Here's a page with tuning tips and various other tricks of the trade. Send them in!
Onroad Cars Offroad Cars Tricks of the Trade
Pan Cars
In a pan car, there are relatively few tuning adjustments when compared to a touring car or an offroader. However, the ones that you have available to you are very important. The differential
would probably be the most important adjustment on a pan car - the car is little more than a pan with a differential on it! If the diff is too 'tight', or hard to turn (when holding the spur gear
so that the opposite wheel turns the opposite way), the inside wheel will slip in a corner, and the rear tires will slip under hard acceleration. If it's too loose, the diff may not fully engage
- the motor will rev high, but the spur is slipping between the diff plates. If the diff is too 'notchy' (does not turn in a smooth fashion or hangs up on one spot) it just plain won't work
right. A properly adjusted differential will let the tires turn at the correct rates in turns, act (just a very small amount, and mostly for low-grip tracks) as a slipper so the rears don't spin,
but transfer the most power to the ground. On my LW, I adjust the diff so that it is 'too loose' and you can audibly hear the motor slipping. Then I tighten it up from there to suit the track.
Longer and/or higher-grip tracks use a tighter diff to get more power down (otherwise it will slip even at top speed), and a easy throttle finger to keep wheelspin down. Shorter or low-traction
tracks use a looser diff since you'll be basically going full on, full off the throttle. Then the diff acts as a slipper.
Tweak is another vital adjustment on pan cars. The whole point of adjusting the tweak is to adjust the load of a car on all four corners evenly. No matter how carefully you place all of the
electrics, chances are the car will be out of balance (and it changes as the tires wear). Using the tweak screws, you can even it out. There are tweak boards available to make the task easier,
but it simply comes down to getting the ride height even from side to side. Speaking of ride height...
Ride height (in the rear) and side-to-side travel of the rear pod on a pan car are two very carefully intermixed adjustments. If the ride height is too low (or the side-to-side is too great),
the chassis will scrape the ground. This can and often will snap the car out of control. If the ride height is too high (or the side-to-side is too low), the tires will have to try to make all of
the grip, and you may see the car 'shuddering' around corners as the tires bite, then lose grip as they are pushed past the limits, then bite, then slip, etc. Cars like my RC12LW like more ride
height because there is a lot of side-to-side. However, I felt my friend's L3 - the ride is lower, but the side-to-side has been greatly reduced. The perfect mix depends on the car and the track.
Very smooth tracks can run low ride height and low side-to-side, and get the handling benefits of it (lower ride height seems to have a better affect on the grip than increased side-to-side).
However, if your car has a lot of side-to-side travel and/or you run on a rough track where you need the height to get over the bumps without bouncing too much, more ride height helps. Ride
height can be adjusted with taller tires (adjust the gears to keep the same rollout) and moving the axle carriers so that the axle is as low as possible in the car (making more ride height).
Tire saucing is a critical point on pan cars. Before you use it, you should determine how your car handles. If it is 'loose', or spins out too much, no matter how carefully you adjust the
differential, you should sauce the rears only. If it 'pushes', or doesn't turn enough, try saucing the fronts only, or then fronts and rears. One other problem is that sauce builds up on foam
tires. Pros let tires dry out for a day between runs, but that's awfully expensive. A better solution for most of us is to only put a full coat (the whole tire, wipe off excess) on for the first
run, then do about 1/3 the amount (down the center, spread on the whole tire) for each run thereafter. If you notice your car handling poorly, then getting better later in the race, you have too
much sauce on your tires. (or the track may be dusty as well.)
Tires. Sort of an expansion on saucing. On my 12th scale, tall tires are cool. Very cool. It handles much better with them. TRC Green Dots at about twice the thickness of factory-trued (not
diameter, just the actual tire thickness). Mounting your own donuts is easy. 1) Soak old wheels/tires in lacquer thinner until tire slips off easily. 2) Coat rim and inside of tire with contact
cement - let dry. 3) Dip rim, then tire in lacquer thinner, and slip the tire onto the rim. (If your tires aren't exactly the same width as your wheels, line up your fronts flush with the outside
edge, and the rears flush with the inside edge.) A conical device helps here. 4) Let dry overnight, then true to desired shape / diameter. I guess my car follows an old-school philosophy - higher
ride height with more side-to-side roll. Not quite as fast as the lower, stiffer setups of newer cars, but easier to drive.
Smoothing out the differential. Is that diff feeling a little more notchy than it used to be?
Here's the easy way to make it smoother than it's ever been. (Works on AE pan-car diffs with large
rings only). It's quite simple: buy some new rings and fill all the holes in the spur gear with balls,
not just the outer ring. It's amazing how smooth it is. (It may even help people with small rings -
try switching to the big ones and filling all of the holes.)
Many people who don't race their offroad R/C vehicles like to take them through all sorts of terrain and insane situations. Chances are it includes grass, rocky dirt lots, gravel, pavement, and
who knows what else. However, in many of those situations, the stock shock positions do not provide enough ride height to clear the obstacles properly. The car slows down in grass and gravel,
bottoms on the huge jumps, and gets hung up on rocks that are just a little too big. The easiest solution is to not drive there at all, but that's no fun! If your car has adjustable shock mounts,
move the front shocks to the innermost mounts on both the arm and the bulkhead. Out back though, you need to find the mounts that will give you more ride height but not pop the dogbones out. You
may be able to set it up so that the dogbone doesn't come all the way out, but the more that it does come out, the higher the chances that you will pop it out, necesitating a trip to the
workbench to fix it. At any rate, you'll get more clearance for higher speeds in grass, sand, and gravel, less snags over the big rocks, and less bottoming out with little or no visible loss in
handling.
Battery maitenance is a hot topic in the newsgroups. The only points agreed on is that a) Discharging batteries to a set point is good for them, and b) Sticking to a 'regimen' is also good. When
you set up your charger, use the same charge rates, and if you watch the voltmeter to peak it, go by the same standards to determine a peaked pack every time (i.e. pulling it off once it levels
out rather than waiting for it to level then drop say .03 volts). Also, when discharging, be careful what you use. The dischargers built into some timer-style chargers can do more harm than good
- they just discharge and keep on going until you yank it off. Going down to a set voltage per cell - anywhere from .9V to 1.1V is a good recommendation. This can be achieved with either
discharge trays that drain each cell individually, or a discharger and a 'black box' that cuts the pack off at somewhere between 5.4V (.9V, 6 cell) and 6.4V (1.1V, 6 cell). This way, the cells
aren't damaged by over-discharging.
Good power supplies can be hard to come by for an R/C charger setup. People use everything from a 12V lead-acid battery to computer power supplies and purpose-built units. Since virtually all
chargers require an external 12 volt power supply, all of these work well. However, they work to different extents. Charging batteries from a car battery provides plenty of power, but can only be
used so many times before the car battery needs charging (especially if the car battery needs to be used to start a car!). It also provides 'clean' power - without a lot of spikes and the like.
Automotive battery chargers - the chargers that are used to charge the car batteries - can also be used as power supplies, but some say that they have 'dirty' power - lots of spikes, drops, and
surges. These can mess up more sensitive chargers, although some chargers (like the Tekin BC112 series) actually filter the incoming electricity. Computer power supplies work well, but some
cannot carry the current, and they need a signifigant load before it actually switches on. The best solution is a supply from a place like Radio Shack - a 15 amp one can run at least 2 chargers,
and they have clean power. However, for the really high-quality ones, the price can get pretty high. But a good power supply should be in every racer's toolbox - even most AC/DC chargers can
benefit from one. It lets the charger itself run cooler (it doesn't have to drop the power from 120VAC to 12DC), and chargers like the base-model Hobbico timer-charger actually charges faster
(higher amperage) when run from an external power supply, and doesn't get too hot to touch (like it normally would). Some AC/DC chargers have a good enough power supply (like the BC112C) that
they can actually drive another charger! The BC112C, when running from 120VAC, can output 24VDC to a BC112A (DC only version), letting both chargers charge up to 12 cells each at up to 5 amps
each!
That's about all for now...so go home.
