RC Servos: What They Are and How to Choose the Right One

A servo is the small motor-and-electronics package that turns commands from your transmitter into movement: it steers an RC car, moves a plane’s ailerons and rudder, or works the throttle on a nitro car. A good servo makes the car turn precisely and always return to center.

How a servo works

Inside the case there’s a small motor, a gear train and a potentiometer that measures the output shaft’s position. The receiver sends a signal with the desired position, and the servo’s electronics drive the motor until it gets there, then hold it, even when the wheels or the control surface push back.

Which specs to look at

• Torque (kg·cm or oz-in): how much force it can exert. The heavier the model and the bigger the tires, the more torque you need.
• Speed (sec/60°): how long it takes to rotate 60 degrees. Fewer seconds means faster response.
• Voltage: standard servos run at about 4.8–6 V; HV (high-voltage) servos accept higher voltages and deliver more torque and speed when powered at their rated voltage.
• Gears: plastic (light, more fragile) or metal (better at taking hits to the wheels).
• Analog or digital: digital servos correct their position more often, are more precise and hold with more force, at the cost of higher current draw.
• Size: standard in most 1/10 and 1/8 cars; mini and micro in small models and light planes.
• Water resistance, if you’re going to drive through mud or puddles.

Which servo to choose for your model

• 1/10 entry-level car: a standard servo with metal gears is a good upgrade over the stock one.
• Crawler: lots of torque and metal gears, because the steering works against rocks and with big tires. See RC crawlers.
• 1/8 buggies, truggies and monster trucks: high torque and speed to steer heavy wheels at high speed.
• Touring cars and drift cars: speed and precision matter more than torque. See RC drift cars.
• Planes: lightweight servos (micro or mini) for ailerons and rudders; the torque you need depends on the size of the control surfaces.

How to install and center a servo

1. Plug the servo into the receiver on the steering channel (usually channel 1 on pistol-grip transmitters).
2. Turn on the transmitter and receiver with the steering trim centered: the servo will move to its center position.
3. Mount the servo horn as close to perpendicular to the steering link as possible, without forcing it.
4. Set the end points on the transmitter so the servo doesn’t strain against the stops: if it buzzes at full lock, reduce the travel.
5. Use a servo saver if your car has one: it protects the servo gears in crashes.