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Hello,

In the RRA troubleshooting tips on the Best Practices page, the suggestion for dealing with pelvis drift/FY is to "check that the body mass and force calibration are correct." However, I'm not sure I quite understand what is meant by this direction. Could someone please help by elaborating on ways to adjust the model/settings to fix the pelvis drift issue?

Just as a side note, I did adjust the location of the COM of the pelvis in my scaled model. I'm using the Arnoldetal2010 v2.1 model but the actuator/tasks/control constraint xml files are the gait2392 files. I'm not sure if this could be a source of error in my simulations as well.

Thanks,
Sarah

Hi Sarah,

RRA is a essentially a Forward Dynamcis simulation with a bunch of controls thrown in. If I have a really small mass, and really large GRF, The model would be projected upward (F=ma). So often, when pelvis drift around Fy occurs, its because the model mass and the external forces differ by a large enough margin that it accelerates the model.

Hope that helps,
-james