Introduction: Scooter Powered Wheelchair
I saw a video of an attachment to a wheelchair that snapped on an electric front wheel which made the basic chair quick and agile. Looked like a swell idea. Priced at about $700 or about what you would pay for one of those kits to electrify your bicycle. Sounded about right as it included all the same parts. Later I was visiting downtown and got to see myriad people using the Lyme electric scooters, tearing up and down the sometimes steep hills there. Get on, wave your credit card, and take off. Quick transport and no long term investment. Put the two together and suddenly a person in a conventional wheelchair can get to the 16th St food court and back on a corporate lunch hour. I happened to have a couple of Razor scooters, and with a bit of scavenger hunting, I rustled up a chair: See pic above. This was originally a potty chair designed to back over a toilet, hence the replacement plywood seat. Imagine a nicer seat. Like the one on your chair.
The setup resembles a 5th wheel trailer attachment so the connection between the chair and the scooter needs to allow for some fore-and-aft rocking movement, and rotational left-right movement. The attachment includes a spring since you want some down force on the scooter but you don't want the rig getting high-centered. With a driver on board, the chairs front wheels barely touch the ground and there's enough travel to avoid getting high centered. The bracket on the chair is a close fit on the bottom and a slightly oval fit on the top to allow for the for the fore-and aft rocking as well as rotation. The large white thing is a spacer to make up for a slightly under length spring which is what I had. Mounting the horizontal bar down lower would make the spacer unnecessary.
The cross bar is 1x1x1/16 square steel tubing and is held to the chair with 4 ea ¼ x 2-1/2” U-bolts. The pin attachment is a piece of 1/4” U-channel with a 5/8” hole for the bolt that attaches it to the cross member and 1.05” dia holes for the mounting post. The upper hole is cut slightly oval, about 1.125” to allow the post to rock back and forth a bit. The post is a 3/4” black iron pipe nipple. I'm using a 10” long nipple but the actual length may vary a bit depending on your setup. On top is a pipe cap to hold everything together when there's no scooter. On the bottom of the nipple is a floor flange to attach the thing to a base plate. My base plate is 1/2” plywood here as I didn't know what it would need to look like in the end. The clamps are over center door latches which come from Amazon in a package of 8. They are rated at 350#/ea. The latches attach to the base plate with some 1-1/2” aluminum angle and the hooks are made from 3.4” x 1/8” iron strap hammered into a hook of about 1 in diameter.
In the upper right hand picture you see a piece of wood between the scooter frame and the scooter deck. This is to accommodate the larger than stock batteries and would not appear in a regular setup. The plywood attachment deck would be made from aluminum, probably T-slot or something like it
Scoot up to a scooter, wheelie over it, and use the clamps to get attached. This scooter has lawnmower batteries installed and sits about 1-1/2" higher than normal.
And off you go. Top speed depends on the scooter, but mine top out at 15 mph. I understand that the Lymes will make 20 and the city is trying to get them off the sidewalks as a menace to pedestrians. Maybe the scooters should have horns. Like the kind Texans like to put on the hoods of their Cadillacs. The rig is fairly agile with a 4 or 5 ft turn radius. Since the chair is attached as a 5th wheel, backing is tricky but not impossible. OTOH scooters don't come with a reverse setting so be careful about taking one of these indoors. Not impossible, but really intended for outdoor use. Having built this and tried it out, I notice that no 2 chair makers use a common frame layout which means that the adapter needs to be peculiar to your chair. Again, I don't know enough about the wheelchair market to say, but I would guess that 2 or 3 makers account for most of the market so maybe modest mass production is possible.
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This is the latest revision. I lowered the cross bar and removed the white spring spacer. Also added some seat padding made from foam floor mat.
Step 2: One More Set of Upgrades. Using Aluminum Extrusion and a Stock Scooter.
Here's the latest update. I replaced the plywood with 80/20 aluminum extrusion. The nice part about this is that it doesn't matter where most of the holes are drilled, just that the holes are the right size. The fasteners are 5/16 dia so the floor plate must be drilled out to 11/32 to clear them. The toggles, which were attached to 1-1/4 x 3/16 aluminum angle are unchanged except for the base mounting hole which is now 11/32". The two pieces of extrusion are in there to help provide a flat surface to attach the floor plate to, and to keep the bracket assembly from rotating when the scooter is in use. Note also that using the extrusion raised the plate by 1-1/2" allowing me to use a shorter coupling pin (3/4" NPT x 6" pipe nipple).
One other thing is that I have switched scooters and am using an unmodified Razor E200 with the batteries it came with. This dropped the deck height by 1-1/4" and puts it much closer to where the deck of a rental scooter would be.
At this point I'm beginning to look at the issue of the assembly being non-foldable with the one piece attachment cross bar. I don't see this as a huge problem and I will probably substitute some 1x1 extrusion for the steel tubing and come up with some quick disconnects which 8020 is famous for. This should also address the issue of universal attachment although I've noticed so far that other chairs are 16-3/4 to 17 inches wide across their frames so not that much variance.
Performance: The Razor E100 scooter is too wimpy to be seriously considered here as the company recommends that users push off by foot before engaging the motor. The E200 has a max speed of 12 mph and run time of 40 minutes or about 8 miles. The E300 goes 15 mph and runs a bit longer.
Stay tuned as I will be publishing improvements as they happen and don't forget to vote for this in the assistive projects contest.
Step 3: Further Simplification
As I said, this is an ongoing project. The latest mod is to replace the bracket on the chair with something that eventually will be either easy to mount/demount or something that will fold with the chair. I built 3 plastic blocks that hole the whole thing together. Looking at the closeup,you can see the 10-24 screws that were to hold the attachment bar to the chair. Having built is, and having gotten the holes off by a tiny fraction, I now see that the aluminum cross bar would do the job by itself. All I need to do is trim the blocks back enough that the cross bar is pressed against the frame of the chair. Replacing the screws holding the cross plate to the plastic on one side would allow a quick disconnect so that the chair could be folded up.
Work proceeds slowly this time of year due to the cold, but the crossbar work was done in one afternoon. The post has been reduced from 3/4 pipe to 1/2" pipe which is .84" O.D. This fits through a 7/8" hole and allows sufficient wobble to take up irregularities on the ground. The post is also moved to the rear about 2 inches, and the scooter steering modified to allow more angular sweep. The Razor has what looks like a very small rubber bumper on the steering post near the bottom. This covers a slot with an Allen head screw that serves as a steering stop. Remove the screw, and now the chair can make a U-turn in a 52" hallway. Not shown, because it's not installed, is an aluminum tongue attached to the bottom of the floor plate, and extending forward to the scooter frame. This is needed to keep the attachment assembly from sliding forward during heavy braking. An additional plus: The scooter tires are much softer and stickier rubber than the wheelchair tires, so the scooter brakes are MUCH more effective than the chair brakes.
At the rate I'm going, I should be able to call this finished with a straight face in time for the Denver Maker Faire in March. Test drives will be available then along with detailed explanations of all the stuff I left out here.
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Assistive Tech Contest