getGravCompEfforts calculates joint efforts that compensate
This method computes the efforts that are required to
cancel out the forces on an arm caused by gravity
'Positions' argument expects a [1 x numDoF] vector of
positions of all degrees of freedom.
'GravityVector' argument expects an [3 x 1] vector of the
direction of gravity in the base frame. Note that this
direction vector is not required to be unit length, and the
magnitude of gravitational acceleration is always assumed
to be 9.81 m/s^2.
% Compensate gravity at current feedback positions
fbk = group.getNextFeedback();
gravity = [0 0 -1];
efforts = kin.getGravCompEfforts(fbk.position, gravity);