freewheel sprocket for 11 mm (7/16") shaft

[jdcburg]

Hi folks - I've been working with Jim Welch at SickBikeParts to adapt their gas motor kit to a GT I-drive mtb that I intend to power with a 350W Unite 1016Z3. I've been looking for a freewheel sprocket or even just a freewheel for the output shaft of the Unite. It's a 11 mm (7/16") shaft with a 4x2 mm key. Jim suggested a BMX freewheel and machining an adapter but I'm wondering if anyone knows of anything off the shelf. I've checked the usual suspects - TNC, ElectricScooterParts, Monster and AllElectronics and I didn't see anything that would work. Thanks - jd

 

[Miles]

You can get adaptors for BMX freewheels. Matt (recumpence) had a batch made. Also, Staton sells them, I think. You'll need to make a bush, though.

 

[Miles]

Found the photo of Matt's adapter:
Ref: http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=7180&p=122253

 

[jdcburg]

Thanks for the info Miles. I've been thinking about this and you seem to have a lot of knowledge, so I'd like to run this past you. I'd like to put both the pedal crank sprocket and the motor-driven crank sprocket on freewheels. This is how I propose to do it, using a SickBikeParts crankset: I'll put the pedal sprocket on a freewheel adjacent to the right crank. Attached to that sprocket's backside (toward the bike's midline) would be a flanged male adapter threaded for a LH thread BMX freewheel 16t sprocket (readily available) that would be the motor-driven sprocket. I could bolt a larger sprocket to that if necessary, but I'm using a Unite 1016Z3 350w with built-in 9.8:1 reduction, so we're not talking a lot of power or rpms here. I'll have to have the flanged adapter fabricated, but even the other way I'd have to have a bushing fabricated, and the crank freewheel will save me having to pedal the motor chain. Using LH thread will have the BMX freewheel tightening onto the adapter on the pedal sprocket, which is of course the chain drive sprocket to the derailleur. I wonder if there will be room for the 2 freewheel/sprockets on SBP's 131.5 mm cartridge or if you see any other problems with this. I'm currently using this motor to power a front wheel drive through a 3-speed Sturmy-Archer hub with a 19 tooth sprocket and it works pretty well. Thanks for any advice - jd

 

[Miles]

jd,

I don't think there'd be the space with a symmetric 131mm BB axle. Cyclone sell a cartridge BB with a 153mm axle - it has a LH offset. You should be able to reverse this to give a RH offset, which will give you enough space. You end up with a rather high Q factor, though...

You will probably need to use a support bearing between the motor freewheel and the crankshaft.

You might want to take a look at the double freewheel crankset that Staton sell, too.

 

[jdcburg]

Thanks for the quick reply Miles. What is the Q Factor? - jd

 

[Miles]

Sorry! Width between the pedals

I found it! : http://www.staton-inc.com/Details.asp?ProductID=3427 Their site's a nightmare :x

 

[jdcburg]

Yep that's what I want to do. I think I can piece it together for less than $249 though. I'll continue to search for stuff. Thanks again for your help. I'll post as I make progress - jd

 

[Miles]

Yes, it's a bit pricey for the quality of the parts used.........

I worked out a compact design for this using two ENO freewheels, but it's more complicated to make.

 

[jdcburg]

Miles - that looks great. I assume those are welded tabs on the quadrant teeth and the teeth in between are ground off? I saw in a previous post you suggested a backing ring if someone left the teeth and bolted between them. Would that simplify it? What are the points of attachment to/between the freewheels, sprockets and cranks? That's not obvious to me and I want to understand how you are doing it. Thanks - jd