Problem with ground_torque

[Ezequiel Martín Sosa]

Hello, I opened a topic a few weeks ago. It was about how I could solve the inverse Dinamic problem. A mate of this forum answered me and I got new plots. These were better, but un some plots, the results go on being bad.

I compared the .mot files, the experimental and the theoric, this last .mot file is respecting to Gait2354.

When I compared both plots, I noted that the columns which refer to torque were very different. In general, this situation happened with ground_torque_x and ground_torque_z. I have the same problem with the plots which refer to pressure evolution, ground_force_px and ground_force_pz in both plates. In both cases the column which refers to axes y was correct.

Looking at the plots, I noticed that the theoric plots are very strange, It has got a very strange form.

My doubt is this: Are these plots the result of calculating the torque directly in the plates? or Do I need a postprocesor treatment to transform the plot?, In which point does OpenSim calculate the torque?

P.D: I couldn't upload the plots

[jimmy d]

The input torque will should be the calculated free moment. It will be a single column value (X and Z will be zero) since the moment acts about the Y axis. You will have to calculate the free moment from the forceplate forces, COP and moments.

An example of calculating the the free moment from forceplate data can be found here;
https://github.com/jimmyDunne/c3d2OpenS ... /copCalc.m

Hope that helps,
-James

[Stefan van Drongelen]

Hi Jimmy,

I found your program very useful.
Just the question if you do this calculation with the GRF (as from the forceplates) or with the reaction forces which are input Opensim. I happen to have another program and Tz is mirrored....
I can't find a lot of information on how Tz should look like.

Hope you can help.
stefan