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We mounted the finger on a box-like palm, which is where we installed the hand's motor and controls. The earliest design of this palm included a system of spur gears that had three angular velocity step-downs of 5:1, making for a total mechanical advantage of 125:1. The gear at the base of the finger needed to be rotated 280° for the finger to move along a full sweep, so this gave us the number of rotations that the base gear would need to travel (97 rotations.) The motor's spec sheet states that the motor will run at 100 RPM without load, but it had little information about what its velocity would be with load. We tested its capacity experimentally and noted that with this system's (then fingerless) gear system, the motor's actual speed was far below what was originally expected, and that instead of . We found that, rather than the desired 5 seconds, the finger would need closer to 40 seconds for extension and closure. In future versions of this design, a more powerful motor may be used to obtain the same torque output at the finger. However, for our limited power, we chose to sacrifice torque and grip strength for speed with the prototype, and opted for a redesign with a shorter gear train and smaller mechanical advantage.
Design of palm including the three-stage gear system and accommodations for three fingers.
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