Cable control - cable quick-lock connectors

[Wolf Schweitzer]

I use some old Otto Bock cable quick lock connector to attach the terminal device (with an abutment at the end of the cable) to the prosthetic socket mounted cable (where the cable is attached to a quick-lock connector).

I am about to put up some pictures about the system that they put on my arm but I am not too happy with it. I'll post these images later and put the link up.

The problem is that mostly it inadvertently disconnects if the cable happens to be not under too much tension and the lock automatically unlocks. Conversely, my lock is very easy to use like that and ease of use is its major advantage. I started to put a minimal deformation on the outer shell that is supposed to lock it, by pressing it hard using pliers, and that somewhat improved the situation.

A safer method would be a screw-on system; we tried that but I could not connect it really well single-handedly.

Can we collect information (construction, seller, price), advantages and disadvantages of existing cable quick-lock connectors? Thanks.

[Jon Kuniholm]

I've tried silicone tubing, but that seems to tear. I wonder if icemaker line wouldn't work? That's Polyethylene mostly, although there are PEX types too, and would be thinner and slippery like a straw. The one benefit of the silicone was that it didn't slide off of the ball-ends, and it muffled the banging because it's soft.

[Sean McHugh]

A low tech solution that has worked in my experience is to cut a 1" section of plastic drinking straw, slip it over the open cable, and slide it down over the ball and receiver when connected. The straw must be of a diameter that will slip snugly over the connected assembly. They crack and split in short order but are easily and cheaply replaced. I tried thicker sections of tubing in a search for durability but the surface bulk and texture inhibited a good glide wherever the cable made contact with the socket.

[Jon Kuniholm]

I definitely recommend looking at the integration of harnessing into an UnderArmour shirt or similar. We used cotton webbing and a cotton shirt on a patient in Cuba, and it worked great. You can make the harness any shape you like--figure 8, 9, whatever--and because it is sewed into the shirt it won't move and will stay in place much better than a separate harness. Further, because the shirt pulls the harnessing close to the body, friction allows it to work without axillary pressure, something that bothered me with other designs. Being able to separate the harness from the arm easily, have a few extra, and separately wash the shirt, is also huge. Sure, in an ideal world everyone would handwash their harness every night. The integrated shirt harness means that you can use a washing machine and not smell like a locker room all the time.

I'd really like for someone to try this with a bilateral application, because it would allow the two cable systems to be completely independent. Would need to figure out a good way for them to adjust the cable length with it on, however...

[Wolf Schweitzer]

Thanks! Trying to improve my current harness and as I am about to get a socket redo and a good moment to change cables, I am very happy for these details!

[Jon Kuniholm]

It's interesting that unlike other patents of the era, this one was assigned to Northrop, and not to the Secretary of the Army. I've been unable to find a reference to the order that began this, or to when the practice began or ended.

[Jon Kuniholm]

Looks like these connectors came out of the US post-WWII research effort that funded Northrop Aircraft to improve some of the cabling designs. This patent covers the ball-end and swivel that we're familiar with, but not the quick-release adapter for different length cables for different TDs. The necessity for this, by the way, could be eliminated through being able to adjust overall cable length easily at another point in the cabling system, eg in the harness, through the use of a friction lock as I've done here.

[Jon Kuniholm]

Something else I forgot. In addition to the rubber grommets which serve to keep the ball from sliding up and out of the wider hole in the quick release (and keep the hardware from banging against your arm when the cable is slack), I've also seen felt or rubber inserted into the quick release so that it must be compressed to get the ball to its exit point. A little piece of the appropriate gauge latex or silicone tubing inserted in there would do the same thing. I'm a fan of silicone for all of this stuff, because it doesn't deteriorate or get dirty as fast, and performs better in extreme temps.

[Jon Kuniholm]

I'd guess that you have the same ones we do, which you can see on this page.

The spectra setups are actually from Bob Radocy at TRS. You might like some of his voluntary closing designs. The Grip is the classic. The last page of his catalog shows both the ball ends for spectra and some of the rubber grommets that he adds to the balls to keep them from coming undone as you describe.

Similar parts, "Push-In Military Specification Grommets" are available here, but I haven't messed with sizes. Bob's ferrules for spectra are also cool.