Re: Scale for weighing fully laden power wheelchairs

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Steve Uhrig" <Steve@xxxxxxxxxx> wrote in message
news:bm0kg11tqiielmuo4bhc9rut4o7ttl5t0v@xxxxxxxxxx
> On Mon, 22 Aug 2005 04:29:55 -0400, "Robert Green"
> <ROBERT_GREEN1963@xxxxxxxxx> wrote:
>
> > My question is this:  If I took four identical bathroom scales, a 4x4
sheet
> > or two of 3/4" plywood and attached wood block "feet" at each corner
that
> > would sit on the bathrooms scales, would their readings (assuming each
scale
> > was zeroed out to start) total up to the weight of the object?
>
> Think of this:
>
> If you had TWO scales, and a board bridging them, and put a known
> weight on them, would each scale weigh half the tare (weight minus
> board) weight?

I'm not sure.  Right now I have only one bathroom scale so I can't test the
concept.  What I would expect is if the scales are zeroed out and a 50 pound
weight were placed equidistant from each scale on that board that they would
both read 25 pounds or that one would read 25 and the other 24.  Anything
else would seem to be creating or destroying mass.  Cold fusion Phase II.

> I think you have to add these algebraically, not directly. Each scale
> is seeing more than the 1/4 load.
>
> Simple enough to test the concept. Weigh something like concrete
> blocks, or a stack of phone books, on several scales and take an
> average so you have a 'standard'.

When the scales come, I have some large barbell weights I am going to use to
calibrate it.  Until then I have only the queasy memory of college physics
and levers from so long ago, the neurons have been recycled to hold old
episodes of Seinfeld.  Maybe someone with two bathrooms scales will straddle
them and report back before then.

> Then set up your 4 scales and see what you get.
>
> Or take two scales, weigh yourself, then straddle both and see what
> you see.

Even if the basic premise of simple totalling is wrong, there will probably
be a function revealed through a number of test runs that will tell me how
to process all four numbers to get the proper result.

> I am an electric wheelchair user, and the specs for anything in the
> last 20 years are available on the web. That might save you the
> effort. There may be some minor differences due to accessories like
> baskets, cane or oxygen bottle holder, etc. but all well within your
> tolerance requirement.

But Steve, where's the *fun* in that?  :-)

> As wheelchairs must all be approved by some or another letter agency,
> you may be able to find a database with all needed info in one place.

Abledata has a lot of info about mobility devices that they assembled under
some sort of government contract but I'd be dubious about its accuracy.  I
just ran a CarFax report on my on VIN.  It's pretty inaccurate.  The Feds
can't have done much better.

> Don't forget dead batts will weigh 5-10 pounds less than good ones.
> And some have chargers onboard which may be missing, so look for that
> and consider the weight.

I'm probably going to try building a robotic "tender" that follows the main
chair around with a selection of tools, chilled drinks, cordless phones and
what not.  Non-standard enough that I'd like to know the aggregate weight
although I could weigh each piece separately before construction.  Damn,  I
had my heart set on a big, roll-on platform scale.

> Tires are high wear items and generally are replaced as standard every
> year. Batts may last a year or two, rarely longer, depending on how
> they're used. Brake linings need replacement periodically. Bearings
> need lubrication esp if the thing is used outside or they will need
> periodic replacement.

So far, I haven't popped open any of the wheelchair motors.  They look a
little intimidating compared to a standard electric motor.  I assume that's
because they need to be well-sealed, traveling low to the ground the way
they do.  I also think I've not cracked them yet because the gearbox housing
is bolted down like the power steering pump that once blew up in my face,
literally.

My wife ran into the garage after the loud bang and the cloud of PS fluid
that hit the manifold turned into thick, black smoke.  She turned the corner
and saw me emerging from the smoke cloue with my face covered with brigh red
PS fluid and she fainted dead away.  Thank God for goggles.

I'll have to research the proper torque settings and techniques.  I know
that there isn't 2000PSI building up in the wheelchair gear housing but
traumatic events stay with you!

Right now I am de-gunking, re-painting, cleaning contacts, inspecting welds,
tires and controls and generally doing light stuff.  On the powerchair I'm
adding a separate 12V electric system to power various accessories like
running lights, a radio and turn signals.

> Each manufacturer will have a maintenance schedule for his chair, and
> a service manual. You'll start seeing more than one of the same type
> as there are models distinctly popular and unpopular. Manuals may be
> worth the expense.

Most of the manuals I have seen are user manuals and are nearly worthless in
doing a motor or gearbox or brake rebuild.  Fortunately, almost all of them
seem to come from one manufacturer or the other.  The motors on very
different brands of scooter lifts are often identical and look much like the
motors that activate automatic chair swivels.  I assume once you get the
hang of the basic model, the rest comes easy.  If you know of any sources
for Merits, Shoprider or Everest & Jennings manuals, please share!  I alway
buy detailed manuals for cars I own, but they're a little more complex.

A car manual can save you immense trouble, especially when it comes to
knowing the "magic techniques" to remove plastic covers, reach hidden
screws, etc.  I'm not sure a scooter or wheelchair manual will reveal much.
Do you have one for your chair?  What did it cost?

> Good luck with your project ... Steve

Thanks!   You've given me a number of things to think about.

--
Bobby G.