Snag wrote:
Here's the deal - a friend of mine is a below-the-knee amputee , and he
wants to rollerblade . He's done some research and others have done this
before . Next week I'll be receiving a prosthetic ankle and a rollerblade
... and my job is to fabricate a plate to mate the 'blade truck to the ankle
.
I've got the engineering pretty much done on how it'll be made , but I
have a question . How stiff should the plate be ?

Very. the stress on a normal ankle is tremendous.
I can't flex my ankle in any direction because of the stiffness of the boot
(pretty hard molded plastic).

There's a little flex in
the sole of the skate , but how much of that flex is actually transmitted to
the truck and wheels ?

I'm thinking it's some but not much. That's what you steer with.
Leaning one way or the other causes the trucks to turn (just a little bit!)

I'm leaning towards a fairly thin plate with ribs
below for rigidity with minimum weight . This will be cast from (probably)
A356 aluminum or similar casting grade alloy .


Is there some reason not to use a regular boot type arrangement on an artificial
foot?


Can't help much there. One would think the loads are mostly compressive,
but there is a substantial side load, and a bending load on the toe brake .

Would sure like to see it when it's done.


--

Richard Lamb
http://www.home.earthlink.net/~cavelamb
http://www.home.earthlink.net/~sv_temptress