Set the AMotor axes. The anum argument selects the axis to change (0,1 or 2). Each axis can have one of three ``relative orientation'' modes, selected by rel: * 0: The axis is anchored to the global frame. * 1: The axis is anchored to the first body. * 2: The axis is anchored to the second body. The axis vector (x,y,z) is always specified in global coordinates regardless of the setting of rel. For dAMotorEuler mode: * Only axes 0 and 2 need to be set. Axis 1 will be determined automatically at each time step. * Axes 0 and 2 must be perpendicular to each other. * Axis 0 must be anchored to the first body, axis 2 must be anchored to the second body.