by Rick Cantrell
RC boats use two types of electric motors; the brushed motor and the brushless motor. What is the difference between the two types of motors? Which one do you want on your RC Boat if you are a speed junkie? Let’s take a look at the differences between the two types of motors.
All electric motors have magnets and coils of wire (windings). The coil of wire moving in a magnetic field creates an electric current. A varying current through a coil of wire will move relative to the magnetic field and make the motor spin. That is where the similarity between the the two types of motors ends.
The Brushed Motor
Most electric RC boats use a brushed motor for their propulsion. It looks kind of like a small metal can that has an axle sticking out of one end and battery leads on the other. Inside you will find the wires, commutator shaft, an armature, carbon brushes (therefore the name brushed), and magnets. Friction is caused by the brushes pressing against a spinning commutator. This contact completes an electrical circuit between the battery and the armature’s coil windings. Voltage applied from the battery leads to the brushes causes the motor to spin which in turn gives forward and backward propulsion to your RC Boat.
Unfortunately the problem with this configuration is that the friction puts extra strain on the motor. The brushes wear down and have to be replaced on a constant basis. Another problem with the brushless motor is that the windings are very heavy and, being in the middle of the motor, they have a hard time dissipating the heat. When speed increases the contact between the brushes and commutator becomes less proficient which causes the motor to be less efficient. A brushed motor typically only gives about 65-70% efficiency. This means that you do not get the full power for the size of the motor and your RC boat cannot go as fast as speed demons would like.
The Brushless Motor
The brushless motor is becoming very popular with RC boat enthusiasts. Its design allows it to be much more powerful than its brushed counterpart. It does not have the brushes which cause friction and overheating, the biggest problem with motor performance. The owner can spend more time with the RC boat on the water instead of spending a lot of time cleaning it and replacing brushes.
Brushless motors can handle much higher voltage than brushed motors. This increased voltage supply allows brushless motors to attain blistering speeds that are not possible with the brushed motor. In contrast to its brushed counterpart, the brushless design contains a permanent magnet in the rotor or shaft. There are sensors that determine how fast the magnet turns in order to produce voltage. Since these sensors do not touch the armature, there is no friction problem like the one that occurs with a brushed motor.
In a brushless design permanent magnets rotate and the armature remains static. This eliminates the problem of transferring current to a moving armature. In this setup the brush and commutator assembly is replaced by an electronic controller. A solid state circuit performs the same power distribution function you will find in a commutator/brush system. Since the friction problem is eliminated the RC boat will have much greater efficiency and a huge increase in power. The problem of constantly replacing brushes is eliminated plus it can be up to 300% more powerful than the brushed motor.
Brushless motors require less maintenance and can be more reliable. They also will provide more torque and provide much more power than a comparable brushed motor. The initial cost of a brushless design is higher than the brushed motor, but if you factor in the lower maintenance and other costs that are associated with a powerful brushed motor you will find that the cost is well worth it. Make sure you find out before you buy your RC boat if local race circuits allow brushless motors.
If you crave extraordinary speed in your RC boat, then the brushless motor is the obvious choice. If you cannot afford the brushless boat now you can always buy the brushed counterpart. You just have to remember that you will have increased downtime and maintenance associated with the brushed motor. Budget considerations can be a problem but you can always buy the less expensive RC boat now and when you are ready move up to the faster, more reliable brushless motor when you can afford it.