Using two drive chains to one hub - one on each side?

[svejkovat]

I'm very early in the learning curve here, but I'd like to weigh in. I found my way to your forum by searching some of the ideas I had in mind for adding a 4cycle weed trimmer motor to a bicycle. There are a heartbreaking number of really rash cobble-jobs out there, with 'friction drive' on the rear tire (ouch) and 80cc import bolt-on kits pretty much the norm. The bolt-on kit is commonly an ultra simple two stroke with basic gear reduction and a simple internal clutch for starting the engine while the bike is in motion. When pedaling, the motor drive train is in motion.

Is it possible to drive the motor through the bicycle's present chainsets and derailleurs? Has anyone done it successfully?

I'd really like to discover a way to integrate the motor and the pedals so that they are truly independant but complimentary. With a left hand and right hand freewheel (both functional.... not a 'flip flop' as is commonly the case) on the rear hub this is a pretty straighforward proposition. But wouldn't it be nice to be able to actually use the bike's drivetrain for electric/gas power as well? Ideally, especially if the motor is to be used as a supplement and kept relatively low power/torque, it could be integrated into the drivetrain at the crank instead of at the rear hub. This way the chainsets and derailleurs could be used for pedaling and for power. But now the problem is that the motor will spin the pedals at all times. Sounds dangerous. Always compromises.

The ideal starts to get really complicated. A freewheel on the left of the crankset shaft for the motor, another freewheel that the front chainset spins upon, and the crank arms somehow on a third freewheel so that they could spin independant of the main shaft yet engage the chainset freewheel when desired. There's a hollow and coaxial shaft in there somewhere unless all three freewheels are packed onto the right hand side. Now my head is spinning. Maybe you don't need three freewheels, but the logic is escaping me. But I'd love to make it work somehow in order to make use of the motor through the existing gear train, and be able to pedal completely independant of any part of the energy sucking motor transmission.

 

[Miles]

svejkovat,

The simplest way to do this is to have a RH motor drive with a freewheel in the drive between the motor and the cranks and a freewheeling crankset.

A LH motor drive with a highly engineered custom bottom bracket would be too much work for the gain ........

The downside to driving the cranks is that (assuming that you want to be able to pedal in tandem with the motor at all times) it requires extra reduction to cadence speed, which is then inverted in the subsequent drive to the wheel.

 

[svejkovat]

I came to almost the same conclusion picturing this all in my head last night. My imgagined crank would have a single chainring on the crank (that is how my road racing bikes were set up anyway, it suits my riding style, sheds weight, and simplifies. For integrating the motor, this chainring would be free wheeling and to its left would be a chainring with handlebar actuated clutch. To this would be connected the motor via the most compact method of getting the ratio to match (double jackshafts or a planetary gearbox).

And ah... you're quite right about that inversion loss; it'd be a big one too. I was too busy with the little details I guess to see that one. All things considered however, it's still tempting.

 

[Miles]

Coupling the motor drive directly to the chain (behind the chainring) eliminates the extra reduction step, but introduces a small amount of extra slack-side drag, when pedalling without the motor. You could use a pivoting disengagement system for the motor drive, to avoid this.

 

[oofnik]

I used Matt's idea on my Mongoose:


I machined an adapter on the lathe to fit over the left side brake disc mount. It's done in two pieces so that I could get a chain line offset large enough to clear my chain stays. Otherwise the giant sprocket was too far out and the chain wouldn't clear.

 

[John in CR]

I'm cheap and lazy, so for a dual side 2 chain drive I just took two steel rear hubs, cut them in half, and welded the two threaded halves together. Since the RH threads of the left side freewheel would unscrew, I just cleaned them well and put epoxy when I screwed it on. When the freewheel wears out the hub is junk, but it was quick, cheap and easy, as would be the replacement.

John

 

[svejkovat]

Ok, after a little poking around I came across the following video. You guys might find this interesting.

http://sickbikeparts.com/SBP%20Video3.wmv

Voila! Yes? This is VERY close to what I was working up in my head. The little Chinese two cyclethat this kit requires is usually 80cc and interally gear reduced. After this gear reduction it is jackshafted to the front crankset giving it one more reduction. But it seems to work. I've read some comment from guys on another forum that installed this and they're pretty satisfied. Looks like you'd sacrifice the lowest gearing of your mountainbike in order to integrate the motor in this fashion.

The only part that I'd be unable to reproduce in the shop is the front freewheel. The site that sells this kit offers the freewheel alone for 65USD. Do you know of better options?

I strongly prefer going with a robin/subaru or honda 4cycle motor instead of one of these chinese bolt on 2cycles. Those bolt on kit motors (all over ebay and the web) have an internal starter clutch that is handlebar actuated. I guess I'd have to keep the pull starter unless I can find a version of centrifugal clutch that that can be manually locked up.

Edit: come to think of it, a little handlebar actuated clutch/freewheel in place of the small gear on the right of the jackshaft (just before the crankset) as shown in that video would be ideal! This would enable the engine gearing and transmission to be isolated when pedaling with the motor off, and allow the motor to be started while rolling. It would also eliminate the centrifugal clutch. It would need a tab to lock the lever while riding with the motor off. I realize I'm straying farther and father from electric drive ideas here, but I hope I'm not wearing out my welcome.

 

[flyinmonkie]

I've test run my drive in the stand to make sure everything turns smooth and there is no rubbing. So far so good. It is quieter than I expected, but only the gear reduction and the motor drive chains move under motor power. Unfortunately all the chains turn when pedaling, but the drag isn't too bad. I just have to finalize the bracket fore the right side of the gear reduction. You can see the layout below. It is 2 chains on the right side. One from the crank and one from the motor. There is no freewheel crank needed as the chain from the crank is on a freewheel threaded onto the rear hub. The chain from the motor drives the rear hub. With a standard bike the motor could run through most of the gears on the rear hub and the crank could run through the front gears with an added chain tensioner.

FM

 

[svejkovat]

HOly crap is this frustrating. I found this..



...and there is a model that would fit a motorized bike well. Weighs about 4lbs, very compact, and will accept toothed sprockets. It's over 2000USD.

I called about a dozen manufacturers and as many racing kart parts vendors. One guy, unbelieveably, without having told him what I needed it for said "Only centrifugals. I occasionally get guys who are building motorizing bicycles asking for the thing you described. As far as I know it don't exist"
You mean to tell me I stepped right into the only damn application (outside of very exotic manuf processes) where this sort of thing would solve many problems?

 

[unclesam123]

B E A U T I F U L ! ! ! EXCELLENT AND VERY CLEAN JOB.

 

[Hummina Shadeeba]

The easy way:
https://www.profileracing.com/product/freewheel-hub-drive-bi-hub/

I’ve seen u can flip the ratchets in some of these bmx driver hubs but haven’t seen one that comes with a driver on both sides, yet. It’s probsbly out there and every bmx possibility under the sun seems out there.

Another likely easy way to do it is you have access to a lathe would be take a single sided screw-on freewheel style hub and just thread the other side backwards and get a left hand drive thread on freewheel.

Trying to find something “dual-drive” that has a 14mm axle so as to be able to use the many bmx frames out there these days with 14mm dropouts is a goal for me

 

[Balmorhea]

Trying to find something “dual-drive” that has a 14mm axle so as to be able to use the many bmx frames out there these days with 14mm dropouts is a goal for me

There were many RH/LH BMX hubs with 14mm axles in the mid to late ‘90s. They haven't been made in a long time, but there are still some around to find if you’re patient. The best treasure of them all was the DK Dual Drive hub, which had M30x1 threads on both sides, but came with 1.37”x24 threaded adapters for both sides. I wish I had bought some when they were available; they are an extremely versatile way to hack an unforeseen drivetrain. I did get a couple of Specialized Flipside hubs, which have come in very handy for two-sided drive. Odyssey Hazard hubs were also made in an RH/LH 14mm axle version.

The sealed bearing versions of such hubs use 15mm bearings, so it’s relatively easy to reverse engineer a 15mm axle to fit the spacing and offset your project requires. On the other hand, the loose ball versions usually came with super long axles to accommodate axle pegs, so you can add spacers to fit non-BMX frames. They can be retrofitted with 14mm axles that are flatted to fit in 10mm axle slots, or machined to accomplish the same thing.

 

[Hummina Shadeeba]

wow you sound like a rare person who knows about these hubs.

i have the profile dual drive hub i linked earlier and it's got a 3/8" axle but these days it's so hard to find a 3/8" dropout frame and while i remember profile selling an adapter do you think i could replace the axle with a 14mm? probably will have to ask them.

im guessing its not possible to just get an extra driver or freehub or whatever theyre calling it and add it to the other side and switch the ratchets on some other bmx 14mm axle hub right?

what you think is my best bet at getting a dual drive on a 14mm axle hub? other than the simple adapter. i dont like adapters psychologically!

or if you know of a 26" wheel single speed frame with rim brakes and 3/8" dropouts that'd be another solution. (my 24" bmx bike i was planning to use is too narrow between the chain and seat stays to get my pulley and belt through for the middrive im making.)

wrote to see if these are still available:
https://bmxmuseum.com/forsale/244211

 

[Hummina Shadeeba]

maybe this can notify you by quoting you. on the hunt.

what you think of finding someone with a lathe to just cut threads on a one sided hub and screw on a left hand freewheel?

maybe get this bike and get the hub lathed?
https://jrbicycles.com/products/subrosa-2021-malum-dtt-26-bmx-freestyle-bike-matte-raw?_pos=3&_sid=3e59bad85&_ss=r

 

[Balmorhea]

https://www.amazon.com/Black-Ops-14mm-Adapters-Pair/dp/B07BYFRGQD

These are 3/8"-26 on the inside, like most 3/8" axles. Coaster brake hubs and older American BMX axles tend to be 3/8"-24. Profile might use 3/8"-24, but I don't know that for a fact.

 

[Balmorhea]

maybe get this bike and get the hub lathed?
https://jrbicycles.com/products/subrosa-2021-malum-dtt-26-bmx-freestyle-bike-matte-raw?_pos=3&_sid=3e59bad85&_ss=r

I would have tried it during my days as a machinist, but it never came to that.

If the axle bearing is the same on both sides, it's plausible to add a LH freewheel thread to the left side. Some BMX hubs have a bigger bearing on the left, just because they can.

 

[Hummina Shadeeba]

[*]Bought this:
https://www.bikebling.com/Subrosa-Salvador-26-Bike-Matte-Translucent-Teal-p/subrosa21-540-12221.htm

So hard to find a 26” bmx these days

And will hopefully convert my bi-drive hub to 14mm so ultimately can fit a pulley and belt through this wider rear triangle of a 26” wheel bike.


Just an idea but since you sound mechanical and bike smart:
With these big bottom bracket shells how possible would it be to put chainrings on both sides and make Bi-drive w freewheel in the bottom bracket essentially. So chainrings not fixed to the cranks and would only engage when pedaled. The goal bring use the bb shell to support the jack shaft and simplify.

 

[Hummina Shadeeba]

https://www.amazon.com/Black-Ops-14mm-Adapters-Pair/dp/B07BYFRGQD

These are 3/8"-26 on the inside, like most 3/8" axles. Coaster brake hubs and older American BMX axles tend to be 3/8"-24. Profile might use 3/8"-24, but I don't know that for a fact.

I’ll look into that and call Monday and see if can convert with that

 

[Balmorhea]

With these big bottom bracket shells how possible would it be to put chainrings on both sides and make Bi-drive w freewheel in the bottom bracket essentially. So chainrings not fixed to the cranks and would only engage when pedaled. The goal bring use the bb shell to support the jack shaft and simplify.

Have a look at Torrington needle roller clutches. I don't think it's necessarily a great idea, but if I wanted to put freewheeling chainrings on an American BB shell, that's what I'd look at first. It would mean making some high precision, high finish quality, hardened steel parts to go with the clutches.

It's probably easier and safer to put the freewheels at the rear axle.