instability of the muscle activation when using CMC with external loads on elbow movement

[Wahyu Kasendra Sugiarto]

Hello,

i have a problem with the output of the muscle activation when using CMC. Here i simulated the elbow movement of flexion with and without exoskeleton with CMC. The external loads are just the actuator torque from the exoskeleton on elbow for flexion movement (applied on ulna and express in ground). The muscle activation of the model with external loads is not stable as you can see on the picture below (with EXO - the red line and marked with black circle)

muscle activation 1.png (194.64 KiB) Viewed 627 times

The setting for the external loads is below:

external loads.png (68.2 KiB) Viewed 627 times

the external loads' values of torque in x and y axis are all 0, but the torques in z axis are not 0
Here is the sample of the external loads:

external loads values.png (42.46 KiB) Viewed 627 times

The simulated model with exo:

model.png (106.17 KiB) Viewed 627 times

i don't know why it has insability in the earlier time frame. The muscle activation of the model with exoskeleton should be smaller than without exoskeleton, but it spiked and instable on earlier time frame. Can someone help me or give me insight?

Thanks
Wahyu

[Carmichael Ong]

You may want to try using a shorter "CMC look-ahead window" setting in the first panel of the tool. This could allow the solver to react more quickly to changes in torque, at the cost of taking longer to solver the CMC problem.