Legged robotics creates the demand for high torque compact actuators able to develop high instantaneous torque. Proprioceptive actuator design theory is a design theory that removes the need for a torque feedback device and relies on the stiffness in the leg for absorbing the high Ground Impact Forces created by walking locomotion. It utilizes a high torque density motor paired with a gearbox with a high gear ratio for torque multiplication. Previously work has been done to design a proprioceptive actuator design that utilizes a planetary gearbox to create a modular low-cost actuator for legged robotics. The purpose of this thesis is to design and analyze a proprioceptive actuator that utilizes a cycloidal gearbox design to test the feasibility of the gearbox design and look at the advantages it might bring over a planetary gearbox design. A cycloidal gearbox utilizes eccentric motion of cycloidal disks, made of epicycloids, to create a high gear ratio in a very limited space without having to rely on expensive gears for torque multiplication purposes. A prototype low-cost actuator was developed using a 2-disk cycloidal gearbox in its design. It was tested for wear life and torque control and was able to meet the torque and operation requirements of the Cal Poly legged robotics project. The design was also optimized to be made using low-cost additive manufacturing techniques rather than relying on conventional machining.