Bushing forces and CMC

Provide easy-to-use, extensible software for modeling, simulating, controlling, and analyzing the neuromusculoskeletal system.
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Moe Curtin
Posts: 43
Joined: Fri Oct 02, 2009 5:40 am

Bushing forces and CMC

Post by Moe Curtin » Tue Jun 05, 2012 5:18 am

I have found that if I try to run CMC on a model with bushing forces in the model file it fails very early in the simulation. If I remove the bushing forces from the model and put the very same forces in the reserve actuator file for the CMC setup it works ok. Is there a reason for this? And is there a recommended method for using bushing forces with CMC?

Thanks!
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Ajay Seth
Posts: 136
Joined: Thu Mar 15, 2007 10:39 am

Re: Bushing forces and CMC

Post by Ajay Seth » Tue Jun 05, 2012 5:16 pm

Congrats! You found a bug in CMC. The issue is a miscounting of muscle states, which CMC uses. When other forces, like a BushingForce, add states to the system (i.e. to calculate dissipated energy) the assumption that the states are all muscle states is wrong, and causes the failure. This has been fixed for future releases. As a work around, you can use the CoupledBushingForce in the force plugin example (OpenSim2.4.0\sdk\APIExamples\ForcePluginExample), which is a bushing but with the full 6x6 stiffness matrix (allows cross coupling of deflections). Sorry for the inconvenience.
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