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Although the second iteration improved compactness and actuator integration, it also revealed a new problem. Because the flexures were thinner, the TPU was less stiff, and the tendon slots were narrower, friction became too high and the finger became overly compliant. As a result, the finger did not reliably return to its resting position after curling. This iteration was still valuable because it highlighted the tradeoff between compliance and recovery. Based on this result, the next iteration should increase stiffness by either using a stiffer TPU, increasing flexure thickness, widening the tendon slots, or combining those changes. Overall, these iterations helped us move from a simple manually driven concept to a more integrated motor-actuated prototype while identifying the main design changes needed for the next build.
Final Iteration
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The final implementation expanded the design from a single compliant finger into a two-finger pinch gripper actuated by a shared motor-driven pulley system. Rather than treating each finger independently, the final design used a redesigned spool that allowed both fingers to be connected and actuated simultaneously, creating a more realistic gripping mechanism for object manipulation. This required the overall system to become more compact, modular, and structurally stable so both fingers could operate consistently without excessive friction or misalignment.
Additional iterations focused on improving the finger’s ability to return to its neutral 90° resting position, reducing tendon binding, and matching the compliance of the TPU flexures to the available motor torque. Tendon slot dimensions were adjusted to reduce friction while maintaining accurate tendon routing, and nylon straps were sewn into closed loops at the distal end of each finger to create a cleaner and more reliable attachment to the pulley system. Once the mechanical connections were validated, a PLA housing and handle assembly were designed to improve system stability, protect the electronics, and create a cleaner final presentation.
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