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Question regarding CMC actuators....

Posted: Fri Aug 21, 2009 8:40 am

by ananthgk

Hi,

I am trying to simulate the action of a knee brace with a rotary actuator which applies a pure torque about the joint axis. Now, this means that the moments applied to the femur and the tibia will be equal in magnitude and opposite in direction. So in the CMC actuators file, under <objects> if i specify <body A> as the femur and <body B> as the tibia, would OpenSIM automatically apply equal and opposite moments on the two bodies?? Or would I have to specify them as separate moments??

Thanks!!

RE: Question regarding CMC actuators....

Posted: Sun Aug 23, 2009 6:35 pm

by twdorn

Hi Anantharaman,

If you want to apply a pure torque about a specified generalized coordinate, it would be best to fit the joint with a GeneralizedForce actuator (almost identical to a reserve actuator).

If you want to drive the model forward using tabular values of joint moments, you will need to run a forward simulation, but I believe that currently in the GUI, you can only drive the model forward using muscle excitations, not torques.

Cheers,

Tim

RE: Question regarding CMC actuators....

Posted: Mon Aug 24, 2009 12:17 am

by aymanh

Thanks Tim.

But actually, it is possible to drive a model using torques only in forward simulation. In the GUI, go to the "Actuators and External Loads" tab, and
1. Select the radio button to "replace model's actuator set".
2. Choose a file with GeneralizedForce actuators in it under "Additional actuator set files".

Hope this helps,
-Ayman