educates, teaching basic mechanical sense and (hopefully) inspiring a "tinkering spirit" in a fun package deal. As such, I'm a big proponent of the class and I look forward to helping as many new racers as possible dial in their Box Stock cars and have an enjoyable experience their first time in Mini-Z. :) ]]> color0 http://tinyrc.com/forums/blog.php?b=290 The Super GT Wall Handling Problem: Solved! http://tinyrc.com/forums/blog.php?b=288 Wed, 18 Jan 2012 23:34:17 GMT As tinkerer first and a racer second, I don't like admitting that the Mosler MT900 is the fastest and only competitive body at the top levels of Mini-Z racing. I admit it's fast: with great corner speed, on-throttle stability and superb wall handling, I'm not surprised that the PN Worlds this past year was contested almost entirely of Moslers. But on the other hand, the Super GT Nissan GT-R and Honda HSV-010 have a little less stability but noticeably more corner speed: whenever I put them back-to-back against the Mosler, the Mosler always wins overall but the GT-R/HSV's fast lap will be up to 2 tenths faster! This discrepancy almost always comes down to wall handling.

Simply put, the GT-R and HSV suck at it. Just take a look at their huge front splitters (image borrowed from Kyoshosan):



The splitter can literally cut through RCP rail foam if you go in hard enough, and so the HSV and GT-R can not ever touch the wall if you want to go fast. The problem seems to be bad enough that Kyosho released bumpers for these bodies, but this doesn't help because the bumpers still have sharp corners, and the bumper truncates early, leaving the wheels still unprotected if you're trying to run wider offsets up front (+3N, etc.) to avoid traction rolling.

The older method that has been explored thoroughly is cutting off the splitter entirely:



Which works -- the body does glide off the walls better -- but considerably weakens the front bumper and reduces the protection of the front wheels (doing this forced me to run +1.5N maximum up front rather than the stock +2N offset). Within just a few races of cutting off the splitter I cracked that GT-R from the ground all the way up through the headlight, shattering the lens! So that's a no go.

Now I think I've discovered (or rediscovered, as the technique isn't new) the ticket to success with the GT-R and HSV, which is the Kyosho clear bumper intended for the Mazda 787 (MZN303-4). It's just the right length and width, and it has rounded corners! Exactly what I've been looking for. The modifications are fairly simple to get it working: I cut off the rear mounting points to shorten the clear bumper, letting me use the front mounting points to bolt it to the MR02/03's extra holes up front.



I notched the clear bumper just inside the outside edge to make some clearance for the front tires when steered. I drilled out the mounting holes in the 03 chassis, then used 2 countersunk 8mm screws and 4 PN blue metal shims (2 per side) to attach. The 2 shims lined up the clear bumper perfectly even with the bottom of the chassis -- you can go higher or lower depending on your preferences.



The PN interchangeable front clip doesn't play well with the gusseting on the bumper so I shaved it off. Next I turned the bumper into a bona fide splitter by cutting out the center section. I smoothed out all the edges (just in case) with 1000 grit sandpaper.



Next: because I didn't want to raise my body, I cut off the front splitter and then shaved the front bumper upwards to compensate for the height of the clear bumper/splitter. It's about 1.5mm worth, you may consider cutting a little more if you find that you can't pop the body on without dangerously bending the clear bumper.



At this point I popped the body on (carefully) to check ground clearance and body clearance. The GT-R's front bumper touches the clear bumper at the front grill area but neither is stressed or bent -- good. This gives a good aero seal without threatening to break anything. I shaved the GT-R's front bumper a little further upwards on the sides to give the clear bumper a little room (~1mm) to bend up in a collision. Ground clearance is perfect, 1.5mm and the splitter lies flat. It also truncates later to protect the wheels better than Kyosho's GT-R/HSV-specific front bumper. Everything's looking good so far!



The bumper/splitter has the perfect shape to glide off walls like an F430. Which is excellent, because the F430 is even better off walls than the Mosler we're trying to catch up to.



It's also wider than the GT-R by about 1.5mm each side, so I can turn to almost my full steering travel (74%) with +3N front wheels and still protect the wheels! With +2N fronts (stock offset) you would be able to use 100% steering travel with absolutely no fear.



And you can see that the clear bumper re-forms a nice short splitter under the front bumper, for downforce. Theoretically the flat underside will also generate downforce through the "venturi effect", but that will have to be tested later.



Initial testing around the dorms has been super promising! The car glances off walls even when the wheels are steered towards it, so wheel protection: check! lfsminiz on the forums has confirmed that the bumper does in fact help on RCP rails, presuming that you don't misjudge the turn TOO badly lol.


So, assuming I don't break anything in the first race, I believe I've successfully tackled the Super GT wall handling problem! I'll cut an HSV the same way too to test: since the HSV has a shorter nose than the GT-R it would be safe to assume that more front splitter area will be exposed = even more downforce! We'll see soon. ^_^ ]]> color0 http://tinyrc.com/forums/blog.php?b=288 The Penny Drop (or Quarter/Dime/Spur...) http://tinyrc.com/forums/blog.php?b=286 Sun, 15 Jan 2012 20:02:40 GMT Today, a quick and simple test for tweak brought to you originally by the 1/12 pan car crowd: the penny drop test. Basically, it's a really easy way to see if your chassis is places equal weight on the rear tires, so long as your front end is already guaranteed even.

Why that last sentence is so: The penny drop test can only tell you if the car is overall tweaked -- it cannot tell you which part. So if your front end is tweaked but your rear end is fine, or your front end is fine but your rear end is tweaked, this test returns the same result. For most of us Mini-Z owners (barring those with double A-arm suspension), the front ends are only adjustable with shims, so once you get that visually even, the front end is "just about" even and we're going to assume it's no longer tweaked. And under that assumption, we can use the penny drop test to figure out the rear. So, here's the setup:



I use spur gears because I have spurs but not pocket change. :p Anyways, lay your spurs across the front tires, not flat, since you actually want them to roll off the wheel the instant the tire leaves the ground. Then you stick a sharp object underneath the car at its centerline and lift up the front end like so:



And if you see that, it means your rear left wheel is pushing down harder than the rear right, causing the front right wheel to lift first. A quick adjustment with shims (if you run disk damper) or spring collar (if you run tri-shock) and you should get the two spurs falling simultaneously on your next try:



There you go! No more tweak. Again though, this is only going to tell you if the chassis alone is mechanically sound -- once you've got this test out of the way, if your car is still driving like it's tweaked, then you need to start looking at the other possibilities: tire issues, body issues, drivetrain/bearing issues, etc. etc. Sometimes the way the track is will make the car feel tweaked as well, and in those cases, you just gotta use your best judgment and perhaps even deviate from what was perfect on the bench. I often purposely tweak a little to the right for clockwise tracks, and vice-versa. Whatever works, is whatever works. :) Have fun!

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Next week: I've solved the Super GT wall handling problem! An aerodynamic solution that will give you more front downforce while allowing you to run +3N front wheels on your GT500 GT-R/HSV body AND protecting its fragile front end at the same time! ]]> color0 http://tinyrc.com/forums/blog.php?b=286 MR03 Chassis Swap (or Why I Hate the 03 Sometimes) http://tinyrc.com/forums/blog.php?b=285 Fri, 30 Dec 2011 05:44:22 GMT Hope everyone had a merry Xmas! Just about 1.5 weeks ago I went to Inside Line Racing for their last points series race, and managed to come home... Hope everyone had a merry Xmas!

Just about 1.5 weeks ago I went to Inside Line Racing for their last points series race, and managed to come home 3rd in Expert Modified, not saying much though as there ended up only being 4 cars in the running! Anyways, my setup sucked -- traction roll and a complete lack of grip compared to the other cars, my fast lap was a full 0.6s behind everyone else! I suspect that the combination of low roll center from the double A-arm and stiff SP grey chassis on the 03 is combining low roll resistance with super-fast steering response, causing my traction roll issue. I've had enough of that, so we're going to revert back to my pre-RCX setup which actually worked well for most anything. Here's the old setup (goodbye!):



And we're going to swap to the stock black 03 chassis, and the PN reverse-kingpin setup. Softening the chassis will slow steering response and make the car more stable, while raising the roll center using the reverse-kingpin front is generally a good measure to stop traction rolling.

First off, prepping the chassis:



In RED is the spot that you need to cut into in order to make room for a 2x2 stack of FETs underneath the board. The MR03 comes with two 1x2 stacks, but I have a 1x2 above and a 2x2 below the board (AN0113, btw) so a little room needs to be made. To avoid heating and possibly warping the chassis, instead of a Dremel I use an Xacto knife to dig out the necessary plastic.

In BLUE are the two latches for the battery clips. I cut my battery clips in half to save weight, so I have no use for those two latch points and cut them off with side clippers.

In GREEN, finally, is the non-optional prep step, removing the plastic flashing on the main chassis. You must cut all the flashing away from the chassis tub or the top cover will not fit properly. I don't think the location I've circled is the only one, but it's the most common one that I've seen.

Next, plugging the switch hole:



If you haven't removed the power switch from your 03's electronics, don't do this step. If you have, however, filling in the hole with superglue is a good idea to prevent RCP dust from going straight up into the center tunnel.

Now to transplant electronics: The 03 is fairly easy in this regard. After taking apart the old chassis to expose the servo and PCB, you unscrew the battery terminals and just pry up the PCB with a pair of tweezers:



And then yank it out of the chassis by the servo case. Comes right out as a unit. :)



Plop the servo into the new chassis, but before you nudge the PCB back into its detents, one more modification. If you have soldered wires to your PCB instead of screwing them in, they will probably stick out through the board and if you tighten down the PCB like that, can tweak the chassis. So I carve out both screw holes with a knife to avoid all contact whatsoever.



Now for the (NOT) fun part: Reassembly. I like to use M2 threaded (machine screws, like the type that goes into aluminum motor mounts) screws in the chassis as they stay tighter, but the black chassis strips out way too easily! My solution for now is a tissue/rag.



Using the M2 screw itself as a tap, I cut 2mm of thread into each hole, pull it out, squeeze the screw threads (hard!) in the rag between my fingers, and with the other hand, unscrew the screw from the rag. This cleans out the threads of any Kyosho plastic stuck in there, and dramatically reduces the likelihood of stripping something. Then go back in for 2mm more until you've screwed it in and tightened it without feeling anywhere like you're close to stripping the threads. This takes time: For a 4mm screw you only have to do this once, but for 6mm it's twice, 8mm it's three times, etc. etc. and all together it took me 45 minutes to get the car back together without stripping a screw hole. I've already wasted three black chassis not being patient before, so I learned my lesson lol...

Once everything is painstakingly put back together, sit back and enjoy your handiwork:



I kept the grey top cover and battery clips because I need the extra strength in those two areas (that and my battery clips are cut already, too lazy to modify another pair). Now, since you completely replaced the base tub chassis it would be a good idea to re-tune the car's tweak and make sure the settings have stayed consistent through the chassis swap. I'll detail a quick and easy way of check that tweak, next week. ;) ]]> color0 http://tinyrc.com/forums/blog.php?b=285 Kyosho 10d Radials -- Impressions http://tinyrc.com/forums/blog.php?b=282 Mon, 19 Dec 2011 00:26:15 GMT Hi everyone,

Winter break is finally here for me! So 1) finally there's time to race and tune again and write again, and 2) there's a LOT that I've missed in the last couple months that I should get back to covering. So, without further delay let's get back to business. :)

About two weeks ago I decided I had enough of schoolwork and took a break to go to Kyosho's Route 241 Raceway (carpet!) for the Fall Classic race, taking with me my MR03 (under the F430 I've been building) and coming back with two MR03's and a setup board. (Shoutout to Kyosho for their incredibly generous prizes :D) Anyways, the race was pretty much won by a last-minute application of these:



These are the recently-released Kyosho 10d Radials. As advertised, they're super soft, rather gummy, and they must have some sort of silicone content in them as they don't stick well to the R246 tire tape like other Kyosho tires do.

Long story short, I put on one pair in the morning, dialed in the car, and by the time I had dialed it in, the grip was fading already. :confused: I did not have the fastest car in the qualifiers by a long shot, although I managed a fast lap just two tenths behind TQ Ryan C. it was mostly due to 1) pushing the car far harder than is prudent and 2) using the tall ride height necessary to run at R241 (the IC Tag transponder goes under the chassis!) to jump over curbs. :eek: I literally hopped up on a curb at least once every two laps -- they weren't that tall and my ride height was nearly 5mm, so hey, why the heck not?

However, I could tell that between the qualifiers I was steadily losing rear grip, to the extent that other cars running Kyosho 20 radials were getting more on-power traction than mine -- and I was running an F430 too, so not expected! By the end of Q3 I managed to keep my 2nd place qualifying position, but there was no way I'd be able to catch Ryan C. if I didn't find more rear traction. So I ripped off the old pair of rear tires and mounted the other pair in the package, pretty much hoping grip. Now the fun begins...

I've gotten much better at reacting to start signals -- normally, because I have less rear grip than other racers and therefore need to not lose position. This time, however, I was completely unprepared for the amount of traction provided by the Kyosho 10's. Right off the start I almost ran into the back end of Ryan's car and barely backed off in time -- I had a ridiculous traction advantage, much more than I could handle! The added traction also made the car push, upsetting the balance I had tuned the F430 for. Coming out of the first chicane, I again almost ran into Ryan's rear and had no space to back off! So I tried to move to the inside but ended up hitting the inside board. And in a chain-reaction of bad luck the rebound somehow sent Ryan into the outside board. D'oh. :o Anyways, within a minute the understeer went away and I pressed my traction advantage to run away from the field for a bit. Even this faded off by mid-run, the F430 starting to step out the tail more and more as the main went on. In the last few minutes of the main, the remaining traction I had didn't feel much different than a scrubbed-in pair of Kyosho 20 radials.

So: Do they work? Well, on carpet, absolutely -- for the first run or two. I've never launched my Mini-Z so hard before that I almost ran into the guy ahead of me twice. On the other hand, they fade so quickly you can tell the difference between the start of the run and the end of it! I don't mind having extra traction at the start as a safety envelope, but these tires take the fading behavior to an extreme and the traction when new upsets the handling balance of the car (major understeer).

Are they worth the money? I'm not sure. On the one hand, they grip. On the other, they don't grip that much more than Kyosho 20 radials that I could justify using them regularly. For two pairs of Kyosho 10's you could do four pairs of Kyosho 20's, scrub them in to the optimal amount and have consistent traction for four times longer. Furthermore, these are an advantage only at carpet tracks that outlaw silicone -- these tires are too soft and wear too quickly to even consider for RCP, but they're not full silicone tires, so they don't grip like PN and Atomic silicone tires do on the carpet tracks (say, Cruzin' with RCs) that do allow silicone. So for me, it's an expensive proposition I'd only save for really important races that happen on no-silicone-allowed carpet tracks. And while more races like that may occur in Japan, they're rather rare here in the US. :rolleyes:

-----------------------

Next week -- It's Xmas! Inside Line Racing Reindeer Rumble short report + my frustrations with the MR03 chassis. :) ]]> color0 http://tinyrc.com/forums/blog.php?b=282 General Setup Bad Ideas. http://tinyrc.com/forums/blog.php?b=281 Wed, 23 Nov 2011 12:32:38 GMT Well, I have some sad news to report after returning from Kenon last Saturday. 1) The front diffuser broke within 10 minutes of actual racing --... Well, I have some sad news to report after returning from Kenon last Saturday.

1) The front diffuser broke within 10 minutes of actual racing -- the small front lip got torn straight downwards resulting in a lot of scraping against the track. Couldn't get that bend out of it either, a shame...

1a) (Not sad news) The front diffuser worked like a charm, as expected. Toning down the initial steering response and increasing on-power steering, it's almost like running softer springs front but you don't roll more; you just get more grip.

2) The combination of A) a Reflex top cover (2g in the top of the chassis), B) an F430, C) the loss of my front diffuser, on D) the narrower MR03 chassis at E) a high grip RCP track (RC Kenon) is a 5-combo Grand Bad Idea. I've never traction rolled double-digits in one day before, and I have totally learnt my lesson. :eek:

3) My setup theory was wrong, at least for Kenon. :o The amount of time I gain from having a car 5mm narrower than my opponents is unfortunately inconsequential, and the penalty I pay for it (traction rolling) is all too consequential. So -- the narrow and short setup will be used not to slip into tighter lines, but create more weight transfer at tracks that do not provide enough grip. RCX's fresh RCP and the carpet at Kyosho R241 come to mind...

4) Warming up grippy, temperature-sensitive tires by truing them two minutes before a race is most definitely a Bad Idea. I did this twice in my last race/tuning outing, once with PN 8 slicks (in front!) and once more with PN 15 X-Patterns. Truing tires from ~24mm down to 22.5mm creates a fair bit of heat, and both the slick 8's and the X15's get nice and gooey when they're hot. Result: insta-traction-roll! I could feel the tires go from hot to warm during a run, and would have to drive oh-so-gingerly for the first two minutes of an eight-minute A main (triple A main's in GT Stock 80t last Saturday) in order to avoid the wrath of the front tires, lol.

5) Not reacting quickly to the track conditions is generally a bad idea. I had severely underestimated how much the track would grip the new-compound PN 8's and PN X15's, and seriously didn't learn fast enough to try a significantly harder tire up front. Oh well. :o Hindsight is 20/20, and I'm pretty sure I would have fared better in the mains (somehow I ended up 2nd/3rd that night despite traction roll mania) with the less aggressive but safer X25, and definitely would have been OK with trued-down Kyosho 30's.

6) If your setup is sensitive to tire grip, then not having multiple sets of identically prepared tires is a bad idea. For club racing and experimentation I typically care less, but when we get to big races (RCX, PNWC, ATMWC, etc.) I find it much less hectic to prepare and race if there's at least 2-3 sets each of multiple tire compounds, front and rear, that I can swap around. Real race teams do this too, it's all about maximizing your chances to win. Rest assured that I will be stocking up on tires before RCX next year. :)

7) Careful with your offsets! I've determined that +1.4N/+1.2W is the practical maximum offset for the street F430 body -- even +1.5N up front starts getting risky as the tires begin to catch on the RCP rails. Accidentally mounting the tires a little too wide on the +1.5N's was also a terrible idea. Typically the F430 glides off walls; if your tires stick out just that tiny bit too much, you will stop DEAD in your line when you scrub a rail. (Things I learned recently.) Of course, if you have no track rails, feel free to stuff up to +2.5N/+2.2W tucked in under the F430's fenders.

8) Throwing away slow but usable tires is a Bad Idea. :) I am totally guilty of it, I should not have thrown away my year-old X15's which were, if not fast, at least very forgiving and consistent. My sin is that I'm always looking for the fastest setup that I can still drive, and so one of these days I'll have to sit down and tell myself "no Brian, just focus on consistency today." It does all accomplished and aspiring racers a lot of good -- consistent racing is also clean and enjoyable racing.

9) That said, my general approach to Mini-Z is a BAD idea from a racing standpoint -- I'm not out there to win, I'm out there to build the fastest car and a win to prove it is icing on the cake. ;) Which is why I pretty much talk only about setup and sciency things on this blog, I don't exactly have a lot of wisdom to share as as racer, lol...

10) Lastly, forgetting to bring food and water to a day-long event is a TERRIBLE idea! Humans are not machines, and we need fuel to keep our minds and motor neurons happy, and you need those to components to drive your Mini-Z to its full potential. A mac-n-cheese dinner in a cup was not exactly the best thing I could've eaten to keep my performance up come A Main 1, lol. Granted we also had pizza after that, but hey, if everyone's eating it at least you're not disadvantaging yourself. :D ]]> color0 http://tinyrc.com/forums/blog.php?b=281 Diffuser Aerodynamics, Rd. 2 Pt. 2 http://tinyrc.com/forums/blog.php?b=280 Sun, 13 Nov 2011 17:38:06 GMT Sorry for skipping October, everyone, it has been a helluva school term so far (and not even for academic reasons!) and it won't be until January that I'm back to regular Mini-Z updates. :o

Anyways, the F430 is back from the Dr. Kustom shop and even with some racing wear it looks gorgeous:



It's probably stupid to run those large offset wheels (+2.5N/+2.2W! Didn't think it'd fit under an F430, didya? :)) and so the actual racing setup is mildly more conservative than the above, at +1.4N/+1.2W.



Rear diffuser's lookin' fine after one day of practice. Surprisingly, between the Super GT wing and the rear diffuser/underwing and cutouts, this F430 is producing crazy amounts of rear grip! It understeers so badly that testing out any rear diffuser designs is just fruitless, I can't register pushing vs. more pushing, lol. So I simply need more front steering, thus we return to the front diffuser. :)



As I mentioned in the previous post, the main reason why I chose the street F430 was for its higher front bumper -- which I've fully taken advantage of for diffuser inlet space. We will see how the concave inlet affects front diffuser performance vs. the flat (lack of) inlet of my previous diffuser designs. I doubt that it will act like a 1/1 scale front diffuser, where the concave inlet allows more air to go in = more air out = more downforce. But I need to see for myself, and now we have two concurrent experiments going on at once, front AND rear diffusers. :)



And the chassis update -- due to the extra weight of the diffuser and Reflex top cover I'm now using stiffer springs all around (purple A-arm front; red and blue in the tri-shock with a PN G10 #4). My car should be quicker than most Mod cars on technical layouts due to its smaller footprint, and so I will be testing and relying on the aero to improve the high-speed cornering performance, something the F430 is not well known for. It's worth a shot, it's hard to make a big car more nimble at low speed but it's possible to make a small car more stable at high speed. :)

]]> color0 http://tinyrc.com/forums/blog.php?b=280 Rear Diffuser Aerodynamics, Rd. 2 Pt. 1 http://tinyrc.com/forums/blog.php?b=279 Mon, 26 Sep 2011 21:51:54 GMT Recently I've picked up a new F430 body, but instead of choosing the ubiquitous F430GT, I bought the street-version F430 instead for two reasons:

1) The front bumper sits higher off the ground, allowing me to lower the front end of the car more with minimal plastic trimming. I don't like to trim the front bumper horizontally across the front as it's hard to keep it perfectly level. And keeping it perfectly level is the key to obtaining consistent aero properties across the width of the front end.

2) The rear diffuser actually rises off the ground and slopes upward, a good shape to mount a functional Lexan diffuser to as well as test on its own.

So with the lower ride height comes less frontal area and lower CG, as well as a bit of rake towards the front, so we should see a little bit less drag, a little bit more downforce over the body, and less body roll in a corner, which will reduce the F430's pivoting tendencies and smooth out the steady-state cornering. You can see that this F430 actually sits just as low as its rival SC430:



And here is the rear diffuser! Obviously the stock white body does not come like this, I've cut the holes into the rear bumper using a dremel.



You can see that the stock F430 rear diffuser might act somewhat like an underbody wing/spoiler, and that's exactly what I'm expecting it to do -- if I block off this gaping hole in the rear I expect to lose rear traction when I test this body on the track. And, if I add a Lexan rear diffuser to the stock diffuser, I should expect this underbody wing/diffuser/*shrug* effect to increase, and I should gain rear downforce and reduce the amount of rear end "swing" when heading into a corner at high speed.

Track testing will commence whenever I get the body back from Dr. Kustom -- hopefully I can get some time on carpet where the smallest changes in rear downforce can be noticeably felt. Carpet driving is a little bit like drifting, so just a little more or less rear traction will affect turning radius quite a bit. :) ]]> color0 http://tinyrc.com/forums/blog.php?b=279 Downstop/Rebound Spring Tuning http://tinyrc.com/forums/blog.php?b=278 Fri, 23 Sep 2011 19:42:27 GMT Last week I had a conversation with fellow SoCal Z racer mugler about tuning the downtravel on the top shock of a pan car chassis -- as you might... Last week I had a conversation with fellow SoCal Z racer mugler about tuning the downtravel on the top shock of a pan car chassis -- as you might imagine our conversation was very related to my previous post here about the downstop adjustments on the PN and Kyosho shocks. I tried my best to explain why and how the downtravel adjustment works and my reply is repasted below. :)

Quote:
Originally Posted by color0
When you brake for a corner, the weight transfers towards the front, this we know; but the amount that gets transferred forwards is dependent on both the front and the rear wheels, and we also have to make a distinction between weight and dynamic loading.

Say you have 0 downtravel -- full extension of the rear pod is the resting ride height. There's some weight on the rear wheels, and some weight on the front wheels. But the moment that weight begins to shift to the front, the downstop limiter will pick up the rear wheels off the ground, resulting in all of the car's dynamic load on the front wheels and 0 load on the rears. The weight hasn't shifted a whole lot though: action = reaction, so the full load on the front wheels means that the ground will push the car's weight back up through the front tires. Since the front wheels lie ahead of the car's CG, the net result is that the ground is pushing the car back to level, very hard. So a car with 0 downtravel will experience high load fluctuations on the tires (from full car weight to 0 car weight), but will corner very flat. The high load but low weight-shift on the front tires creates lots of front bite, and the zero load on the rear tires means you drift into the corner.

When you put a rebound spring on like the PN damper, you're still limiting the amount that the rear wheels can come up before they leave the ground, however, there's a middle ground in between where the rear tires are partially loaded, thanks to the rebound spring pulling the rear wheels up a little bit, but not all the way unlike a downstop would. So, when you brake, then a large majority of the load will go to the front wheels... but not all of it, since now your rears are still on the ground (just barely). Accordingly, more weight is allowed to shift to the front, but just barely. As a result, turn-in front bite is mildly reduced vs. a downstop arrangement, and rear grip is mildly increased since your rear tires are no longer leaving the ground as easily (they still might!) under braking.

When you leave the thing willy-nilly (no downstop at all), the rear suspension is free to extend as it pleases (spring action) or as gravity pleases. This means that the rear tires almost never leave the ground, and thus you get maximum rear traction. On the other hand, you will also allow more weight to shift to the front, which reduces turn-in performance since you're no longer taking load off of the rear wheels to give to the fronts, AND you're giving them more weight burden to cope with.


This is, of course, only smooth-track theory. On bumpy tracks, having a hard downstop and 0 downtravel is usually bad since the rear wheels will leave the ground on bumps as well as under braking. Hence why you see me use the PN top shock more often than the Kyosho. A rebound spring is IMO the optimal way to balance bump handling with turn-in response, since the black-and-white boundary of downstop tuning often leads to inconsistent handling: the rear wheels might leave the ground in one corner, but not for the next -- I noticed this a LOT this month at Inside Line, it's no longer predictable and precise like my old Kenon setup and I somewhat regret giving EMU my PN top shock.

I have one legitimate usage for a no-downstop rear shock setup, and that's the MRCG. I don't even understand the magic but the MRCG creates stupid amounts of steering up front, and can overwhelm the rear unless I artifically keep the rears on the road using infinite downtravel. I can get away with the increased weight transfer because the MRCG is super, super low.
Mugler got it, but I don't even begin to imagine that this was a comprehensive reply, so feel free to leave a comment if you'd like more detail on anything! ]]> color0 http://tinyrc.com/forums/blog.php?b=278 Comparo: Kyosho vs. PN Top Damper http://tinyrc.com/forums/blog.php?b=277 Wed, 07 Sep 2011 21:41:49 GMT ...And welcome to the second edition of our series of parts comparisons. This time, it's about top dampers, specifically the Kyosho Oil Damper vs. the PN Racing Dual Spring Center Shock as adapted to my personal car setup. So yes, once again this is going to be strictly my opinion, and I don't think there is a totally superior product between the two of these. So think of today's article as a pros-and-cons list between these two great top shocks. :)

A little foreword to the rest of this article: I realize that I have left out three other brands of popularly used top shocks, namely Atomic, 3racing and Route 246 (which is basically 3racing-made). With all apologies to Atomic, I simply can't fit your oil damper into my car and leave space for a transponder... :o As for 3racing and R246 oil shocks, I've never purchased one because all the ones I've bench-tested feel inferior to the "original" Kyosho oil shock. So on that note...

If you'll excuse my picture quality, here is the Kyosho Oil Damper doing its thing on my current chassis setup:



The Kyosho Oil Damper is a "true" oil shock absorber in that you have a chamber of oil, and there's a piston inside moving back and forth which churns the oil to provide damping. So because of that large volume of oil, it does feel very smooth in your hands. Well, at least until all of that leaks out, which is another issue...

Yes -- it leaks like a shattered bathtub. If you build this shock according to Kyosho's instructions, you'll lose some 20% of the internal oil within a few runs, and when you bring the car back and test out the shock, it'll feel grainy. Not exactly "good" damping characteristics. The solution to this is inherited from 1/10 touring car shocks: before you add any oil to the Kyosho shock, take it all apart -- unscrew the cap, unscrew the black ball end from the shock shaft, and pop the shaft out of the shock body -- and add a little bit of specialized O-ring grease to the bottom of the shock body where the single O-ring resides. I was taught to use Associated Green Slime, however there are definitely equivalent products that work just as well. Don't put too much in! This stuff is only for sealing the O-ring, it's not for damping purposes. After you pop the shaft back in, the seal should be well-formed; clean the threads on the shock shaft and screw the black ball end back on.

Another quirk of the Kyosho shock is its lack of downstop adjustability. Fully extended, it's about 2mm longer than it needs to be -- while this makes it perfect for certain 96mm wheelbase applications, it leads to comical amounts of rear suspension downtravel on "standard" wheelbase settings (86/90/94/98/102mm). Once again, clever solution from the 1/10 gang:



The yellow part is the shock body in this diagram, and the T-shaped thing the shaft and piston. The orange part is what we add to get some downstop adjustability from this oil shock. :) It turns out that small plastic straws (think: WD-40, compressed air cans) are the perfect size to fit in this space, so find yourself a straw, snip off a 2mm chunk and rebuild your Kyosho oil shock. Typically, a 2mm piece of straw will make the shock the perfect length for standard wheelbases -- the rear pod will sit level with the main chassis when the shock is fully extended. A lot of people like this, but sometimes you do need a little bit of extra downtravel, and to do that, you can partially unscrew the black ball end. Don't go overboard! I wouldn't recommend unscrewing more than about 0.75mm worth, the black ball end is easy to strip so you want as much thread contact as you can afford.

With these two tweaks to the shock, it performs very well -- the oil volume produces fluid damping and you can even adjust "rebound" damping by closing the shock body at different stages of shaft extension. As a final note, I am using the optional spring set also offered by Kyosho (Red-Green-Yellow, soft-medium-hard respectively). On very soft T-plates such as the PN G10 T-plates, the Red spring is a tad too soft, so only the Green and Yellow are really that useful. Save the Red spring for those times that you're using a stiff T-plate, and using the top shock only for damping and maintaining level ride height.


Now for our other contender: PN Racing's Dual Spring Center Shock.



The PN shock is NOT a "true" shock absorber, but it's a tube damper, using the thickness of the grease you apply to provide damping. Ironically, because you have to use thick grease on this shock, it rarely ever leaks out, and so it lasts a lot longer than the Kyosho shock between rebuilds. I've cleaned mine twice -- once because I got fed up with a rough spot on one part of the shaft, and the second time because I was giving it to fellow Greyscale driver EMU for an experiment. Despite the exposed greasy surfaces the PN shock is incredibly grime-resistant. An occasional re-greasing is all that's needed to keep up performance, very user-friendly experience for me. Preload adjustments on the PN shock are a breeze, turn the collars and nuts however much you need, definitely more useful than the Kyosho shock's preload spacers.

The "bottom" spring on the PN shock is the main spring, and the "top" spring is the rebound spring, which essentially is a downtravel adjustment like we implemented on the Kyosho shock. However, since it's a spring, you get to not only control your resting ride height, but also how strictly your chassis will enforce said ride height. :) In my experience this is a great tuning tool for drivers who rely on weight-shifting techniques: a softer rebound spring creates a milder turn-in response, and harder begets sharper turn-in response. On high-grip tracks I sometimes forgo the top spring and insert a block instead for the quickest turn-in, but on low-grip tracks sometimes you need a little forgiveness, and I'll use an MR02 front spring, medium to medium-hard.

The PN shock isn't without its faults, however. It excels where the Kyosho shock is the biggest pain in the butt (longevity, ease of use) and the weight is not so bad (a tick heavier than the Kyosho), but the length! Because the PN shock is a through-shaft design, it doesn't ever get shorter when you compress it. So, when you're racing your Mini-Z and need a space to mount the transponder, you need to clear a little space ahead of the shock (1-2mm) if you want to have some upward suspension travel. Of course, this makes things difficult when you're trying to fit the chassis under certain bodies that require pushing the transponder back -- I'm talking about the 599XX and HSV-010. Due to this conundrum I have been forced to use the Kyosho shock with these bodies, and use a short motor mount moved backwards in order to allow a normal transponder placement.

As a final note for the PN shock, PN also has an optional spring set for the main spring of this dual-spring shock, and I really like the fine-tuning possibilities it provides. Instead of Kyosho's set of three, you get seven springs of usable spring rates -- the softest Orange spring is really only useful for setting ride height, but the Blue through White springs (2nd softest to 2nd hardest) are all fully useful. I myself have never used the hardest Yellow spring, it just seems like a bit much. I imagine it will be useful on a high-grip track if you have no T-plate (i.e. running the PN Gimbal or Qteq Pivot Ball T Bar system) and need the spring to compensate as such. ;)


So there it is, my thoughts on the two most popular top shocks for Mini-Z's as of current. Can I pick a favorite? No, not really -- I tend to use the PN shock more (I am l-a-z-y! Hate rebuilding shocks), but for certain bodies like the 599XX and HSV-010 I've been using the Kyosho shock and not really minding much at all. I do think the PN shock has an advantage with the rebound spring tuning, but at the same time the Kyosho shock is a bit smoother and lighter, and theoretically at least produces more effective damping. I hope this article was helpful in some way, shape or form, and please stay tuned for more bodywork this month! :) ]]> color0 http://tinyrc.com/forums/blog.php?b=277 Sorry! http://tinyrc.com/forums/blog.php?b=275 Sat, 03 Sep 2011 01:53:47 GMT Hi everyone, My apologies for skipping the month of August entirely. :o Due to work, presentations, flying back across the country and having my... Hi everyone,

My apologies for skipping the month of August entirely. :o Due to work, presentations, flying back across the country and having my wisdom teeth cut out (ZZZZZZZZZZZZZZZZZ -- AAAAAHHHHHH!!) I've been pretty incapacitated from doing any heavy Mini-Z stuff this month. This coming month will be better, I have another parts comparison to write about and will be exploring aerodynamics once again after playing with some bodies over the summer that honestly didn't have so much aero potential to work with. :rolleyes:

So, September here we come! ]]> color0 http://tinyrc.com/forums/blog.php?b=275 Comparo: Reflex vs. PN MR03 Reverse Kingpin Front http://tinyrc.com/forums/blog.php?b=270 Mon, 25 Jul 2011 05:37:25 GMT I am fortunate enough to have owned almost all the MR03 front end setups available, and driven all of them: Kyosho stock, Kyosho aluminum, Atomic... I am fortunate enough to have owned almost all the MR03 front end setups available, and driven all of them: Kyosho stock, Kyosho aluminum, Atomic composite/aluminum, Reflex Long Kingpin, Reflex Reverse Kingpin, PN "hack" long kingpin, PN Reverse Kingpin, and PN Double A-Arm. Of these, I feel that the Double A-Arm provides the absolute highest mechanical grip, while the Reflex and PN Reverse Kingpin setups provide superior precision and consistency. Since I treasure both of those qualities over outright speed, I've come to like the PN Reverse Kingpin setup a lot, and now am beginning to understand the Reflex version. So, given my newfound familiarity with both, I thought it would be worthwhile to do a casual comparison of the two reverse kingpin setups.

Please let me make it clear that I am NOT going to declare one product superior over the other, because 1) I'm not in a position to and 2) honestly, I feel they're equally good, but in different ways. My only aim with this article is to provide a little bit of insight as to how these two front ends are different, how they are the same, and what prospective buyers should expect when deciding which one to purchase for their Mini-Z MR03.

Let me start with the PN setup. This is the front end that I use in the weekly races at RC Kenon, and the one that helped me TQ the RCX Challenge race earlier this year.



PN's configuration reverses the kingpin for proper smoothness, but keeps the stock spring mounting location. There's good and bad associated with that. Good: wide selection of MR03 springs, and you can go as soft to as hard as you want. The inboard springs are also out of harm's way, and easy to remove and change. Bad: well, the effective spring rate changes depending on how the arms are angled. If your arms are flat, like mine, there is a small region of (almost) linear spring action, but if you angle them up or down beyond a small range, you can feel that the spring rate is progressive. This makes the car a little difficult to tune quickly, since changes in ride height, preload or droop can affect the effective spring rate the car "thinks" it has.

On the other hand, PN offers Teflon balls for this front end, and once installed and broken in (the latter took a while), the suspension becomes almost frictionless. The balls are extremely tight at first, and it took about an hour of working the balls back and forth to break them in properly. I didn't need any polishing of the kingpins though -- they were mirror smooth out of the package. I think this front end actually has less friction than the Double A-Arm setup: whereas I can always feel the joints sliding on the Double A-Arm, when the Reverse Kingpin is maintained properly I don't get any hint of the sliding metal-on-metal "swish swish" kind of feel. Very impressive smoothness, which combined with the tight tolerances of the whole setup results in very good precision and "placeability" on the track.

More recently, I removed the PN kingpins and balls to try out the Reflex Reverse Kingpin kit -- not the whole front end, just the balls, kingpins and springs which are compatible with the PN arms.



Reflex Racing's reverse-kingpin setup places the spring underneath the lower arm, instead of inboard. It took a long time to put together, I'll say that much -- the springs are tiny and the E-clips have to be put in and removed every time you want to change something. However, the balls did not come out of the package too tight for the kingpins, and so there was no hour-long break-in period before the car was driveable -- this front end performs immediately. The spring-under configuration changed my car's behavior vs. the inboard spring config. Firstly, I liked the new linear feel of the front suspension, compared to the PN front end. Knowing that the spring rate will not go negative-progressive if the full suspension travel is used means that I'm free to set the upper arm angle to whatever I want/need for the day. And, no matter what arm angle I set, the effective spring rate the car sees will not change, so I can worry about fewer interfering factors when tuning the car.

I feel that the Silver spring was a little too stiff, and the Black spring a little too soft -- but that's just me being picky and the spring choices are not out of the correct range for carpet or RCP. When I raced at Cruzin' with RC's with the Reflex front end setup I tried the Silver springs and had a hard time getting the car to rotate, since the front end just wouldn't dig in. In retrospect I should have went with the Black springs, and preloaded them a bit to keep the ride height reasonable. On a high-grip track I would love this front end a lot more: it is as precise as the PN Reverse Kingpin, almost as smooth (the Reflex kingpins are not as polished as the PN ones), and the Silver spring would be absolutely perfect for my preferences.

And the end of the day, these two front ends perform at about the same level: on two separate visits to Cruzin with RC's, I managed to capture each time 2WD Mod 2nd place and the 2WD Lap Record. The change from PN to Reflex front end between the two visits did not drastically change my pace, but the Reflex front end was better in quick transitions (surely because of the spring rate?) while the PN front end provided more absolute steering and off-throttle steering (again, probably the spring rate). Both of them caught a LOT of carpet fibers that I had to clean out, although here the Reflex front end is at a disadvantage: with the springs under the lower arm, anything caught in there can jam up the spring and kill the car's handling without you realizing why. You can't raise the kingpin either without preloading the spring more than you'd want. With the PN front end at least the carpet fibers can't interfere with the springs, and you can shorten the kingpin to avoid scraping as long as it still fits in the lower arm balls.

There is of course a footnote to this experiment -- I didn't use the full Reflex Racing front end setup and instead tested a PN/Reflex hybrid. The Reflex tower bar adds some much-appreciated functionality to the package with its free camber adjustment and 2-4 degrees caster rather than 0-2. Those are my biggest gripes with the PN front end actually, the fact that I need to change the arm angles (altering my roll center) in order to get the camber I need for even tire wear, and that I can't get more than 2deg caster even if I actually need it.

If you've been keeping track, this puts my "cons" list for both front ends to 3 vs. 3, hence why I said at the beginning that I feel the Reflex and PN Reverse Kingpin front ends to be equally good. Both provide high performance and precision, are low maintenance by design, and are representing a good value for the serious racer. They are, however, limited in different ways, and so if you're shopping for a new MR03 front end, on top of deciding which type (stock? Reverse-kingpin? Double A-arm?) you want, I hope this article will be helpful to sort between the two most popular reverse-kingpin setups to make your decision. :) ]]> color0 http://tinyrc.com/forums/blog.php?b=270 Body Comparo: SC430 vs. F430GT http://tinyrc.com/forums/blog.php?b=264 Tue, 19 Jul 2011 01:20:41 GMT And continuing on from last week, a body comparison that has been done several times before and that I will add one more to: the Lexus SC430 GT500... And continuing on from last week, a body comparison that has been done several times before and that I will add one more to: the Lexus SC430 GT500 vs. the Ferrari F430GT. These are by far the most popular 94mm racing bodies out today, you will usually find at least one of each at any given Mini-Z track in the world. Why are they so good? That's exactly what I'm going to look into this week. :)

First let's start off with the F430GT.



The F430 is the model of efficiency. It looks like a ladyshave -- with no extraneous plastic, no sharp edges, everything is smooth smooth smooth. This means that 1) it slips through the air very easily and 2) it will almost never catch on the rail! The F430's ability to handle wall collisions is astounding, unless you hit it head on you are sure to escape with little more than some lost pace. It's not too wide and not too narrow, coming in with offsets of +1N front and +1W rear, and also fairly light, weighing around 33g lightly modified.

Note, however, that the F430GT is no lower than its street counterpart. This is a relatively tall racing body, and it produces a lot of body roll. This roll gives the F430GT a lot of grip, but at the expense of being prone to traction rolling if you're not prepared for it. The tall CG also makes this body sluggish in quick transitions, so the F430 is a good body for pivoting around hairpins, but not so much for frequent chicane/rhythm sections.

The F430 is a cab-forward design, and at that, one with a fairly long front overhang. This puts a lot of weight up on the front wheels, which generates a lot of steering. Strangely enough, however, in my experience it does not rotate around the front end like the Mosler we reviewed last week. Rather, the F430 will turn in hard but stay very planted on its rear wheels. If you give it too much speed and it stays planted... traction roll! An annoying, but for this body at least a predictable, behavior.



Out of the box this body is ready to race -- there's no need to shave front splitters (there isn't one), the rear spoiler is functional, you may want to carve out the window glass to make it lighter and lower the CG but otherwise this body is good to go! Even though the rear end is tall, there doesn't seem to be much of a parachute effect that you might experience on other bodies, and as a result, cutting out the rear bumper of the F430 doesn't seem to help a whole lot other than lightening the rear end and making it easier to flick the car into a corner. The Ferrari F430GT is popular because it's effortless performance, you just slap the body on the car and get instant steering and traction. As the grip levels come up, you might even get traction roll too, but that's where our F430's favorite rival comes in.

Enter the Lexus SC430 GT500:



You can tell right away: the SC430 is lower, wider, and has a squatter stance. Although Kyosho sold it with stock offsets of 0N front and 0W rear, in reality this body can comfortably fit +1.5N front and +2W rear. These specs make the SC430 corner extremely flat, like the GT-R GT500 we reviewed last week. Just like the GT-R, the SC430 does not generate a whole lot of grip; but on the flip side, you can drive it extremely hard, and its low CG and low weight (30g or less in whitebody form!) make it exceptionally nimble in quick transitions, exactly where the F430 is weakest.

That said, the SC430 is also the weakest where the F430 is the strongest -- wall handling. The SC is notoriously bad at recovering from wall impacts, often wedging itself under RCP rails thanks to the side skirt design, and the front splitter needs to be aggressively shaved off in order to avoid digging itself under at the slightest brush. But don't shave off too much! Like the GT-R GT500, the front bumper's strength comes from the front splitter. Remove it entirely and the front bumper is very susceptible to race damage. Once these modifications are done it becomes acceptable off the walls, and can press its other advantages.

The SC430 is a short-front, long(ish)-tail body, so low-speed handling is much milder than the long-front, short-tail F430. The rear bumper is already cut high for you, so the parachute effect is minimized, and a gigantic plastic spoiler provides the weight and a little downforce to plant the SC's rear end into the track. The flip side to the heavy rear is that at high speeds, the car will oversteer, and although it's resistant to traction rolling, you still need to watch your steering input lest the car get a little loose. Being a cab-neutral design, the SC430 behaves much like the GT-R in terms of rotation: you can change where the car rotates simply by changing your setup and biasing it towards under- or oversteer. Very convenient, versatile body, which is why it has gained a very loyal following among Mini-Z racers.



One quick note about this body, there is very little space under the small canopy to fit a tri-shock system. The Reflex tri-shock is said to fit with a few minor modifications, but the PN tri-shock takes some serious reconfiguring and shaving of the body to get it to fit.

So as I asked last week, which one do you choose? :) The F430 is a very point-and-shoot body, great for rotating around single corners but not for multiple quick transitions. The SC430 is the opposite, unbeatable in quick transitions but will be outpaced by the F430 in slow single corners. I'd say plan accordingly with the track layout: if it's a rhythmic layout, the SC430 will tend to be faster, and if it has a lot of tight corners, the F430 will tend to be faster. The driving feel you prefer will also play a part here: I honestly cannot make the F430 behave the way I like it to -- it seems to have a way of driving that it likes, and cannot be pushed out of that comfort zone. It works for some people (Chad Nelson can do incredible things with an F430), but not for me. The SC430 is more versatile setup-wise, I can bend it to my will to a greater extent. It will never generate the same amount of steering and traction as the F430, but I can make it try and it will listen. :) And of course, if the entire track is high-grip, high-speed, I would suggest putting these two very good bodies back in the pit box -- 98mm is the way to go once the road opens up and gets sticky. ]]> color0 http://tinyrc.com/forums/blog.php?b=264 Body Comparo: Mosler vs. 599XX vs. GT-R GT500 http://tinyrc.com/forums/blog.php?b=263 Wed, 13 Jul 2011 23:51:03 GMT Hi folks, going back to a more general-racing theme this week -- today's article will be about three of the most popular 98mm racing bodies, the Mosler MT900, Ferrari 599XX, and Nissan GT-R GT500 2008. Since I've raced and done well with all of them we can explore their characteristics, quirks, pros and cons, and hopefully it'll be some additional insight that you can use to improve your Mini-Z game. :)

First let's look at TRP's racing phenomenon, the Mosler MT900:



This body is BIG. Though it comes with wheels that have +2N and +3W offset, it can handle waaaay more than that, I'd venture even +3.5N/+4.5W would still tuck under the fenders. It's also heavy. Even with a lot of shaving and trimming effort on my part, it still weighs 37g with paint -- an unmodified example could easily surpass 45g. All this width and mass makes the Mosler an exceptionally stable body, perhaps not the fastest in lap times but very forgiving to drive for long times.

That said, even though it's so wide, the Mosler can still traction roll! In stock form the Mosler is a high-roller, leaving plenty of space for suspension travel but in doing so, placing a lot of plastic up high, creating lots of body roll. This amount of body roll generates a good amount of grip on RCP and carpet, but at the same time it makes the car sluggish, and transitions are not the Mosler's strong point.

Speaking of transitions, the Mosler's cab-forward design places weight, pressure and downforce on the front wheels, creating steering and rotating the car around the front end. Not at the front wheels exactly, but the point of rotation is definitely front-biased. Entering a corner, if the rear wheels slip out you'll notice that the drift is being carried by the fronts. Like the body roll characteristic of this body, it creates great steady-state cornering but it's not going to be fast in dynamic transitions, which favor mildly understeering bodies. To tone the effect down with the Mosler body you'll have to adjust your setup towards understeer to compensate for the Mosler's dive-bomb-into-a-corner character.

To get the most out of the Mosler body involves a great deal of work: I lowered mine 5mm (5mm!), shaved some of the inside, cut out the windows individually, took out the rear bumper almost entirely, and finally added a Gurney flap-type spoiler to get rear downforce without restricting the rear from swinging out (I like it, actually, it's fun). These modifications brought the shell down to a reasonable 37g weight, very low (tucking tires low), transitions are made much faster and the Mosler's corner speed is largely unaffected, so it becomes an all around better body when you shave and slam it.

(Nevermind the Reflex scoop wing, it was sitting there as a mockup)


One last note about the Mosler is that available clearance for tri-shock suspension setups is slim: if you don't lower the shell, the PN tri-shock will clear the fenders and the Reflex tri-shock can fit with some coaxing, but if you've lowered it you can expect to cut two gigantic holes in the rear fenders to clear any tri-shock setup you might be running.


Next then is the body I ran for everything before getting the Mosler: Nissan's GT-R GT500 2008.



It may not look like it, but this body actually has the same-height roofline and lower CG than the Mosler! It isn't nearly as wide as the Mosler, coming stock with +2N/+2W rims and not really accepting any more than that safely (+3W rears will fit, but be wary of race damage...). It's also much easier to get into running shape, and sits at 34g with only mild modification and full paint. It's still wide enough and heavy enough to be a forgiving ride, but the first thing people notice about the GT-R is how nimble it is for a 98mm longtail body.

The GT-R rides flat -- unless you purposefully spring the car way soft, you can't see it roll in the corners. The lack of roll makes the GT-R extremely nimble for its weight, it likes transitions much more than the Mosler. The flip side is that it doesn't generate a whole lot of grip since it just doesn't put any pressure on the tires. This relegates the GT-R to usage only when there's enough grip, such as high grip RCP, regupol, or for AWD cars on carpet. As I demonstrated to myself at RCX, the GT-R becomes a drift car when there's insufficient traction -- it's only nimble and quick when the traction is already there.

Being a neutral-cab design (a little to the rear, but not extreme) the GT-R rotates around whichever tires have more traction (hopefully, the rears!). So it's fairly versatile for driver preference in that you can move the car's pivot point to where you want it to be rather than complying to the shell's natural characteristics. Playing with tire combinations I've been able to make the car rotate around the rear tires, super stable, all the way up to drifting every corner entry like the Mosler does. Its dynamic behavior is very easily tuned and that's the cool thing about the GT-R.

Unlike the Mosler, the GT-R is good out of the box: sure, the rear diffuser creates a parachute effect and the front splitter catches on the rails, but cut those off and you're already good. Downforce is balanced front and rear and it's really your choice if you want to run a custom rear wing -- I've tried both and the car works great either way.



One last note for the GT-R: the front splitter is the source of the front bumper's strength. Cut it off and the shell becomes a lot more fragile immediately. As I've found out, it can crack all the way through from the ground to the headlight if you hit another car hard enough at just the right angle! I would suggest trimming down the front splitter on this body but not shaving it all off.


Lastly, let's look at the recent "hot body" of choice, the Ferrari 599XX:



Given the front-engine GT shape of the 599, the easiest comparison to make is that between the 599 and the GT-R: the 599 is the same height, nearly the same dimensions, heavier and wider and extremely cab-rear in design -- just take a look at those front fenders! The 599 comes stock with offsets of +3N front and +3W rear, and honestly that's about the practical limit for this body. Going any wider would seriously endanger the wheels, and the tires would rub the body too unless you raised it. Weight falls in between the GT-R and Mosler, at about 36g with paint after mild modification. As you might imagine, the result is a body that is neither as stable as the Mosler or as agile as the GT-R, but a nice compromise between the two.

Like the GT-R, the 599 rides very flat. Given that most of the plastic in the front half of the car is very low, traction rolling is pretty much out of the question unless your tires are folding over. Given its in-between weight and wide, stable offsets, the 599 will not be the quickest through the chicanes but it's certainly safe to push it through, unlike the Mosler which will sometimes fight you to stay on its own trajectory instead of yours. However, the extreme cab-rear design places more weight on the rear wheels than the other two bodies, and the 599 generates grip even in low-traction conditions, making it more adaptable than the GT-R.

The cab-rear design has two more important characteristics. First, the weight and pressure being focused on the rear half of the car leads to naturally "pushy" or "planted" tendencies. Unlike the dive-in Mosler, the 599 sits on the rear wheels and will push in the infield unless you compensate for it with front grip. However, it's so far back that it also seems to block airflow to any wing you may have on the back, making it a little less efficient, thus counter-intuitively freeing up the rear end! This gives it a lot of steering at speed, which is good and bad. Unlike the Mosler, which will happily carry a drift with its forward-biased CG, the 599 will hook the front tires and spin if you let the rear step out too much. So in terms of driving behavior, the 599 is not a car that you want to let loose -- its natural tendencies are to stay planted and it simply doesn't like being pushed out of that.



The 599XX is honestly very good out of the box, very little modification needed. In fact all I've needed to do to make it fast are cut out the rear spoiler and rear diffuser, and tack on a Reflex wing. Didn't even need a dremel -- all of this can be done with a humble Xacto knife. That said, if you lower this body you'll quickly find that transponders won't fit in between the hood of the 599 and the top cover of your chassis. Plan accordingly, I've started to run my transponders on either side of the top shock. ;)

So which one should you choose? The Mosler, being wide as it is, seems like the go-to choice for wide open layouts -- high corner speed, stable, produces downforce. It's also a good body for those who like a more "dynamic" driving style. The GT-R is the fine precision scalpel for high-grip, quick tight tracks -- extremely agile, very sensitive to tuning, and a bit narrower than the other two so it can squeeze in tight spots if you're on your game that day. And finally there is the 599XX, which I'd say is the easiest to live with of the three: it doesn't take much work to get going, the rear tends to stay planted (i.e. it doesn't EAT tires), hooks up on low grip and doesn't traction roll on high grip. All three are excellent in their own ways, so I would encourage you to use this review to choose one based on what kind of car character you like the most.

Next week -- SC430 vs. F430. :) ]]> color0 http://tinyrc.com/forums/blog.php?b=263 Happy July 4th! Now Back to MOD. :) http://tinyrc.com/forums/blog.php?b=262 Tue, 05 Jul 2011 06:21:05 GMT Happy July 4th everyone! I myself just got back from a fireworks showing on the Charles river (between Cambridge and Boston), looked great. :) Now... Happy July 4th everyone! I myself just got back from a fireworks showing on the Charles river (between Cambridge and Boston), looked great. :)

Now continuing on where I left off last week, my changeover from RCP to Carpet Mod racing.

First of all, I was gently reminded that the carpet at Kyosho and Cruzin is LOOOOW grip, no matter what tires you use -- the surface itself simply feels too powdery to let any kind of tire stick too much. I suspect there is a lot of internal slip between the carpet fibers, so even if your tire can grip the surface layer, it still has to go through the rest of the thickness of the carpet before the track exerts any moving force back to the tire. It's also soft, which lends an advantage to heavier cars that sink better into the carpet (giving you mechanical leverage as well as chemical adhesion). RCP is like this too, but to a MUCH lesser degree, so it feels more like a road surface (though still not true tarmac at all).

Thus I quickly learned two lessons:

1) Low CG is not the king on carpet! On RCP with Mod power, there's enough load on the tires to warm up the tires to the point of overheating, so avoiding traction roll is priority #1, finding steering response is priority #2, and preserving the tires is #3. A low CG promotes all of these things quite well under the given conditions. My light, low and flat setups are therefore good on RCP, I just need to find the right tires for the day and then drive the wheels off the car. Carpet is different. Because there is so little grip, I've found that the tires don't warm up enough, no matter how soft and squirmy the tire is. So what can you do? You can try "forcing" the tire into the track, raising its load and thereby warming it up, to try and obtain better grip. Without changing anything else, the easy way to go about it would be to raise the entire car. This would increase the magnitude of weight shifting as you pitch the car in a corner, loading the outside tire more, warming it up more -- exactly what we want. Warmer tire = more grip = faster car.

2) Low weight is also no longer king! Because RCP usually has ample grip, we often try to reduce the load on the tires by reducing the weight of the car, keeping the tires from getting overloaded and fading. Once again, this logic is broken by racing on carpet, when you find that your tires are not being loaded enough! As I suspected and EMU tested, heavier cars will sink better into the carpet, load the tires more, and generally produce more grip, for the same tire combination, than their lighter opponents.

Now you could then reach into your book of tire physics and tell me "but Brian, doesn't that mean you could get the same effect by running narrower tires?" This would, as you might imagine, reduce the contact patch of the tire against the carpet, increasing the pressure on the rubber and warming it up more. I.e. exactly the thing Grant recommended that I try at RCX. And you know what? Theoretically I think you'd be right. More grip should be able to be generated without purposely adding weight to the car. That said, I personally feel that carpet tires right now are too soft and squirmy already, leading to a very mushy steering response which I honestly don't enjoy. Although the carpet surface is more consistent than RCP, the way the tires squirm actually negates that gain and my car feels no more precise than it was on RCP with stiff-carcass PN RCP tires.

So if not narrower tires, why not make even softer compounds? Again, my comment about tire squirm. Right now Atomic has recently released an uber-soft 7-degree compound silicone carpet tire, and meanwhile PN has had 6- and 8-degree silicone carpet tires for a while. I've ordered some of each to test, but my suspicion is that they're all just going to feel way to squirmy to have positive steering feel. In which case, however, I'm not entirely out of options. Gluing the sidewalls of the tires, as Grant M. taught us in the past, would stiffen up the sidewall enough to provide more positive steering response, but without affecting the compound of the contact patch actually touching the track, so it should be the best of both worlds as I continue to refine my carpet Mod setup.

If the tire dilemna weren't enough, carpet offers an interesting opportunity to tune the traction balance via scraping off the surface gunk that accumulates on the tires after a while. At Kyosho less gunk accumulates because there's less silicone run into the track (mostly, just whatever percentage is inside Kyosho 30 and 20 "Racing" Radials). But at Cruzin with RC's, WOW the stuff builds up within two runs and lowers grip considerably. So as you might imagine, scraping the gunk off will temporarily increase traction at the tire. I figure this could be used in multiple ways:

1) Scrape both rear tires right before the main of a race. This will give better traction at the start buzzer, and calm down the car a little bit while you settle into your rhythm.

2) Correct tweak (what a hack! :eek:). I'm always running a side-shock setup of some sort now, but for those of you on disk dampers and on carpet, if you feel the tweak, try scraping tires to balance it out! It won't be permanent, it's crude and you'll laugh at yourself as you do it, but hey, if you need a quick fix after you got hit and can't find the source of the tweak, why not give it a go.

One quick note about driving differences: Mod on carpet feels waay more relaxed than Mod on RCP. This is clearly due to the low grip slowing things down. I'm no slouch on the driver's stand, but I'm no god either: Mod racing on high-grip RCP like Kenon just feels frantic to me, there's no time to actually adjust and refine your cornering line, and it's all point and shoot, and you better have your car setup perfected to a "T" or it's just not going to go where you need it to go on faith. Meanwhile, on carpet, it's slower, you have more time to make corrections, blip the throttle, adjust your line, pick where to go, and it's a mental driver's game much, much more than on RCP where it's extremely technical. At least that's how I see it at the moment. Once I go back to RCP after this summer, and run Mod again, surely I'll be less overwhelmed and begin to see the finer points of driving such ballistically fast and agile cars on a high-grip surface. :) ]]> color0 http://tinyrc.com/forums/blog.php?b=262