One type of the Outputs from Joint Reaction Analysis

[Wahyu Kasendra Sugiarto]

Hello all,

I have a question about 1 type of the output from Joint reaction analysis. From the OpenSim Documentation and from the OpenSim youtube webinar the outputs from the joint reaction analysis are only the 3 force vectors in x,y,z axis and 3 torques in x,y,z axis, but i get another type of output from it. they are px, py, pz. The value of each p is complete 0 for all time frame. Can anyone explain it to me about this p output?

Information: i'm doing a joint reaction analysis with the muscle force input from CMC simulation and i have adjust the time frame for joint reaction analysis with the time frame from the muscle force input from CMC simulation. The movement for this simualtion is elbow flextion from 0 degree to 106 degrees with only 1 DOF from the elbow (like "hammer curl" movement with now movement from the humerus and shoulder) (i have locked all DOF except the DOF of elbow).

One more question. To validate the results from the joint reaction analysis of elbow flexion movement i have to plot the torques on the elbow and see if it is 0 or near 0, right? because there is a movement of elbow, i meant the position of the elbow is static but it does a flexion movement to lift the weight on the hand. Am i correct about this? or there is a misconception from me?

Kind regards,
Sugiarto

[Carmichael Ong]

px, py, and pz are the coordinates of the location at which the force vector is applied. The location of px, py, and pz would affect the torque vector (since the torque vector is calculated such that the system is an equivalent system). If these are all 0, sounds like the force is applied at the body's origin.

[Wahyu Kasendra Sugiarto]

px, py, and pz are the coordinates of the location at which the force vector is applied. The location of px, py, and pz would affect the torque vector (since the torque vector is calculated such that the system is an equivalent system). If these are all 0, sounds like the force is applied at the body's origin.

Thanks for answering my question. What you meant with the origin of the body is the coordinate of the first body on model (0 0 0), isn't it? In my case it is the thorax (The mass of the thorax is 0 and it's COM is (0 0 0) too), but i want to know the force/torque applied on the elbow. Have i done wrong during setting the analysis? There is a screenshot of the model below.

this is the model i used for the simulation.

The model

Simulated_Model.png (87.33 KiB) Viewed 436 times

Kind regards,
Sugiarto