In this article http://www.cim.mcgill.ca/~hamid/Robotics/Lee_Mechatronics_03.pdf are written Newton-Euler equations for the Stewart platform. In equation (2) it is written the torque relative to Bi and in this equation I don't get the sign of torque of f(I think it should be plus) and the 3rd and 4th terms on left hand side. I suspect they are resistive torqe(they clearly are torque of inertia force).