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Sunday, May 17, 2009

Wheel Dilemma

I had thought at first glance that I would be able to simply swap the wheels/hubs from the wheelchair to the ex-stroller/nee'-trailer's axles, but unfortunately they're different diameters.

The wheelchair axles are around 7/8", and the trailer axles are around 3/8". The sealed bearing units on both of them are, however, the same apparent outside diameter, for one side of the wheelchair hubs, but not the other. The inside of each WC hub appears to be the same as the trailer hub, but the outside of each WC hub is just very slightly smaller (perhaps 1/2mm), so the bearings from the one won't fit the other.

I haven't gotten the bearings out of either WC hub's inside holder yet to verify, but since the outside ones are recessed for the quick-release button, it's easy to see the problem, by attempting to insert one of the trailer bearings, which *almost* fits into the hole, but not quite. It's possible the inside ones are the same, but eyeballing them with the trailer bearing sitting on top of the WC bearing, it *looks* the same.

This means that unless I use the whole WC bearing, axle, hub, wheel, and mounting plate at the same time on one vehicle or the other, I can't use them at all. That's disappointing, as it makes my decisions harder.

If I use the WC wheels/hubs on the trailer, it'd make for a no-flats-causing-me-to-unload-cargo-to-fix-flat advantage. Also, would keep the trailer from bouncing around as much from the pneumatic tires, as the WC tires are solid, but can only be used on the WC rims. I don't think that in the condition they're in, that I could get them off the rims in one piece, or if I did that I could get them back on in one piece. I'd have to take them off to easily unlace the rim to use it with the trailer hubs, or to change the rims on the WC hubs for bike-sized ones, with pneumatic tires (probably would use 26" ones, right now).

The trailer rims/hubs are steel, 20". I can easily change the rims on these, so that makes them a better candidate for the trike wheels. I can also weld to the hubs if needed, and more safely machine them in various ways, so that I can attach whatever drive mechanism is necessary to them.

However, the trailer hubs are narrower, by nearly an inch, meaning they'll have less side-strength against stresses during turns, etc. This won't be a fast trike, but it will be heavy. Even with three wheels supporting it instead of two, it'll still need as much wheel strength as I can give it, while still keeping them light.

I think the trailer axles are smaller diameter mostly because they are solid, where the WC axles are hollow so the QR pin can move inside them. The QR pin itself could be bearing some of the load, too, I guess, but I doubt that it is--if it was, it'd be very difficult if not impossible to move it in and out with a load in the chair, and it's just as easy to move the pin in and out with the chair full (of big lead-acid batteries and other heavy objects) as empty.

I suspect they can both handle the same weight of load, but I *know* the WC was designed for at least 250lbs on it, while the former stroller only 75. Primarily I think that low limit is because of the plastic frame interconnects, and that the axles could bear much more, but I have no evidence for it, and can't find out without testing, which may destroy the axles if I exceed their limits.

Got more thinking to do.

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