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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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Posted 03-08-2011 at 09:19 AM by color0
Updated 03-08-2011 at 09:28 AM by color0
Setting up a Mini-Z for club racing is not extremely difficult -- you start off with a working baseline, get your parts installed, jump on the track and it's typically good enough to work with. But if you want to get the absolute most out of your car, set lap records, go race the Worlds', then you have to start back at square one: assembly. This article will go over all the little places I've found so far where you can make an improvement from a stock Mini-Z -- once your base is good, you can go back to your car setup and optimize it for the track. By no means is this a new guide, but this info should always be somewhere handy for new racers and it hasn't been on my blog yet.

1) Slop/Play

In a car as small as a Mini-Z, the slightest lack of precision means you'll make that one extra mistake during a race, which means you take that one extra second to recover, which means that you probably give up a position if you're in a competitive field of racers. Reducing slop is paramount to your car's performance and degree of confidence that it inspires in you!

Starting from suspension: Steering knuckles, tierods, and suspension arms all must have minimal play. If there's one particularly sloppy part, you're going to have to be anal -- fix it, sleeve it, shim it, or replace it. Otherwise your steering may wander, bump steer can happen (hey, the tierod's not 100% controlling the knuckle angle!), all sorts of things that make the car feel vague.

Rear end (RWD): Invest in a locking rear left hub if you have a gear diff (ball diff packages come with one). When you lock the hub down, you want to make sure there's NO visible play in the rear axle. I will half-tighten the locking hub at a position that leaves the axle loose, and pop on the rear left wheel. As you tighten the wheel nut, the hub will gradually be squished down the axle -- just before it binds, stop tightening the wheel nut, and crank down the locking hub's set screw. Now your axle is slop-free!

In addition to the rear axle, also make sure your suspension's working bits have no play: disk damper disks should fit snugly on the post; oil or grease shocks should not wiggle on their respective mounting balls. If anything wiggles, replace the offending part ASAP because it's not doing your car any good! If you are running the new Qteq pivot block T-bar, or the PN Gimbal system, make sure all the pivots are slop-free -- shim what you can and replace what you can't, having a solid base for suspension movement is necessary for you to even begin tuning.

2) Binding

The opposite of slop, binding restricts your parts from moving freely, which makes your car run like crap or in the worst case (motor/diff seizure) can completely stop your car. If you find parts that are binding, fix or replace them ASAP before they wear out or damage something else!

Suspension: kingpins and hinge pins are the most common sources of binding, and easily fixable too. If the pin diameter is a bit large, just polish it down with a dremel, or open up the hole with a drill bit. Ball pivots sometimes suffer from this too, in which case the solution is a ball reamer. Sand down suspension arms rather than hinge mounts if that's what's binding -- keep as much hinge mount as possible as a general rule of thumb.

Rear end (RWD): Make sure your disk damper disks don't bind on the post -- it makes your car feel inconsistent as the disks load and unload on the damper plate. Likewise, if you have a tri-shock, oil shock or side damper, make sure you don't overtighten the balls, which will bind up the shock ends.

(RWD) Make sure your motor wires are long enough to allow free rear pod movement, but short enough to avoid hitting anything inside the body -- don't let your motor wire become an extra spring, the car will feel very strange when you drive it.

(PN Pods) If you use PN's Reconfigurable Motor Pod, make darn sure that your screws are securely fastened, and that the uprights are correctly aligned. If they are not, your bearings will have a slight drag to them and that could easily cost you 0.1-0.2 seconds per lap. The motor mount itself should be checked for straightness every so often -- I accidentally dropped my car between races and it took me quite the while to realize that the tweak was coming from the motor pod getting knocked a tiny bit forwards.

3) Tweak

Hugely important! Make sure your car steers the wheels to the same angle in both directions, check the chassis for flatness, and make sure your left/right wheels protrude the same distance from the chassis centerline. Short of slop and binding, tweak is the biggest factor in making your car handle poorly. If you find tweak, fix it as best you can (sometimes you can bend and set Mini-Z chassis, T-plates, etc.), if you can't fix it, replace the main chassis as that's sometimes the cause.

4) Bearings

Buy good ones, and clean them! You don't necessarily have to have ceramics to be competitive -- I buy Avid shielded bearings and after clearing out the grease with an alcohol bath, they spin just as free as the best ceramics. Of course they won't last quite as long, but that's a tradeoff you can choose to make or not make (ceramics really do last forever though, pretty amazing). Clean them regularly -- a bound bearing will make the car feel like it's tweaked!

(RWD) I would highly recommend ceramic bearings in two places, for RWD Mini-Z's only: The rear right wheel, and the right diff hub. These two bearings get a lot of abuse when you're racing and it makes sense to use a bearing that is more durable.

5) Tire mounting

Do what's necessary to keep your tires on your wheels. For most of us that means tire tape; if your tires are REALLY soft then I highly suggest gluing them (I have a tutorial on this blog, actually, just look back a few pages). Tire sidewalls sometimes fold under high cornering loads and that causes a troublesome chatter at the affected wheels. Chatter makes your car slow and inconsistent, so get those tires mounted right.

On top of securing your tires, you should have at least some method of making the tires as round/true/concentric to the wheel as possible. Doesn't matter if you don't have a truer -- squeeze the tire on the rim to make it more true, and utilize spare drivetrain parts (the entire rear end off a stock MR02 will do) as a lathe so you can sand tires. For the ultra-nitpicky, a truer will always be the best solution though, as you can strictly control your starting tire diameters as well as heat-treat your tires before they go to the track to be broken in. If you're going for the absolute best performance, I'd suggest getting or borrowing a tire truer to prepare your tires.

6) Batteries

I haven't done anything fancy with my batteries yet, but I know I will have to to compete with the world's best Mini-Z racers -- currently I just discharge and charge my TRP 900's in packs and call it a day. To get more out of them, try taking care of your cells individually, and discharge deeper (to something like 0.7V) and charge higher (1.5-2A) and you'll get more power out of them. Keep in mind that it does shorten your cell's life, but you may decide it's worth the extra power you get.

7) Motor

The standard maintenance should apply to all your motors: clean out the motor with compressed air at the very least, and motor cleaner if you can swing it. Lube up the bushings/bearings with good oil (I like the Reflex Purple Stuff actually), make sure the brushes are broken in but not worn down.

There's a bit of debate as to how motors should be broken in. I tend to just run the motor on a bench at 4.8V, but no load (i.e. car on a stand), let the brushes seat themselves slowly and clean out the debris afterwards. Others will dip the motor in water, which flushes out debris as it forms, but you have to carefully clean out the motor can afterwards to avoid rust/corrosion. In any case, find a break-in regimen for your motors that works for you -- popping a fresh motor into your car isn't going to give you the best power, at least not till the brushes are broken in from you driving it.

8) Differential

Make sure the diff(s) has enough ball diff grease left inside and that it's correctly set: it should slip just a little bit from a standing, full-throttle launch, while providing free differentiating of the left and right wheels. If there's anything gritty-feeling and it doesn't loosen up after a couple laps, you need to rebuild that diff.

If you're still using gear diffs, I highly recommend putting some grease or shim in there to set a small amount of anti-slip. It's not ideal and difficult to adjust, but the slight LSD effect will make your car faster when the wheels aren't always in contact with the ground (as is the case with bumpy RCP).

9) FETs/Current handling

The less resistance in your electrical circuit, the more power you can send more efficiently to your motor. Even in Stock class racing nowadays we go to 2x2 or 3x2 FET stacks to get the juice going. On that same note, you can reduce the resistance as well as weight by removing your power switch. Some people upgrade their wiring within the car entirely, and for Mod I think it might be worthwhile. For Stock even I'd say it's a bit too much effort for minimal gain.

10) Body preparation

The normal rules apply, but in addition to those, pay attention to your body's ground clearance, overall height, and clearance to tires. Current PNWC rules allow bodies to be shaved for ground clearance, so if you've slammed your car already but it's still tall and you have plenty of tire clearance, shave the bottom and slam it more! I'm of the camp that for racing, lower is better. If you need more body roll, go narrower!






That's more or less the checklist I go through when putting together a new car -- next time, I'll cover the actual setup and tuning process. Cheers!
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