Geneva Mechanism (Redesign & Second Implementation)

Because of the brittleness of acrylic, we chose to re-cut the gears out of Delrin. This plastic is extremely durable and can withstand high stresses and temperatures. It was also noted that the crack on the previous acrylic gear was near the center where the material was thin, so we redesigned the gear to be thicker around the center (See Figure 1). A TEXAS and Longhorn were incorporated in the design for aesthetics. "What Starts Here Changes the World" and our names were engraved on the front surface of the pinion. Since the Delrin was 1/4" thick (which is at the limits of the laser cutter's capabilities) and extremely tough, the laser cutter had to be placed on a power setting of 100%, moving at a slow speed and making two passes. Despite these parameters, the gear had to be tapped out of the raw material. The final result can be seen in Figure 2.

Figure 1. Pinion gear laser cut from Delrin (Before removing from raw material)

Figure 2. Pinion gear laser cut from Delrin (After removing from raw material)

Since Delrin is a machinable material, we were able to drill out the holes for the shafts and rods with ease, unlike the brittle acrylic gears. Figure 3 shows the implementation of the geneva mechanism on the exoskeleton.

Figure 3. Improved Geneva Mechanism

When we were running experiments on the exoskeleton, we noticed that the motor shaft was slipping on the pinion gear. To fix this problem, we used a shaft connector (Figure 4) that was fixed onto both the pinion and the motor shaft. This prevented slipping and allowed transferring of power from the motor to the gears.

Figure 4. Shaft connector attached to driving gear.

Laser Cutting Video

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