Hi all,
I am wondering about the definition of "reaction force" (common problem in biomechanics!) in MocoJointReactionGoal. Is this force the "resultant force" from inverse dynamics (i.e. the force labeled Fk in the knee diagram below) or is it the "contact force" (i.e. the sum of the two forces labeled fc1 and fc2 below, calculated from the resultant and muscle forces)?
Ross
Definition of "reaction force" in MocoJointReactionGoal
- Ross Miller
- Posts: 372
- Joined: Tue Sep 22, 2009 2:02 pm
- Karthick Ganesan
- Posts: 119
- Joined: Thu Oct 10, 2013 12:11 am
Re: Definition of "reaction force" in MocoJointReactionGoal
Hi Ross Miller,
I believe that Moco uses same definition as that of opensim. In opensim joint reaction includes muscle forces and resultant from inverse dynamics. The reaction force Ri is calculated from the below free body diagram. The following links may be helpful.
https://simtk-confluence.stanford.edu/d ... seDynamics
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3319529/#
I believe that Moco uses same definition as that of opensim. In opensim joint reaction includes muscle forces and resultant from inverse dynamics. The reaction force Ri is calculated from the below free body diagram. The following links may be helpful.
https://simtk-confluence.stanford.edu/d ... seDynamics
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3319529/#
- Ross Miller
- Posts: 372
- Joined: Tue Sep 22, 2009 2:02 pm
Re: Definition of "reaction force" in MocoJointReactionGoal
Thanks Karthick
- Nicholas Bianco
- Posts: 1003
- Joined: Thu Oct 04, 2012 8:09 pm
Re: Definition of "reaction force" in MocoJointReactionGoal
Hi Ross,
MocoJointReactionGoal uses the values returned by Joint::calcReactionOn*ExpressedInGround() (where * is either Parent or Child depending on the setting you choose). These values are re-expressed in a different frame if specified by the property on the goal.
As Karthick says, these reaction forces include both the muscle forces and resultant from inverse dynamics.
Best,
-Nick
MocoJointReactionGoal uses the values returned by Joint::calcReactionOn*ExpressedInGround() (where * is either Parent or Child depending on the setting you choose). These values are re-expressed in a different frame if specified by the property on the goal.
As Karthick says, these reaction forces include both the muscle forces and resultant from inverse dynamics.
Best,
-Nick