3-Speed motorized bike experiment

dont give up my brothers it is not all hard things break find a new and better way to fix it i do my projects but if something goes wrong i dont get angry i just think about it look at parts i can use and try to perfect it and eventually it goes right i too am starting on a 7 speed pocket bike engine powered mens racer bike will use pocket bike sprockets on the left side and normal bike stuff on the right like derailers.sprockets,chains,shifters cables......etc i will have a 6t on the motor standard pocket bike sprocket tht is 54 on the hub and on the other side i will have the same diameter but in bicycle size to drive from the jackshaft to the wheels hub it will not have pedals tht function as it is pull start centrifugal clutch im starting work on it tommorrow will postup when done

Blaze said:

No pop starting this bike. It will have a rope pull-start to get it started.

I thought about using a multi-speed hub for the transmission, but I remembered reading somewhere that the torque from the motor would turn it to shrapnel. I know you could probably just let off the gas to shift, but if I'm going to build it, I'm going to build it idiot-proof. That means being capable of shifting under at least some power. The 3-speed hub idea is a great idea, though. Definitely let me know if you build it.

Click to expand...

I realize I'm a bit late sounding in on this but I have some relavant info...
I'm using a 49cc chinese motor with a jackshaft and 7 speed internal shift rear hub. When under motor power, or even just sufficient pedal power - the internal hub will not shift.
Positive drive line torque must be released for the prawls inside the hub to shift to the next gear...even down shifting.

I'm not trying to say there's no risk of the hub grenading, only that if you ride like you drive a manual shif car that you don't want to fix daily, it will last you a good long time.

I've put 700 miles on my bike in '14. Motor is still going but the hub is getting a hiatus. The fork broke and my internal hub (still in working order) doesn't fit my new bike :-(



Which brings me to my question:
My new bike is a flip flop fix. I've heard they make a 3 speed free wheel for it but I'm having trouble locating a retail source.
Another issue I realized is locating a 3 speed shifter compatible with a rear derailer. The cable pull distances are all set for 3 speed hubs and triple chainrings.

Any ideas on where I can source the parts?

Really it's a good idea.
I have been thinking about using a two or three speed hub as a transmission. My idea is to use it as a gearbox mounted directly behind the motor.

www.heliobikes.com

I've see a few posts on using an internally geared hub as a transmission. But seeing how my Nexus7 works, I can't wrap my head around how using it as a transmission would work. I also don't see the space for it on my current bike.
I'm not trying to say it won't work, its just not for me right now also taking budget in mind.
Until I replace my front freewheel, I'm stuck with direct drive :-( but having to remove/bypass the jackshaft has shown me I will deffinately need a chain tensioner for the chain to clear the seatstay. The two washers I added to the left side of the axel (between the locknut and the dropout) will do little for clearing the seat stay when the cog the chain runs to is moved 2" to the left. I currently have the chain cut so tension is maintained by pulling the wheel back like a BMX bike.
Which poses another obstacle... the motor pulls from the top run of the chain. Will the seatstay hold up under the strain of holding the chain down while the motor is trying to pull it straight :-\
I can only guess right now that I'll have to forgo the tensioner and use a sprocket tooth number small enough to give me the chain to seatstay clearance I need.

UPDATE:

As you can see in my last post, I've swapped the single speed FW for a three speed FW.
I've racked what little brain I have trying to find a JS mountable FW for my bump start with gears idea. So far all I found was a JS kit on the staton.com site for $75.
While my 2stroke shift kit is stalled waiting for parts (my last front FW jammed). I poked around for an electric kit for my next build...
Found my self @sickbikeparts.com and they carry a FW adaptor that mounts to a JS for $16.95 http://www.sickbikeparts.com/catalog/product_info.php?cPath=23&products_id=113
I can reuse the SS FW I pulled off the hub on the adaptor (blonde moment).





Another delay I'm facing is waiting for the three speed shift lever I ordered. Its been two weeks and the tracking number stil shows "being prepared" :O
For now the rear D is set to 3rd gear as that is as far as the stop screw will go. And I only have use of high low on the pedl crank until the other lever arrives.

While I'm waiting...I'm trying to figure out how many rules I can break with the electric kit... like side mounting the motor and using it with a shift kit ;-)
But being electric, that may be for another forum...

The only question I've yet to figure out the answer to is the gear ratio/tooth number combination I need on the left sprocket and FW on the JS to keep the two sides of the drive line from chewing each other up...
I know I'll be able to start the motor with the left sprocket and the cog on the FW.
Once the motor is running, the RPM's needed for first gear on the right side will spin the motor up, making the FW on the JS act like a centrifigul clutch in reverse...high RPM will cause it to disengage, so to speak...
But the actual speed will eventually spin up the FW on the JS and possibly cause the two drive lines to jam :-(
As I don't see my self needing to go faster than 40mph, I just need to figure out what tooth numbers to install on the left side of the back wheel to be compatable with the 18T FW I have for thee JS...

I haven't given up my bump start with gears idea, but I have shelved it til I can figure out the gear ratios and speed limitations the dual drive line will cause...

I did however find a less expensive option for the JS mountable FW than statons JS kit ($75).
SBP has a FW adaptor that mounts to a 5/16" shaft for about $17+shipping. The FW can be grabbed from ebay for $10-$20 and screws on the same as it would to a hub. I just happened to salvage the one I snatched from my flip flop fix when I installed the 3 speed FW ;-)

local partsu

what about RPM? if the gears are from the bike, arent they smaller? wont it make the engine "scream" cause of the higher RPM?