Do I rerun ik & id after rra?

[Julian Atkinson]

Good day

Once I have run ik, id and rra and I have my adjusted model calculated by rra, do I then use that model to rerun ik and id?

Also, would it then be better to use the adjusted model to run ik and id on different trials from the same session, or create an adjusted model for each and select the best one?

regards,
Julian

[Dimitar Stanev]

A simple test would be to compare the results from ID only with the initial model and the model produced by RRA and see if there are any differences in the moments. My opinion about this is (and I may be wrong):

When you perform ID you solve your problem exactly, meaning that you satisfy the equations of motion for each joint based on your knowledge about the external forces and motion. The problem is that indeed residuals will be present in the pelvis joint. By adjusting the mass properties of the segments (RRA), slightly different joint moments may be required to perform the same movement. Unfortunately, the problem is not well defined, meaning you can't pull a rabbit out of a hat and you need more information. Your estimations are as good as your model.

[Julian Atkinson]

Hi Dimitar

Thank you for your help. Yes, that makes sense!

Julian