RC cars are becoming more and more popular, with enthusiasts from all over meeting up to race or bash their vehicles to the limits. In either case, control is vital. So, if you notice your car moving when it should be idle, should you be worried about costly repairs?
Throttle trim on an RC car is in place to tell the car what to do when it’s idle. When properly calibrated, this setting lets the car know when to start and stop, preventing it from moving when you release the throttle. If it’s not calibrated correctly, the car may move without your control.
This article will explain what a throttle trim is, how it works, and how you can adjust it. Then, if your RC car isn’t responding correctly, I can help you calibrate both the vehicle and the controller, hopefully fixing any issues so you can get back to bashing.
The Purpose of Throttle Trim on an RC Car
Anybody who plays games regularly on a Playstation or Xbox has experienced controller drift: when you take your thumb off the joystick, but you keep moving right into an ambush.
Usually, a drifting game controller needs to be replaced. However, it’s a little different with RC cars.
Every radio controller has at least two channels:
- Steering control: When you turn the wheel slowly, your car makes wide turns. Turn it quickly, and your RC car makes sharp turns.
- Throttle control: Pull the trigger, and your RC car moves forward. Push the trigger back, and your car brakes or reverses.
As the radio controller sends signals to the car, the motor’s RPM goes faster or slower. When this happens, the car speeds up or slows down. However, when there’s no pressure on the trigger, the radio controller should be sending no signal at all. This lack of a signal causes the engine to stop.
The purpose of throttle trim is to keep your RC car still while it’s in neutral. So, much like your real (automatic) car doesn’t roll when in “park,” your RC car shouldn’t move when it’s idle. However, an improperly calibrated RC throttle will still send a signal even if you let go of the trigger.
The good news is, you can generally take care of throttle issues by adjusting the trim dials.
How To Tell if the Throttle Trim Needs To Be Adjusted
Most of the time, you should leave your trim dials alone. Once the settings for your system are dialed in, your car should stop and accelerate properly.
However, if you notice any of the following, it may be time to reset your throttle trim:
- Your RC car moves forward or backward when you’re not touching the throttle.
- Your car spins out too quickly when you pull the trigger.
- Your car suddenly stops or jolts into idle as you’re releasing pressure on the trigger.
How To Adjust the Throttle Trim
To make trim adjustments, follow the steps below:
- Put your car on the ground or a flat surface with the wheels facing forward. Make sure the controller is on.
- Locate the trim knob, one of two on most controllers, the second being for reverse. Check your car’s manual if you’re having difficulty finding it. Some RC cars have their throttle trim on the bottom of the car.
- Make sure you’re not touching the trigger and that it’s centered. You need an accurate reading when you’re not in control.
- Turn the throttle trim dial clockwise until the car starts drifting forward. Do this very slowly so you can see how the car responds.
- Turn the throttle dial counterclockwise until the car stops. Again, do this slowly so the calibration will be as accurate as possible.
If your RC car has been starting too quickly, turn the trim counterclockwise until it starts at your desired speed. If your car is stalling or stopping, move the trim knob clockwise until it slows down properly.
I find turning the throttle trim rate down can help when I’m driving on loose surfaces like gravel. It’s also helpful when I let a first-time driver take my RC car for a spin.
Limiting speed helps me maintain control or ensures my friend doesn’t damage my car. But, if you do that, make sure you return the trim to baseline when you or your friend finish.
Adjusting the Throttle Trim With a Transmitter
There are many different transmitters on the market at every range of prices.
Below I’ll cover a few of the most popular models. If you don’t see your transmitter listed, check your owner’s manual.
How To Adjust the Throttle Trim With a Traxxas Transmitter?
If you’re using a Traxxas transmitter with the Electronic Speed Control (ESC), the transmitter does most of the work for you.
Here are the steps for adjusting the throttle trim:
- Connect a battery pack to the ESC and make sure that it’s fully charged.
- With the throttle at neutral, turn on the transmitter.
- Press and hold the EZ-Set button until the LED changes from green to red.
- Release the EZ-Set button.
- When the LED blinks red once, pull the trigger to full throttle.
- Hold the full-throttle position until the LED blinks twice.
- Pull and hold the trigger at full reverse.
- When the LED blinks green, programming is complete.
This YouTube video from Traxxas shows in detail how to adjust the ESC:
The neutral throttle adjustment is located on the transmitter’s face and controls the forward/reverse travel of the throttle trigger. You can adjust between 50/50 (equal movement for acceleration and reverse) or 70/30 (more acceleration motion and less reverse travel).
NOTE: 50/50 is the default factory setting on Traxxas controllers. If you change it to 70/30, you’ll have to reprogram the speed controller, too.
How To Adjust the Throttle Trim With a Radiolink Transmitter?
Here are the steps on how to adjust the throttle trim with your Radiolink Transmitter:
- Go to Channel 3, the throttle channel, and switch the throttle to the lowest setting before using your controller.
- Switch on the controller and connect to the receiver.
- Go to the Subtrim screen, then adjust CH3 between 0 and 100.
This video explains how to calibrate the steering and throttle trim on a Radiolink RC4GS controller:
How To Adjust the Throttle Trim With a Futaba Transmitter?
Here are the steps on how to adjust the throttle trim with your Futaba Transmitter:
- The throttle trim lever (DT2) is near the steering wheel and can be moved in small increments to ensure your car does not move in neutral.
- You can also adjust the throttle trim digitally by going to the Throttle Trim (TRM-CH2) screen.
- Reverse the transmitter’s throttle channel direction either with the throttle trim lever or with the digital screen.
- Consult your model manual for further instructions.
Ryan Lutz of Team Futaba gives pointers on how he has customized his throttle curve and other settings on his Futaba transmitter. Watch his YouTube video below for more information:
Troubleshooting RC Car Throttle Problems
If you’ve followed all the steps above and are still having problems with your RC car’s throttle, there are a few more things you can do:
- Check the trigger. If you’re having throttle issues at certain speeds, the trigger’s electronic contacts may be worn out and drop their signal at one or more points.
- Check the carburetor. If you’re running a nitro engine, you may need to adjust your carburetor. Too rich a mixture can lead to sluggish acceleration, while too lean a mixture will cause stalling.
- Check the idle speed. Change the idle speed adjustment screw to ensure that your RC car idles at a healthy but not overly fast rate.
- Check the transmitter: If your car will only go at slow speeds or stops working, your transmitter’s amplifier may be damaged, and your transmitter will need repairs. Or you may need to change your batteries.