Cathy's Lucky Fin V2 - Prosthetic Hand - Bowden / Push-Pull Variant

thingiverse

<h2> Outline </h2> <ul> <li> This prosthetic hand model does not rely on elastics for finger return, adopting a more efficient push-pull actuation system based on the Bowden principle </li> <li> Outside of the tendon cables, anchors, and screw for tensioner, all other components are 3D printed, showcasing versatility in design </li> <li> This revised model is a remixed version of a previous design I've been working on for my daughter, aiming to improve functionality </li> <li> The most notable difference compared to the previous design lies in the single tensioner system for tendons from all four fingers and the centralized routing of cables through the wrist, minimizing lateral movement-induced finger bending </li> </ul> <h2> Specifics of this design </h2> <ul> <li> The hand operates on the Bowden Cable principle, where cables used to close fingers also push them back open, achieving efficiency </li> <li> Fingers feature a single channel for each cable, streamlining the mechanism </li> <li> Finger positions are offset relative to one another, ensuring varied and adaptable movement </li> <li> No external hardware is required for finger operation; pins integrated into phalanges click into place, securing them in position </li> <li> The Gimbal mechanism adds an additional degree of freedom – radial and ulnar deviation </li> <li> Design accommodates crimps for terminations (I utilize #1 single-barrel fishing crimps) </li> <li> Distal and Proximal phalanges are divided into two parts: one printed in PLA (files named solid) and the other in rubber, utilizing either molding or flexible filament </li> </ul> <h2> Tendons </h2> <ul> <li> This hand is specifically designed for push-pull actuation, which means strings used in other e-Nable prosthetic designs will not be compatible </li> <li> After extensive experimentation, I found Nickel Titanium cables to be the most suitable choice due to their flexibility, kink resistance, and effectiveness as Bowden cables </li> <li> Aquateko offers fishing leader cables made from this material at reasonable prices, available in various sizes – https://www.aquateko.com/collections/buy-knot2kinky-leaders</li> <li> As a reference point, 25lb single-strand cable for a hand scaled to 65% proved satisfactory; thus, using a higher gauge would be recommended </li> </ul> <h2> Grip </h2> <ul> <li> Fingertips can be printed directly with flexible filament; however, the filaments I tested lacked tackiness in my opinion </li> <li> The alternative option is to use the provided mold, designed for "pourable" materials. I experimented with Smooth-on's Mold Star 15 and achieved excellent results – tips come out soft and tacky (Shore Hardness of 15A) </li> <li> The proximal joints have an alternate version featuring a slot for an additional grip point on the finger, allowing insertion of O-ring cord or rubber band </li> </ul> <h2> Assembly </h2> <ul> <li> Phalanges feature slots for pin alignment and clicking into place </li> <li> Similarly, the Gimbal is spread slightly and slid onto the palm until pins pop into place </li> <li> The Gauntlet is inserted into the gimbal, with a printed pin entering from the top; cables are routed through this pin, ensuring proper orientation </li> <li> Each tendon has a crimp at one end that sits in the groove of the fingertip – glue or melted PLA secures it in place effectively </li> <li> Tendon cables are routed through fingers, palm, and terminate in another crimp residing in the tensioner – same securing method applies </li> <li> Routing cables is easier in two parts: first at the palm behind the proximal phalange toward the wrist, then routing the other end of the cable toward the fingertip </li> </ul> <h2> Printing </h2> <ul> <li> Parts print well in the orientation as loaded on Thingiverse </li> <li> Components requiring supports for printing – Gauntlet, Palm, Gimbal </li> <li> All other parts print without supports </li> </ul>