This paper presents the mechanical design and mathematical modeling for the first joint of a five degrees of freedom collaborative manipulator. The robot is actuated using Magneto-Rheological (MR) clutches in order to ensure full backdrivability and intrinsic torque control for safe human-friendly operation. One of the unique features of this design is the usage of a single motor for powering all five joints of the robot simultaneously and independently. After a brief description of the MR clutch principles, the details of the mechanical design and a state-space representation of the first joint are discussed. The paper will conclude with some preliminary simulation results.