Setting up a new radio: EPA, sub-trim, dual rate and expo

A transmitter has a lot of menus and you need about five of them. Set them in this order, because each one assumes the previous is done.

1. Sub-trim: centre the servo

With the car on a stand and the steering untouched, the wheels should point dead ahead. If they do not, first check the mechanical side — the servo horn should be as close to square as the splines allow, and the link lengths equal.

Use sub-trim for the small remainder only. It shifts the servo's neutral point, and a large sub-trim value eats into the travel available on one side. Get it mechanically close, then trim the last of it electronically.

2. End point adjustment: stop the binding

EPA (also called travel adjust) sets how far the servo moves at each extreme. Turn the wheel fully one way and watch the steering. If the linkage reaches its mechanical limit before the servo stops, the servo is pushing against a stop it cannot move — that is binding. It draws current continuously, gets hot, drains the pack, and eventually strips the servo gears.

Reduce the EPA on that side until the steering reaches full lock without straining. Set each side independently; they are rarely the same.

Do the same on throttle if your ESC needs it, then calibrate the ESC to the transmitter so full throttle and full brake are recognised properly.

3. Dual rate: how much steering you get

Dual rate scales total steering travel from the wheel. Lower it and the car turns less at full lock everywhere.

This is the setting to reach for when a car feels twitchy on a fast track. Around 70–80 % takes the nervousness out without making the car unable to turn. On a tight track, wind it back up.

4. Exponential: how the steering feels near centre

Expo changes the shape of the response rather than its limit. Negative expo (on most radios — check yours, the sign convention varies) makes small movements around centre gentler while keeping full lock available at the extremes.

This is what you want on a high-speed track where the car darts on the straight but you still need full steering in the hairpin. Try 10–20 % and adjust to taste. Some drivers love it, some cannot get on with it.

5. Fail-safe: the one people skip

Set this. If the signal drops out — interference, a flat transmitter battery, driving out of range — the receiver applies whatever you configured.

Set throttle to neutral or to brake. The default on some receivers is to hold the last command, which means a car that loses signal at full throttle keeps going at full throttle into whatever is in front of it. Most clubs will ask you to have this set, and it takes thirty seconds.

Test it before you rely on it: with the car on a stand and running, switch the transmitter off and check the car does what you expect.

Then save it

Save the model memory and name it after the car. When you swap between cars, you are one menu away from the right settings instead of resetting everything by hand.