Problem with ground_torque

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Ezequiel Martín Sosa
Posts: 5
Joined: Thu Nov 20, 2014 2:24 pm

Problem with ground_torque

Post by Ezequiel Martín Sosa » Sat Apr 18, 2015 1:30 pm

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

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jimmy d
Posts: 1375
Joined: Thu Oct 04, 2007 11:51 pm

Re: Problem with ground_torque

Post by jimmy d » Thu Apr 23, 2015 1:12 am

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

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Stefan van Drongelen
Posts: 8
Joined: Fri May 13, 2011 12:49 am

Re: Problem with ground_torque

Post by Stefan van Drongelen » Tue Jun 02, 2015 7:08 am

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

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