Achievable position control bandwidth

#1

Hi,

What control bandwidth can be achieved with the position controller of oDrive?

I learned from a previous question that the sampling rate of the controller is 8kHz. I would assume that with that rate we can achieve about 500 Hz bandwidth in current, maybe 70-100 Hz in velocity and from there like 10-25 Hz for position.

I understand that this largely depends on the gains we select, but I would like a ball-park figure from your practical experience.

I am building a setup that would require a minimum of 15 Hz in position control bandwidth, and really need to know if it’s feasible (or at least I get close) with oDrive.

Thanks a lot!

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#2

Yes your ballpark figures are correct, though for short moves where you don’t hit the velocity limit, you can probably have the same bandwidth in velocity and position. The achievable bandwidth depends on your encoder resolution (lest discrete counts cause too much reaction), but a ballpark figure is probably around 50Hz for both vel and pos.

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#3

Hi Oskar,

Thanks for your answer. A small comment about it, as I’m a control engineer.

I don’t see the possibility for a cascaded control system (position -> velocity -> current) to achieve the same bandwidth at two loops simultaneously. A conservative rule of thumb is to design each external loop 10 times slower than the inner one. A very aggressive design would mean making it 2-3 times slower. More than that is almost a guarantee for instability.

What I think you mean is that the velocity can easily reach 50 Hz bandwidth, and that position will be reasonably fast for the majority of applications. And that’s still enough for me :slight_smile:

Thanks a lot!

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