[PAR_WIG1350]

Torque is equal to the distance from the axis of rotation times the force tangent to the radius available at that distance.

for an arm, the distance should be considered to be the distance to the center of mass of the arm.

The torque that the arm applies TO the motor equals the tangential component of the weight times the distance from the center of mass to the axis of rotation.

If the torque applied to the arm BY the motor equals the torque that is applied by the arm, then the arm will be stationary. if you exceed this torque, then it will move up (signs [+ or -] matter here). If the arm applies more torque than the motor, it will go down.