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I'm working on a robot with differential drive (2 drive wheels equipped with rotary encoders and 4 free spinning omni wheels for stability) and each wheel is controlled via a separate arduino nano.

I have implemented two PID loops, one for position control and one for speed control (first one gets a position in number of pulses and second gets an RPM as their goals).

The position PID works fine by produces jerky motion and acts more like a "bang bang" control where it starts at full speed. I'm not sure how I can combine these to plan a move that reaches a certain number of pulses with a given maximum acceleration and / or velocity.

I know 3D printers for example, have settings for jerk,acceleration and velocity so I tried to go through marlin to see how that's implemented but I had no luck! Can anyone please provide examples or links to tutorials / papers regarding this?

I think an easy solution would be pre calculating the motion profile and then tracking it with the position PID, but I'm not sure if there are better solutions for this.

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  • $\begingroup$ Check out articles on position control with via points. $\endgroup$ – SteveO Mar 16 '20 at 2:47
  • $\begingroup$ searching that doesn't find anything useful. can you please provide a few links? $\endgroup$ – OM222O Mar 16 '20 at 10:58
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I believe the resource https://robotics.stackexchange.com/a/21571/6941 already pretty much answers your question.

In essence, both the following approaches are valuable and can be combined together:

  • A pre-calculated motion profile helps the system reduce the jerk.
  • Cascaded PID controllers allow for improving the system response.
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