Need a method that returns the coriolis/centrifugal force in internal coordinates

[simbody]

Need a method that returns the coriolis/centrifugal force in internal coordinates

[chrisdembia]

Is there a more efficient way to obtain this than:

Vector calc{CoriolisAndCentrifugal,QuadraticVelocity}Forces(const State& s)
{
Vector f_inertal;
smss.calcResidualForce(s, Vector(0), Vector_< SpatialVec >(0), Vector(0), Vector(0), f_inertial)    

Vector f_gravity;
smss.multiplyBySystemJacobianTranspose(s, gravity.getBodyForces(s)), gravityMobilityForces);

return (f_inertial - f_gravity);
}

?

[kingchurch]

+1. This is super useful to building walking controllers.

[chrisdembia]

@sherm1 just told me that this method exists now:
https://github.com/simbody/simbody/blob/master/Simbody/include/simbody/internal/SimbodyMatterSubsystem.h#L2560

It might not be in a released version yet though.

On Fri, Apr 25, 2014 at 6:34 PM, kingchurch [email protected]:

+1. This is super useful to building walking controllers.

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.

[sherm1]

It is probably this method you want: https://github.com/simbody/simbody/blob/master/Simbody/include/simbody/internal/SimbodyMatterSubsystem.h#L2584

The routine that returns only the Coriolis acceleration is not that useful -- you almost always want the gyroscopic force included as well. I called that "total centrifugal forces" for lack of a better term but it means all the forces that arise just from rotational motion.

That is available in the Simbody 3.4 release which is posted on the release page.

[sherm1]

The original topic was to add a routine that would return the rotational forces in internal coordinates directly. I’m still not clear exactly what would be the most clear & efficient form for these methods. I would like to leave the issue open until you are happy with your task space control code.

Please check out the doxygen for the methods calcBiasForSystemJacobian https://simtk.org/api_docs/simbody/api_docs33/Simbody/html/classSimTK_1_1SimbodyMatterSubsystem.html#a43d9b54ce86f55165488b2dd270d5995 (). There is a signature that returns a Vector_ like Force::Gravity does. But this is just the Coriolis acceleration and not the mass-weighted Coriolis force and gyroscopic force so probably isn’t what you want. I would like to make sure the API includes some obvious methods that get all the op space control matrices in a straightforward way.

From: Christopher Dembia [mailto:[email protected]]
Sent: Saturday, April 26, 2014 1:08 PM
To: simbody/simbody
Cc: Michael Sherman
Subject: Re: [simbody] Need a method that returns the coriolis/centrifugal force in internal coordinates (#28)

Does that mean this issue can be closed?

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