Adapters to attach Prosthetic Hand to Black Ram Mount and updated Pins by AlwaysTinkering

Last crawled date: 2 years, 11 months ago

This is a merge of two great projects and is a continuation of projects they were built off of.
This parts library only contains additional parts or modifications to existing parts when needed. You will need to download the parts and instructions from the original libraries to complete this mod.
The PINS can be used in the existing Black Ram models in places you don’t want to use the plastic screws.
I added an STL for a flat sided screw for the Black Ram so that they can be printed on their side.
The Prosthetic hand source https://www.prusaprinters.org/prints/12224-prosthetic-hand
By SoniaVerdu. It will on the Black Ram Hand (Robotic/Prosthetic Hybrid) - Mark V by Black_Ram_Industries
at https://www.thingiverse.com/thing:1717809
And credit to the flex hand that I have not printed but was referenced by the creator of this version of the prosthetic hand - "Flexy-hand" http://www.thingiverse.com/thing:380665 I used part of a connector brought forward from there model.
I have a family member that had finger surgery on the left hand. It could take a year or more to return to full functionality. I printed the Black Ram Claw to bring some humor to their situation. Then I started to wonder if it could provide basic practicality… could it hold a jar while they opened a lid? I found challenges:
• Being above and in front of the hand is awkward for movement.
• The holding pressure on most claws is in-adequate (for all ends)
• Slippery plastic is a challenge
So I started looking at prosthetic prints. There is some insane work that has been done in this area. They are largely designed for people that are missing an appendage. So I decided to try to adapt one to the Black Ram Assembly. It is a lot of pieces to get it to work well together. Getting the assembly to generate enough power to overcome the pull resistance took some time. After several pull designes, I eventually reduced the pull pressure enough to where to where my wrist did not hurt using it.
The Prosthetic does not solve all the problems. I printed the end fingers in flex with the recommended high fill. So its kind of like pla, with a more tactile touch. The visual motion is great. The hand sits pretty far out. I did this to reduce it hitting a healing finger. I was also trying to place the pull cord entry into the hand level with the Black RAM pull. Unknowingly I removed the designed in leverage of the low pivot point in the original Prosthetic design. Do to the nature of the Black RAM design, the hand is mounted fixed and the ram moves. I did consider angling the hand down more.
Parts I am providing for the BLACK RAM ASSEMBLY:
• I cut the side off a screw so I can print a plate of them lying flat. If I print them without supports I lose a little thread detail as I transition of the bottom. Since they were PLA I printed them with support off the plate giving great threads all around. Works great you can let them all print at once. I used a .15 layer height.
• I designed Pins to replace the screws in places they don’t need screw tension and tend to fall out from the rotation. The pins have nuts to just latch in place. The 10mm short slots are probably best but a little harder to insert.
• The Prosthetic Mount adapters for the RIGHT and LEFT hands (right hand not tested yet).
• A tensioning box to hold the prosthetic cords using tensioning_piece from the prosthetic hand design. It is the same piece, I had to trim the knobs so they did not hit each other… so the trimmed version is included.
• Tension Box cover if I can get it to stay… I spaced it with tape to prevent rattle… this cover is optional.. once our hand cords are adjusted the tension will hold them in place. Lift them so the top octagon clears the block and turn them to tighten. Nice design Sonia.
• The lever to pull the hand. The lever requires two 688 bearings (16mm diam, 5mm wide, 8mm hole) or print the plastic SHIM I will provide to reduce the hole).
• 8mm Pins for the new lever to go through the bearings.
• Stub-Tendon to go in the lever
• Fixed Tendon for the gauntlet port. This is required to raise the pull position… my first version was a tall fixed tendon. I recommend the half height for improved leverage.
• The gauntlet to lever tendon requiring 8mm pin on the lever side (top tendon).
Improvements that I think could be made:
Black Ram Assembly
The joint between the gauntlet and the wrist assembly could use a conversion to a ball bearing. That joint counters the pressure applied to the apparatus at the end. While testing the prosthetic in its first version the pressure to close the hand was about 7 to 10 pounds (3.1 to 4.5kb) of pull. I was bending the pins I had put in addition to the squeak. It also made my wrist hurt.
The hooks are great but in the double claw you have too little leverage to keep the claw closed. This is true for all the hooks. There lots of ways to increase leverage at the end of the gripper such as a mod on this https://www.youtube.com/watch?v=YX1MsP7aRvo or one of the many other examples online that could be converted.
Prosthetic Observations
I know nothing about Prosthetics. These are my observations.
1) Compounding the grip pressure at the tips to be able to hold things securely. Maybe sleeving the channels through the hand with something like Teflon would reduce friction. While I did not use the original wrist, my hack could use some way to compound the pressure I apply to a significantly increased factor at the tips of the fingers.
2) Independent suspension? Slip differential? The 5 fingers travel as a unit. The first two to hit can prevent the others from making contact. It was harder to pickup items with the fingers than the simple tri-claw. How do we make each finger travel independently so the travel of the others is not interrupted… and not compromise the overall grip?
3) A floating palm? The fixed palm gives a surface to close against. If the closing pressure of the fingers is increased and stabilized, could the palm apply additional counter pressure and close the grip on the object without releasing it from the fingers? We are mimicking the hand, but we are not limited to what a hand can do if a feature adds benefit.
4) The thumb. School always taught us this is what differentiates humans from other species. This mimics the two external joints, but the inside joint going to your wrist is what provides the real wrapping action in our thumbs and the closing pressure on the object to push it into the palm and the fingers. I would see a requirement that the fixed assembly holding the current thumb design would need to move as well to close the grip. This prosthetic model overall is missing a section in all the other fingers and therefore may be wrap challenged in some situations.
Other files I am providing…
My openscad hacks to make the parts.
Several openscad files to cut the large parts for printing… I then glued them back as suggested in this youtube video. Made printing so much easier. https://www.youtube.com/watch?v=stry5kibhyY&t=86s
Prosthetic assembly notes:
10mm and 20mm long 2mm machine screws are too long and will need trimming in many holes. I think I will prefer the piece of metal and seal it with filament. I don’t know how that will work in the flex.. I tried melting some flex with an iron and it burnt at the same temp I do PLA with. No science in that test though. I was afraid a PLA plug would pop out of the flex. The metal pieces save you money in bolts… and no MICROSCOPIC nuts to come off… glued or not.
I started with nylon fishing wire. Stranded is so much easier to work with. I didn’t even tie it… I just would the extra around the octagon fitting.
This was actually my first flex print. I have 5 incomplete fingers to prove it. It took me that long to figure out the config I downloaded that was tuned by someone for flex on my Prusa MK3S still had retraction on… at reduced settings, but the speed of the retraction was way too high. The finger would get almost to the top and fail.. I assume there was more retraction required there.
If I print a hand body again I will print it with a bit more fill. I can see it warping slightly under the strain of all 5 fingers pulling at once. I likely did it at 20% for this one.
Thanks to all the creators of these items. In addition to working correctly right off the printer, they provided a great documentation.