Society of Robots - Robot Forum
Software => Software => Topic started by: Robot Attack on July 06, 2011, 01:25:21 PM
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Does anyone know what control algorithm is used by standard hobby servos?
They seem to work extremely well. Is it just standard PID control or something else?
Thanks
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A hobby servo could be using a few different internal control methods. The older and less expensive servos use analog circuits. The newer 'digital' servos use a u-controller. Both have feed-back loops that probably use PID or just PD.
Links about the servo circuit:
http://www.seattlerobotics.org/encoder/200009/S3003C.html (http://www.seattlerobotics.org/encoder/200009/S3003C.html)
http://www.seattlerobotics.org/encoder/200009/Servos.html (http://www.seattlerobotics.org/encoder/200009/Servos.html)
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I think hobby servos use a well tuned proportial control loop - there's not much need for integral or derivative terms. Of course, I could be wrong - but purely proportional is also the easiest one to implement without a microcontroller, and many analog servos don't seem to have one.
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Thanks very much for the info. Those links were very helpful.
Looking at the first link, you can change resistors and capacitors to change the gains of the controller. I assume you could then back out the original gains of the controller just by examining the original resistance / capacitance of those components. Is that right?
Thanks
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The R would only give you the gain the the control amp, not the entire control loop as the motor/gears are part of the loop.
The block diagram doesn't show all the details so it would be difficult to model the entire control response.
A search of the ICs shown will find you the data sheets and maybe some app notes. These will have more info on how the ICs work.