GRF: problems to import and associate

[Monica Armengol]

Hello,

I am modelling a movement which is 40s long. I have scaled, donde IK and ID in my model. I am trying to associate the GRF I used with the Coordinates (in Motions). I was surprised to see that the forces don't seem to last the length of the movement (40s), but just stop (keeps the last force in the same place) at about 8 seconds.

When I plot the forces through Tools>Plot, it only imports 5 seconds of it, however if I plot my forces using matlab (from the same file), I can see the variation for the entire length of time.

Additionally, i have a question about the centre of pressure. I wanted to verify if I use the forces as point Force, are the coordinates expressed in global coordinates (generalised) and Body Force is the CoM of the body you've assigned?. At the moment if I use Point force is slightly off, but if I use Body Force it applies it in the centre of mass of the body, rather than of the segment I specified.

Anybody has any ideas what I'm doing wrong?

Thank you!

Monica

[Dimitar Stanev]

Hi,

When I plot the forces through Tools>Plot, it only imports 5 seconds of it, however if I plot my forces using matlab (from the same file), I can see the variation for the entire length of time.

Check the header of the .mot file to verify that it is imported correctly. It may be that the .mot file is not correctly formatted so OpenSim has issues reading it correctly.

You use point forces that are expressed in ground frame and not body local frame. These forces are applied on a specified point (must be provided) on a some body (e.g. calcn). Please see the following:

https://simtk-confluence.stanford.edu:8 ... ernalLoads

Try to understand how to apply the external forces correctly, by looking at the examples in the model folder (OpenSim's installation). You can also visualize them (File->Preview Experimental Data...).

Best