how to calculate d τθ/ d θ

Simbody is useful for internal coordinate and coarse grained molecule modeling, large scale mechanical models like skeletons, and anything else that can be modeled as bodies interconnected by joints, acted upon by forces, and restricted by constraints.
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Jiang Ping
Posts: 132
Joined: Sun Aug 26, 2012 4:09 am

how to calculate d τθ/ d θ

Post by Jiang Ping » Mon Aug 31, 2015 11:40 am

hi,

I read the following document and understood how to calculate the joint torque.
http://wiki.simtk.org/opensim/FrontPage ... entArm.pdf

Now i want to calculate d τθ/ d θ, where τθ is joint torque at θ, θ is the joint angle.
Is there any guidance for how to calculate it?

Thanks in advance,
jiang
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Michael Sherman
Posts: 800
Joined: Fri Apr 01, 2005 6:05 pm

Re: how to calculate d τθ/ d θ

Post by Michael Sherman » Mon Aug 31, 2015 1:10 pm

Hi, Jiang. I think you would have to calculate that by numerical perturbation. You could use Simbody's Differentiator class to get a first- or second-order estimate, or just calculate it yourself by perturbing theta.

BTW, we have a more complete write-up of the moment arm calculation in this paper, although it doesn't directly address the problem you asked about.

Regards,
Sherm
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