[ODE] building a foot with pressure sensors

[Stefan Castille]

I'm trying to create a model of a foot that has 4 pressure sensors located
on the foot. The idea is that with help of the pressure sensors i would be
able to detect where the center of gravity of the whole robot is located.

My first idea was simply to put 4 small objects located at the corners of
the foot, connected with a simple joint, and use dBodyGetForce on each of
the 4 "sensors" and calculate
pressure from that.

dBodyGetForce always returns a 0 vector. Does dBodyGetForce only return
extra forces added by the user and not simply all forces applied to that
object?

would it be a good idea to make those 4 objects easily penetrable and then
use the amount of penetration as a measure for pressure? I know the
penetration depends on how far from contact the objects were right before
calculation so i was thinking of getting an average from the last 5
timesteps. The idea is that if there is constant pressure the penetration
would quickly become stable.

Am i completely missing the point or would this be an acceptable way fo
determining pressure?

Stefan Castille