Part Implementation

The rotation shoulder joint was modeled as a linear bearing with rotation provided by a plastic turntable. Two of these joints were used in the robot.

Figure 6. Rotating Shoulder Joint

A worm gearbox was used to generate as much torque as possible. The gearbox provided a gear ratio of 336:1. The motor’s stall torque was 4.9 mN*m with a speed of 5040 rpm. With this gear ratio, the stall torque was 14.58 in*lbs, and the new speed was 15 RPM. We calculated our torque requirements to be 12.25 in*lbs based on the weight of the parts, so this motor and gearbox was sufficient.

Figure 7. Worm Gearbox. Figure 8. Assembled worm gearbox with rotary wheel attached

The rotary wheel, ball bearings, and rod eyes were used together to connect the gearbox’s axle to movement of the arms. The arm, a ¼” diameter hardened steel rod used specifically for the linear bearing, was threaded through the rod eye and held in place using ¼” O-rings. The bearing was press fit into the rotary wheel, and the rod eye was attached to the inner part of the ball bearing. The angular portion of the arm was made by bending metal tubing around the rod.

Figure 9. Parts used in Arm to Wheel Connection

Figure 10. Arm Implementation Concept

A set of bevel gears were connected to the gearbox’s axle to provide motion for the tail mechanism. The gear was attached to a aluminum mounting hub which was attached to the axle via set screw.

Figure 11. Bevel gear CAD file and Aluminum mounting hub.

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