What Does a Servo Do in an RC Car? Steering Servos Explained
In an RC car, the servo is the small motorised unit that steers the front wheels. It receives a signal from the receiver telling it what angle to move to, and an internal motor, gearbox and position sensor move the output arm precisely to that angle and hold it there. Cars may have extra servos for two-speed transmissions, locking diffs, winches or lowrider “hydraulics”. A stronger, faster servo makes steering more precise, especially on bigger cars with large tyres.
By Kyle HilsonUpdated: October 20263 min read
How a servo works
Inside a servo are a small motor, a reduction gearbox, a position sensor (usually a potentiometer or magnetic encoder) and a control board. The receiver sends a pulse whose width corresponds to the desired position. The board compares that with the sensor’s reading and drives the motor until they match. This closed loop is why a servo holds its position against forces from the wheels. The whole steering system is explained in how RC car steering works.
Key specifications
| Spec | Meaning | Typical car values |
|---|---|---|
| Torque | Turning force (kg·cm or oz·in) | 5–10 kg·cm (1/10 racing) to 25+ kg·cm (1/8, crawlers) |
| Speed | Time to move 60° | 0.05–0.20 s |
| Size | Standard, low-profile, micro | Standard for most 1/10 cars |
| Gears | Plastic, metal, titanium | Metal for bashers and crawlers |
| Voltage | Standard or high-voltage (HV) | HV servos need a matching BEC |
Other jobs for servos
- Shifting two-speed transmissions.
- Locking and unlocking differentials on crawlers.
- Operating winches and scale accessories.
- Lifting suspension on hopping lowriders.
- Throttle control on nitro and gas cars.
Servo savers
A servo saver is a spring-loaded link between the servo and the steering. When a wheel hits something hard, the saver flexes instead of stripping the servo’s gears. Too soft a saver makes steering vague; too stiff passes shocks to the servo. Most bashers keep a saver; many crawlers use a solid horn with a strong metal-gear servo.
When to upgrade
- Steering is slow or doesn’t return to centre.
- The car won’t turn with heavier or bigger tyres.
- The servo buzzes or jitters at rest.
- Gears strip after crashes.
- You’re racing and want faster response.
More on choosing servos is in the RC servo guide.
Installing a new servo
- Centre the servo with the radio on before fitting the horn.
- Use the correct spline horn for the servo.
- Set steering end points so the servo doesn’t stall at full lock.
- Check the BEC can supply enough current, especially for HV servos.
- Re-check trim and steering direction.
Analog vs digital servos
Analog servos update their position fewer times per second and hold less firmly at small corrections. Digital servos update much faster, giving quicker response, stronger holding power and better centring, at the cost of more current draw. Brushless and coreless servo motors add smoothness and efficiency. For racing and crawling, digital servos are standard; for basic bashing, a good analog servo can be enough.
Waterproofing
Many RTR cars have waterproof servos, but cheaper cars may not. If you drive through puddles and wet grass, a waterproof servo prevents corrosion and failure. Dry the car after wet runs anyway.
FAQ
What does a servo do in an RC car?
It steers the front wheels, and can run gearboxes, diffs or winches.
How much torque do I need?
5–10 kg·cm for small cars; 20+ kg·cm for 1/8 and crawlers.
Why does my servo buzz?
It’s holding against load or end points are set too far.
Do I need a waterproof servo?
If you drive in wet conditions, yes.
More on this topic: the complete RC Cars guide covers the basics behind this article.
About 20 years in RC. Mostly boats in the NAVIGA Mini Eco Expert class, with many self-made parts; also a King Motor Baja 5B, a home-built electric plane, home-built nitro planes he has flown, and an RC helicopter. More about SwellRC
