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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
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