# Any ideas for a clutch at the crankset?



## frascati (Sep 23, 2009)

I'm trying to come up with a method of engaging/disengaging a chainring on the crankset via handlebar lever. I'm so frustrated with this I could weep.

I posted in the framebuilding section since I'm certain that this is something that does not exist and will require an idea or two from from genuine tinkerers.

I wish I didn't have to explain my purpose because it tends to illicit a "you're in the wrong forum' response too quickly. I've tried every "appropriate" forum on the web, with no help whatsoever. 

I'm going to spend the winter in my workshop bolting a 35cc Honda 4 cycle engine to a Specalized Hardrock mountainbike. I realize I'm in the wrong forum. Please humor me for just a moment if you will. This iproject is intended for 95 percent road use. The motor is purely supplemental and not intended to accellerate the bike from a stop. It is only intended to permit longer distances with less effort when desired. I have a pretty good assortment of bikes at hand but this one has front suspension, a very strong frame, and is not so expensive that I worry about ruining it if all goes south, I already own mopeds, road racing bikes, and mountain bikes. I'm intruiged with the idea of assembling an ultra-lightweight true moped.

I have never been on a bicycle and wished that it were, for the moment, a moped or motorcycle. That's not what I'm on a pedal bike for in the first place. But there have been many, many, times when on a moped or motorcycle (I have a BMW R65) that I wished I had a bicycle along.

There is presently no (petrol) motorized design that allows a rider to use a bicycle completely free from the added drag induced by the motor's speed reduction gearing when riding with the motor off. Because of the centrifugal clutch at the motor's crankshaft, the entire geartrain (belts, chains, gears, or combo) must be driven by the pedal cranks while the motor is not in use. This makes the idea of a real "moped" a practical misnomer. No motorized bicycle or moped riders actually pedal their bikes except to start the motor. 

A bare gx35 Honda weighs about four pounds and generates one HP @ 6000rpm. A reduction transmission of approx the same weight can be built to drive the crankset at 50 to 100 rpm. .5 gal of gasoline is approx three lbs. A front chainring freewheel would enable the motor input at the crankset without windmilling the pedals. The centrifugal clutch needs to be eliminated. A clutch mechanism at the chainring that connects to the motor input would enable pedal start of the motor and allow desengagement when coming to a stop. It would most importantly allow the use of the bike's geartrain independant of the motor if wishing to pedal the bike under your own power. Weight added to the bicycle would be less than twenty lbs. Possibly less than fifteen.

The simplest concept I've been able to come up with is to mount the motor and transmission on a gimbal/pivot at it's center of gravity and link to the chainring via flat (serpentine multi-v) belt. Rising and lowering the motor/transmission with an eccentric ball bearing cam would tighten/slacken the belt. There would still be minor drag at the chainring pulley with the slack belt resting against it when the motor was not in use, but perhaps minor and likely not much more than the bearing resistance of any other mechanical clutch design. A bell/pulley taken from an automotive electric air conditioning clutch would be ideally suited to bolt onto the crankset for this purpose. Lightweight and a usable diameter. 

Any other ideas? It seems like such a simple proposition. But I've searched Google for weeks and come up with literally nothing that applies to manually engaging a chain or belt drive. Everything is electric today.


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## Linnaeus (May 17, 2009)

Shimano used to have a really low-end road groupset that had fixed rear cogs and a freewheeling chainring set up. I had a bike like this but only robbed some really junky components off it for a commuter years ago. If you could find one of these bikes you could probably make something work.


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## AZ (Apr 14, 2009)

Sliding spur gear .


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## zipzit (Aug 3, 2005)

Check out the old horizontal shaft lawn mowers. There are those that have cable cam actuated clutch (similiar to the BB7 Avid brakes) but larger. I'm not talking about V belt slack systems, but actual plate clutches. In the old days guys would use those clutches on homemade minibikes, way better than the centrifigal clutches.

Actually if you are clever (and have access to a milling machine) you could take a BB7, some motorcycle clutch plates and a few bearings and make your own... You'd have to squeeze a lever to engage, but for a low horsepower assist system that's no big deal. (If you wanted springs to engage the system that requires lots more engineering.)

Do check out an automotive air conditioning system to understand how the compressor clutch engages. Obviously you won't be using a big heavy electromagnet, but you can easily copy the leaf springs on the clutch plate. You can also see from an A/C compressor that you don't need any fancy clutch plates out of exotic materials. In the power range you are talking about metal to metal single plate is just fine. With the engine off on your car, crawl underneath and push the A/C clutch plate to see what I'm talking about. An A/C compressor clutch plate transfers approx 7 or 8 horsepower, so you can gauge how small you can make your clutch. (Oh, I'm an automotive engineer in my day job, can you tell?) You could use a couple three or four bearings to push the flexible clutch plate 'down' to hit the drive pulley. You have to space the bearings radially, and push them outboard to miss the clutch plate leaf springs, but that would totally work. I'd use skate bearings (mainly cause I have a ton of them laying around.)

Another idea for the home machinist is a cone shaped clutch (see http://en.wikipedia.org/wiki/File:Cone_clutch.svg ) That would be much easier to machine and integrate with chain sprockets. It would be easy to make this pretty compact.

Sounds like an interesting project. Did you float this across any of the maker forums? Those guys may have some ideas as well.

--zip


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## CapricornZA (Aug 30, 2009)

maybe you should try running a CVT, where when the sheeve is furthest apart (clutch disengaged) the belt runs on an idler. but since you running a chain, CVT wont work to begin with.


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## flatfoot1 (Sep 8, 2009)

There are trials cranks that use a bmx freewheel on the crank, that might work. I have a 50cc two stroke that is designed to go in the crotch of the top tube/seat tube. It uses a centrifugal clutch and has a drive roller that is lever actuated and rubs on the rear tire. This makes the CG high, but it is still fun to ride. I only think your stupid if you let that arrogant p***k influence your decision to pursue the project.


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## j-ro (Feb 21, 2009)

sounds like a fun project, when you are done with it, paint the whole thing the same color and put like a 75 degree riser stem on it and maybe pvd will like it.........


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## dr.welby (Jan 6, 2004)

A few thoughts:

If you go with a V-belt, it would be easier to clutch it by tensioning it with a movable idler than by moving the engine. Though you probably thought of that and are trying to reduce the total amount of parts that mount to the frame.

I also noticed something interesting: in order to keep the engine from windmilling the pedals you need a ratchet so that the engine can overrun the crankset. However to keep the pedals from turning the engine when it's not running, instead of decoupling them you could have the crankset overrun the engine. So a possible solution would be something like in a ratchet wrench, and it would be connected to the throttle so that it would engaged in the right direction when the engine is running. Whether it's actually practical to make and would not end up sucking for a bunch of reasons is another story. But it seems like it could be fun to think about.

As to plate clutches, maybe you could use some of the parts from an old Bendix coaster brake hub? Or maybe you could use a freecoaster as an intermediate jackshaft, since as long as the sprocket is not overrunning the hub, the hub can rotate in either direction, decoupled from the cog. Hmmm, that might work with a front freewheel crank - have to think about that one....


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## cartographer (Jun 20, 2006)

I have a tandem with an Independent Pedal(ing?) System. This allows either the captain or stoker to pedal or not. You may be able to adapt this to your purposes.


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## frascati (Sep 23, 2009)

Hey, thanks for all of that. 

There's nothing particularly inventive about this project. Everything is off-the-shelf with a little searching. TB Woods Roto Cam, CarlyleJohnson MaxiTorq, and Hofmo Comet Cone Clutch, are three (rare) examples of purely mechanical clutch designs out there. None quite right for this project, but the ideas exist, and I'll eventually build my own on those ideas. Everything else is right at hand through various surplus outfits like SurplusCenter.com and others. White Industries makes the two chainring front freewheel that is actually designed for motor assisted applications and would solve the pedal windmilling problem. I can have it delivered from sickbikeparts.com. There are some very nice high pressure road tires available for mountainbike rims. Schwalbe Durano or Michelin Pro 3 look pretty good. 

I've been tig welding and running a 9" Southbend lathe for quite a few years. No mill yet, but that's next. Never built an entire frame. 

I can see that there is far more creative thinking going on here than at other forums I've posted at. The sliding spur gear is certainly an idea in the running, but requires more complexity. Since it is only really effective (as far as I can see it) in engaging a transmission in one direction, it would require the use of another freewheel in the design somewhere. The coaster brake conversion was something I was diagramming on paper for a while. It's already got many of the components for a workable manual jackshaft cone clutch. A verticle shaft mower blade clutch is also an idea I've looked into. All the versions I've seen so far appear to be set up as blade brakes that couple/decouple the spinning mass of the blade and hub with the mover deck, rather than couple the spinning mass of the blade and hub with the motor shaft as a true clutch would do. The latter probably exists, but I have not found it. None of these have been optimized for weight either and would require lots of trimming. Zipzit mentions a horizontal shaft mower clutch. Do you recall the brands these were used on? I've also looked at quite a few 12vdc electric clutches for ideas. Zipzit's roller bearings on the friction plate would work but might be noisy and bulky. A pressure plate on ball bearing detent ramps pushing a thrust bearing would be best. In fact, that might be what's going on inside of the the mower clutch. Crazy that I can't find just what is being described here in some catalog somewhere. 

But In all, for weight savings and simplicity, the see/saw mounting of the engine and transmission inside the triangle of the frame (all clamping without mods to the frame itself) in order to couple/decouple a small serpentine belt seem to be the way to go until a better solution presents itself. One part of that I was toying with was trying to locate a steel corded version of a small flat belt. Most reinforced belts use aramid, fiberglass, kevlar, etc, but steel corded versions can be found, in garage door openers for instance). The steel corded belt would need to be flexible enough to conform to the smallest pulley and that might be a problem. But if it were flexible enough I might fab a 'chainguard' around the larger pulley with a lining of neodymium magnets beneath a teflon strip. When the belt was slackened, the neo magnets would draw the belt against the teflon strip and create an airgap between the belt and the large (crankring) pulley. Zero drag. The SS steel reinforcement would also need to be non-austenitic to work with the magnets so it might be a problem as well.


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## Clockwork Bikes (Jun 17, 2006)

Positron?


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## Live Wire (Aug 27, 2007)

Random thoughts: 
Does there have to be a transmission?
How about a left side drive to a freewheel on the hub? It would be lighter- you'd have to be careful about applying the power as that's a lot for a freewheel to take all at once.


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## frascati (Sep 23, 2009)

Left hand side drive would be simpler. Since I don't intend the supplemental power supplied by the little Honda to exceed (or at least by much) the component design limitations of a modern mountain bike, it would be very nice to make use of the gear range of the rear cluster. Left hand drive also does not get me around the problem of the centrifugal clutch. I'm very reluctant to resort to pull starting in any final design.


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## MrCookie (Apr 24, 2005)

Random thought. Normal bicycle drivetrain on the right. Belt drive on the left (turn down the disc mounts to maintain whatever clearance you need, mount a pulley direct to the hub) run your motor and belts on the left with the aforementioned idler pulley/tensioner?

I know it's more complicated than that, you would want to run a shaft somewhere on the seat tube to transfer the power, so you don't have a belt constantly running through the rear triangle. And then you'd have to run the belt between the CS and SS to avid having a trap door to feed the pully through (See spot belt drive rear dropouts).

The company that makes the independent drives for tandems is DeVinci
http://www.davincitandems.com/dv2.html

Another place to get interesting ideas is the Schlumpf mountain drive guys. They do some crazy innovating that is below the radar in the US. (C'mon, a 2 speed crankset that you shift by knocking a plate with your heels... BRILLIANT for some applications.)
http://www.schlumpf.ch/antriebe_engl.htm


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## dr.welby (Jan 6, 2004)

Belt drive on the left = Whizzer

http://www.moped2.org/whizzer-bike.htm

I'd think digging up old motorcycle designs might give some ideas since at first they were all converted bicycles essentially. Check Google Books / Project Gutenberg.

Also might be worth checking the library for 1950s DIY books from Popular Mechanics and Science and Mechanics Publishing. They're usually full of projects like building your own rototiller and such. You might be able to get some clutch ideas from there.


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## NEPMTBA (Apr 7, 2007)

*Interesting...*

..as I have a similar project going on, a 1974 Honda MR 50 engine in a bicycle frame to be used off road. bolting up to a disc brake hub on the rear using a cog and Magura HS33s.

In the mc frame it's a rocket, I'm hoping with larger wheels it will be smoother.

:thumbsup:


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## herbn (Sep 17, 2005)

i wonder if you ran a chain from the motor to the largest cog on the cassette,locked out the deraileur so you can't shift the pedal chain to that gear(of course) then run powercranks and big timetrail gearing. The cranks would freewheel when you're not pedaling fast enough.


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## zipzit (Aug 3, 2005)

I was playing around with this at a slow day at work. Wasn't able to get a .jpg right away. (Anybody use Google sketchup for simple CAD? How do you do a screw cam in that tool?) Obviously its only a first prototype drawing.. I figure it would take three or four more interations before you could get this right AND SAFE! Obviously this iteration doesn't have a robust way to ensure clutch disconnect, and therefore NOT SAFE TO USE. Its just a simple design iteration to get the gray matter warmed up.










After playing with this for awhile, and glimpsing the effort necessary to bring this one home, my conclusion was if you want an fun way to take power offroad, buy a used 100cc dirt bike as a project, fix it, use it, have some fun with it, and sell it when you are through. The payoff is just much better.

Good luck, zip.


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