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Saturday, June 28, 2008

Roller Skates and Molly Bolts

Apparently using roller skate wheels to connect a radiator fan motor to a bicycle tire is more difficult than I thought. ;-)

Today, a bit over two weeks from the first attempt, I finally got a workable solution, and though it involved a lot more components and work than I wanted, it was possible to use recycled bits of other things instead of making anything from scratch or buying anything new, which is part of the point of this whole exercise.

I don't have pics of the solution yet, but these are the two things I needed to connect together, also showing the holes described below:

Basically the skate wheels have two layers: a black nylon-ish core that has 4 small equally-spaced holes in it just outside the much larger main axle hole, and a blue rubber layer that's molded around that core, which extends thru the 4 holes to keep the layers from peeling away from the core at the center under sideways pressure (which will happen a lot during skating, but not at all on my contraption).

I took advantage of those holes and cut away the rubber from the center section, exposing those holes so I can more easily put screws thru them. I used those holes as a template to drill 4 identically-spaced holes in the aluminum motor-attachment hub that came out of the plastic fan originally on the motor--this was very difficult because the holes needed to be right on the transition edge from the flat plane of the hub to an angled section of the hub, forcing me to hand-drill (for each of the 4 holes) a partial pilot hole with a very small drillbit to make sure I didnt' slip and either screw up the hub or break my power-drillbit.

Since the plastic of the wheel is too soft to guarantee any hardware I use to secure the hub to the wheel will not just gouge or crush the plastic, I cut a circular mounting plate (for the opposite side of the wheel from the hub) out of some metal structural plate of an ex-copier/fax unit donated to me some time ago for parts. The steel was soft enough to use my grinder to cut and shape, and easily drill a matching set of 4 holes into (as well as a central larger hole for the assembly's mounting nut to be attached to the motor thru), but hard enough to not bend or crush easily from the force of tightening the nuts down during assembly.

I took 4 old molly-bolts (saved from somebody's junkpile in the alley years ago) apart and used some other nuts from that same ex-copier that happened to fit these bolts, along with lockwashers, and secured the hubs thru the wheel to the handmade plate above, so that the thing can't just come off the hub like it did during my first test run over two weeks ago.

It *should* work well, but won't know till I go test it. Already verified it turns the wheel fine as a "bench test", but that's with no loading. I'll do a little ride-testing tomorrow--I don't want to test tonite for a couple reasons--first is it's dark out already, second is that I am also still working on a battery-box to sling *under* the bike, instead of in those rear baskets. Assuming it survives the basic testing, I'll put pics up on the next blog entry, too. I won't be doing any thorough testing until daylight, though, as I don't relish the thought of finding pieces that come off in the darkness. :-)

Most of the other solutions involved making a whole new hub from scratch, which would require a lathe and a drillpress, neither of which I have, nor have I had the time to build either one (though I probably have all the parts). One other solution involved welding one of the motor-hub attachment nuts to a threaded rod, which would have been of the same diameter as the skate wheel axle-hole. The hub would be screwed down with this "motor axle extension", then the skate wheel clamped to the hub by a washer and nut on the outer end of that axle extension. I tried a few times, but could not weld a nut perfectly straight onto the rod, which caused so much wiggle at the farthest end of it that it would shake the whole bike like one of those motel vibration-massage-beds. So I had to give up on that idea, simple though it seemed at first. I'm sure if I could come up with the right jig to hold it all, I could weld it on straight, but it measured straight before welding the ways I already tried, and not straight afterwards, so I suspect something in the heating process is uneven and moving the parts around as I do it, or as it cools. I simply don't have enough experience at it yet.

If I had a drillpress and a tap-and-die set, I could also take the threaded rod and drill a hole in it to match the motor's threaded mounting axle, then tap threads into the hole so it could be directly screwed onto the axle without any welding--that would probably work fine, as long as I drill the hole into it perfectly centered and straight.

Part of the problem with batteries in the rear baskets is that the roughly three 12-packs of weight is at and behind the rear axle, meaning the front wheel is actively being pulled a bit away from the ground, even with my own weight on the bike. It doesn't actually lift off the surface, but it doesn't have anywhere near the traction it should, and doesn't steer responsively because of it.

Another problem is that all the weight of those batteries is focused on the rear wheel, which is what broke a spoke and damaged the hub on it (forcing me to rebuild it essentially from scratch earlier this week). That also has damaged my baskets, breaking some of the welds between their wire-sections, and even cracking one of the mounting points on it's lower mounting arms (which are some really tough steel!). I'll have another post about that later, as a warning to anyone else trying similar power-assist schemes of potential failures.

Moving 2 of the batteries to just below and in front of the pedals, and one of them to the frame triangle just above that will move the balance and weight load of the bike back to the center, where it would normally be, and also lower the center of gravity significantly (as the battery mass will now be about a foot lower down), making the bike much less prone to skidding or tipping than it was with them in the baskets. Also frees my baskets back up for cargo. :-)

Anyway, enough rambling, back to hacking some clothes-washer steel casing into battery enclosures.

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