CompetitionX CompetitionX is the most up-to-date source for RC Car News, Reviews and Videos for Radio Control. We also have the most comprehensive Manual Database on the web.
If you’ve spent any time around RC cars, you’ve probably heard people talk about servos. They’re one of the most important parts of an RC vehicle, yet they’re often overlooked until something stops working.
In simple terms, the servo is what turns the wheels. When you move the steering wheel on your transmitter, the servo receives that signal and physically moves the steering linkage on the car.
That’s the basic idea. But inside that small plastic case is a surprisingly clever system made up of electronics, gears and a motor all working together to give you precise steering control.
Let’s break it down.
What Is an RC Servo?
A servo is a compact device that converts an electronic signal from your receiver into controlled mechanical movement.
In an RC car, the servo is almost always used for steering, although it can also control other functions such as shifting transmissions, operating accessories or, in a Nitro vehicle, controlling the carburetor on your engine.
When you turn the steering wheel on your radio transmitter:
- The transmitter sends a signal to the receiver in the car.
- The receiver sends that signal to the servo.
- The servo rotates its output shaft to a specific position in relation to your movements on the wheel.
- That movement pushes or pulls the steering linkage.
- The front wheels turn left or right.
The key here is that the servo doesn’t just spin like a motor. It moves to very specific positions depending on the signal it receives.
That’s what gives RC cars their accurate steering control.
The Main Parts Inside a Servo
Even though servos are small, they contain several important components working together.
1. Electric Motor
At the heart of every servo is a small electric motor.
This motor provides the power needed to move the steering system. However, the motor itself spins very quickly and doesn’t produce much torque on its own.
That’s where the gear train comes in.
2. Gear Train
The motor connects to a series of gears called the gear train.
These gears do two important things:
- Reduce speed
- Increase torque
By the time the motion reaches the final gear, the servo can produce enough force to move the steering system of the vehicle.
Servos typically use one of two types of gears:
- Plastic gears – lighter and cheaper, but easier to strip
- Metal gears – stronger and more durable, especially in larger RC vehicles
The final gear connects to the output shaft, which is the splined shaft where the servo horn mounts.
3. Potentiometer (Position Sensor)
One of the most important parts inside the servo is the potentiometer, often called a “pot”. This component acts as a position sensor.
It constantly tells the servo’s internal circuit exactly where the output shaft is currently positioned.
Think of it like feedback.
If the servo moves too far or not far enough, the potentiometer reports that information back to the control board so it can correct the position.
This is how the servo can move to precise steering angles instead of spinning endlessly.
4. Control Circuit Board
The control board is the servo’s brain.
This small electronic circuit receives signals from the receiver and decides how the motor should move.
When a signal arrives from the receiver, the control board compares two things:
- The desired position (from the transmitter signal)
- The current position (from the potentiometer)
If those two values don’t match, the circuit activates the motor until they do.
Once the servo reaches the correct position, the motor stops.
This constant feedback loop happens extremely fast, allowing the servo to hold a position with surprising accuracy.
How the Signal From Your Radio Controls the Servo
Your transmitter communicates with the servo through something called PWM (Pulse Width Modulation).
This may sound complicated, but the concept is simple.
The receiver sends a repeating electrical pulse to the servo. The length of the pulse tells the servo what position it should move to.
Typical servo signals look like this:
- 1.0ms pulse → full left
- 1.5ms pulse → center position
- 2.0ms pulse → full right
These pulses repeat about 50 times per second.
The servo constantly reads these signals and adjusts its position accordingly.
This is why steering responds almost instantly when you move the wheel on your transmitter.
What Happens When You Turn the Steering Wheel
Let’s walk through the process step by step.
You turn the steering wheel on your transmitter:
- The transmitter sends a signal to the receiver.
- The receiver sends a PWM signal to the servo.
- The servo’s control board reads the signal.
- It compares the desired position to the current position.
- The motor spins through the gear train.
- The output shaft rotates.
- The servo horn moves the steering linkage.
- The wheels turn.
The entire process happens in milliseconds.
Servo Horns and Linkages
The servo horn is the small arm that attaches to the servo’s output shaft. This shaft has a specific number of teeth on it, usually 23-25T (25T has become the most common). Keep this in mind when purchasing a horn for your servo.
This is what physically connects the servo to the steering system.
Common types include:
- Single arm horns
- Double arm horns
- Servo saver horns
Many RC cars use a servo saver, which is a spring-loaded horn that helps protect plastic servo gears during crashes.
Without a servo saver, a hard impact can easily strip plastic gears inside the servo. However, with today’s line of advanced servos (with metal gear trains), you can easily rely on a single or double arm horn.
Digital vs Analog Servos
You’ll often hear people talk about digital servos and analog servos.
Both work using the same basic mechanical system, but the electronics behave differently.
Analog Servos
Analog servos send power to the motor in short bursts.
They are:
- Cheaper
- Efficient
- Perfectly fine for many beginner RC cars
However, they may feel slightly slower or have plastic gears, reducing reliability.
Digital Servos
Digital servos update their position far more frequently.
This allows them to:
- Hold position more firmly
- Respond faster
- Provide stronger steering control
The downside is they typically:
- Cost more
- Draw more power from the battery
Many racers prefer digital servos because of their quicker response and, in most cases the all-metal gear train.
Servo Specifications Explained
When shopping for a servo, you’ll usually see two important specs.
Torque
Torque measures how much turning force the servo can produce.
It’s usually listed in kg-cm or oz-in.
Higher torque is important for:
- Heavy RC vehicles
- Large tires
- High-speed steering
Speed
Servo speed measures how quickly the servo moves from one position to another.
It’s usually written like this: 0.10 sec / 60°.
This means the servo takes 0.10 seconds to move 60 degrees.
Faster servos make steering feel more responsive.
Why Servos Sometimes Fail
Even good servos eventually wear out.
Common causes include:
- Stripped gears from crashes
- Burned motors from overload
- Water damage
- Electronics failure
If your steering suddenly stops responding or makes grinding noises, the servo gears may be damaged.
Luckily, many servos allow you to replace the gear set instead of replacing the entire servo.
Why the Servo Is So Important
In many ways, the servo is what makes an RC car feel controllable.
A weak or slow servo can make even a great RC car feel sloppy, while a strong, fast servo makes the car feel precise and responsive.
That’s why experienced RC hobbyists often upgrade the servo early when building a new vehicle.
Final Thoughts
Even though it’s a small component, the RC servo is a clever piece of engineering. Inside that little box is a motor, a gear reduction system, a position sensor and a control circuit all working together to turn your wheels exactly where you want them.
In addition, the next time someone asks what a servo does, you’ll know the answer: It’s the tiny machine responsible for every turn your RC car makes.
RC Car Servo FAQ
Q: What does a servo do in an RC car?
A servo controls the steering of the vehicle. When you turn the steering wheel on your transmitter, the receiver sends a signal to the servo. The servo then rotates its output shaft, which moves the steering linkage and turns the front wheels left or right.
Q: How does a servo know where to move?
Inside the servo is a component called a potentiometer, which acts as a position sensor. It constantly tells the control circuit where the servo shaft is currently positioned. The servo compares this position with the signal from the receiver and adjusts the motor until the two positions match.
Q: What is the difference between a digital and analog servo?
Analog servos send power to the motor in small pulses and update their position less frequently. Digital servos refresh their position many more times per second, which allows them to respond faster and hold their position more firmly. Digital servos are usually stronger and more precise but cost more and use more battery power.
Q: What does servo torque mean?
Torque measures how much force the servo can produce. Higher torque helps the servo turn larger tires or handle heavier RC vehicles. Torque is usually listed in kg-cm or oz-in on servo specifications.
Q: What does servo speed mean?
Servo speed refers to how quickly the servo moves its output shaft. It’s usually measured as the time required to rotate 60 degrees. For example, a rating of 0.10 sec/60° means the servo can rotate 60 degrees in one tenth of a second.
Q: Why do RC servos strip gears?
Servo gears usually strip because of hard crashes or steering impacts. When the wheels suddenly stop but the servo is still trying to turn them, the gear teeth can break. Many RC cars use a servo saver to absorb impacts and protect the servo gears. This is a typical situation when using a servo with plastic internal gears.
Q: Can you replace servo gears?
Yes. Many servos have replacement gear sets available. If the gears strip, you can often rebuild the servo instead of replacing the entire unit.
Q: How long do RC servos last?
A quality servo can last many years, especially if the vehicle uses a servo saver and the servo is not overloaded. Water damage, crashes and excessive steering loads are the most common reasons servos fail.
