Automatic Wheelchair Turntable

I just got my Dad a wheelchair van with an electric ramp but we've hit a snag. There's not enough room to turn the wheelchair around inside the van. If he goes in forward, he has to come out backwards.

I toyed with some automatic guidance systems to make sure the backup procedure didn't run him off the ramp, but I don't think that's a wise solution.

I decided that since there's almost a 4X4 foot flat area inside the van, I would take a 4x4 sheet of 3/4" plywood and make a turntable on the van floor. When he transfers to the driver's seat, I want the turntable to automatically rotate 180 degrees to position the powerchair so that it will go down the ramp front first.

I'm not sure how I would contstruct and power the turntable, however. It's got to be as thin as practical - there's very little extra headroom in these types of vans and it's got to have some sort of autodetection of exactly 180 degrees - probably some sort of limit switch.

Should I rout a channel in the outside of the circular-cut plywood panel to run a belt? That why I could mount a motor in the corner and still have a pretty low overall height. Sort of how some belt-driven record turntables are designed. I could also cover the ends of the belt that are likely to drag loose seat belts into the works pretty thoroughly with a motor mounted in the corner.

Does anyone know if they make commerical turntables for this purpose? As much research as we did on vans, lifts, ramps and options, it kind of floors me that we didn't realize there would be a "wrong way out" problem. Just a reminder to always model things, even if they seem trivial.

Well, any suggestions, inputs, discussion or ideas where to post for good feedback will be appreciated!

(posted to: comp.home.automation & alt.support.wheelchairs)

-- Bobby G.

Reply to
Robert Green
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How about asking the maker of the ramp what they'd suggest?

Reply to
wkearney99

Does he drive it? There isnt room for me to turn either, but I go in backwards, transfer to the driving seat. And come out forwards.

There's not enough room to turn the wheelchair around inside the van.

Do it the other way around, come out forwards?

You will never make it thin enough as well as strong enough. Its going to be almost impossible to do. A microswitch can turn it off at 180 degrees.

You will need thicker plywood, anyway so use a smaller disk underneath, to run the belt then the motor can go under the disk.

Well I do this the other way around from a side door and its never been a problem.

My van

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Reply to
Burgerman

A simple, compact approach would be a cable (or rope) and pulley/drum system. Two cables each wrap 2/3 to 3/4 of circumference of the turntable. One reversible or two uni-directional motors with drum -- or a hand pull -- turn the table. If friction/resistance of the table is made low enough, a motor may be unnecessary.

Jist thots .. Marc Marc_F_hult

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Reply to
Marc F Hult

How 'bout just having a shaft sticking out of the floor that extends, engaging a coupler in the wheelchair, spins the chair and retracts? (The extension and retraction could even be manual.) It would only need to handle the chair when it's empty and it wouldn't add any height. It could even be left extended to secure the chair while in motion.

(The mechanism could also be mounted in the chair and engage a coupling in the floor.)

--kyler

Reply to
Kyler Laird

I think your biggest problem will be to devise a thin turntable with a bearing that can handle the weight. A zillion (± a few slew) marbles sandwiched between two flat metal surfaces might work. For the drive, bicycle chain (industrial chain comes in a multitude of sizes) fastened to

1/2 the circumference should be simple to work with.

How is the chair secured when the van is >I just got my Dad a wheelchair van with an electric ramp but we've hit a

Reply to
Dave Houston

Reply to
Dave Houston

. Some years ago we had an exercise device consisting of lazy Susan bearing ring that would simply not quit no matter how heavy the person doing the movements. The same lazy Suzan innards is a regular sale item at any Home Depot. Also circular pieces of plywood to which you might add some sliding door rollers on the edges to keep balance. You should be able to make a device, manually controlled, with manual locks for less than $200 if you have any skills at all with skill saw and drill.

Wayne

Reply to
Wayne Lundberg

Reply to
Stu Alden

"Burgerman" wrote in

Yes - that's one option. But the whole idea of him driving up the ramp backwards under any circumstances gives me the willies. Driving it DOWN the ramp backwards gives me the willies AND the heeby-jeebies. :-)

I believe it might be possible to do if I can figure out some way of insuring he doesn't back himself off the ramp while entering.

Yeah - if I want to put a power ramp and a power door on the driver's side too, it would be a question of entering through one side and exiting through another but that's putting the price of this project into the stratosphere. I've already run about $5K over budget.

I'm still mad at myself for not realizing that a swing-arm type scooter lift would have solved this problem, as well as the problem of people parking so close to the van that the ramp can't deploy or can't be boarded because it's too close to an adjacent car.

I might end up putting a swing-arm lift on the non-power door side so that there's always more than one form of assist. It may be a better solution in the long run because the turntable will involve removing $400 worth of chair tie-downs bolted to the floor. A swing arm lift would be a lot easier to install, although I really don't like them for a number of reasons.

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Sweet! We did not get a power transfer seat, and I now think that's a serious oversight. I hope they're not outrageously expensive.

-- Bobby G.

Reply to
Robert Green

"wkearney99" wrote in

Good idea - I'll ask them as soon as I read through their FAQ at:

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Thanks!

-- Bobby G.

Reply to
Robert Green

That one should be easy enough. Add a 3" lip on each side of the ramp (unless there already is one). He won't back over that. It might make him more comfortable backing up the ramp if you were to add a bicycle mirror to one armrest. This could be angled down so that he can see how he's lining up with the ramp as he moves.

There's a solution to people who do that. Operate the ramp several times, leaving a "reminder" on the roof of their car. :^)

Reply to
Robert L Bass

"Kyler Laird" wrote in

That's a pretty interesting idea and would solve two problems at once: reversing the chair and securing it as well. I am not sure how well it would work in practice. Interestingly enough, there's an "EZ Lock" solenoid device that's suppose to lock the wheelchair down in transit. It has an interesting V-shaped entry point that's designed to dock easily with a powerchair, even one that's slightly off the mark. I'd be afraid that moving the chair to the precise "lock in" point might turn out to be very difficult for dad.

I could also mount a roll cage of sorts in the compartment that could have a central point lift capable of lifting the chair so the user could spin it around and drop it in the right orientation.

Thanks for the input. It reminded me to focus on spinning the chair - something that might be accomplished with just a few parts.

-- Bobby G.

Reply to
Robert Green

"Robert L Bass" wrote in

There is already a lip, and it can't be extended because of the way the device deploys and refolds itself.

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You would be surprised at what a fully charged 24V scooter or powerchair can mount when they're angry! In a worst case scenario (already happened) where Dad's got the speed control set to 10 and he's now in close maneuvering space (where it SHOULD be set to 1 or 2, but usually isn't), you can bend a fairly stout metal cane in half if the conditions are right. These puppies have plenty of low-end torque. At the 10 setting, you're thrown back in the seat, hard, from the acceleration. It's something you don't even feel in a Shelby Cobra - well, maybe a little! :-)

I've been thinking about both mirrors and/or a tiny, onboard camera system with a small LCD TV mounted in the tiller to handle reversing and a number of other status functions. You can get pretty amazing pinhole cams that draw next to nothing in current and can see in near darkness. Plus, these cameras could serve to relay status information via cell phone, a project still floating around in my head.

Tiny "curb feelers" on the rear chassis could beep if the chair was going off-center. While a powerchair could be controlled remotely via such a function, and, in theory be steered up the ramp by external microprocessor control, a scooter could not remotely controlled. They have a single motor and are steered by a tiller. Powerchairs have independent motion and were the chair to drift left, the proper reduction in power to the right motor would correct the course.

Yes - easy confirmation of "fair or foul" reversal is going to be essential. Most likely it will be visual, but I'd sure like it to be robotic as well. I could, I believe mount some sort of reflective strip to the ramp deck's two halves. Then, a phototransistor and an IR LED mounted on the rear of the scooter could easily relay when the scooter had gone off the mark. Three such devices would even tell me which way the scooter had drifted. The question is, what do I do with that information?

My first inclination is to look toward avionics controls. This is an application where a small display of a two lines can be shown converging or diverging might make up for head turning and ramp edge tracking. I am thinking the ramp center AND edges need reflective tape in any event. The ramp is painted flat black and even *I* have a hard time seeing it with my much younger eyes than Dad's.

Might need to have some of those little, incredibly bright yet power stingy white LEDs mounted to illuminate the wheel-ramp edge contact zone.

Damp ramp HW costs way too much for that. The real solution is to park in the far corners of parking lots across two spaces diagonally. At the mostly empty edges you can find spots where no one can park you in.

Next time you're out and about, look at the far edges of mall lots. I'll bet you'll eventually find an Entervan parked as described. Since Dad's got the scooter, even an added 1/4 mile to the van isn't going to make much difference in trip time. It does mean a longer ride through the parking lot, which can be pretty dangerous, but getting parked in by a dodo, on the other hand, is both dangerous AND time consuming.

I was in a Home Depot the other day and one of their new scooters has a tall mast and a rotating yellow light at the top. I'll bet that's a good thing to add to Dad's chair to make in more visible as he drives the scooter to the lot fringes. I also bet that there have been some serious or at least near-miss collisions in the store aisles driving that decision. Expensive modifications don't sprout on these things without a driving force.

-- Bobby G.

Reply to
Robert Green

"Marc F Hult" wrote

Yep. That's sort of what I had in mind. There's room in the corners for one or even two motor assemblies. I'm coming to realize the real problem with any of these turntable and drive systems is that they add height to the floor of the van.

The Entervans have a 10" dropped floor, but even that's almost not enough to accomodate a person sitting in the van in a wheelchairs.

Well, that's the great value of Usenet - kicking around ideas to find the weakspots or some previously undiscovered approach. I'm beginning to like the idea of a guidance system more than a turntable because the former satisfies some collateral goals I have, namely remote chair status monitoring.

-- Bobby G.

Reply to
Robert Green

There are clearly going to be some severe engineering challenges with the turntable method.

Oddly enough, there's already plenty of bicycle chain in the van. Both the power sliding door and the ramp extender depend on it. I've decided I have to build a shroud because too much chain was exposed. It's just waiting to pull Isadora Duncan and her scarf down into its mechanical gizzards.

Well, right now, the scooter is secured by its electromechanical interlock which, I assume, it some sort of pin that drops when power is removed. It's nearly impossible to push in that condition. (Yes, I know, in an accident that's likely to come flying forward and crush and kill either the driver and passenger!)

The plan, however, is to move the "EZ Lock" system that mates a special pin on the scooter to one in a solenoid device bolted to the floor. The previous owner had tie downs installed on the wheelchair bay's floor, but that's because it was a manual chair that was occupied during travel. Dad's scooter sits empty in the back. The lack of a way to secure the scooter satisfactorily on a turntable may be the kiss of death for the turntable idea. Too bad. It seemed like the right way to go until the idea was exposed for public comment! (-:

-- Bobby G.

Reply to
Robert Green

Reply to
Patrickg

Well, I'd buy that one! Nice find. Too bad it's a prototype. It's obvious that it a device that's both needed and practical. The problem is that there's not a mass market for it.

-- Bobby G.

Reply to
Robert Green

I suppose you're right. I had intended to place bearing supports at the outer edges of some type. If vertical height wasn't a problem, a lot of small caster wheels around the outside edge might support it. However this problem, at a few others, have caused me to rethink the turntable in favor of guidance systems or an on-board hoist mounted at the opposite door.

The Chancellor of the Exchequer happened to notice the four bathroom scales in the cart at Target and used her pocket veto. I won't repeat what she said, but she was certain it had something to do with that "damned newsgroup." Interestingly enough the money didn't mean nearly as much as the space the four scales would consume in one of the closets. As it turned out, the chair was weighable in pieces on the bathroom scale we already owned. It weighs over 400lbs when fully loaded.

-- Bobby G.

Reply to
Robert Green

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Yes - that is a great source, and with load ratings, too. It almost makes me think this is doable again. I use smaller models to swivel shelf-mounted AV gear. If the 12" supports 1,000LBS, it might indeed be what I need to make a prototype. Thanks!

-- Bobby G.

Reply to
Robert Green

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