Calibrate F/T sensors

[andreadelprete]

A calibration of the F/T sensors in HRP-2's ankles may be beneficial, especially in the estimation of the ZMP, which is crucial for balancing and walking on flat ground.

The normal force calibration could also be achieved by attaching a known load to the foot. Then, by applying forces on the four corners of the foot we could easily calibrate the tangential moments.

[andreadelprete]

An important detail to take into account is that the F/T sensor is not located at the level of the foot soul, but 10.5 cm above. Thus before applying the well-known expression to compute the center of pressure (CoP) as the ratio of the tangential moment and the normal force one needs to compute the equivalent wrench at a frame located on the foot soul. Intuitively, the force should be the same, but the moment would be different because there is a cross product between the lever arm and the force.