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Transmitters (Radios) Explained, Pt. 2

Posted 04-24-2009 at 09:54 PM by color0
Updated 03-08-2011 at 09:35 AM by color0
Ok, so you have your transmitter/radio in your hand, have turned on the radio and the car (remember, radio first and then the car!) and want to use your radio to get the most out of your car setup on the track. What to do? This week I'll go in depth on transmitter adjustments and what you can, can't, should and shouldn't do with them.

Let's go feature by feature, from low-end to high-end.

Steering Trim: As I mentioned last week this is the single most crucial adjustment on a radio. Adjusting this one is easy: do whatever you need to make your car drive straight when you tell it to. If you race oval, you could actually bias the steering in the direction of the turns; you can do the same if your car wanders a little bit on the back straight of a road course. DO NOT use steering trim to compensate for a tweaked car (that veers to one side under acceleration); it'll just not track straight when you're coasting, and that's just as bad.

Throttle trim: We're racing electric cars... set this to zero, the electronics in the car will know what to do. On the Perfex KT-18 (ASF 2.4GHz stock radio) you may want to put the throttle trim a couple steps towards the reverse, this makes engaging reverse a bit easier. But that's the only special case I've seen for Mini-Z's.

Steering dual rate: Like steering trim, this one's pretty important. You don't want your steering travel to go any further than you need on the track; this will improve the "resolution" that your right hand gets to work with, improving the control that you can have over your car. However, do not turn down the steering dual rate to calm a car that is obviously unstable; it's ineffective and you should be working on your car instead if its setup is that far off the mark. Steering dual rate should only be used to fine-tune at the last minute the minimum turning radius your car needs to get around the track most quickly.

Steering EPA: Endpoint adjustments are extremely useful, it's a shame it's only found on mid-range radios and up (and the KT-18 too, fortunately). Steering EPA allows you to set the maximum travel of your left and right steering range independently, i.e. you can make your car steer perfectly symmetrically. Again, DO NOT use steering EPA's to compensate for a tweaked car; fix the car first! Otherwise it will never feel quite "right" when you drive it.

Throttle/Brake EPA: Use this to limit the power of your motor and/or brake if necessary. Normally you don't limit your power going forwards (who likes to go slower? ) but reducing the amount of brake is often a good idea to keep the corner speeds up -- and if you drive a RWD car, to keep the rear end from overtaking the front. Note that on some radios, the full throttle/full brake value is reached on the ESC before it's reached on the radio. For example, on an ASF Mini-Z controlled by the ASF module on a KO Propo EX-1/EX-10, the throttle/brake EPA should only be set to 60% maximum either way. 60% on the radio somehow translates to 100% on the ESC, and anything more is useless.

Steering subtrim: Not crucial, but quite convenient to have. It basically adjusts your trim and both associated EPAs in the same direction in one fell swoop, so if you change your servo linkage on your MRCG or something and need to correct for it, use the steering subtrim adjustment. Like EPAs and trims, this is not to be used for curing a tweaked car.

Throttle subtrim: Not really useful for a Mini-Z... on nitro cars you use this to set the neutral position of the throttle.

Steering and throttle ARC/Punch: A diagram from the KO EX-10 manual is the best for explaining this adjustment:

The best use for this feature that I've found so far is to get around the "dead band" that is incorporated into the Mini-Z's electronics. By setting steering or throttle ARC/Punch to a small amount you can get around the dead band easily but have linear control for the rest of the wheel/trigger travel. But that's really it, play around with it if you're curious.

Steering Expo/Curve: Quite useful for last-minute adjustments of steering response/speed. Again, a diagram from the EX-10 manual is the best explanation:

Setting this to a positive value increases the "turn-in" of the car, akin to yanking the wheel harder into a corner. As the trajectory of a car usually follows the initial turn-in, the net effect of positive expo/curve is slightly livelier handling. Of course, a negative expo/curve will tone down the initial steering response as if you weren't twisting the wheel as hard. I love to use this feature a lot for long race days: since traction can change over the course of a day, instead of messing with a dialed car setup (of course, you DID dial in the car before the race day, right?), a small change to the steering expo can give a bit more or less steering as needed. Again, don't use this to compensate for a poor setup; your laptimes will not improve if the car itself is not actually any better.

Throttle Expo/Curve: Used to alter the throttle response characteristics of the car and/or to tone down really hot Mod motors.

A positive value here gives the car more initial punch when pulling the trigger; a negative value gives the car smoother, more progressive throttle response. I haven't messed with this a lot: I leave it at 0% for a nice linear feel. But some drivers, especially those who drive Mod, will set a negative throttle expo/curve to keep the power levels sane in the infield, and then go ballistic on the straight.

Steering speed: Controls the maximum speed (as a percentage of the physical maximum) that the steering servo can respond to your inputs. I personally recommend against having anything less than 100% steering speed, because you never know when you need to avoid a collision.

Throttle speed: Controls the max. speed that the motor can respond to your inputs. This one, on the other hand, CAN be used as a form of traction control. If you're having traction issues because you pull the trigger too hard, too fast, you can limit the throttle speed to 75% or so and observe as your car stays planted for longer when exiting a turn. However, I stress again that you MUST NOT use this as a band-aid for poor car setup! Limiting the throttle speed actually does limit how fast you can shoot yourself out of a corner, so before you worry about this adjustment you should make sure that the car actually has decent grip/a decent setup (if you're not sure of your own evaluatory skills, ask your local fast guy or the track owner to test drive the car -- more often than not they'll be glad to help!).

ABS: Not that I've ever seen this used for a Mini-Z (we don't brake all that often, do we now?) but it's worth a look. From the EX-10 manual:

You can set parameters like the pulse frequency, pulse duration, and pulse magnitude ("width" in the pic). So it works almost like real ABS, just without the sensors. If you race your Mini-Z on a very slippery track, or if you're trying to perfect your drifting (the brake pulsing can help slide control if done right), this may be worth a look.

Traction control: As I said before, this is like ABS in reverse. "Throttle acceleration", at least implemented in the EX-1 and EX-10, pulses the throttle when you pull the trigger within a specified throttle range.

Fun to look at, but I don't recommend using this. It's probably better to adjust the throttle speed if you're having traction issues from being trigger-happy.

Lastly, Model memory: If you have it, use it. Storing different settings for different cars gets extremely handy as your Mini-Z collection grows, and also if you have others drive your car, they can save the settings that work best for them. On my EX-1 UR I save a model for me driving my MRCG, and one for Binh, and one for TJ... the list will grow as more people drive my car.




So, hopefully this article gave you an idea of what you can do with your radio to make your Mini-Z driving experience as enjoyable as possible. But always keep in mind: the most important thing about car racing is the driver, then the car, and finally the radio. Radio adjustments, I'd say, are the very last 1-2% of winning a race -- if you don't work on your driving and your actual car first, you'll never even get within 2% of victory. As long as you keep your priorities straight, having the extra radio adjustments on hand will allow you to reach that last 2% and race to your full potential.


(One last note: All pictures were respectfully gleaned from KO Propo's user manual for the EX-10 Helios for the sole purpose of explaining the concepts of Expo/Curve, ARC/Punch, and traction control and ABS. Please don't sue me!)
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