Re: Automatic Wheelchair Turntable

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Robert L Bass" <robertlbass@xxxxxxxxxxx> wrote in message
news:NZ-dnaSCGvwn3d3eRVn-

<stuff snipped>

> > The problem now is that backing up into the
> > van is made considerably more complicated
> > because Dad has to position the scooter to
> > mate with the EZ-lock device.
>
> Is there any way to use guide rails to keep the front wheel aligned while
> backing into place?  Without seeing pictures of the ramp it's hard to
figure
> what would work best for him.  If you can modify the ramp surface to guide
> the scooter into place, he should be home free.

The problem with any wheel-centric approach is that we occasionally need to
transport one of the other chairs, like for an extended stay at our house or
a vacation trip.  Whatever design I come up with should accommodate as wide
a range of chairs and scooters as possible.  Car wash guides pretty much
assume a pretty standard 4 wheel configuration.  I don't believe that any
one of the chairs has an identical wheelprint.

A small footprint rear or mid-wheel drive power chair wins hands-down for
tackling small quarters.  Tiller steering just can't do what two powered
wheels sitting under a person's seated center of rotation.  But Dad *really*
likes the tiller and the ease of steering it offers compared to a joystick
for tooling around the neighborhood and for shopping trips.  He also likes
the idea that there's considerable metal between his foot and the front of
the unit.  In a powerchair, you're often forced to lead with your bad foot
elevated.

<stuff magically snipped because I mistaken toggled INS off!  You'd think a
modern PC wouldn't let you overtype by accident!>

> > it involves
> > both installing a folding ramp and a power unit
> > for the sliding door.
>
> I wouldn't do it that way.  It sounds like an expensive and only partially
> workable solution.

It's got pros and cons.  Sometimes, you can't find a front-in spot with the
passenger (left for you Brits) side clear.  That's when having a door and
ramp on the driver's side becomes pretty handy.  As you point out, it's very
risky to unload streetside - if we were to do that, I'd get two rubber
traffic cones with LED flashers and an orange flag and insist that he only
do it with a flagman to deploy the cones and wave off traffic while he
boards.  In the cellphone age, too damn many people just aren't paying the
attention that they used to.  I think some recent studies proved that just
about everyone is a worse driver while using a cellphone - some incredibly
so.  I'd be afraid that with two flashing traffic cones and a flagman that
someone would still hit him if he tried loading from the streetside.  It's a
big negative in the "dual door/dual ramp" approach column, I will certainly
agree.

> > The turntable idea is just about dead...
>
> I didn't think that one was going to float.

It's still probably the easiest solution for the end user.  I haven't even
begun a exhaustive industrial turntable search.  If the Bismarck's main guns
worked on turntables that apparent relied on gravity to keep them in place,
the physics for large load turntables is there.  The trick is thin, cheap
and safe.

We're still in the very early evaluation stage of addressing a number of
different problems.  Entirely new facets of the problem reveal themselves
daily though discussions here and via actual field experience with the van
and the various EMD's

> > When parked sideways, using its own internal
> > locking mechanism, it takes an awful lot of force
> > to move the scooter.  While I don't believe that
> > any amount of forceful braking would cause
> > significant movement, a front-end collision
> > certainly could.
>
> I think you're wrong about that, Robert.  The vehicle's braking capacity
> will most certainly exceed the friction between the scooter's wheels and
the
> floor of the van.  Unless the scooter is securely fastened to a heavy-duty
> locking mechanism designed for the weight and installed in a manner that
> will reduce flexing (remember, metal fatigue has brought down some mighty
> structures), you should consider it a loose cannon on deck.  Even a sharp
> turn at 25 mph can tip one over if it's not secured.

The way Entervans are designed, the scooter, which sits in a lowered "tub",
will bang up against the bottom pylons of the front seat which are made of
structural steel members, or so I was told.  It's an expensive process and
done to specially modified new factory vans.   It's probably not like what
you're visualizing.  I'm going to have to take some pictures to post of the
inside and the ramp and EZ-lock assemblies because it's clear that without
such reference, a lot of issues will be hard to understand.

> > That means the scooter has to be locked down
> > somehow.  The securing straps are too difficult
> > for Dad to use, but I am reluctant to remove
> > them because there might come a time when
> > the situation changes and he's no longer a driver
> > but a passenger.
> >
> > I'm not as worried about the scooter becoming
> > a missile since watching a recent episode of
> > "Myth Busters" on the Discovery Channel.
> > They did an entire show on what types of
> > objects could become lethal missiles in a high
> > speed crash.
>
> Let's assume the scooter weights at least 60 lbs.  If the car is traveling
> 35 mph and it makes an abrupt stop, say mid-way through a brick wall, the
> scooter will continue traveling at just under 35 mph until it reaches a
> point just forward of where the dashboard used to be.

Interestingly enough, the local paratransit service has never secured his
scooter.  The straps are there (usually in awful condition) but aren't used,
at least whenever I accompanied him.  Those guys all drive a hell of a lot
worse than Dad does and it seems not to be an issue for them.

I'll inform him of the risk potential and make sure that when I am with him,
we'll use the currently installed floor-mounted lock downs.  The problem is
that those are designed for Nadia Comenici, an elf or some other tiny
gymnast with super strong hands.  You couldn't design a harder-to-use device
for someone with severe arthritis.  It's hard for me to do - it's impossible
for him.  We'll sort the EZ-lock problem out eventually and probably live
with the risk until then.

> > ...Another option might be to install guide bars
> > on the floor similar to those found in automatic
> > carwashes where it's important to line the vehicle
> > up exactly.
>
> That's pretty much what I was getting at earlier in this post.

That gets pretty complicated considering that we now have 5 different
mobility devices of significantly varying wheelprints along with multiple
combinations of drivers, passengers and seating arrangements!

I think the best design would be a stripe up the ramp's centerline and
devices on each chair or scooter that can detect and do *something* upon
deviation from that centerline.

In fact, it might be useful to have some sort of look-ahead sensors to tell
him whether there was enough clearance in crowded store aisles to get
through.  Those are situations in which he has to back up, and those always
give him trouble because he can't turn around easily in his seat.

The problem with side mirrors that we've come to discover after a trip to
the bike shop is that to be useful, they have to extend pretty far - so far,
in fact that they actually become the widest point of the scooter.  If one
of them catches on something while backing up, it  yanks the tiller into a
hard turn and might even force Dad's hand against the tiller mounted speed
control.

I've found out the hard way that the last thing you want to do is add to the
overall EMD dimensions in any way that's not retractable.  The boom on the
scooter in Home Depot with the rotating light is great for permanent
in-store use, but whatever I design for Dad has to be collapsible enough to
fit in the Entervan or the paratransit vans.  In any event, a safety feature
shouldn't create a liability that wasn't present before.

I just bought a cheap BW backup camera kit from Supercircuits for the van
which I may test out first for the scooter.  It reverses the image from the
backup cam so it looks like a rear-view mirror to the rider.  $89 for camera
and B&W LCD with all the wire and mounting HW.  Light and small enough to
actually mount on a scooter, too.  It might keep him from inadvertently
running over someone's granny someday if it works!

Someone I spoke to today reminded me it's not impossible to fit a scooter
with and auto-steering control - find a way to mount a gear on the tiller's
steering rod and mount a stepper motor to that.  Have some way to allow the
stepper motor to engage only when needed, sort of like a starter motor does.
That would be a lot of work but it's something Dad seems interested in, so
maybe we'll pursue it if some of the other options don't pan out.

One thing's certain: the guidance system is something that will have to be
built before any control system would be workable.  Covering the edges of
the ramp with reflective tape is the first step because that will assist us
in manually getting up and down the ramp by making the edge boundary stand
out.  I might even mount a 12V UV lamp above the door to make the edge
strips really stand out at night.  If I go that route, I might be able to
use a UV phototransistor to do the ramp edge sensing.

--
Bobby G.