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Homemade tracked wheelchair project

undy

New member
A buddy of mine owns a cabin on an island, but he's got MS and hasn't actually been able to reach the shore for several years. Several companies sell tracked wheelchairs in the 8k-16k$ range, so we're shooting for homemade. He acquired a power wheelchair, and I hope to convert it for him. A gas engine is not an option as it's Nature Conservancy land.

I'm hoping some of you might be able to help me with a few design questions I have. I'm camera-illiterate presently, but I'll try and resolve things soon so I can share pics as things progress.

Currently I have the wheelchair and 180x60x37 tracks (only) from a Honda power carrier. I hope to build track carriers using solid bogie wheels (ebay or similar) and probably homemade sprockets. I plan to utilize the chair's original joystick controller, batteries & charger, and drive motors. It looks like I'll scrap the original chair frame.

First question. I can buy Honda sprockets and hubs to fit the track for about $200 (but I do not know the i.d. of the hubs and the axles are NLA). Making them myself will allow me to determine the number of teeth, choose the hub i.d., plus may save money (labor's free, right?). A while back, one of you posted directions for laying out a sprocket, but danged if I can find the thread again. Can anyone help me with this info?

Have any of you here ever tried to build one of these, and have advice?

Thanks!
Paul
 

undy

New member
Thanks, but nope. That wasn't it. The one I'm remembering had details on how to actually lay out a sprocket, based on the pitch of the track, IIRC. Maybe it was the other way around - how to space grousers based on pitch of the sprocket.

At any rate, I have tracks with a given pitch, and I need to lay out a sprocket somewhere around 10" diameter to fit those tracks.
 

300 H and H

Bronze Member
GOLD Site Supporter
Really interesting project undy...

was the wheels on the chair about 10"? It would keep the ground speed roughly the same using this size to power the tracks.

My first thought would be to measure from the center if the gouser across the tooth opening to the middle of the next grouser/drive hole. This would establish the distance from the middle of the tooth to the next. Cut your poly to a 10" disc, and use a partial hole saw cut to for the bottom of the teeth. This would probably require at the least a drill press and a secure way to clamp the disc... I am afraid how ever that this distance and the tooth spacing my actually decide the size of the that disc of poly or what ever... I hope you can see what I am saying..

Keep us posted. Lots of idea will come from it...

Regards, Kirk
 

MrLiberty

Bronze Member
Site Supporter
what kind of power chair are you working with? One of the problems you will encounter is the small anti tip tires that some chairs. Also, not all chairs are water tight, any little bit of water that gets into the motor area or where the brain is will kill the chair. And the motors may burn out if you use tracks as the tracks would draw more power than they should. I've known a couple of people who have attempted to do this with little success. They do have chains for the bigger tires and this may be a better option to look at.
 

dep6113

New member
Here is a link you might read with some good pics
http://www.forumsforums.com/3_9/show...+tracks&page=2

I will take a stab at explaining it a bit

remember its all about PI =3.14 circumference of a circle is diameter X pi or 2 times the radius times pi
if your track has windows measure how big the window hole is and how far apart they are. so for example the holes are 1x1 and there is 1 inch of rubber between each one --- the center of each tooth would be 2 inches apart. ( the 1 inch of rubber plus half of each window) if you wanted 5 teeth the circumference of the sprocket at the belt contact point would be 10 inches 10 inches /3.14 would give you a diameter of 3.18 or a radius of 1.59. 10 teeth would be 20 inch circumference 10 teeth would be around 6.3 inches. if you made the teeth .75 wide at the base along this circumference diameter the valley of each tooth would be 1.25 wide.

good luck on your project, Mobility is a huge gift to give.
Dave
 

dep6113

New member
another thing you might try is to make a track out of a tire. I once saw a vehicle that a guy took a tractor tire and cut v notches out of the sidewalls and then put it over two flat tires and aired them up. the air pressure kept them tight and no teeth required, kinda similar in looks to the ones below

https://www.youtube.com/watch?v=Eb6FoKUvfFA

a 28 inch tire would give you an 88 inch track
Dave
 

undy

New member
Thanks guys for the suggestions, both here and via pm's. I'll try and answer things.

The original rear (driven) tire diameter was 12" nominally. There is a fair amount of mass to these tracks, so I anticipate having to gear things down in order to have the torque to spin them. I plan to downsize the sprockets below the 12" as a start, and figured I could introduce a chain on ratio'd gears to further reduce load on the motors.

The chair originally had a very high top speed and good low speed grunt. Since the original tires were 12" diameter, I expect to be reducing the load on the motors a lot by gearing things down. I can sacrifice top speed in order to maximize torque. I thought I'd begin by downsizing the sprockets by 1/6 (10" dia.)

The motors have a gear reduction 90 degree drive end on them already, and I may try to mount them (and possible chain/gear reductions) within the tracks, if there's room. I'll have to investigate whether these motors are water tight, as this may require shielding or limit wet use of the chair. (Good point, Mr. Lib.!)

Dave, That link wouldn't open for me. However, your explanation of laying out the sprocket mirrors my intuition. Somewhat like laying out a stairway to fit an application, I can resize the sprocket diameter up or down depending on the number of teeth I wish. Figure the pitch (window + rubber) and make sure the circumference at the belt contact point is divisible by the pitch measurement - then add to the diameter enough to create the sprocket teeth. I was planning on using HDPE or UHMWPE.

I'd initially considered using a tire as you suggest. I followed Steinbruchsoldat's build where he started with tires, but he abandoned that route. Then these tracks appeared for cheap, so that's what I'm starting out with.

As a fallback, in case I'm unable to power the tracks with the wheelchair motors, I also have two hydro motors and pump from a Dixon ZTR mower which could be powered by a gas engine. I think they belong on something a bit bigger than this wheelchair, but...? It would prevent using the chair on Nature Conservancy land however.

And you're right Dave, about mobility. Turns out, I know a little about that too. I spent part of '74 as a quad, after breaking my neck. I mostly recovered, but I do understand what others are going through. It's my intent to get my buddy down to the beach at his cabin under his own power. Thanks to you all for whatever help you can give me.
 

Track Addict

Bronze Member
GOLD Site Supporter
Nice project. Let me know if you need any wheelchair parts. I am in that business and can get you anything you need for cost.
 

undy

New member
TrackAddict,

Wow. I'll sure keep your off in mind. Thank You!

I've seen a couple utube videos of homemade chairs, but no build details were given. If (WHEN) this one runs, it would be nice to be able to provide details for others who might need to build one.
 

Track Addict

Bronze Member
GOLD Site Supporter
I have driven the tracked production chair from this company: www.actiontrackchair.com and while I wish nobody every to rely on one to get around are fun to cruise around and quite capable.

Think they will have some up at the New Hampshire Snodeo this weekend.
 

DAVENET

Bronze Member
GOLD Site Supporter
That is pretty kickass. But it looks like you would have to be very careful not to get high centered. I'm guessing it has a pretty kickass price tag as well . . .
 

undy

New member
A short update: The chair is an Invacare P7E model. It originally had 12" dia. drive wheels. Those are now gone.

I've ordered a piece of 1" thickness HDPE that I'll cut into drive sprockets. I'm planning to reduce the size of the drive sprockets by 50% from the original wheels, so speed will be cut by 1/2 but I'll have twice the torque to turn the tracks.

The output shafts on the Invacare motors is 17mm, not a real common size to find drive hubs for. So I've ordered two with 5/8" i.d. that I can ream out to 17mm. I'll attach the HDPE sprockets by bolts to these hubs.
 

undy

New member
It has a speed potentiometer, IIRC, but I didn't realize that effected the torque of the motors. Looks like I have some more research to do!

FYI, the joystick assy is Action MK IV RII, if that gives you more details.

Thanks for the input!!
 

undy

New member
I found a manual for the chair online. It's probably not the ideal donor, but the price is right.

The original specs list 4mph top speed and 12-14 mi max range. Considering it'll be for off-road use, half as fast should be okay (2 mph) and even a couple mile range would be acceptable for my friend's uses.
 

undy

New member
Thanks much.

More info, just FYI: The tracks are 60mm x 37, so the sprocket circumference needs to be sized in 60mm increments. The original tires were a nominal 12" diameter, so the circumference is 37.699" or 957.5546mm. I guessed at a 50% reduction in speed, so the new circumference will be 957.5546 / 2 or 478.7777mm. Dividing 60 into that gave me 7+, so I rounded it up to end up with 8 teeth on the new sprocket. 8 x 60 gave me my new circumference of 480mm and a diameter of 152.788mm or 6.012". That's the diameter at the track inside surface, so I had to add some for the teeth. I'm planning on having 3/4" deep teeth on the sprocket, so my overall diameter will be 7-1/2".
 

it's all about downhill

Nuts
GOLD Site Supporter
Hey undy, Looks like you have a good understanding of what you are about, and are getting good advice. A great reference book that gives the formulas, drawings, and explanations for making everything is " Machinery's Handbook" by Industrial press inc. Mine is the 22nd revised edition, and the only thing I regret for not getting an earlier one (probably just a few years) is all the metric junk in this one. Just a FYI. You are doing a very good thing for your friend. Fred
 

undy

New member
I.A.A.D.,

Thanks for the encouragement and book suggestion. I was able to look some of it up online (fasteners, etc.). I've always just designed things by the 'seat of the pants' method (and luckily most of them have been successful). But there are times it would help to have some better background info along the way. This book looks interesting, and it might keep me from pestering my friends over details.

By the way, welcome to the forum. Nice name you've chosen. Skiing I assume. It's what got me into snowcats to begin with, and if I'm lucky I'll die in my ski boots.

Cheers,
Paul
 

jask

Member
I don't want to be a rain cloud but that frame is not going to last, it is designed to be ablr to fold up for travel when the battery box is pulled out and even in regular use had a reputation for twisting and cracking cross frames under normal use - especially when used by heavier people or if the upper cross bars were not fully locked into the u shaped seats. I think the battery box is only able to carry group 22 batteries and I would want to use minimum group 24 for a project like this. look around for an old invacare "ranger" or "ranger X" it is a bomb proof base with independent swingarms for the motors. I probably have an extra MK4 stick and controller here if you smoke the ones you have.. (Those motors are great for for power boat racks as well :))
Have you discussed what plan B will be if he loses power at the far end of the trail? is he in cell phone coverage? I have seen power wheel chairs high center on muddy trails and the have a very small base of support and high center of gravity when being used on anything but solid level ground.
 

undy

New member
Hi Jask,

No worries about the rain cloud. I'd actually prefer to shoot down this balloon mentally, if it ends up with a better machine down the road.

I can understand your concerns about the structural integrity of the Invacare frame, although in fairness Danny is a pretty light fellow (170#) and he has already used this chair around his yard for a few seasons. As I got to the point of laying components out to get a feel for the spacing of things, I had already come to the conclusion that there was just too much Invacare in the way and I'd need to create an entirely new frame for the machine. I didn't need the fold-up feature anymore, the seat's got no side bolsters, and I was already planning on bigger batteries so the tray won't fit.

As to an emergency, yes they recently got cell coverage at that end of the island. I would also insist on being present the first time he ventures down to the shore. (I'll be the one to deliver the chair to the island, so I know that's what will happen.) I fully expect to have to grub out a few roots and small rocks on the way down to the shore, but I also hope to raise the ground clearance somewhat, to be able to clear things better. So long as he doesn't straddle obstacles, the tracks should help avoiding high-centering.

As it is, he's already tumbled into a plastic tote and gotten trapped there, whilst alone at the cabin. Luckily, somebody came by and rescued him, because it's pretty remote. Nothing in life is a guarantee, and he accepts the hazard/s.

I'm expecting that the frame, tracks, and batteries will weigh in excess of 250 lbs. (more if I add extra batteries), and that will all be mounted quite low. I also plan to utilize a lightweight plastic seat. I'm looking at around 36" width and about that for length. So I expect it will have a pretty low center of gravity. I'll add a footrest and wheelie bars to prevent tipping forward or rearward.

The HDPE for the sprockets arrived yesterday, and my buddy with the machine shop is now planning on cutting the sprocket with a CNC router and boring out the hubs I found to fit the motor spindles. Finding 17mm i.d. hubs was impossible in the o.d. I needed. The plan is to drill out the 5/8" i.d. ones I found. (If I increase the size of the sprocket, I'll buy aluminum hubs made for small wind turbine shafts, as the o.d. will then clear the sprocket teeth.)

The bogie wheels are due in early next week. I selected 6"x1.25" w/ bearings. I'll order the steel after I get them in and can better determine clearances.

Can anybody give me info about the batteries? Seems to me that 12 volts is 12 volts. Can I use gel auto batteries, or is there some reason I have to use wheelchair batteries?

Thanks to all of you who are tossing out ideas. When it comes to brains, there's strength in numbers. :w00t2:
 

undy

New member
Thanks for the link. I'll do some more researching there. From the thread you linked me to, it seems like the current batteries are probably still okay. Maybe not great, but okay.

The chair came with two chargers. One small one, and a larger more complex unit. I had to go through an extensive charge procedure before they took a charge, and I still have to do the load test from the manual once things are up and running. But they'll at least serve for design purposes, I believe.

Thanks for the info.
 

undy

New member
Short Update: I've assembled the track carriages, but not the motors yet. I'm still waiting for a finished sprocket and hub before I weld the motor mounts in. It's essentially a "roller" for now. I plan to fab up the seat mounts once the thing is moving.

On another front, the local industrial arts teacher is now involved, and he dropped by last Friday with his three top students. They printed up a prototype hub on their 3D printer, and also cut some prototype sprockets out of styrofoam with their CNC router.

I'm not sure how (or if) this will tie in with the parts already planned. But it's sure interesting to compare how the future generation will plan and execute something like this. It's a far cry from my compass and jigsaw!!

I will get pics when I can, but thanks to the last computer "upgrade", I can no longer figure out how to get them from my camera to this dam computer. I love progress...:hammer::hammer::hammer:
 

sno-drifter

Bronze Member
GOLD Site Supporter
This is off the project but can be a help. If you have a rock crushing operation near by, they have a hard time getting rid of the rubber belting which comes in many sizes. The three foot wide belting makes for a super highway for wheel chairs to go over round rock areas and soft ground so that a wheel chair can go well around the ranch. Two narrow belts works too. Here, they will even load them up for me, as a long roll is pretty heavy to move around. And the price is right- free.
 

undy

New member
Thanks for the input Sno-Drifter, and funny you should mention that. As it turns out, there's a place in Milwaukee that sells used conveyor belting. I got belts for my cat for $100 total(!), cut to width, just needed holes. I also got two 12" x 25' strips which I saved for some future project.

For this particular application, I have to get Danny about a quarter mile through a woods to the shore. It's rough and off camber and just too far to "pave" it. But I'll suggest it for around his cabin, in lieu of any concrete sidewalk/s. Good idea!
 

it's all about downhill

Nuts
GOLD Site Supporter
Not ignoring you, I just noticed your reply. Yes, downhill snow skiing is the reference. Be sure to check out the intensive thread on "Cat's Meow Jamboree" My brother (sno-drifter) is the tucker-aholic. And I see no way to overcome it. But if he can get me up the hill I can figure out the rest. If you are in the Portland, OR area, let me know. My grand kids come first, but there's almost year-round Skiing at www.timberlinelodge.com and a very negligible excuse will get me up there.

Isn't it amazing the resources that have turned up for you on this forum. who knew that there would be folks in the industry to spice up your project. This all has to be exciting for you and Danny. I know a few partially paralyzed skiers, and part of the thrill for them is to be able to move with the freedom that anyone can enjoy.
 

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undy

New member
Well, shame on me! I didn't read most of the Meow thread, simply because it was way too far away for me to attend. Had I realized that there was a chance to cat uphill and ski downhill, things might have been different for me. I believe I spotted a pair of twin-tips on board one cat. Looks like I missed a lot. Great photos and it sure looks and sounds as if you all had a lot of fun.

Yeah, I was pleasantly surprised that so many folks offered info and more. I didn't really expect anyone here to have familiarity with wheelchairs. It's just a small world, when you tie it all together online.

Danny's pretty excited. I just wish I could move the project along a bit faster. Waiting for components bites.
 
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