Integrated Flexible Finger

thingiverse

UPDATE 8.30.2016: Just uploaded V9 of this design, although I will leave the old version up as well. V9 removes some of the flex filament that made up the springs and only includes it in a strip along the back, which reduces the amount of force required to contract the finger. It will also probably extend the life of the part because there is much less TPU being moved. I created this design because I was curious about the potential for combining flexible filament with stiff PLA. Thermoplastic polyurethane or TPU comes out of the extruder slightly tacky. Once cooled it doesn't stretch, but will flex and bend when force is applied returning to its original position afterwards. My idea was to incorporate a flexible joint with stiff structure to make it bend in predictable ways. This is my first design using TPU, so I decided to make something that I could test simply. After several versions figuring out print settings and rules of thumb for flexible filament I made a quick edit to test the finger out using a Raptor Reloaded from the e-NABLE foundation . Later on I would like to design a solution that incorporates flexible filament in the entire prosthetic, but this is a start. Printer Settings Modified Folger Tech 2020 Prusa i3 Rafts: No Supports: No Resolution: 0.2 Infill: 50% Notes: I used Hatchbox PLA and Sainsmart SemiFlex TPU on my own printer which uses an E3D Cyclops mixing extruder. Infill % shouldn't affect the flexible filament, but make sure that your perimeters are 1.2mm so that the slicer doesn't try to put infill inside the flex springs. Post-Printing After being removed from the printer and getting cleaned up a little bit, you can attach the finger to a Raptor Reloaded hand. Stringing & tensioners work just like in their tutorial, except that you don't have as many parts. I have had success using nylon coated wire, alternatives like fishing line were too thin and caused layers to split or crack. Demonstrating the key grip with V8 of the flex finger. The squeaking is from the nylon scraping against the plastic of the Raptor Reloaded palm (which I'll fix later, honest!). How I Designed This I designed the part in Fusion 360, sliced it in Cura and printed it out on my prusa i3 using an E3D Cyclops to handle the dual extrusion. In my later designs I decided to trap the stiff filament inside flexible filament to reduce retraction and stringing. Preliminary tests are promising! I'm looking at ways to reduce the amount of flexible filament used. This would allow me to save material as well as making the finger take less force to close.