Joint motion map

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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Kishor Bhalerao
Posts: 21
Joined: Thu Mar 13, 2008 12:52 pm

Joint motion map

Post by Kishor Bhalerao » Mon Feb 08, 2010 10:11 pm

Hi Sherm,

What is the easiest way to obtain the H matrix in equation 5.2 described in the
Simbody theory manual ? I am looking only at coarse grained RNA applications
and expect just the regular joint types (free, rigid, revolute, spherical).

The method i used previously was to call the function
matter.getRep().getRigidBodyNode().getDOF() and use a simple switch statement
to generate the required H matrix. However, I also had built all the libraries
from source. I am right now working just with the Simtk2.0 core (its difficult to
build from source and I would like to use some machines in the lab rather than abuse my laptop for longer simulations.). As i understand it, with Simtk2.0 core, i would not have access to the functions declared in RigidBodyNode.h, is that right ? If yes, what are my options ?

Thanks,
Kishor Bhalerao

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Michael Sherman
Posts: 807
Joined: Fri Apr 01, 2005 6:05 pm

RE: Joint motion map

Post by Michael Sherman » Mon Feb 08, 2010 10:36 pm

Hi, Kishor.

I think you might like this MobilizedBody method:
/// Expert use only: obtain a column of the hinge matrix H corresponding to
/// one of this mobilizer's mobilities.
SpatialVec getHCol(const State& s, UIndex ux) const;

It returns a column of the H matrix; call it once for each mobility of the joint (after you have set q's and realize(Position).

Regards,
Sherm

User avatar
Kishor Bhalerao
Posts: 21
Joined: Thu Mar 13, 2008 12:52 pm

RE: Joint motion map

Post by Kishor Bhalerao » Thu Feb 11, 2010 11:40 am

Hi Sherm,
I tried using getHCol() and it works out fine for my current purposes.

Thanks,
Kishor.

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