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Monday, May 4, 2009

Wheelchair-Based Trike

A donation intended to provide essential parts for my flatbed trailer inspired a trike almost as soon as I started working with it. It's aluminum, so I can't weld it, but I can bolt things to it, and it's capable of supporting at least 250 pounds on it's two tiny front wheels plus it's rear spoked wheels.

Since I'll be removing the tiny front wheels regardless of what I do with it, and almost certainly re-lacing the hubs onto bike wheel rims, most likely using this whole cage as the rear of a trike, it might be able to support even more weight (but I won't push it unless I have to).

I don't have any really lightweight small frames to use for the front end except for the Magna that's already part of Crazybike2, but I do have a nice-looking copper-colored Mongoose frame that will probably fit the project well enough for at least the first try.

A quick first idea, just setting the parts together in a first-guess position:

The bike frame has a 20" front wheel, with the 24" tire-size wheelchair wheels on the back. Unfortunately they're not the same as 24" bike wheels, as the tires are much smaller thickness, and so the rims are larger diameter than 24" bike wheels. Currently they have the urethane foam flat-proof "tubes" in them, and very very badly worn tires (past the tread, into the fabric).

A few problems arise, of course. First, since there's no place to put a normal bike chainring set on the wheels, I have to come up with an alternate way to get the power to the wheels. Front wheel drive is out, as I don't want to deal with those kinds of complications. I could move the handrails to the inside of the wheels, and either cut gear notches in them or replace them with smaller bike rims (or wheelchair rims if I can find any) and use those as pulleys.

In the pics, I've already moved the left handrail to the inside of the wheel just to see if there was clearance, which there is plenty of. I need to take at least one of the tires off the rim anyway, as there is one broken spoke tensioner head (the tensioner is still on the bent-up spoke, but is missing it's head; I assume that's still in the wheel). Once I do that, I have the option of unlacing the wheelchair rim and lacing on a bike rim instead. Then I need to decide if I want 24" or 26" tires, since I have more 26" tires with road-style vs MTB-style tread, and I'm more likely to run across 26" slick tires than I am 24", anyway.

If rim-as-pulley is used to replace the handrails, a belt would then drive the wheels, and be attached to a device at the other end that takes the bike chain drive from the front pedals/etc and converts it to the pulley drive, along with a freewheel and shiftable chainrings (pretty much like the device I made for the treadmill motor setup, but with the pulley on the left side and the chainrings on the freewheel as normal).

Alternately, I can clamp a chainring to the spokes on the wheel(s), driving it from a chain fed from that device, in place of the belt/pulley. (this would be better for traction and torque, and is like the way Eric Peltzer did his bike at ).

Since the wheels are on separate axles already, they'll freely turn separately when I steer, unless I use a drive system that drives *both* rear wheels (which would be better to do, but more complicated).

I'll probably need to alter the small bike frame so that it's rear triangle is replaced with a triangle of small tubing spread far apart at the rear, so it can be inserted into the former foot-rest tubing post holes (where the black posts go in from the bottom front of the chair right now), and secured in place there with the bolt pins. Probably it will also need an upper set of tubing to connect from the seattube area to the top of the wheelchair frame, to stiffen it against folding up with weight in the middle (me).

The second set of pics below show the bike frame upside down, with the pedals up higher. I'm not sure it'd work as well as the other way, but I'd have more ground clearance, and a teensy bit more fork rake.

The seat would be similar to the one on my current bike, and placed in front of where the wheelchair frame's seat would have been, with the base of the seat about the same height the pedals are at in the pic above, or a tad lower.

I should be able to do the same remote-steering and forward-located pedals I have now, although since I have no other square-taper threaded-in bottom brackets I'll be using the old one-piece cranks that came on the frame I'm considering using. Remote steering because I don't like tiller-style steering, and I'd rather have the bars right back where I'm actually sitting. More convienent for mounting things on with switches and stuff, too.

The three U1 batteries will fit very well along with their charger and the motor controller in back of the chair, between the axle points, on the double-barred part of the frame (in a box made for the purpose, probably from aluminum).

The motor(s) would be wherever they need to go to fit into the drivetrain before the shifting part of it, just as now on the current bike. I might be able to use the treadmill motor easily on this one (with a double-reduction setup), as I could enclose it in a fan-cooled/filtered-air box to keep road dirt out of it, as there's plenty of space inside the wheelchair frame. If you can think of a
better motor to use, I'll try anything out.

I *will* need to get or make a longer cable for my bike lock for it, since the wheels can be taken off so easily--I can imagine someone stealing *those* off the bike (or trailer) just for wheelchair use. :-(

As I don't have a front shock fork for it, I will probably make one like those seen on several of the freakbikes, where it has a lower fork that supports the wheels for turning, and an upper fork that
contains the springs or whatever, which should allow me much more freedom in the steering design. (I can't believe I never imagined any kind of shock fork in front other than the kind that comes on MTBs and common road bikes, until I saw the freakbike forum pics--I apparently never noticed or never saw anything like them in my google searches of bike designs previously!).

All in all, this looks like a workable idea, mostly dependent on making a way to easily and reliably transfer power to the rear wheel(s). I've already come up with several possibilities in the few hours I've been thinking about it, so it should be possible to do this with stuff I already have laying around.

With the big heavy U1 batteries, the trike would be MUCH better as a ride than the bike is. Then I can maybe find some small batteries to assist the Crazybike2 for short jaunts, and use the trike for longer trips, since I can easily put the third U1 on there for either spare power or for more overall power the entire trip (a more likely-to-be-used solution).

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