The Infinite Speed Potentiometer Mod (tm)

[actofgod]

Single Speed? Two Speed? How about a fully adjustable throttle for your bit?

This is the completion of my Rechargeable Li-ion adjustable voltage mod (http://tinyrc.com/forums/showthread.php?threadid=4179) thread posted 12-2-02. Thanks to Akura and Ovgron for the responses on that one.

I started off with my Layman's Dual Cell Mod (tm) (http://tinyrc.com/forums/showthread.php?s=&threadid=6045) for the 2.4v. I could have fit 3.6v or more in there, but 2.4v is already pushing the limits of control with a fast engine IMHO. Lithium rechargeables are too hard to recharge for now anyway. This mod would work with a single cell, but I've never felt the need to "dial down" the speed of a single cell bit. :)

I have tried many different potentiometers (see pics) from various sources, and I'd like to save anyone else working on this project (like LEE50GURU (http://tinyrc.com/forums/showthread.php?threadid=6006) , I just noticed) from buying any more potentiometers than they need to.

Akura was right about the necessary resistance being less than 30 ohms. To get an idea, I started out rearranging Ohm's Law as:

Resistance (ohms) = Voltage (volts) / Current (amps)

I referred to Namuna's multimeter readings (http://tinyrc.com/forums/showthread.php?s=&postid=12100) for the bit char-g; he found that a single cell bit puts out 275ma, so I doubled that for a dual cell bit and got 550ma. The current per cell is 1.2v, so I used 2.4v for the dual cell.

Resistance (ohms) = 2.4v / 0.550 amps (1 milliamp = 1000th of an amp) = 4.36

Using 4.36 as a starting point, I calculated that to half the current going to the motor you would have to double the resistance. I wanted the minimum speed to be about 1/2 the speed of a single cell bit (that's 1/4 the speed of a dual cell bit), so I'd need to double the resistance twice. That gave me 4.36 * 4 = 17.45 ohms. If my math is off, someone please correct me.

Finding a resistor in that range was tricky. At first I had forgotten that the result was in Ohms while most resistors are in Kilo-Ohms, so I got a 20k resistor. I thought my calculations were wrong, so I just started trying some at random like 10k, 5k, and 1k. When even the 1k didn't work, I realized my mistake and found a 100 Ohm 25-turn potentiometer and a single turn 20 Ohm pot. While the former would allow more precision (each full revolution changes the resistance by 4 Ohms, allowing for 5 complete revolutions of control to get to 20 Ohms), I decided I didn't really need THAT much precision. I opted for the single turn 20 Ohm potentiometer, and it gives me all the control I need.

Wiring was very simple. Current is interrupted from the batteries to the entire PCB rather than just from the PCB to the motor. I desoldered the red +V wire from the PCB, leaving the other end attached to the positive battery terminal. That free end attaches to the center (wiper) pin of the potentiometer. I had to solder on a little bit of extra wire to make it long enough to reach around. I took another piece of wire and soldered to the top of the +V connection on the PCB and ran it to the left pin on the pot. Either one will work, but I wanted the speed to increase as I turned the pot clockwise and decrease as I turned counterclockwise, so in the case of this pot it was the left pin. I drilled one tiny hole for the left pin and put the center pin through the hole below where the antenna clip is (genuine bit char-g pcb cover; clones may not have this hole) and bent the right pin up out of the way. I ran the wires from the pcb up through the holes and soldered them against the exposed part of the pins, then superglued the pot to the pcb cover, leaving plenty of slack in the wires for when I need to remove the whole cover to swap batteries, etc. The Fairlady body fits perfectly on top, but since it is snug you may experience some wires grounding against the pcb. Use a tiny strip of clear plastic tape across the PCB and under the added wires if you have that problem.

Ok, enough talking.. I have pics and even a sound clip for you all. To hear the sound clip (mp3) go to http://users3.ev1.net/~actofgod/potentiometer.mp3

What you're hearing is my Fairlady 350Z getting 3v 500mah from the charger base I use. I wanted the motor (a cannon ball clone motor.. faster and torquier than a bit 2.6) to be loud enough to hear the increase and decrease in RPM. This is with orange gears and back axle in place. After "revving up" and back down, I punched the boost button and revved it again. Now I can adjust both speeds to run as fast as possible on any given track, depending on how many curves and straightaways it has.

If you'd like to do this mod, you can purchase a 20 Ohm resistor like the one I used at allelectronics.com (http://www.allelectronics.com/cgi-bin/category.cgi?category=470&item=SVP-20&type=store), CAT# SVP-20

Let me know if you find this post useful or have any questions. Happy modding!

[actofgod]

view of installed potentiometer

[actofgod]

blurry closeup of installed potentiometer

[GT-ahh]

yeah i added a speed adjustment pot to my dual battery 2.2 bit... its good, u can wind it down to 1.0 equivalent...

[ZipZap "SS"]

I referred to Namuna's multimeter readings for the bit char-g; he found that a single cell bit puts out 275ma, so I doubled that for a dual cell bit and got 550ma. The current per cell is 1.2v, so I used 2.4v for the dual cell.

Just for reference, when you add a battery you don't increase both the amperage, and voltage. You get one or the other depending on if you wire them in series or paralell. If in series, you increase the voltage with the same amperage. If you wire them in paralell, you increase the amperage at the same voltage.

Chris

[actofgod]

Thanks, I was wondering about that part. In that case, the base number should be:

Resistance (ohms) = 2.4v / 0.275 amps (1 milliamp = 1000th of an amp) = 8.73

Since I couldn't find anything but 20 ohm and 100 ohm I guess 20 ohm is still the way to go. It seems to be working well.

[Namuna]

Off you go...

[tinyrc]

actofgod, this is a really amazing Mod!!! Great work! :D

[evileric]

Cool cool, now all we need is fully proportional steering and we'll all be happy now won't we! :) Good stuff, I think I'll have to try this for myself.

[akura]

Fantastic to see you got this working, wouldnt it be fantastic if you could control the voltage flow REMOTELY then! Now _that'd_ be a project to think about.

[SPEED]

Just got done reading your posts, all i can say is WOW!! Thsi is a GREAT MOD to do!!!! So let me get this stright:

Red + battery wire connects to middle pin of POT
Left pin of POT connects to + connection for the battery wire on the PCB

ANd the right PIN of the POT is not used correct??? Just trying to clear things up because i may use this mod!

You said you used 20 OHM POT, can this be found at another electronic store such as Radio shack??? I seen a few POTs there.
Also, what type of POT would you have to use if you wanted to put this into a 1 cell bit??? Thanks!

[actofgod]

Originally posted by SPEED
Red + battery wire connects to middle pin of POT
Left pin of POT connects to + connection for the battery wire on the PCB, ANd the right PIN of the POT is not used correct???


That's correct. Nothing to it if you can solder a little.


You said you used 20 OHM POT, can this be found at another electronic store such as Radio shack??? I seen a few POTs there.



The smallest rated pot I've found at radio shack is 1k, which is much too high for this project. I found the 100ohm 25 turn pot at Fry's Electronics; Allelectronics.com is the first place I found anything under 100ohms. If you buy from them I highly recommend getting the battery pack mentioned in the other post for an extra buck or so.

Originally posted by akura
Fantastic to see you got this working, wouldnt it be fantastic if you could control the voltage flow REMOTELY then! Now _that'd_ be a project to think about.


What you'd need is an appropriate motorized potentiometer (http://www.allelectronics.com/cgi-bin/category.cgi?category=470&item=MPOT-10K&type=store) and an extra two buttons to control the motor that turns the pot. I haven't seen anything small enough though, and even if you used the booster controller's extra button to turn the motor one direction, you wouldn't be able to turn back the other direction except with some type of spring return mechanism possibly, which wouldn't allow you to lock in on one speed.

You could overcome the channel limitation by adding a second PCB of a different freq and merging the two remotes into one; however, with a second PCB and motorized pot you'd probably need a custom bus-type body due to the size. Hats off to anyone that accomplishes that, but I think I'd rather just buy a digiq, lol.

Thanks for the feedback, everyone. Post your results or questions if you try this mod.

[actofgod]

Originally posted by SPEED
Also, what type of POT would you have to use if you wanted to put this into a 1 cell bit??? Thanks!

Plug in 1.2v for 2.4v:

Resistance (ohms) = 1.2v / 0.275 amps (1 milliamp = 1000th of an amp) = 4.36

To half the speed, you'd need 8.73ohms; to half it again you'd need 17.45ohms. Actually, these are the numbers I used by mistake when selecting a pot rating for the two cell mod the first time. A 20 ohm resistor would work just fine for both; you may just have a little smaller "usable speed range".

Incidentally, a 20ohm would work on a 3 cell mod too, it just wouldn't slow it down as much. You'd need 26.18 ohms to half the speed at 3.6v, so you'd be able to tune it from a little over half speed to full 3.6v speed. Still a useful addition.

I think this mod is most useful for two or more cells, though, since going below 1.2v not only sacrifices torque and acceleration but if you go low enough could affect your steering coils' effectiveness and the ability of the car to receive the signal from the transmitter. A slower engine is probably the best way to slow down a one cell car, unless you're trying to race on a single paper plate. :)

[SPEED]

Hey thanks for the info!!! I may just go ahead and oredr the things i need and do these mods!

[mrcdemon]

this mod looks pretty nice... i think i might have to try it

[FMZPLAYER1]

If you put that pot in series with the motor, you could set it real slow, and still have receiver and steering 100%. (only affects motor voltage/current, not main battery voltage)

[actofgod]

True. I don't imagine anyone would need to go THAT slow, however. :) The lack of resistance from the PCB would give you slightly different results than mine, but it shouldn't be anything worth mentioning.

If you had some LED headlights running off the PCB or something, you'd probably want to go that way (pot between PCB and engine) so they'd stay at a constant brightness. Unless you wanted to give them a dimmer switch, heh. They'd probably cut out abruptly below a certain voltage, though.

---

As a side note, if you happen to have a Motorworks clone (the one with a motor that turns the steering instead of magnets), I imagine you could install this pot to fine tune the steering speed; less voltage = slower, wider turns; more voltage = faster, sharper turns. That'd be a little step closer to proportional steering. I've never been able to find a MW clone, unfortunately.

[furiousbob]

wow, this is the first forum where there's actually people who think like me. whenever i posted anything about "pots" on other forums, they'd all call me a pothead. grr. but anyway, great mod, i'm considering layman's 3 cell mod for my thunderbolt and your beautifully thought out pot mod. thanks for all the info! cya

add-on edit: hah, sorta contradicting what i said before, but i'm sorta blurry on the different sorts of pots. would a 25 ohm trim pot work for a 3 cell?

[actofgod]

Originally posted by furiousbob
would a 25 ohm trim pot work for a 3 cell?

Sure thing. Anything close to the 20 ohm range.. just whatever you can find that will still fit between the PCB and the inside top of the car body. Do a test fit before you wire it to be sure.

[Kingofjapan]

I have many other PCB's from broken clones and other ones from broken bits. Do you think i could use the POT from that if i successfully remove it from the board???

PLEASE LET ME KNOW!!!

[FMZPLAYER1]

That's not really a pot on the board, it's an RF tuning coil / inductor. It wouldn't work as a pot, maybe as a wirewound resistor, but that's about it.

[Kingofjapan]

If it's not a pot, then how come everyone refers it to be one, even questformadness says: POT mod, as one it's main mods. Ah well, i doubt that i will be able to find one here. But i will try, this is worth every penny. thanks FMZplayer

later

[Kingofjapan]

anyone out there? I am sure someone knows if that POT wannabe on the board is useful otherthan it's use right now. I used one of my boards to make my 2 motor mod, so some of the FETs are removed, perfect donor for the POT.

Please let me know if this will work.

[FMZPLAYER1]

I just measured one, and it has very low ohms (0.3 ohms according to my DMM). That was 49Mhz coil, I think the 27Mhz (with more wire on it) would be almost 1 ohm, still not much resistance though. I have rewound coils for different frequencies, and found that the lower the freq. of the coil, means more turns of wire. (did this on Canned Heats/ Auldey).

You could wind up a coil with lots of wire to make a resistor, or even use an old steering coil as a resistor, but that is still just a single fixed resistance. Maybe with a tiny switch, that either shorts across the resistor for full speed, and is left open for low speed. Something like a micro version of a MSC.

[Kingofjapan]

can i wind up the coils on the pot thingy on the board. if i can, can i use the tuning function similar to the mod mentioned above?
that would kick arse, as well as being cheap, well the cost of the bit board *sniff*

anyhoo, thanks

I'll give it a try when i have some time. Can you send a pic of how you wound the coil?? (FMZplayer)

later

[FMZPLAYER1]

My last post might have been a bit confusing, making one think that the wire amount changed with the frequency adjustment when you turn the black core in/out.

The tuning core won't do anything for straight dc voltage, the coil would always be the same resistance with or without the little black core. It only works on RF signals

49Mhz coils are pre-wound with 7 turns of wire and 27Mhz are 12 turn coils. Tuning the core in/out only changes the frequency it will resonate at, maybe down to 45mhz or up to 53mhz at the most, but the coil still has the same turns of wire it started with.

[Kingofjapan]

thanks for that clarification...

OH MY GOSH!

where in winnipeg do you live?? A buddy and i have started a mini rc club. We hope to have posters up at cellar dwellar soon.

are you at university?

quick! answer the questions..

later

[FMZPLAYER1]

Actually I live outside of Winnipeg, in Oakbank (about 15 mins out from Winnipeg).

I'm not in university, though I was at Red River College a few years back. ;) Though I've been messing with electronic stuff ever since I was 8 years old, when my first RC died, and I decided to dissect the remains to determine the cause of it's demise. Been addicted ever since, I should sign up for AA (alkalines anonymous :D )

[actofgod]

Hmm, never thought of trying to use the tuning coil as a resistor. Doesn't sound like it would work too well though.. not enough resistance and not adjustable like a potentiometer.

Kingofjapan, rather than sacrifice a bit board, you might try some online vendors for a pot if there are none in your area. To my knowledge, allelectronics.com (http://www.allelectronics.com/shipping.html) does ship outside the US; check their shipping page or call them to be sure.

---

Also, while this fits perfectly with a Fairlady 350Z body, I tried it with a Honda s2000 body and it is a very snug fit. Still works, but double check the fit before gluing the pot to the pcb cover. The s2000 body has very little clearance compared to most bodies I've seen. I imagine if it will work then everything else should too.

[Kingofjapan]

i found some 100 ohm POTs with 25 turns. Can i use these? I read above that it would only have about 5 turns before it would completely cut off the voltage flow. If I can, oh man, i am going to put that sucker in.

thanks for the tips

and FMZplayer, nice to hear that the people that live out here have similar interests, even tho you are in Oakbank.

[actofgod]

As always, just do a test-fit before you go to the trouble of wiring it up. The multi-turn pot I found like that was a longer rectangle shape insead of a square, but the height was about the same. You may have more than 5 turns before the voltage cuts off, but probably only 5 or so "usable" turns.. I'm assuming you don't want your bit to run super-slow. If it fits ok, post your results when you're done!

[LEE50GURU]

:D
We now have a ZipZap (black Civic, and SOON an Eclipse) with 3.6v, potted, and headlights which are also potted to adjust brightness. The car looks completely stock from the outside, and uses the stock charging base. other than the weight, you'd never know it was modded! Using the 1.6 motor and red gears, the thing screams.

Next is the a/c charger and finishing the Eclipse with headlights/tailights.

[Racer9]

How much for 350Z with POT installed.:confused:

edit actofgod How much for 350Z with POT installed.:confused:

[Racer9]

how much for another eclipse LEE50GURU:D :cool: :eek:

[actofgod]

LEE50GURU, if you get a chance, post some pics of your completed work. It'd be nice to have more than one example.

Racer9, you'd be better off doing it yourself instead of buying a pre-modded bit. It'd be a lot cheaper, plus you get the satisfaction of finishing the job. You also learn a lot about the way a bit works in the process. If you bought one and something went wrong (like a wire came loose during a high-speed crash) you wouldn't know how to fix it unless you had done the work yourself, and it'd be really expensive to ship it back to somebody just to solder one wire back in place.

So.. grab a cheap clone if you're worried about messing something up, get yourself a $10 soldering iron from Radio Shack, and have a little fun. It's really not so hard once you get started, and you can always ask questions here in the forums.

Good luck.

[MadMicroDoc]

im not quite sure how you got the POT to stay on the pcb or where u soldered the wires ! and what wires to solder ?? I just recently completed the Layman's dual and tri cell mods, im totally obsessed, i just need a better charger. i really want to do this mod, sounds pretty sick !

[MadMicroDoc]

im not quite sure how you got the POT to stay on the pcb or where u soldered the wires ! and what wires to solder ?? I just recently completed the Layman's dual and tri cell mods, im totally obsessed, i just need a better charger. i really want to do this mod, sounds pretty sick !

[bdebde]

[i]Now I can adjust both speeds to run as fast as possible on any given track, depending on how many curves and straightaways it has.
[/B]

Wouldn't it be easier to adjust the speed by changing motors or gears? If it is too fast with three cells, then just use two cells. Now if you could adjust the pot from the transmitter while driving (can you say proportional speed control) then it would be worthwhile. I don't mean to knock your mod, just seems like a lot of extra hassle. BTW it is kind of cool though.

[BenCloned]

See the Proportional Steering Emulator thread. There is a theory being tested that may work for steering and throttle.

[actofgod]

Originally posted by MadMicroDoc
im not quite sure how you got the POT to stay on the pcb or where u soldered the wires ! and what wires to solder??

You can either put the pot between the batteries and the pcb or between the pcb and the motor. The first way will decrease voltage to the entire car, including dimming any LEDs you have (to some degree). The second way came from those who experienced a decrease in steering performance at low speeds due to the lower voltages available for the electromagnets. I haven't had this problem myself with two or more cells b/c I never want to go slower than 1.0 speed, but keep it in mind.

Reread the first post explaining the wiring. I'll recap: one wire goes from the +V battery terminal to the center pot pin; a second wire goes from the left pot pin to the +V connection on the PCB.

Use superglue to attach the pot to the pcb *cover* -- not the pcb itself.

[actofgod]

Originally posted by bdebde
Wouldn't it be easier to adjust the speed by changing motors or gears? If it is too fast with three cells, then just use two cells. Now if you could adjust the pot from the transmitter while driving (can you say proportional speed control) then it would be worthwhile.

At first, changing motors was the only way to change bit speeds. The problem with that is that it is expensive; if you wanted to buy every speed of bit motor, at about $7 a pop, you'd end up paying quite a bit more than the car itself cost. You still wouldn't have fully adjustable speed; you could only adjust speed in increments based on their RPM rating.

After the first (legendary) dual cell mod, another way of changing bit speed was born: increasing voltage. It effectively doubled (or tripled) the number of possible bit speeds, since each motor could operate at 1.2v, 2.4v, or 3.6v. It still required owning several motors if you wanted to adjust speeds, and otherwise it was generally not practical to go back from 2.4v to 1.2v again, since so much modification of the chassis had to be done.

This mod builds on the voltage concept and takes it to the next level: you no longer have to own several motors to change speeds (which is also a relief on the wallet). You can pick a nice, fast motor with a good balance between torque and speed, and after doubling or tripling the voltage can adjust the speed back down to slower speeds. The degree of precision possible is much greater than swapping motors; you can have an infinite number of speeds, including a wide range between the RPMs of the available motors that you couldn't otherwise reach. Swapping motors can get you close to the speed you want, but this can get you *exactly* the speed you want, whether it's matching the speed of another car or realizing that you need to take those corners at somewhere between a 2.2 and a 2.6 speed.. like a 2.4253 or so speed. : )

The next step in this evolution will be when, as you mentioned, the speed can be adjusted while driving. On page one of this thread, this was discussed in terms of a motorized potentiometer, but it is not currently feasible due to the size limitations. I'm very excited about the Proportional Steering/Throttle Emulator being worked on; it represents the end goal we're after.

As for difficulty: the more advanced you want your control to be, the more complicated it will be to achieve it. Swapping a motor is child's play. Adding more batteries is a little more complicated, but if you use the Layman's mod it's still easy. Adding a potentiometer requires adding batteries and having two wires where there once was one, a beginner to imtermediate level soldering job at the most. The Steering/Throttle Emulator looks to be the complicated of all, but that's what you'd expect from something that gives you full control.

[actofgod]

Oh yeah; I made icons for the Layman's mod and potentiomer mod over in the Misc Discussion Area (http://tinyrc.com/forums/showthread.php?s=&threadid=8304); if you have either mod on your car and want an icon for it, go show your support over there.

I'm talking to you, Chelboed :)

[ph2t]

Hey actofgod, thanks for the reference to my proportional controller emulator in your earlier thread. I've updated my work with some video, you'll be interested to see it in action.

Check it out, here (http://tinyrc.com/forums/showthread.php?s=&threadid=7108)

cheers,

ph2t.

[Spongebob]

Let me get this straight. If you want lower speed, you turn the little dial on the pot counterclockwise? And if you want faster speed you turn the dial clockwise?

[actofgod]

Exactly. As you turn it to the left, the resistance increases, allowing less power to the pcb and motor, and causing the car to go slower. Turning it to the right decreases resistance, allowing more power and more speed, up to the max speed available with your battery setup (recommend at least 2.4v).

[ph2t]

Heya actofgod! Welcome back! It's been a while.............

long time no tech! :D

ph2t.

[Mr.Qla]

ok i red on a nother site about the potentiometer thang but it was just the normal one so which screw is the pot screw?????????