Hello Everyone
I am building a Simscape model for a single pendulum with 3 rotational DOF “Degree of Freedom” XYZ (one revolute joint for z-axis rotation & one universal joint for x-axis and y-axis rotations). I do this model trying to mimic the human shoulder joint motion. Check the attached file for the simscape model “PendulumModelProblem.slx” and the below picture.
Her is the problem that I have with this model:
1- Let’s say I simulate the initial condition response of the system with x-axis rotation only (I do this by setting target x-axis velocity in the universal joint setting = 1 rad/s and y-axis & z-axis = 0 rad/s in revolute joint). When I did that I got the below (FIG 1) x-axis rotation angle “qx1”, angular velocity “wx1” & angular acceleration “ax1”. While y-axis & z-axis measurements = 0 which what I expect (there should be no rotational motion in y-axis & z-axis)
2- Now when I introduce z-axis rotation in addition to x-axis rotation by setting target z-axis velocity in the revolute joint setting = 2 rad/s). I expect to see motions on x-axis and z-axis only and NO motion on y-axis. However, check the attached (FIG 2) where you can see that there is motion on the y-axis.
3- In addition, I expect to see no change in the x-axis rotation measurement since I didn’t change anything for x-axis. However, check the attached (FIG3) there a change in the x-axis measurements comparing x-axis ONLY simulation with x-axis & z-axis simulation.
4- It seems to me that the x-axis rotations are not independent of each other and what I’m looking for is an independent rotation of all axes. This problem gets worse when I simulate double or triple pendulum. The case we are discussing is for the single pendulum. I don’t know if I should expect this independency in axes rotations from Simulink/Simscape? I guess this should be possible and logically make sense for me.
5- an additional information, I’m looking to measure rotational kinematic values (angle, angular velocity & angular acceleration). I’m implementing 2-axis or even 3-axis rotation to mimic human shoulder joint motion. My goal is to simulate a triple pendulum with 7-DOF (3-DOF 1st pendulum, 2-DOF 2ndpendulum & 2-DOF 3rd pendulum).
I hope the above explanation describe my problem with this model and I hope someone can help me with a solution to this problem of axis rotation & measurements independency.
Thanks
