Calculating the joint space inertia matrix

Discussion in 'Simulation' started by Travis DeWolf, Oct 29, 2019.

  1. Hello!

    I am trying to recalculate the joint space inertia matrix (mjData.qM) on my own, and running into difficulties. For a simple two-link arm, I'm calculating it as

    qM = sum_i (J_i^T * M_i * J_i)​

    where J_i is the Jacobian for the COM of the arm segment i (mj_jacBodyCom) and M_i is the inertia matrix of the arm segment (diag(body_mass, body_inertia])).

    I'm wondering if I need to be rotating the inertia matrix for the arm segment from it's diagonal form before doing the multiplication. Can you provide some insight into what I'm doing incorrectly?
  2. I've reposted this in the Official support forum, but i'm not sure how to delete this thread.