The motor is one of the most important parts of an RC car. In this article we go over how they work and what makes them different.

This article is for electric motors only, we are currently working on an article for nitro/gas motors.

BRUSHED VS BRUSHLESS

You may have noticed there are two different electric types of RC cars, brushed and brushless. Lets look at what the differences are.

First of all, both motors use 'charged' coil windings to repel and attract magnets, which have a fixed polarization, which in turn creates a rotating force.

The biggest difference between the two is Brushed motors use a tool known as the commutator which periodically reverses the current direction inside the coil. Which switches the respective side of the armature to repel or attract the magnets inside the motor. The commutator rubs against the brushes, which is where the name "Brushed" comes from. When sent power, the brushes are pushed into the commutator, which is what makes the contact, turning the motor.

Brushless motors do not have the commutator or brushes. They rely on a controller to alternate the current. In most RC cars, the ESC handles this action.

Some people have just simplified this by saying the Brushed motors are mechanically driven and brushless are electronically driven.

The biggest physical difference between the two that you can see without disassembling the motor is Brushless motors will typically have three or more wires coming from the motor, these are the wires used for power and for the ESC to communicate with the motor. Brushed motors usually just have a red and black wire coming from them.

Although Brushed is definitely the more efficient, durable and quicker motor, there are pros and cons for both. Brushed motors offer a more simple approach, making them easier to repair, replace and setup. They're also much cheaper than their Brushless counterparts. Brushless motors are much more expensive, and they also require more expensive equipment, such as an intelligent ESC and high power batteries. In some cases the motors have their place, most rock crawlers and slower vehicles use Brushed motors. Although most high-performance, fast vehicles use Brushless motors.

SENSORED vs SENSORLESS

As the name implies, Sensored motors have tiny sensors in them, and Sensorless motors do not. Sensored motors use their sensors to capture and send data back to the ESC, the ESC uses this data to determine where the motor is relative to its rotation. This can make it very smooth to take off from zero RPM and offers great performance at low speeds.

Sensorless motors do not have sensors. They simply are sent power from the ESC and the ESC has little to no data to go off of. Sensorless motors are more common for RC Boats, Helicopters and Planes as none of these need high torque at low RPM and more often are operated at a constant high RPM; which sensorless motors are good at.

Some sensored motors actually switch to sensorless syncronization at high RPM, the ESC will alter the timing, giving the most power and effeciency out of the motor. Sensorless, although not as common in the surface RC world do have some pros; they are much less complicated and much less prone to failure in comparison to their sensored counterparts.

TURNS "T"

Some motors you may have noticed are labeled as "21T" or "12 Turn" or something along those lines. Turns, typically abbreviated as just "T" is just the amount of internal wiring there is wrapped around the armature. There is some wide range in Turns, some as low as 5T and as high as 55T. To make it easier to understand, the higher Turn means the vehicle will have more torque but less RPM. High turn motors are typically found in Rock Crawlers and low turn motors are usually found in speed racers and zippy buggies. "T" or Turns can actually be converted into a "Kv" rating, although most motors are only rated by "T" or "Kv" not both.

Kv

The Kv number is used to determine the amount of 'theoretical' rotations you could make with 1 volt of power if the motor was unloaded, sometimes referred to as "RPM per volt." Kv actually stands for "Constant Velocity" in some cases; the "C" is switched out for a "K", this is thought to be because, in most math equations, the letter "C" is often already present, making the letter "K" a more suitable choice. This means the higher the Kv, the faster the motor can spin. Although this value is for an unloaded motor, meaning it can only give suggestions of the motor's capability.

HOW DO THEY STOP?

Brakes are something just about any vehicle needs, but on RC cars it looks a little different.

REVERSING THE MOTOR

One way RC cars stop themselves is by reversing the motor rotation. When the "brake" command is recieved in the controller, the ESC begins to reverse the rotation of the motor, causing it to brake. Vehicles with a neutral position will just reverse the motor until the vehicle has come to a complete stop and then the motor stops turning entirely.

LOCKING THE MOTOR

Another method for stopping would be locking the motor. The ESC sends a command to lock up the motor, this is the least common method as it can create unnecessary wear on the motor. It though typically mimics the real effect of braking without ABS (Anti-Lock Brake System) as the wheels completely lock up and skid as the vehicle comes to a stop. It is usually found on extremely high-performance cars as they typically need to be stopped quickly and have parts replaced often anyways.

REGENERATIVE BRAKING

One way the RC vehicles stop themselves is with regenerative braking. The ESC will send a command to purposely short out the motor, making it act as a generator, which makes it much more difficult to rotate. This slows down the vehicle quickly and creates minimal wear. This is one of the most common methods along with reverse rotation.

MECHANICAL BRAKE

Some mostly gas/nitro-powered vehicles have an actual mechanical brake. This is a brake system in which there are brake plates attached to the driveshaft, and a servo fitted with brake pads is setup next to the plates. When the servo is activated it presses the brake pads into the brake plates, creating resistance and slowing the vehicle down.

DRAG BRAKE

Drag brakes are usually used by vehicles that race on tight, typically indoor tracks. It is automatically applied as you let off the throttle and shifts the weight, making it easier to make sharp turns.

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