Finished prosthesis and review of project

by trixter on Nov.07, 2010, under Prosthesis

I have done the final steps in making the prosthesis suitable for use on a bike. I put a CB antenna mirror mount bracket on the end, which is suitable for bolting to something round. To allow for a quick disconnect of the socket I used a clevis pin and secure that with a hitch pin clamp (cotter pin). I wanted a turnbuckle for the wrist which gives me pronation and supination, or rotating of the wrist. This allows me some freedom of movement that a fixed connection would not. To allow for bending of the wrist I did not want the turnbuckle attached to the CB antenna mirror mount bracket without something like the clevis pin.

The hole in a standard CB mirror mount bracket is 1/2 inch in diameter, however my turnbuckle which was chosen for its overall length was too small for the clevis pin to fit through. I had to spread the loop of the turnbuckle to make this fit. In doing so I felt that the loop of the turnbuckle was too open and that it could become separated from the clevis pin too easily. To remedy this problem I pulled out my welding rig (GMAW) and welded the loop of the turnbuckle to the clevis pin. I am not the best welder but I think that the weld is solid and think that it does not look terrible. For illustration purposes I painted the CB antenna mirror mount bracket red which allows it to be identified easier. Since there is minor rubbing the paint will come off soon enough, so I do not think painting is a suitable solution.Here are stock photos that are the components I used (they are not the actual components I used they are just for illustration purposes).

Turnbuckle

On one end of the turnbuckle I replaced the loop bolt with a standard bolt. This was mounted to the socket by taking the bottle cap and drilling a 1/4 inch hole. I then placed a fender washer on both the inside and outside of the bottle cap. A 1 inch fender washer fit perfectly in the cap, and with the particular one I used there was a recessed area that was exactly 1 inch in diameter. This means that the washer snapped into place and does not slide around on the inside allowing me to drill a hole in the exact center of the bottle cap. By placing one on the inside and one on the outside that helped to reinforce the cap so that it should not be pulled out. Since the socket was coated in fiberglass this should actually be one of the stronger points on the whole system. One end of the turnbuckle is fixed so it cannot rotate, the other end will be screwed in almost all the way and anti-seize grease applied. This means it should not come loose from intended use or vibration.

The turn buckle is only a couple dollars, the fender washers and replacement bolt was similarly a couple dollars combined.

CB antenna mirror mount

This is not exactly what I used but it is close. This is made out of aluminum, so it should be fairly strong. It is 1/4 inch thick, and there is not that much weight to it. If you look closely you can see a hole at the top left of the image. This is the hole that the clevis pin will go through. When the pin is not present it will act similarly to a palm rocker. These generally cost $15 and is the single most expensive item in the whole project, equaling about 50% of the project cost.

Clevis pin & Hitch pin clamp

The clevis pin attaches the turnbuckle to the CB antenna mirror mount bracket. The pin is secured in place with the hitch pin clamp, also referred to as a cotter pin. I used a 1/2×2 inch pin, and the first hole was just over 1/2 inch from the end. This worked well since the turnbuckle and the CB antenna mirror mount bracket are each 1/4 inch thick. This means that the hitch pin clamp is next to the antenna bracket so shearing forces on the hitch pin clamp should be reduced.

Since the clevis pin is a much larger diameter than the turnbuckle loop I had to expand the loop a bit making it more like a hook. While the hook would grab the clevis pin, I was afraid that it might expand through use and then fall off. To remedy this I welded the loop to the clevis pin with a GMAW welding rig. These parts are all steel (zinc coated) so that welding rig is suitable. I welded both the top and the bottom on the turnbuckle loop to the pin so that even if the entire top part of the weld came off it would still be attached. I would rather overweld than underweld and have it come apart at a critical moment. The total cost for this part was about $3.

The entire project cost is about $30 which includes the plaster bandage used to make the mold of my arm ($1), the plaster of paris to make a postive mold ($1 or so), vasoline as a release agent (pennies) and the fiberglass coating ($5 max). The soda bottle is essentially free, but I live in California where we pay a deposit on the bottles so that was maybe $0.25. For this project I also purchased a heat gun which was $25, all other tools I had laying around. The surplus vasoline will go into another project, namely coating cotton balls with it as fire starter while camping.

Comparing this cost to having a medical one made there is no comparison. Even with insurance the co-pay and other costs would quickly exceed $30 to have someone else make a prosthesis. The other aspect of this is I can tweak this one to suit my particular needs and work the way I need it to work. One feature that I have, which is a combination of socket design and the ability I have with my arm is that I can lock it into the socket when I want, holding roughly my body weight with it, or I can release the socket at will. This gives me a quick disconnect system should I fall on the bike. I realize that not everyone will be able to release this way, however this is my project for me so it works I am publishing this information in the hopes that it helps someone else who wanted to go down a similar road.

Kliktronic Klever2

The only other modifications that are required is moving the front brake to the left side. I will be using a hydraulic clutch assembly as the master cylinder for the brake while its on the left. I may have to get a shorter lever so that I can use it in a similar fashion to the Kliktronic Klever2 system, but that depends on where and how everything gets mounted. The Klever2 is $1900 and that is just too much money, so I am not planning on getting that but rather making something work functionally the same. For the brake light I will be using a banjo bolt with a pressure switch integrated, this means when I apply the brake the rear light comes on. I may have to replace the brake line with a custom one a couple inches longer depending on how it is routed to the brake lever. I would upgrade to stainless steel lines if that is required, several companies make custom stainless lines.

Here are some photos of the finished project.