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Simscape model, not matching theoretical one.

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I have a problem to replicate on Simscape, a theoretical model. By comparing the bode diagram of the theoretical model (left) and the simscape model (right), we can see that the simscape model has a strange behavior in high frequencies.
The output is defined as y(t) = theta(t) + alpha(t)
I suspect the problem comes from the "Revolute1" that I use as a rotational spring in the Multibody part , but I'm not sure and I don't know how I should modify it.
I put in the image the parameters of Revolute1 and the last solid and the mechatronic part, just in case the problem come from there.

Accepted Answer

Vasco Lenzi
Vasco Lenzi on 26 Oct 2020
Hi Kamyar
as far as I can tell you are not closing the kinematic loop between multibody and the electric motor, so the rotational spring in the revolut joint is not considered as load into the 1D network.
Please take a look at this example that showcase how to connect Simscape 1D and Multibody:
Usually the kinematic loop is closed like this to give you an idea:
Vasco Lenzi
Vasco Lenzi on 28 Oct 2020
Modeling the torsional spring in the Jint Revolute is correct, and it does seems to work correctly if isolated.
Are you linearizing at the right equilibrium point? It may be a problem on how the linearization is setup, eg if you are linearizing at the wrong time you capture the wrong dynamics.
Kamyar Taher
Kamyar Taher on 28 Oct 2020
I tried modeling the spring and damper like this and I get the correct behavior now. I think I was misinterpreting how the damper and spring were acting. Thank you for your help!

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