Reference Frame and Estimation of CoM & Swing Foot States

I’m trying to implement the DCM-based step planning method (Majid et al., 2018) and MPC-based trajectory generation method (Elham et al., 2021) to my robot model, and I’m wondering which reference frame CoM and swing foot states are based on.

  1. In my guess, the reference frame of CoM states is the stance foot frame, since we are interested in how much the current DCM position is diverged away from the stance foot location. The reference frame of swing foot states is probably the global frame since the swing foot dynamics equations is based on global…? I’m not sure if I’m right…

  2. What was the estimation method used in actual hardware test? Was it Kalman Filter or EKF or other methods?

I’ll greatly appreciate if I get a reply ASAP. Thank you in advance!