Unable to properly feedback an updated signal in simulink

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.

Answer 1

[Ameer Hamza]

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.

[Anthony Maalouly]

Hi Ameer,

Thanks for your quick answer. I am having trouble integrating your suggestion.

Essentially, I would like to have V0 just the initial loop, and from there it takes the updated signal, which in this case is vr.

[Ameer Hamza]

Remove the Vo from outside the model and inside the MATLAB function block, write something like this

if t == 0
    v = 10;
end

[Anthony Maalouly]

This works now, thank you!

[Anthony Maalouly]

Answer 2

[Paul]

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:

[Anthony Maalouly]

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.