This is the first hard step to be implemented, following the graph described in #14 (closed). We propose to have 4 stages:

• joint admittance control
• possibly 3D admittance control of one effector in the air (likely useless)
• COM admittance control on the ground
• ankle admittance control, possibly in the air with a switch to deactivate when fz~=0, or possibly directly on the ground.