Question regarding CMC actuators....

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Anantharaman Gopalakrishnan
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Joined: Fri Oct 10, 2008 2:38 pm

Question regarding CMC actuators....

Post by Anantharaman Gopalakrishnan » Fri Aug 21, 2009 8:40 am

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!!
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Tim Dorn
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RE: Question regarding CMC actuators....

Post by Tim Dorn » Sun Aug 23, 2009 6:35 pm

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
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Ayman Habib
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Joined: Fri Apr 01, 2005 12:24 pm

RE: Question regarding CMC actuators....

Post by Ayman Habib » Mon Aug 24, 2009 12:17 am

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

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