Error of kinematic positions

Discussion in 'Modeling' started by KyleSJYoo, Apr 13, 2018.

  1. Hi, I am studying floating body system.

    I set up my model and solve kinematic positions by joint positions earned by d->qpos.

    However, there are errors between d->subtree_com and a CoM position(p_G) earned by kinematic map.

    The most interesting part is that the error is increase when the main body move but it go to zero when the main body is static.

    See the plot where e_Gx, e_Gy, e_Gz are each error of x, y, z CoM position and \omega_{B} is and angular velocity of main body from d->qvel. (e_G = p_G - subtree_com)

    Of course, it is about 0 to 6 mm but I want to know why these kind of error occur.(I use the position of main body from d->qpos and rotation matrix which earn by mju_quat2Mat to calculate p_G)

    Please inform the reason and if this error is general, is there any method to reduce this error?

    Thank you.

    Attached Files:

  2. Emo Todorov

    Emo Todorov Administrator Staff Member

    How exactly are you computing your CoM (p_G)? subtree_com is the CoM of each subtree, so I am guessing you are comparing to a different quantity.