External Moment Origin Coordinates

[Daniel Dorman]

When apply external loads from a force plate in an inverse dynamics analysis, how should the external moment data be defined? Should it be the moment with respect to the model origin, or the moment with respect to the center of pressure, or the moment with respect to the force plate origin?
Thanks,
Dan Dorman

[Daniel Dorman]

I compared my gait inverse dynamic simulation results to the results from tutorial 3, and noticed that the knee moments for my results were much higher than the tutorial. I'm wondering if this could be due to incorrectly applied ground reaction moments? I need to know how the ground reaction moments need to be applied for the inverse dynamics analysis, and what origin the moments should be defined with respect to.
Thanks,
Dan

[Maria Isabel Orselli]

Hi Daniel,

I have the same doubt. Did you discover anything about how to report the ground reaction moment ?

thanks
Maria Isabel

[Tim Dorn]

I believe you need to report the GRM with respect to the center of pressure. For all level gait, the GRM in the X and Z direction will be zero, and the GRM (vertical free moment) in the Y direction will be non-zero (but not very big ~ usually less than 10Nm in magnitude for normal gait, so this shouldnt effect your results too much I would imagine).

-Tim

[Maria Isabel Orselli]

Hi Tim

You are right. I took a careful look inside the data in an grf archieve in the exemple directory and all make sence.

Thank you
Maria Isabel