Sensing, Actuating and Controlling
Choosing an Actuator
14 min · 2 worked examplesFree
Brushed, stepper, servo or brushless, what each is genuinely good at, and how to size one properly.
After this lesson you can
- Choose between brushed, stepper, servo and brushless
- Size a motor from the torque you need
- Explain back-EMF and why stall current is the dangerous one
Four common choices
A brushed DC motor is the simplest: apply voltage and it spins, faster with more voltage and harder with more current. Cheap and easy to drive, with brushes that wear and no idea where it is.
A stepper moves in fixed increments and holds position without any feedback, which makes open-loop positioning possible. It draws full current even when stationary, runs warm, and loses steps silently if overloaded, the worst kind of failure, because nothing reports it.
A hobby servo is a small motor, gearbox and control loop in one package, commanded by a pulse width to an angle. Excellent for limited-range joints, usually restricted to about 180°.
A brushless motor is efficient, powerful and long-lived, and needs an electronic controller to commutate it. It is what serious drives use, at the cost of complexity.
In the full lesson
- Four common choices
- Sizing
- Back-EMF
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.