A force transmission mechanism includes a chassis that supports a rotatable arm, which includes a slot. A rotatable lever is supported by the chassis. A protrusion at an end of the lever engages the slot. A sliding drive element is supported by the chassis. A proximal termination of the drive element engages a second end of the lever. The chassis may support an elongate tube with an end effector fixed to the tube. The drive element may extend through the elongate tube. The elongate tube may rotate relative to the chassis. The drive element may rotate in unison with the elongate tube with the proximal termination rotating relative to the fork. The drive element may be a tube that provides a fluid passage to the end effector. The lever may be a bell crank with arms at a right angle.