About the calculation of Frame velocity

[XuSen-Proto]

I have implemented a bipe robot simulation using MATLAB and Raisim. I gave the states q and their derivetives u, and then chose one frame to get the Frame Jocabian J and the frame velocity v using the API. It turns out that the equation v = Ju doesn't hold, I wonder why.

[jhwangbo]

can you share your code?

[XuSen-Proto]

The code is in the attachment and the execution environment is MATLAB R2021b. Run demo.m, and you will find that the frame jacobian will be OK once the function setGeneralizedCoordinate is called, but the Frame Velocity will not equal Ju until the functions setGeneralizedCoordinate and getFrameAngularVelocity are called twice. Also, the nonlinear force terms from the two calculations are different, and the result is shown in the picture. The amended MATLAB interface, raisim_interface_mex.cpp, where the bug of getNonlinearForce is fixed, is also given in the attachment. I'm looking forward to your reply.

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[XuSen-Proto]

Yes. Besides, it's a fixed-base system.

[jhwangbo]

Do you use the PD controller? if so, can you set the gains to zero and test again?

[XuSen-Proto]

No, I just set the gc, gv, and then call getNonlinearities.

[XuSen-Proto]

I have zeroed the gains and did another trail, and the problem still existed.

[jhwangbo]

Please post different questions in a seperate thread