Jackshaft Dual side freewheel crank?? No jackshaft needed!

Discussion in 'Transmission / Drivetrain' started by mbatl, Feb 12, 2012.

  1. mbatl

    mbatl Member

    Is it possible to construct, if it's not already available, a freewheel crank that will allow me to attach a sprocket on the left side? This will eliminate the need for a jackshaft, which limits the type of bike it can be installed on. Im not using a standard v frame bike and I've already figured out how to mount my rs35 engine, I just need the freewheel to transfer power without a jackshaft. I don't like the complexity of a jackshaft.

    My plan is transfer power from my robin 35 to the left crank sprocket then to the right sprocket which will allow me the shift gears. A splendid idea I believe!

  2. 5-7HEAVEN

    5-7HEAVEN Member

    It is common to transfer engine power thru theright side gears.....but not like how you think. Power chained to the left-side will not be transferred to the right side and somehow thru the gears. Power needs to be sent to the bike chainring. THEN power will be sent to the rear gears.

    Please do research here. The matter has been covered many times.
  3. mbatl

    mbatl Member

    I did research it, just under the wrong keywords. Anyway, this idea was to allow the common dual suspension frame bikes a way to be motorized through it's gear system since space is often limited for a jackshaft on dual suspension bikes.
    Last edited: Feb 12, 2012
  4. HeadSmess

    HeadSmess Well-Known Member

    freewheel the engine sprocket.

    large chainring on the left hand side.

    drive is transfeered straight through crank and out on right hand side.

    then drive rear wheels.

    2 right hand cranks(need to buy two RH pedals) and/or a LH crank from a tandem.

    something about having to pedal when under power turns me off these systems.
  5. mbatl

    mbatl Member

    :bowdown: Now we're making progress!! Excellent idea, thanks alot. I can actually use my current freewheel crank from my ht bike with your suggestion. Thanks for the useful info.
  6. 5-7HEAVEN

    5-7HEAVEN Member

    Sorry, I think I misunderstood you.

    So you want to use the bottom bracket as a jackshaft, and install a left-side engine chainring sprocket. Then the right side bicycle chainring connects to the rear sprocket(s) on the right side.

  7. mbatl

    mbatl Member

    Can you explain a little more about needing 2 right hand cranks. Is that to allow the pedals to still operate as usual? I may have been over excited I'm my first response and not understood completely.

    Overall, I defiantly still want the pedals to operate normally, which may be the biggest problem.

    5-7 I wonder if found someone to re-thread a right side freewheel so it will fit the left crank if that would work?
  8. HeadSmess

    HeadSmess Well-Known Member

    its so you have something to mount the chainring to...

    mounting sprockets to standard left hand cranks... with out a machine shop, give up :)

    tandems conveniently have a chainring on both sides at the rear BB ;)

    you can get "southpaw" freewheels. but if its on the INSIDE of the LH crank you would want a standard freewheel.

    you also need a lot of teeth. 50+ on the chainring.

    aim for at least 12:1 reduction BEFORE the cranks...
    Last edited: Feb 12, 2012
  9. mbatl

    mbatl Member

    Ok, I understand now that the right crank has the proper sprocket mounting hardware. The reduction is already solved with the engine mounting that will allow a conservatively geared sprocket for the left side crank without having a large engine gear.
  10. 5-7HEAVEN

    5-7HEAVEN Member

    You need 2 right hand cranks because the rh one has the threads to mount the freewheels. The left one does not. It simply slips onto the square shaft.

    They make cheap, low-quality left-side Chinese pocket bike freewheels. Unsure if there's high-quality White Industries left freewheels. Then you'd have to machine the right arm to accept left-hand threads.

    Once, I installed my right-side freewheel backwards on the crank arm. Then it acted like a left-hand freewheel. It is EXTREMELY difficult to remove the freewheel from the crank arm. Locktite and pinning the freewheel to the arm would lock it in good to work on the left side. The engine would always be trying to loosen/unthread the freewheel, so you need to prevent that.

    The left-side crank MIGHT have to be extended further out. Also unsure if the engine and chainring sprockets would line up.

    Also unsure if the chain would run from engine to chainring, even with the cover removed.

    If everything aligns, then a 10-tooth engine sprocket and 48t chainring would be 4.8:1 x 4.1 engine = 19.68. A standard shift kit has gearing of (4.1 x 1.7) x (44t/10t) = 30.67:1, BEFORE connecting to the rear cassette. By the time it got to the 32t 1st gear on an 8-speed cassette, the weakest combination of a 30t chainring and a 32 1st gear would be 29.44:1.

    If you could fit a 9t on your engine and use a 52t on the left chainring, that's be 23.68:1.
    Then with a 24t right-side bicycle chainring and a 34t 1st gear on the rear cassette, you'd be okay with 33.56:1. Using a 22t chainring would give you 36.61:1 gearing.

    Eighth gear would be 11.84:1, comparable to a 29-tooth rear wheel single sprocket on a Happy Time install.

    It is always advisable to gear your bike as low as possible. In doing so, you get a granny gear for very steep hills. You also get to use 7th or 8th gear as a highway cruising gear. I use a Tanaka engine with a shift kit. My 1st gear is 46.36:1, which I find VERY handy. My 8th gear is 15:1, which is also very usable.
    Last edited: Feb 13, 2012
  11. mbatl

    mbatl Member

    Thanks for sharing your experiences.

    Haven't replied because I'm researching to see if the freewheel concept is worth the effort compared to constructing a jackshaft somehow on a dual suspension frame.

    My sbp jackshaft may work with some modification in how it is secured to the frame since the ht motor wont be supporting it.

    *Just give ideas to others who it may help, my plan was to use the staton axle mount assembly and instead run a chain forward to the left freewheel transferring power to the right side dereailer. This would allow the use of my otherwise limited use robin 35cc that is very reliable. Sounds crazy?
    Last edited: Feb 14, 2012
  12. MotoMel

    MotoMel New Member

    If you are still interested in this solution, we've virtually finished the design on a crank system that operates as you describe. You can see it at BikeMotive.com or youtube.com/bikemotive. We are now scouting around for economic production. Would enjoy hearing from you.
  13. Neon

    Neon Member

    I know i'm going to regret asking this, but what would be the cost of the crank system as is ? If you haven't already i would get a patent on your design as quick as possible.
  14. thearcticfisherman

    thearcticfisherman New Member

    You need to think out side the box!!!!!!!!!!!!!!!! Grubee just needs to make a right side drive, clutch on the left. TA DAAAAAAAAA!!!!
  15. MotoMel

    MotoMel New Member

    Sorry I missed this a month ago. Cost in prototype quantities is around $2K. Ouch! Gotta get it down, gonna get it down! Patent is pending; investment into the engineering and 4 rounds of prototypes ran *well* into 5 figures. Real ouch!

  16. lowracer

    lowracer Member

    How about putting a 135mm offset fork (Surly Pugsley/Moonlander) onto a bike or stretch a 100mm fork using some threaded rod w/nuts to 135mm & install a rear wheel into the front fork. Then drive the largest cassette sprocket (32 or 34) from a front rack (or DAX/BMP channel) mounted engine using a 5:1 pocket bike transmission w/10 tooth sprocket & some fixed gear chain (Sram PC-1). Keep the rear for pedaling & the front for motoring. When you let up on the gas the front wheel will freewheel, the clutch disengage, for better fuel economy & less clutch pad heat & wear.
    I'm actually thinking about doing this since I got a 5:1 transmission recently (bonus w/engine purchase) & it seems to be a solid unit.
    Gort likes this.
  17. fasjake

    fasjake New Member

    Although it would eliminate the use of pedals... i had a brief thought in my head involving two right hand crank arms from a vintage cotter pin style 3 piece crankset. Cut the crank arms off, leaving you with just the chainring. Through those on right and left sides. Connect engine sprocket via chain to the left side, effectively powering the right side to be connected to the rear cassette. I want to try it..... does anyone see any problems with this im not thinking of?
  18. Steve Best

    Steve Best Active Member

    How about flipping the motor around and running it backwards? Just need to alter timing to do it.