How can I read ground reaction force data from my simulation?

[stephane-caron]

First, you need to schedule your robot's wrench distributor to the simulation (see for instance the horizontal_walking.py example):

sim.schedule(robot.wrench_distributor, log_comp_times=True)

Reaction wrenches for each link in contact are then stored in the attributes of that link:

In [1]: robot.left_foot.wrench
Out[1]: array([-6.73440074, 16.54042313, 197.4917738, -9.4901811 , -21.72409512, 1.29245446])

In [2]: robot.left_foot.force
Out[2]: array([-6.73440074, 16.54042313, 197.4917738 ])

In [3]: robot.left_foot.moment
Out[3]: array([-9.4901811, -21.72409512, 1.29245446])

The wrench array is the 6D net wrench applied at the contact and given in the (local) contact frame. See the documentation of the find supporting wrenches function for details. Note that these wrenches are computed as a contact stability criterion, as Pymanoid itself does not provide forward dynamics.