simtk.org

Hi,

we are studying balance strategies due to bus acceleration/deceleration perturbations.
our volunteers show different strategies to sustain balance, e.g., stepping. They move their are arms and head quite dymanic at some frames which results in larger maximum errors (recommendend IK max errror: 4 cm).

the guidelines for IK states that the recommended thresholds can vary depending on the movement being studied.

Questions:
1. is that referring to more dymanic (violent) movements? So I can tolerate 8 - 10 cm maximum errors for the arms, for example.

2. We are more interested in the response from the lower body (hips, knee, ankle). can this larger arm max errors affect the lower body angles?

regards,
ary silvano

Hi Ary,

To answer your specific questions:
1. IK is solved on a frame by frame basis, so the fact that the motion is fast should have no effect on the quality of the IK solution (as long as recording/capture can handle it). You may have issues down stream when using tools that utilize dynamics (e.g. CMC), but not with IK.
2. It's unlikely that changes in kinematics of the arm would affect lower body, though if interested only in lower body you may consider using a model that lumps the modeling of the upper body.

In general you should know that performing dynamic analyses will require recording or modeling of ALL external forces acting on the body.

Hope this helps,
-Ayman