Automatic Wheelchair Turntable

That and the fact that cantilevering that much weight outboard of most turntable bearing systems will bring problems. If there was a simple solution you'd likely find lots of commercial turntables.

How much does the chair weigh? Did your DIY scales work?

Do ideas become better by repetition?

Physics 101: the force on the lazy susan bearing ("weight") will be applied _on_ the bearings regardless of how "far outboard of the bearing " the wheels of the chair sit on the rigid platform affixed to the bearing.

As long as the lazy susan (a thrust bearing) has adequate vertical load capacity, and the lateral force is negligible (which it is), the diameter of the lazy susan becomes important only if the vertical force cannot be made symmetric. An imbalance places the force on fewer bearings.

Having bearings "under the entire surface" makes the construction much more complicated and would as a practical matter would increase friction. What would be the surfaces on which "bearings under the entire surface" would roll? I suppose one could arrange them in a circle with a mechanism to hold them captive and provide a surface both top and bottom for them to roll on that itself would be mounted to flanges that could be attached to the fixed and rotating structures. I wonder what we would call this newly invented device?

If there were "bearings under the entire surface", what would be their geometry of their traces on the rotating platform if not a circle? If it is a circle, why not use a "lazy susan". If one did have multiple concentric lazy susans, how would that help in any way in the case that weight was transferred to the outermost bearing of the outermost lazy susan in the case of weight imbalance? (It wouldn't).

Marc Marc_F_Hult

You might contact the university to see whether anybody is manufacturing it.

In the machine tool industry, transfer balls are used to support heavy loads while allowing free lateral movement. You could use these at the perimeter of your turntable but you still have the problem of securing both the turntable and the chair in the event of an accident.

Is the 400+ lbs with or without the chair's occupant?

I'm missing something. The chair is capable of spinning adequately on its own, right? A turntable or lift doesn't allow the chair to spin any tighter, does it? (I have a Quickie power wheelchair that easily spins "in place.")

The problem you're fighting is that when the chair is occupied it can't spin in place because the occupant protrudes from the chair enough to strike obstacles. Is that right? So you just need something to spin it once the user has dismounted?

Is there some other issue (like the need to fold a manual chair slightly) that requires lifting it?

Also, for backing up the ramp...is a winch ever used (for manual chairs)? Seems like it would be a trivial addition.

--kyler

It's a scooter with a tiller in front. It's turning radius isn't anywhere near that of mid or rear wheel powerchair. A powerchair would probably be able to spin around, even in the tight area, but a scooter won't. I've tried to sell him on the powerchair but he REALLY likes the scooter a lot more, at least for outside the house. I don't want to revisit that battle. I've finally gotten him out and around on the scooter and he's taken to it. It took a long time for him to conclude that his arthritis was bad enough to warrant electric mobility.

As explained.

Got a Masterlock winch at Walmart just half an hour ago! I was going to use it to hoist the chairs and scooter in and out of the basement for maintenance, but I'm going to look into what it would take to mount it in the van.

Thanks for the input!

-- Bobby G.

"Dave Houston" wrote in > "Robert Green"

Yes - accidents! We acquired yet another Ebay special - a mid-wheel power chair that managed to get stuck tight going off-ramp (my fault) with the forward caster on the outside of the ramp edge and the main wheel on the inside.

If it had happened to my Dad, he would have been stuck. The frequency of these off-ramp excursions, both forward and back, leads me to believe my best efforts as a die-hard technogeek would be to work on wheelchair ILR. Some sorting of guidance system that would show which way to steer.

With a "lighter than me" occupant!

-- Bobby G.

I suspect Mr. Houston may be concerned that the lazy susan (plywood has been suggested for the disc) will flex under the weight of the chair and occupant. That might merit considering outer and perhaps mid-circle bearings. Certainly there is no need for bearings under the entire surface. That could be accomplished if the disk sat in the middle of a plate covered with ball bearings but it seems like a really bad idea.

My concern with the whole bearings-under-plywood idea is that the plywood would quickly become rutted, increasing drag and eventually binding.

I think the best suggestion yet was to back in and drive out forward. Backing down a ramp would be more hazardous than backing up, presenting a serious chance of tipping over given the geometry of wheelchairs and scooters (the front axle is usually more forward of the occupant than the rear axle).

At first I hadn't noticed that this is a scooter rather than a wheelchair. The first thing you should do IMO is find a way to ensure that the chair cannot be shifted into reverse unless it is in the lowest speed mode. A sensor on the tiller could also kill the power if the tiller is moved too far L or R at a speed that could result in tipping during a tight turn.

You could rig visible strips on the ramp to warn of proximity to the edges as you mentioned. You may wish to consider rigging a reflective strip and a pair of photoelectric beams on the back of the scooter. A loud alarm and/or application of a brake could be triggered if the chair crosses the line in reverse.

By limiting automatic braking and/or motor kill functions to low speed, reverse motion you can avoid the possibility of a false trigger messing him up while traversing a puddle or some other reflective surface while traveling along the sidewalk or crossing the road.

If you would like to experiment with a photo beam for this sort of project I'd be happy to provide one at cost.

Robert,

I'm wondering how mobile your Dad is within the van once the chair is inside. Can he exit the chair, take a side step or two and then sit or does he need to slide from scooter seat to car seat?

The reason I ask is that it may be easier to secure the scooter to the ramp mechanism than to the floor. If he can exit the scooter and make his way to the driver's seat alright, it should be relatively easy to use two or three modified seat belts to fasten the scooter to the side of the van and/or to the stowed ramp.

That would at least solve the issue of flying scooters during an accident or sudden application of the brakes. Remember you don't need to hit anything to make a heavy object fly forward. Just hit the brake at 15+ mph because some kid chases a ball into the street and you have a 200-lb missile heading forward at 15mph. That's more than enough to maim, kill or otherwise insult someone.

That wouldn't be a good idea based on the way the ramp operates and folds. We're going to get a mating pin for the EZ-lock installed on the scooter and move the EZ-lock from its current position on the passenger side seat floor to the area where the scooter travels now, amidships. 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. I would probably have to get two mating pins installed - one on the front and one on the back of the scooter - to enable him to enter either way.

It's beginning to look like the only way certain way to proceed is to put another ramp or a lift on the door opposite the entry door. That's going to be expensive because it involves both installing a folding ramp and a power unit for the sliding door.

The turntable idea is just about dead because of all the issues that it raises, especially concerning securing the scooter. I'd have to mount the EZ-lock to the turntable (with wiring) and then figure out how to secure the table to the van floor while in motion.

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. 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.

The EZ-lock is probably only going to be useful if he goes in front-first unless I am able to design a guidance system that can be accurate to within an inch or two. I appreciate your offer of material at cost but I've got more than enough stuff in the junkbox to build something like this. What I don't have is the time. 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.

-- Bobby G.

Reverse and forward use different gear ratios. The unit backs up much more slowly than it can go forward (thank God!)

It's not going to be easy to hack into the control panel for the scooter. If I could somehow automatically sense the surrounding terrain, then I could figure out some way of determining when a higher speed or an anti-tip control could be useful.

At first guess, a ring of ultrasonic sensors like those on remote measuring devices, could tell me something about the surrounding terrain. If all sensors indicated objects surrounding the chair, then the speed control should be set to 2 or 3. If no nearby objects (like slow-moving grandmothers), then speed can be set higher.

In fact, the highest speed settings should be rigged sort of like an automobile speed control. As soon as you drop speed (the equivalent of hitting the brakes on a car) the dial would reset itself to low speed. I could also try to work with the van's keyfob. Any time the door is being opened or closed by remote control, set the speed control down. Not sure whether that's doable with modern rolling code wireless remotes - it may be that I don't actually have to decode the data being sent - just that a car door opener has been operated nearby.

It might be possible to rig the speed control potentiometer with a DPDT switch so that there's an automatic setting and a manual setting. The automatic settings would be slow and fast and would probably consist of discrete resistors that approximated the value of the speed control when set to 2 and 8. When in close quarters, set to 2, otherwise set to 8. The trick now is to figure out how to sense and relay the appropriate conditions to the microprocessor that would control the resistor selection.

In thinking more about this, a front and rear "range" sensor is really all I need and it might turn out to be a considerable safety addition to force the scooter into the lower speed settings whenever there are objects in front or being the scooter.

It's become pretty obvious why all the scooters I have seen in stores don't usually have a user-operable speed control and are set to a fairly low setting. In fact, it's one of the reasons Dad likes the new scooter so much - because he can go fast where the terrain warrants it. Some store scooters can't make more than 3MPH at top speed.

-- Bobby G.

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 that is your dad may at times want to parallel park. That would mean either entering or exiting into the street where he'll be a target for some jackass speeding his SUV through town. Also, if the nearest corner is some distance down the street he'll have to ride his scooter in the traffic. That may make him uncomfortable with the whole system.

I wouldn't do it that way. It sounds like an expensive and only partially workable solution.

I didn't think that one was going to float.

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.

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.

That's pretty much what I was getting at earlier in this post.

There's another way to do that. Rig a simple RF transmitter to send a code any time the car door opens. A receiver attached to the scooter drops the speed down to 1 or 2. RF transmitters and receivers are cheap. A timer could keep him from upping the speed for maybe two or three minutes each time the door opens.

That should work OK but forget about ultrasonics. They tend to work erratically when there's any wind around.

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.

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.

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

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.

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.

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.

"Frank Olson" Pretty well everything you talked about has been put together here, but I'm

Not exactly - I think the problem with their units would be both height, as in adding too much, and capacity, as in having too little. But the site did have tons of other valuable information, such as how they drive their turntables:

That alone was worth the price of admission. Thanks!

Coupled with the advice given by Stu Alden I can see I am going to be buying a few lazy susan raceways, some formica, plywood and low RPM, high torque motors to "trick out" his work area for working while seated in his power chair. Good find - I appreciate it.

(And yes, I am counting . . .that's 7 in row - I'm impressed!)

-- Bobby G.

Pretty well everything you talked about has been put together here, but I'm not sure about the weight limitations or basic construction. I figure you can probably adapt something from what they have.

If you find you need something huskier than the lazy susan bearings (although probably much more expensive) check out Rotek:

If they have anything with integral or bolt-on bicycle chain sprockets, that would be a plus for driving it.

No prob. I was actually pretty impressed that they managed to accomplish electrically moving the table without any belts. I'm certain that given the correct gear ratio in the motor, a "direct drive" solution as they've illustrated would be far better for you. Don't know what kind of "torque" you'ld get out of an old windshield wiper motor, but perhaps that's an option. The one problem I can forsee with the setup in the picture is if the table becomes warped or deformed slightly. The rubber wheel they're using in the picture may have to be a bit thicker to compensate for minor surface irregularities.

Eight!!