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ACTUATORS - BRUSHLESS MOTORS



note: I have never actually used a brushless motor, so feel free to correct and verify this information

note: this page is a place holder until a better tutorial is written

Differences between brushless and brushed motors

• Brushless motors are more power efficient
• Brushless motors have less electrical noise
• Brushless motors last significantly longer
• Brushless motors are more expensive
• Brushless motors require a special controller

Voltage

• Typically from 5-12V, but can range to extremes in special application motors
• Higher voltages generally mean more torque, but also require more power
• Motors can run above or below rated voltage (to meet other design requirements)
• Most efficient at rated voltage

Current

• When buying a motor, consider stall and operating current (max and minimum)
• Stall Current - The current a motor requires when powered but held so that it does not rotate
• Operating Current - The current draw when a motor experiences zero resistance torque
• It is best to determine current curves relating voltage, current, and required torque for optimization
• When a motor experiences a change in torque (such as motor reversal) expect short lived current spikes
• Current spikes can be up to 2x the stall current, and can fry control circuitry if unprotected
• Use diodes to prevent reverse current to your circuitry
• Check power ratings of your circuitry and use heat sinks if needed

Power (Voltage x Current)

• Running motors close to stall current often, or reversing current often under high torque, can cause motors to melt
• Heat sink motors if not avoidable

Torque

• When buying a motor, consider stall and operating torque (max and minimum)
• Stall Torque - The torque a motor requires when powered but held so that it does not rotate
• Operating Torque - The torque a motor can apply when experiencing zero resistance torque
• Changing voltage will change torque

Velocity

• Motors run most efficient at the highest possible speeds
• Gearing a motor allows the motor to run fast, yet have a slower output speed with much higher torque
• Remember that torque determines acceleration, so a fast robot with poor acceleration is really a slow robot
• If uncertain, favor torque over velocity

Efficiency

• Most efficient at rated voltage
• Motors run most efficient at the highest possible speeds
• Use gearing (opt to buy motors with built-in gearing or gear heads)

Control Methods

• Brushless motors MUST USE A SPECIAL CONTROLLER as it works through induction
• There are many different types of brushless DC motors. These motors can have from 2 to 4 poles for operation
• Encoder - device which counts rotations of wheel or motorshaft to determine velocity for a control feedback loop
• Tachometer - device which measures current draw of motor to control output torque