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Hi,

I am trying to run Static Optimization with an upper extremity model to simulate a power grip and it continuously fails. I have tried adding in reserve actuators at the recommended levels (0.1N - 1N) but they continue to fail. If I increase them, the reserves contribute too much and the activations are minimal.
- Are there any recommendations on how to systematically determine the needed actuator contributions?
- Should I start at one joint and work from there, or should I find conditions that the simulation runs and then try and reduce them incrementally? For context: they are static trials, with external forces placed at the fingers, and the min/max controls are set to (1/-1)

Any recommendations would be appreciated. Thank you

It looks like the maximum force/moment that your reserve actuators can produce might be very small. The total force/moment is determined by (control value) * (reserve actuator force value). So, these actuators are generating 1 N or 1 N-m (depending on if it's a linear coordinate or a rotational coordinate) at most.

You can increase the min/max controls much larger to first get the simulation to run, and then reduce it incrementally. Since the reserve actuator force/moment values are set to a low number (0.1 or 1), the optimizer will still tend to choose to use muscles rather than the reserve actuators.

Thank you,

To confirm as well. the contribution is determined by comparing the moments computed through inverse dynamics to the torques from the force.sto files outputted from the Static Optimization?

Static optimization uses a least-squares approach because there are more actuators than degrees of freedom (see https://opensimconfluence.atlassian.net ... tion+Works). The equations there don't quite capture what the reserve actuators are contributing, but their control values are considered the same as the "activation" values for the muscles in this least-squares problem.