A high-spec radio control system is one of the most popular upgrades as people get more involved in RC cars. There are many benefits - generally improved signal quality with less interference, nicer quality feel in the hand, and a huge variety of (often computerised) adjustments. Popular brands in the UK include Futaba, KO, Hitec, Sanwa and Spektrum.
But this multitude of adjustments can be a blessing and a curse. I see loads of people who have set the radio up incorrectly, and the car ends up running worse than it was with the original low-spec radio system! This guide should help you through the minefield of radio settings. I will use the Futaba names for each function, other brands may differ slightly but the manual should make the functions clear.
These tips aren't just for racers - they are for everyone. Could you imagine taking your full-size driving test in a car that only had full lock on left-hand turns, or where the accelerator pedal only had half-an-inch of travel before reaching full throttle?
Never switch on your radio without checking that nobody else is on the same frequency (either at the track or playing in the park). Interference can send models out of control, damaging them and possibly the people near them. Always switch on your transmitter before switching on the car to stop runaways. Turn the car off before the transmitter when you have finished.
Correct servo installation
The first thing to do with any new radio setup is to make sure the servos themselves are installed properly. Sometimes when you change radio brands the servos will centre in a slightly different position, or even turn in the opposite direction. This needs to be corrected.
Power up the transmitter and the receiver with the servos plugged in. Make sure all the radio trims are set to neutral (if the radio is new they should be at neutral by default). Now fit the servo horns close to where they should be. Generally speaking horns and linkages are set at 90 degree angles, but your car may need to be set up a little differently to get even and maximum throw in all directions.
The first setting to use is Subtrim. Subtrim is a master control that adjusts the neutral position of the servo without affecting its throw in either direction (unlike the normal trim). This should be used to fine tune the servos horns to the correct initial positions.
Example - a steering servo may need some subtrim to get the horn at 90 degrees to the servo case.
ATV (Adjustable Travel Volume), also known as EPA (End Point Adjustment) is a master control used to limit (or increase) the total throw of the servo in one or both directions. Use this to make sure that full travel is reached, and to stop the servo from straining against bump stops (if you can hear the servo buzzing at full travel it is under strain and may be damaged). ATV should only be adjusted with the Dual Rate at maximum (see below).
Example - the throttle servo ATV should be set so that the carb is only fully open at full throttle (no more, no less). This means you will have a progressive throttle response.
Transmitters also have conventional trims. Once the Subtrim and ATV have been set, the car can be given a test run and the trims used to fine tune it. If large amounts of trim are required the master radio settings may be wrong or the car may need mechanical attention.
Example - steering trim must be set so the car runs in a straight line at your usual running speed (I see far too many cars that veer off to one side, trust me when I say that the cars are much easier to drive when they run straight!). Some cars may pull slightly to the side at low speed, this isn't necessarily a cause for concern but if the difference is large something on the chassis may be out of alignment.
The throttle trim may also need setting. On most electric cars it can be left untouched once the electronic speed controller is set, on nitro cars it may need a little fine tuning. Make sure that you do not cause the brakes to engage or the throttle to partially open at neutral.
This is the setting that is most often misused. Many people treat it like ATV (see above). This is wrong. Dual rate is a slave setting used to limit the amount of servo travel within the master setting of ATV. Correctly set up, maximum dual rate will give maximum servo travel, half dual rate will give half that travel.
Example - steering dual rate should be turned down if you wish to limit the amount of steering lock you have, with 100% as full lock. Don't set dual rate at 60% to stop your servo straining, this is what ATV should be used for.
EXP (exponential), also called curve, allows you to adjust the mid-range feel of the throttle or steering. A mild or negative setting will make the servo move less with a partial control movement (e.g. at 50% steering input, the servo will only move 40% of its travel). A fast or positive setting will make the servo move more (e.g. at 50% input, the servo will have moved 60% of it's travel). EXP should only be used in small amounts, if a car needs large amounts of EXP to be controllable, either the master radio settings are wrong or the car itself needs attention.
Example - if the car is very sensitive to small steering inputs, a negative setting can make the car easier to control. Equally, if the car is slow to respond, a positive setting can make the car more responsive.
Beyond the basics
Some radios have an astonishing array of features, including traction control, ABS, and totally customisable throttle and steering curves. My advise is to not use any of these functions until you are totally confident that the settings will help. Traction control and ABS in particular are very demanding on servos. Your fingers and thumbs are the most accurate way of controlling the car - practice is a lot more important than complicated radio settings.
I hope this guide helps, and maybe some of you will read this, take a look at your car again, realise that something was set wrong, and see the benefits immediately the next time you drive.
Director, RC Direct Ltd