Motors

Without these, your robot is a sitting duck

Selecting suitable motors for your sumo bot is essential for giving the torque it needs to do some heavy pushing while also moving swiftly around the ring. There are two types of motors that are mainstay in robot sumo: brushed and brushless DC motors. Let's go over the differences between the two.

Brushed

How do they work?

Brushed motors are electric motors powered by direct current (DC) to produce mechanical force. The rotor, which can freely rotate to drive the shaft, usually consists of coils of wire wound around an iron core (though some motors are "coreless"). These windings generate a magnetic field.

The fixed part of the motor, called the stator, contains permanent magnets that create a fixed magnetic field. The stator is typically situated outside of the rotor.

For torque generation, the rotor's magnetic fields must continuously move. An electric switch called a commutator periodically reverses the current. The commutator has fixed brushes on the stator that maintain electrical contact with the rotor. As the motor spins, different windings are activated or deactivated, causing them to repel or attract the stator magnets. This results in the motor spinning.

Advantages

• Cheaper, more affordable than Brushless motors as less electronics are involved.

• Simple design, easy to use

Disadvantages

• Less efficient than brushless motors in terms of power and speed.

• Brushes prone to wear and tear over time.

Brushless

How do they work?

Without going into too many details, brushless motors operate on the same principle as brushed motors but uses an electronic controller for switching current instead of a mechanical commutator and brushes. A dedicated brushless electronic speed controller is generally required to use brushless motors.

Advantages

• More powerful and efficient than brushed counterpart

• More reliable as result of not needing brushes.

Disadvantages

• More expensive as additional electronics are required

General tips for choosing motors

Now that we've discussed the differences between brushed and brushless motors, there are some factors to keep in mind when choosing a motor for your robot.

Size

Sumo competitions have restriction dimensions depending on the weight class. For mini sumo, maximum length is 10cm so when selecting motors make sure they are small enough such that two motors can fit next to each other comfortably.

Voltage

Motors that are rated for 2S or 3S (approximately 6V or 12V) are generally good for mini sumo.

Pay attention to rated voltage because your battery will depend on this!

Cost

As much as we wished we were, Comet Robotics is not made money, so please choose motors that are in a reasonable price range.