Prototype Version 2 Is Here!

A project log for Hintha Modular Prosthetic Hand

An affordable, durable, bespoke prosthetic hand system developed in and for low-income settings

Jason BenderJason Bender 01/11/2019 at 10:010 Comments

Jason Bender // 11 Jan 2019 // Taunggyi, Myanmar

Version 2 is here! Check it out here:

Major changes include:
- Reposition the thumb joint to increase opening, grip force, and most importantly, reduce change from 3-jaw chuck to lateral grip to a single motion.
- Updated ratchet that is allows for more fine adjustment, fewer parts, and easier assembly.
- Reinforced cable attachment point

Really pleased with this second-gen prototype. Fixes most of the major issues, and I dare say we may be just one final iteration away from a workable product.  I was able to test the function by attaching the terminal device to a ITAL socket I had, and was nice to see that the standard 1/2-20 attachment means its easily interchangeable with a standard professional prosthetic device.  The heat-set inserts are also a HUGE upgrade that helps with assembly and re-assembly.

A few issues left to address:

1. The thumb is still too sloppy.  When the hand is fully pronated there is no issue, but when the hand is in the neutral position and the thumb is in lateral grip (thumbs up) position, the cable tension is enough to pull the thumb into a more opposed position. Will try adding a gasket to increase friction, but ideally a type of indexing or locking mechanism is probably necessary for 3rd gen.

2. Rubber bands to retract 4th & 5th digits. Current prototype uses daughters hair bands, neither robust or strong enough for real function.  Investigating dental bands and other small rubber bands for a more permanent replacement.

3. Gripping band swap. The "castration rings" work great for a prototype, but general consensus surrounding them is that longevity is an issue. Even after a few days of testing I can already tell they are loosening up. Latex tubing seems to be the replacement of choice. There is also an issue with:

4. The pivot bolt for the thumb that also anchors the rubber bands to the palm.  The current screw is fully-threaded and tears at the bands, getting a partially-threaded screw (if possible) will help the bands slide when rotating thumb and reduce wear.  A few other longer screws need replaced w/ hex-drive heads to standardize across entire hand. 

5. Lastly, once the mechanics are nailed down, throwing the STLs into a mesh editor to smooth out the design and improve appearance.

That being said, I think we are really, really close, and it will soon be time to turn attention to the socket and suspension method. Stay tuned! And don't forget to leave a comment or request to join the team if you feel like you have something to add!