A Newbie's Guide To Bottlenecks

[Horshu]

I've been thinking a bit about the inner workings of my car more and more as I slowly but surely start checking off the various improvements, preferrably consisting of "ultimate" solutions, I want to make to my car to bring it to a state of completion. Along the way, I started identifying the various bottlenecks that limit the XMOD's speed as well as solutions to the various bottlenecks. These are discussed in varying levels of detail elsewhere, but I wanted to bring together a succint guide for the newbie that in interested in tricking out the XMODS to the upper limits of its physical design (my XMODS design philosophy is along the lines of Formula 1 or Koenig/Callaway, so I'm aiming to answer the question of "How far can an XMODS go without altering the outer body asthetic?"). If anyone would like to add to or dispute any of my conclusions, please feel free to do so.

1. Drive train friction -> Solution: replace nylon bushings with ball bearings. Radio Shack BBs a start, but TinyRCs are excellent here (although I'm going to eventually test it against some of the VXB ceramic ones, as the VXB wide tracks are expensively bad-ass). Possibly grease the drive shaft, as my CF one shows marks from rubbing the ESC assembly

2. Power supply -> Solution: add lithium ion, although my car's setup has swappable battery harnesses, so I can drop in 4 AAAs or 2 AAs.

3. Weight -> Tricky one. Is light good? I actually like the extra weight of my aluminum a great deal, as it handles like a dream. If you want light weight, keep the plastic and buy a lighter (Zero CF or AtomicMods Switchblade) chassis. If you want the extra weight for stability, aluminum parts do the trick

4. Loose suspension -> Caused by crappy RS lugnuts, play between dogbone & cup joints, servo play, and tie rod-to-knuckle play. Solutions -> two wide track bearings per wheel covers dogbone play(most people say just 1 on the outside per rear wheel, but I use 2 per on the back as well) + wheel shims to fit the wheel on the inner bearing track better. Replace stock steering knuckles with aluminum. Have found no way to remove servo play.

5. Turning restrictions -> Replace surface mount resistors with lower-resistance parts to allow for full range of steering, although this may increase steering jittering

6. FET limitations -> Extra power can overload the onboard FETs. Solutions -> stack FETS to distribute the workload, although it results in more power going to the entire board, affecting braking/reverse (good) and steering (bad). External turbo -> because space is no longer an issue, as the power FETs are placed offboard, bigger FETs can be used for a greater range of allowable power. Also, newer turbos are sending a regulated 5V back to the board, which reduced steering jittering

7. Motor limitations -> Standard XMODS motor size is 130 and can handle 4 AAAs fine. However, lithium allows for more power being thrown at the motor, which means more heat. Also, lithium allows for longer running times, which enhances the heating problem (heat can shorten magnet life and fry the motor, although I'm not sure if a fried motor means the wires are melted or the armature/commutators are damaged). Solutions -> motor with thicker-gauge wiring to handle higher volts/heat, silver wire for better conductivity & less heat dissipitation, ball bearing motor can, carbon fiber brushes, added motor heatsinks, & using a 180 motor instead of a 130, although it won't fit in chassis configurations.

8. Wire/solder limitations -> Yep, even these bad boys can be overloaded. Solutions -> thicker gauge wiring (I'm using 18g superflex, but even that is "only" rated at 5A sustained, so throw enough power at it, and you could theoretically melt wires and/or soldering points, although with a turbo board, the ESC should be safe.