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
gravitational acceleration is assumed to be 9.81 m/s^2.
% Compensate gravity at current position
fbk = group.getNextFeedback();
gravity = [0 0 -1];
efforts = kin.getGravCompEfforts(fbk.position, gravity);