Grinder Drive

I need multiple drivetrains to test for my coast-to-coast without recharge ride in early '09. While I wait on Matt's gearbox along with delivery of a number of hub motors, I want to try a simple one that's been nagging me. The reduction of a single chain and sprockets just won't do without a big heavy motor, but I have a nice little angle grinder 90° gearbox with strong helical gears and a 3.5:1 reduction. The only imperfect thing about it is that it spins CCW looking at the end of the shaft, so requires left side mounting. All I have to fabricate is a mounting plate to mount the gearbox to a motor face, and an adapter to mate the motor shaft to the gearbox input shaft. I'll just put a cassette and derailleur on the gearbox output shaft, and chainring(s) at the wheel. The mounting plate will incorporate the means of mounting to the bike.

This isn't for high power or high speed, but instead a test for efficiency compared to hub motors. I want to run the best speed I can at 300-500W on the flats, which is about 150 miles of the ride, but I have some mountains to contend with which I believe may be the downfall of hub motors for this ride. I have a few sub 1kw brushed motors to try, plus my little Kohlmorgen's that I've been waiting for just the right use. With the relative ease of changing gearing and sprockets, along with the ability to change and fit different motors along the axis of the bike frame this should prove to be a worthwhile and quick project for comparing non-hub to hub motors. I could even attach an RC motor to it, since in it's design use the gearbox accepts a 35krpm input.

I've also been thinking that I may need a second motor with freewheel ability to help climb the mountains even if the hub motors prove better for the flats. Then if it works well, it may prove to be a viable option for a high powered addition for a downhill bike to make it able to race uphill too, another idea nagging me.

Pics of progress to come this week.

John

You should be able to reverse it. Depending on the gear/bearing arrangement this could be a bad idea though.

Are you planning to use the grinder motor?

Ideally I think you would want a bit more reduction and certainly a more efficient motor.
Could a big outrunner be adapted to the gearbox?

fechter said:

You should be able to reverse it. Depending on the gear/bearing arrangement this could be a bad idea though.

Are you planning to use the grinder motor?

Ideally I think you would want a bit more reduction and certainly a more efficient motor.
Could a big outrunner be adapted to the gearbox?

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The teeth of the gears are curved, not straight, so it's definitely designed for one way operation. They make much more sound turning the other way, which can't be good. Virtually silent the proper direction. As I mentioned in another thread, this McCullough gearbox is much more efficient than on my B&D grinder because it doesn't get too hot, even with almost continuous use at a 35krpm input.

No not the grinder motor, too fast, too noisy, and I don't know how to mod it for DC use anyway. Yes, I want good efficiency, but don't know if the Kollmorgen's and wheelchair motors, and others I have are efficient enough or not. The Koll gets fairly hot pretty quick, though some guys report great results using them for years, and they seem well built. Wheelchair motors are silent, and don't seem to overheat in their designed use, so may be efficient and durable enough. Yes, I've been thinking about an RC motor for a while with it, but I would then need more reduction than with the 2-4k max rpm motors I already have, and I'll have Matt's platform for RC anyway. I do have a 3kw continuous big brushed motor that I'd like to get inline instead of the current sideways, so if this works on smaller motors, I'll get a stronger one from an industrial sized angle grinder.

To me, the real beauty is that I can try many different motors by easily mating shafts end to end, which should also be better for the motors with no side load, and with a right angle output shaft spinning in the 1krpm range things start getting really simple.

John

Hey John,

Very cool idea. I like thinking outside the box type projects.

I think this will work fine. One thing, though; the derailer cannot be on the output shaft with a cassett. The reason for that is the tension side of the chain is also the sprocket feed side. So, unless you want to reverse the direction of rotation to shift, it will not work. The derailer would have to be on the tension side. Bummer, I know. I was looking into that myself. Heck, maybe a tension side derailer would be a good second project for me once the reductions are done?

Matt

recumpence said:

Hey John,

Very cool idea. I like thinking outside the box type projects.

I think this will work fine. One thing, though; the derailer cannot be on the output shaft with a cassett. The reason for that is the tension side of the chain is also the sprocket feed side. So, unless you want to reverse the direction of rotation to shift, it will not work. The derailer would have to be on the tension side. Bummer, I know. I was looking into that myself. Heck, maybe a tension side derailer would be a good second project for me once the reductions are done?

Matt

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No problemo. I'll still use the cassette, just no shifting on the fly. I do want more than one option on the drive side, since I don't know the actual speeds and to accommodate different motors. It saves me the complication of trying to figure out one shifter controlling two at the same time. Now I'm worried though about a derailleur even working on the left side. I see a real jury-rig coming.

Too bad the gearbox is one-way. Otherwise I'd go for a retro-direct 2 speed once I come to 2 gearing ratios I want.

John

John in CR said:

I see a real jury-rig coming.

John

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No, no, its a "Field Adjustment".

Matt

recumpence said:

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Being from the south plus 2 years in Jamaica, I typically use different terminology, but too many around here are highly sensitive about political correctness. Even the preceding sentence is likely problematic through insinuation only.

John

I'll just pull a MacGyver instead.

I dropped the stuff off at my machine shop buddies to get adapters made for fitting 2 motors to the gearbox. They have 4 or 5 heavy duty grinder gearboxes from big angle grinders with burnt motors. The one I looked at had a 4:1 reduction, 10krpm output and a 2kw motor. These things outlived a heavy duty AC motor, so I think it would have no problem handling even the biggest RC motors, since they are designed for years of use at 40krpm input with significant power.

John

John in CR said:

No not the grinder motor, too fast, too noisy, and I don't know how to mod it for DC use anyway.

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High speed AC motor with brushes to DC, way one. Bypass any speed control, and feed 70-130 volts DC to motor. Will spin fast. Way two, make a piece of steel of similar shape to the field coil and glue in a bunch of rare earth magnets. Way three, remove copper from existing field coil, expand the hole in the center, and add rare earth magnets. Now simply feed 60-120 volts to the brushes. Expect the motor to spin at about 1/3 to 1/4 it's initial speed, but still need high voltage for decent power.

Marty

If I got this right, seems like you could use a front derailleur on the k7 to shift on the fly using a rear derailleur at the wheel chainring as tensioner. Probably couldn't use the k7's full range that way, but at least with the old style 7 speed k7's you could take em apart and reassemble for whatever gear range you want, even if only over 3-4 cogs.

Mathurin said:

If I got this right, seems like you could use a front derailleur on the k7 to shift on the fly using a rear derailleur at the wheel chainring as tensioner. Probably couldn't use the k7's full range that way, but at least with the old style 7 speed k7's you could take em apart and reassemble for whatever gear range you want, even if only over 3-4 cogs.

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That's what I was thinking. A front derailleur at the rear for changing to 3 different gears, being careful of the load while changing gears. If I use a standard rear derailleur as a tensioner, would it need to be near the front or near the rear to function properly?

John

Mathurin,

No doubt more efficient, but is there potential for slippage of the chain with that triangular chainline? My current chainring is pretty old and worn with a 3 consecutive teeth that got ground down almost flat somehow, and I've had the chain slip a few links on several occasions.

John

Dunno, I've not built one. Just that that bike's shifting mechanism seemed pretty close to what you've described.