Unable to properly feedback an updated signal in simulink

Question

Anthony Maalouly 2020-10-20

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https://ww2.mathworks.cn/matlabcentral/answers/620323-unable-to-properly-feedback-an-updated-signal-in-simulink

评论： Anthony Maalouly 2020-10-20

Hello,

I'm trying to make a toy example work using simulink. I have a particle that i want to go in a circle. Basically what I want to do is to rotate progressively by 10 deg over 36 sec (so it makes a full circle).

How to code this in simulink? For the rotation, I used the 2d rotation matrix about z. I am basically having trouble feeding back the updated velocity as the new reference.

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Answer 1

Ameer Hamza 2020-10-20

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https://ww2.mathworks.cn/matlabcentral/answers/620323-unable-to-properly-feedback-an-updated-signal-in-simulink#answer_519428

If you directly feed it back, you will create an algebraic loop, which is sometimes difficult to solve. Feedback through a delay block https://in.mathworks.com/help/simulink/slref/delay.html. Give a delay of 1 between output and feedback input.

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Anthony Maalouly 2020-10-20

This works now, thank you!

Anthony Maalouly 2020-10-20

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Answer 2

Paul 2020-10-20

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https://ww2.mathworks.cn/matlabcentral/answers/620323-unable-to-properly-feedback-an-updated-signal-in-simulink#answer_519648

Is there a reason why you wan to use a feedack loop where none really exists? Keep in mind that feedback loop is sampled and therefore the model is not integrating a continuous velocity. Why not just implement the equation for velocity directly, like so:

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Anthony Maalouly 2020-10-20

Yes there is a reason. Essentially, I want to use that feedback loop for a similar problem where I am controlling a particle and I want to add delta_v vectors under certain conditions. This toy example that I asked above simulated it well.

I do agree with you, one should not use feedback where no feedback is directly needed, and the solution above works as expected.

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