Mike wrote on 01/27/07 10:01:
The disadvantage of all this is a fixed top speed governed by your
gearing. A TEFTEC is the only kind I've heard of in recent years where
this can be changed, but it's not exactly convenient to change back
and forth. That's why I want the gearshift -- there are times I need a
lot of torque, and others where I need more speed than anything.
Ah... I can certainly see why a tranny is desirable. Do you have
access to a machinist?
A free one maybe every couple of years if I'm lucky. My other two
options are dependent on money:
1) Have a local machinist do work, and charge me whatever they charge, or
2) Learn enough CAD that I can hire parts made it done over the internet.
So... my only choice is basically to try to build my own, if I can
manage it.
A good friend of mine has an MS type disease and I volunteered to build
an electric chair for her when the time came. She still has use of her
arms and isn't ready for one yet but I have thought A LITTLE BIT about
it. But not much as it's pretty far (we hope) in the future.
Appropriate controls and comfort and proper positioning is usually the
most important thing, and there's a LOT of stuff out there made probably
by hundreds of companies, depending on what you might need. I'll send a
representative list of companies 'n stuff off-list if you like so that
you'll have an idea what's out there. For someone with specialized
medical needs, it is frankly better and easier to take a standard chair,
then adapt from there. The equipment can get *really* specialized, such
as muscle-twitch sensors and "cruise control" modes, or eye-gaze
controls, and even voice controls for the seating.
Most people have no interest in the amount of versatility that can be
achieved by a system such as what I am interested in. Some of this has
been a paternalistic cultural mindset that was always pointed at chair
users: "Don't do anything too adventurous -- you could get hurt," or
"You shouldn't be doing anything like that." So, a lot of people have
had a lot of aspirations squashed really before they got started. Many,
many people nowdays still have one main question, "How fast will it go?"
When they get the fastest-geared chair, they wonder why forcing
high-speed maneuvers on steep grades in the middle of the summer results
in cooked motors, burned out controllers, and half the distance
capability, as compared to taking it easier with a slower-geared chair
(all else being equal). Other people just have small or light or stylish
as their primary requirement. Once something more versatile comes out
and a lot of people know about it, and enough people manage to afford
it, the range of ideas of what people expect to be able to do tends to
expand. Stuff like towing a small trailer of groceries, or mowing the
lawn, or getting out in the snow, etc...
Nowdays, if you can finagle a way to afford a racing chair, you can
participate in marathons... Other stuff can enable a person to ski, work
in a workplace that requires you to be able to stand as part of the job,
sit up, lay down, climb up stairs, drive (literally almost anyone can be
enabled to drive, no matter how weak, given the application of enough
money), etc, etc. In my instance, with a new van and about $70k-$80k, I
could drive about as well as anyone else, even though I can barely drive
a standard electric chair. Since money rarely falls out of the sky like
that (I've never heard of it happening), I'm going to try to settle for
something a little bit short of such a miracle: put together my own
chair that will do enough of what I need as cheaply as possible.
I really like the idea of using a pre-existing bike or motorcycle
transmission, but I have some doubts about the long-term survival of the
bicycle units under heavy loading, and/or RPMs I am expecting to use. If
I can operate the bike stuff at higher RPMs and use its speed range
capabilities, then gear that down a bunch for the final output, it would
be great.
Otherwise, a small motorcycle transmission with at least a 5:1 range
(7:1 would be better) would be good.
Since I could do something really radical with a custom gearbox, I'm
inclined towards that. I could get the exact ratios and form factor I
want. I could do a 5-speed 6:1 range first stage, and a second stage
that provides a low-range capability...
jeff
