Electronic – Continuous rotation ‘servo’ vs DC motor

motorservo

Under what circumstances should I prefer a continuous rotation 'servo' to a DC motor, or vice versa?

It seems to me that to use a DC motor, I'm going to need three pins from an MCU — two for forward/backward/brake/coast and one for PWM. On top of that, I'll need an H-Bridge.

For a continuous rotation servo, I'll only need one signal pin and some code to send proper timing signals. I can't control the speed of the servo, can I? Also, it must have something akin to an h-bridge inside the motor, which surely ups the cost, but the motor will always be geared, which is a plus.

So, what are the pros and cons of each, and when should I choose one over the other?

Best Answer

I can't control the speed of the servo, can I?

Yes, you can, but not to a very good degree of control

Also, it must have something akin to an h-bridge inside the motor, which surely ups the cost, but the motor will always be geared, which is a plus.

Continuous rotation servo:

  • Gearing
  • Built in motor driver
  • Single pin control (forward, reverse, speed)
  • Easy to mount the servo, and to attach movements to the horn
  • Hard to 'center' due to temperature drift - ie, without feedback you can't ever fully stop a servo, and even with feedback it continues to hunt for 0, and induces vibration into the mechanism

Motor:

  • Cheaper (even with gearing, especially in quantity)
  • Greater degree of control with a good motor driver
  • Doesn't require a PWM signal
  • Smaller
  • Lower power consumption for most applications
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