Types of RC Motors

Typically used in RC cars and boats, best known as 500 motors. The magnets are ferrite and they are available in many turn and wind combinations.

They use brushes and springs that need to be replaced as required due to wear. They most commonly use wet magnets which are magnets shaped from a slurry. These magnets are less subject to loss of magnetic fields at high temperatures then dry magnets.

These motors have Magnets that are made from rare earth materials like cobalt and neodymium iron boron. These are much more powerful, more efficient and more of course much more expensive than ferrite motors. They are also more resistant to heat damage and loss of magnetic field at elevated temperate than ferrite magnets.

Another importance difference can be seen in the below image. Notice how many comm segments there are ... Motors in this category tend to have greater than 3 poles for maximum power and efficiency. Plettenberg motors are my favorite in this category.

Motors that do not use brushes and rely on specialized speed controllers to provide the current switching normally done by the commutator.

They are more expensive but very fast. Hacker, Lehner and Aveox are the main players here.

How Brushless Motors Work?

A brushless motor looks a lot like a brushed motor that has been turned inside out. The magnets are attached to the armature instead of the can and the windings are attached to the case instead of the armature. In operation your magnets spin and not your windings.

As shown in the figures below, the rotor has permanent magnets mounted to it and is supported by a pair of ball bearings. These are the only moving parts in the motor and are also the only parts to wear out. Compare this to a brushed motor with its brush and commutator interface wear areas.

The stator or armature is made up of a laminated stack and wound with copper windings. Magnetic sensors detect the angular position of the rotor with respect to the stator. These sensors tell the controller (ESC) which loop needs to have the current on and which ones need the current off. This allows the motor to produce a continuous torque in one direction.

The two categories of brushless motors and controllers are sensored and sensorless. These two categories refer to how the armature location is determined (sensed) and then controlled.

A sensored motor (ie Aveox and Novak), you set the motor to a fixed timing to match your specific setup, just as you do with a brushed motor. These motors have small sensors, typically 3 at 120 degree intervals, which determine and communicate the rotational position of the armature. The controllers and motors often need to come from the same manufacture to work correctly.

The speed controllers for sensored motors can be less expensive to manufacture since they do not need to perform any motor monitoring. The down side is that the motor is more expensive because it must have the sensors built into it. These sensors can be fragile and they take up valuable space inside the motor.

A sensorless motor (ie Hacker, Lerner) is just as its name implies. These motors do not contain any sensors and instead leave the determination of armature position to the speed controller.

The Sensorless controllers are more complicated since the controller has to compensate for the lack of sensors in the motor. It does this with added programming and hardware to deal with various magnetic fluxes which occur in BL Motors. Sensorless theoretically allows you to run more efficiently at all throttle settings compared to a sensored setup.

What makes motors work is basic electromagnetism which states that whenever electrical current flows through a conductor, it produces a magnetic field. Conversely, whenever a conductor moves through a magnetic field, a voltage is induced in that conductor, this is often referred to as back-EMF in motors.

The type of electric motor used in R/C racing is a DC, permanent magnet, 3 pole motor. The permanent magnets are mounted in the can, and three coils of wire, the windings, are mounted on the armature. Click on the image for and exploded view of a motor and its parts.

When you connect power to the motor, current flows through the brushes onto the commutator and into the coils on the armature. This causes a magnetic field to form in the coils which will attract one permanent magnet while repelling the other causing the armature to rotate. The commutator determines the polarity of each coil which makes it attract and repel the appropriate magnets at the appropriate time. The polarity is based on which brush (+ or -) is in contact with which coil/comm segment.