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Thursday, September 13, 2007

Reinventing the Wheel

I had a great brainstorm idea (which is probably going to turn out more like the results of an epileptic fit instead) while I was unmelting my brain in Jack-in-the-Box yesterday afternoon, after a multi-hour ride around town searching for books about C programming, a 15/16" star-socket, and anything else interesting and usable I might run across.

-- Take a wheel, strip it of all the spokes, put a toothed surface on the inside rim (yeah, gotta move the valvestem or make the gear work around that somehow).
-- Make a package that would fit in the cylindrical space formed by the inside of the rim, containing batteries at the bottom, motor controller in the middle, and motor/gearbox at top.
-- Take the axle with bearings (and ratchet?) and mount that thru the center of the package.
-- Make the outer rim of the package a gear that transfers the motor output to a set of planetary gears, which ride between the rim gear and this outer gear.
-- Plates on the outside with bearings as needed to hold the whole thing together, leaving enough rim exposed to use for old-stye friction brake surface without modification to the friction brakes.

Not sure how bad friction losses because of the planetary gears might be, which might be able to to be minimized with the right lubricants and precision machining of gear surfaces. Mass might also be too high to do all this.

I don't know if this would be more efficient than simply having the motor gear-drive the rim from inside directly.

All this typing just gave me one more brilliant idea that might be too complex to machine, or physically impossible, as I haven't tried to really visualize it yet:

--Make the inner (motorwheel) gear rim be *several* gearings, in rows, and the planetary gears be shiftable back and forth horizontally to engage those different gearings; I suppose the planetary gears also have to be several parallel gearings, but I cannot envision how that could work. :-( Maybe have the gearings be on the inside, and use the *motor* gear inside to transfer power differently. Not sure, don't know enough about gears yet. They're a world unto themselves, though simple in concept.

Maybe I can invent a new kind of gear that will actually do this. Or rediscover an old one, more likely. :-) Got some more research to do now. But if it *would* work, it would still allow shifting for speed control, to keep the current usage in the motor as low as possible by trading speed for torque, just like you do with the pedal drivetrain and your body.

I need a watchmaker friend, now. :-)

Anyway, that's all for maybe Mark XIII of this thing--it's more work than I could do right now, but it's a definite possible path, as the entire thing would be in a simple easy-to-swap-out wheel. I would want this to be the *rear* wheel, because it's gonna be pretty heavy, and I wouldn't want to have to steer with that kind of mass to deal with.

FWIW, I *just* remembered where I saw something similar before: Neodymics' early design idea "BMU-1". It's similar in concept, but not the same way of transferring power, as far as I can tell. Mine is probably less workable than theirs, but I really don't know enough about the mechanics of it to tell yet, as I am not an engineer, just a mad pseudo-scientist. :-)

I never did find the books or the socket. But I did find about $30 in change and dollar bills (including a fiver) just laying around in the parking lots and streets! If I was a fast rider, trying to get places in a hurry, I probably woudn't have seen any of it--I definitely wouldn't have even noticed in a car. I bet you didn't know you could get paid just for watching the ground while you ride a bike for fun.... :-)


  1. My only real concern with what I think I am understanding is the idea is truing the wheel (and possibly wheel balance). By taking out the spokes, you are removing the method of lateral stabilization. The rim of the wheel is not meant to stand alone. I would think that any structure (outer gear of the planetary assembly) that would be strong enough to provide that support would be prohibitively heavy. I am sure that you aren't going to want to sacrifice your ability to easily move the bike when the battery is dead. Or even more important, you don't want to have to stop the momentum of that wheel in an emergency. Being on the outside of the wheel will cause it to have lots of effect on the stopping power of the bike.

    I don't see how you will be able to get around rebuilding a hub and then building the wheel around that hub. I still think it is an intriguing concept. I have a few extra parts from my old bike if you can use them. I also have several hubs... I think... I would hate to think you are going to be experimenting on your primary mode of transportation. And if you need more parts, Goodwill almost always has bikes that need some love (or to be chopped up and turned into frankenstein monsters).



  2. It is true that taking out the spokes leaves the wheel with several problems I would have to resolve in another way. I don't yet know what that way is, as I had only just thought of the basic idea within the day before posting it. :-) I had thought that the gear assembly would do all this, in combination with the side panels and the bearings that the rim would ride against for those. I don't know enough engineering or materials data/science to know, though.

    Stopping the mass would be a problem if the structure containing all the elements was a heavy material, like steel, but it might be possible to use aluminum to do this, or even a framework of hollow steel rather than anything solid. Something I'd either have to just experiment with, or have someone that knows how to do it calculate out for me.

    I have a feeling (completely ungrounded in any actual facts or evne thought-experiments) that the support mass will be so far below that of the rest of the components (battery, motor, reduction gears, controller) that are required no matter which way I do the project that it will not be that big a deal for the stationary part containing those items.

    But since it's outer rim ring gear would probably mass the same as the rest of the rim, and be attached to it, it *would* effectively double the friction required to slow or stop that wheel, forcing changes to the brake adjustments or requiring larger-surface-area pads (or both).

    As to how to construct it? I don't know yet. Have to figure out what is required to make it work, first, and that will wait for later Electricle™ designs, as I don't even have a simple MarkI prototype of the basic design finished yet (gotta drill out the former pedal shaft and tap threads into it, then bolt in the socket (once I find one) to mate the motor gear to it, so I can actually do some kind of load testing, etc.)

    I'll take you up on extra parts if they're something you're going to toss out, but if you are keeping them as spares for your own, well, *keep* them! :-)

    As noted in a previous post, I did already get one more spare bike, but I am still torn between which of the two spares to cut up, and which to use as the testbed machine. I'm pretty sure since the frame fits me better on the latest acquisition, it'll be the testbed, and Old Yeller will become an organ donor. Before I actually cut anything, though, I will do what tests I can with the pieces of the old Murray Biotech, as pictured previously. It's pretty junky for test materials, but it's better than nothing, and will give me an idea if it works or not. I'm not touching the Columbia until I have a working prototype already. :-)

    For now, the Electriwheel™ will have to wait, as Frankenbike™ is still calling loudly. :-)


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