Otto Bock cable control / Otto Bock body powered

From my experience and observation, the Otto Bock cable control is not to be viewed as established from a design or engineering point of view. As recently commented by others, some issues are of general nature and not specific to a particular brand.

However, the serious problems seem to be identifiable.

They can probably be addressed with a bit of care and interest. And if you think that Otto Bock sucks you may very well think that - but I could not possibly comment.

CABLE DAMAGE 1

The standard issue nylon string by Otto Bock lasted for just about 2 minutes.

Then, their 2-way-pull system hand locked up.

I tried to encourage it to open back up. I am not Incredible Hulk - I'm a normal middle aged average sized guy. But the gentle yank ripped the nylon / Perlon cable out of the shoulder harness ring. The damage was visible over a longer part of the string. Turns out the cable mounts are tiny metal threads that conduct pulling force only to the outmost layer of the string.

Steel Hook Otto Bock standard edition

CABLE FIX 1

At any rate, I was not offered an immediate repair and so I was on my own.

I replaced the whole nylon drama using standard issue 2 mm steel cable and standard issue cable clamps from our local hardware shop.

Steel Hook Otto Bock standard edition

Steel Hook Otto Bock standard edition

CABLE DAMAGE 2

My fix worked well but was a bit rough and experimental.

The prosthetic technician replaced it with Otto Bock's steel cable and that got used up after about 7 days. The wires disintegrated around ridges the hook's hole contained. The hook's hole contained no smooth surface and the filigrane Otto Bock wire had been mounted without protection (German term: Kausche).

Here is how a modern 2008 cable connector with Otto Bock looks like. WTF seriously guys.

Steel Hook Otto Bock standard edition

CABLE DAMAGE 3

The technician then replaced the hook with a steel hook. That contained a bolt that was screwed into place for cable mount. A beautiful looking setup indeed.

Steel Hook Otto Bock standard edition

Steel Hook Otto Bock standard edition

Steel Hook Otto Bock standard edition

After 5 days, *zoing* goes that cable.

Reason was that the cable mount had caused hundreds of bending deformations of the cable instead of providing a straight pull at all times. That, of course, is a steel cable no-no.

Steel Hook Otto Bock standard edition

One wonders why they are not any better. I mean, we are dealing with Otto Bock and it is the year 2008, no.

CABLE FIX 2

I then went and re-re-edited the cable situation. I used some part of the cable sheath, wired it into a loop and I am holding that into place using some wire (yellow).

Remember that I am one handed? So I work with materials that I can handle.

Steel Hook Otto Bock standard edition

Steel Hook Otto Bock standard edition

I then went to the Brugg Drahtseil AG for advice.

We sat down and drafted a solution to my problems. We came up with a clear solution in that a ball bearing was necessary to solve the problem:

After I communicated these results, the connection of the cable to the hook was also termed Achilles Heel of cable controlled prosthetics by some insiders.

CABLE MATERIAL

Subsequentially, I identified the manufacturer of the Python steel cable re-sold by TRS, the Westfälische Drahtindustrie (WDI) in Germany.

http://www.wdi-python.de/

As complementary choice of material, I identified Kevlar reinforced tennis string as an alternative to simple nylon strings; one product would be PRINCE PROBLEND 16.

CABLE SHEATH

Regardless of the totally useless cable connectors to the hook, the cable and its sheath survive for a maximum of 4-10 days until they fall apart or cause the cable to tear up entirely.

Update 2010: I solved the problem and filed a patent application that was granted in January 2016.

CURRENT SITUATION

Otto Bock withdraws defective products.The two-way hand (above) was pulled from the market as it appeared.

As of July 16th, there are technical drafts of a new hook with cable ball mounts such as we suggested. This is good news if the result will work. Everyone and me is interested to see, test and try out that new hook. I am currently running a loose steel hook on a self repaired steel cable and on a socket that is just too long - it rocks, but it could be a hell of a lot better. As of July 29th, I obtain the new Otto Bock MovoHook 2Grip 10A80. A few months later, these fall apart due to manufacturing issues.

Even later, I switched to V2P prehensors and to Hosmer Dorrance hooks that are far better to withstand real usage requirements.

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Otto Bock cable control / Otto Bock body powered; published 10/07/2008, 09:01; URL: https://www.swisswuff.ch/tech/?p=3.

BibTeX: @MISC{schweitzer_wolf_1603883066, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Otto Bock cable control / Otto Bock body powered}}, month = {July},year = {2008}, url = {https://www.swisswuff.ch/tech/?p=3}}


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