Heavy Characters: How do you prevent servo back-driving?

Lisa

So I've been watching the tutorials with Craig Caton-Largent for driving animatronics using the Polulu boards. Great stuff! Super useful!

But I have a question... Do you still use the Polulu boards with larger/heavier characters? Or more specifically, do you ever have a problem with large characters back-driving the servos with their own weight; and if so, do you need to put any voltage protection so that back-driving the servo doesn't spike the board or kill the servo?

Or am I going about this totally the wrong way, and by the time the animatronic is heavy enough for that to be a problem, it's better to use some other kind of actuator? I'm very new to this. I see that you use hydraulics a lot. Is there an actuator that you'd recommend?

Thanks!!!

Chris Ellerby

Hi Lisa,

Extra force on the servo is for sure a concern and can result in burning out servos.  The type of control board you use can stay the same for the most part, as it's just sending PWM signals.

You can use heavy-duty or industrial servos in situations where more force is needed, though they can be quite expensive.  And designing your connections and mechanisms to give a good mechanical advantage can also help take some weight off the servo, but that comes at a cost of speed and range of motion.

Linear actuators, which can be controlled the same as a servo, are also common.

And you are correct, after a certain point, you would want to switch to hydraulic or pneumatic control when things get heavier.

/Chris