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Hello everyone,

I had a question about coordinate limits during a run of computed muscle control. Are coordinates allowed to take on a value above or below the specified limits inside the model during computed muscle control? If so, how can I change that such that they stay inside the limit?

Thanks,

Brandon

Hello Brandon,

I think that the coordinate limits are enforced into the equation of motion by Lagrange multipliers as constraints. So during CMC these equations are integrated, and appropriate forces are applied to keep the coordinates in their limits satisfying the constraints.

BW

Hi Brandon,

If you're referring to bounds on coordinates as specified in the model file and as seen in the GUI, these are only used in kinematics (e.g. when solving IK or moving sliders in GUI) but are not enforced during dynamics or integration since there's no corresponding force producing objects in your model that tell OpenSim how to apply forces to stop a coordinate from going beyond its bounds. You can add CoordinateLimitForce(s) to specific coordinates to enforce the desired bounds during dynamics and it'll be up to you to decide what forces are applied when (e.g. how much force to apply, when to activate etc.) The default behavior, however, is that coordinate bounds are not enforced during dynamics.

Hope this helps,
-Ayman