Problems performing IAA with Gait2354 model

[Pia Stefanek]

Hi,

I am trying to make an IAA with the model 'Gait2354_Simbody'. I have already made an IAA with the model 'Gait10dof18musc'. I found out that one has to Change the external loads file from Point force to Body force (applied to Calcaneus) to get valid results in the induced constraints file. (viewtopicPhpbb.php?f=91&t=9414&p=0&start=0&view=) But when I perform IAA with the model 'Gait2354_Simbody' I don't get correct results.

Without changing the external loads file from Point force to Body force, I get correct results for constraint reaction Ground Forces (total_ground_force_ground_Fx,total_ground_force_ground_Fy,total_ground_force_ground_Fz) which are similar to the Ground reaction forces of the external load file (ground_force_vx,ground_force_vy,ground_force_vz). But in this case the Moments don't match as described with model 'Gait10dof18musc'.

When I Change the external loads file from Point force to Body force I get incorrect results for Forces and Moments. (See Picture Induced Constraint reactions)

Has anybody an idea why this problem arises?


Thank you in advance


Regards
Pia

[jimmy d]

I found out that one has to Change the external loads file from Point force to Body force (applied to Calcaneus) to get valid results in the induced constraints file. (viewtopicPhpbb.php?f=91&t=9414&p=0&start=0&view=)

No where in the link you provided was there a statement that you have had to change the point force to a body force

OpenSim automatically converts point forces to body forces under the hood so you don't have to.

[Pia Stefanek]

I thought About this Posting: viewtopicPhpbb.php?f=1398&t=8339&p=0&start=0&view=
But Maybe I did not understand it correctly.

When I don't Change the external load file from Point force to Body force, I get valid results for the constraint reaction Forces which match with the Ground reaction force of the external load file. But the constraint reaction Moments do not match with the Ground reaction Moments of the external load file.

Do you know what could be my mistake?

[Pia Stefanek]

This is the Setuo File I used. Maybe it contains a mistake?

[Ajay Seth]

The reaction reported is the total reaction force and moment on the calcaneous body as applied to its body frame. You can use it to compute the center of pressure and free-moment.

[Simon Jeng]

The reaction reported is the total reaction force and moment on the calcaneous body as applied to its body frame. You can use it to compute the center of pressure and free-moment.

How to compute the center of pressure and free-moment? I'm working on calculating the ground reaction force and moment during squat lifting according to a prescribed motion. I built a weld constraint between the foot and ground in OpenSim4.0. I found that the resulting reaction force is calculated about one fixed point(i.e. the location of the weld I had specified in the .osim file). However, in reality, the center of pressure is changing during squat lifting so my result is incorrect. How to solve this problem?