dual freewheel front sprocket system

Discussion in 'Electric Bicycles' started by jdcburg, Feb 16, 2010.

  1. jdcburg

    jdcburg New Member

    Hi folks - I'm new here but I recognize some names from other MB forums. For those of you who haven't heard from me before, I've designed a dual freewheel front sprocket system that allows two sprockets on the BB spindle to be linked together by a freewheel. In this way, the motor-driven sprocket can remain stationary while the bike is powered by the cranks and the cranks can remain stationary when the motor is powering the bike, so both motor and cranks can power the bike independently or simultaneously. This reduces drag to a minimum. The rear derailleur and cassette are utilized so the motor and cranks effectively have 8 speeds (ala Cyclone/Eclipse/Elation/SickBikeParts). You can see an early prototype at
    http://www.youtube.com/watch?v=uPVs_g9xseE I have since road-tested it and it runs out pretty well. If people are interested I can elaborate - jd
     

  2. srdavo

    srdavo Active Member

    Yes..... please do.
    range?
    speed?
    volts? (battery type)
    weight?

    I don't want much....:grin5:
     
  3. jdcburg

    jdcburg New Member

    OK sr here are some more details. The motor is a 24V 350W Unite MY1016Z3, which has a built-in 9.78:1 gear reduction. Right now I am using 2 12V 12ah SLAs. Using the Bicycle Analyzer at http://www.arachnoid.com/bike/ a cadence of 80 with a 44T front sprocket and 11T rear will be 24.8 mph. I haven't checked the range with this bike but the same motor/batteries on my previous bike (3 speed front wheel drive) easily went 15 miles with moderate pedal assist. I don't know the additional weight but it's probably around 20 lbs for motor & batts. I haven't done much testing because it's still too cold and snowy here. In answer to your question on the other forum, I momentarily back off the throttle for shifting. It's pretty smooth. I can keep pedaling or not. The only issue so far is the upright chain alignment post is not quite rigid enough. Under hard acceleration at low speed in 1st gear the chain has jumped the front sprocket.

    Keep firing the questions. I'll answer them the best I can - jd
     
  4. dearthvader03

    dearthvader03 New Member

    Crank/freewheel question

    Jd,

    I'm building a custom recumbent that will be utilizing a setup similar to yours. I've seen the freewheel cranks that SBP sells but I don't believe both sprockets will freewheel like yours. Can you give me an idea of how you designed that systems so that both sprockets wheel freewheel? I would like to be able to pedal the bike without spinning the chain that goes to the motor.

    Thanks,

    Josh
     
  5. jdcburg

    jdcburg New Member

    Hi Josh - I got most of the parts from SBP but you are correct - their system doesn't allow the motor-driven sprocket on the BB spindle to remain stationary. It turns with the crank sprocket. If you don't want the motor to turn with the SBP system (or Cyclone, Elation, Eclipse) you need to put a freewheel on the motor-drive sprocket but the motor chain still moves whenever you pedal. I wanted to avoid that in order to reduce drag to a minimum, and also to be able to use smaller motor-drive and -driven sprockets (9T and 36T).

    The design requires the pedal sprocket to be to be the final drive sprocket, driving the chain that goes back to the rear cassette and derailleur. This sprocket must be the outside one (closest to the right crank). Both freewheels work independently to engage that sprocket - the crank from the right side and the motor-driven sprocket from the left side. The motor sprocket freewheel is an ACS Southpaw BMX sprocket with 1.37" x 24 tpi LH threads. I had an adapter fabricated consisting of a flange welded to a right BB cup. The right BB cup has LH threads to match the Southpaw. The adapter flange has the 5 hole SBP sprocket bolt pattern. The adapter is bolted to the midline side of the 44T crank sprocket and the crank freewheel is bolted to the outside of that sprocket using the same bolts. I enlarged the center hole of the SBP 36T sprocket slightly and bolted it to the Southpaw sprocket. When engaged, the Southpaw freewheel tightens onto the adapter, so no thread dope is needed. I got the sprockets, flanged freewheel and cranks from SBP and the 159 mm BB spindle from Cyclone. The Southpaw is widely available. I had a few other parts fabricated: some spacers and a backing ring for bolting the 36T to the Southpaw. SBP has sprockets available from 24T to 48T, but I figured the 36T motor and 44T pedal were about right. The 8-speed rear cassette on the mtb is 11-33.

    I can put up some images if it would help - jd
     
    Last edited by a moderator: Dec 15, 2015
  6. dearthvader03

    dearthvader03 New Member

    Crank/freewheel

    Jd,

    I certainly appreciate your lengthy reply. Generally speaking I understand what you did but some photos to back it up would be really helpful. I want this bike to be efficient so I don't want to turn the motor chain if I don't have to.

    I look forward to some pics.

    Thanks,

    Josh
     
  7. jdcburg

    jdcburg New Member

    OK Josh. Here are a few pix. 01a is the crank/freewheel/spacer/sprocket assembly. The flanged adapter is bolted through on the backside of this and is shown in 02a. 04a shows the crank sprocket assembly edge-on. The main chain to the rear wheel goes on this assembly. 05a shows the Southpaw freewheel sprocket and the 36T ready for assembly and 06a shows them bolted together with the backing ring. The Southpaw is 16T so I had to redrill the 36T to a 4-bolt pattern. The motor chain drives the 36T sprocket. The Southpaw/36T assembly was then threaded onto the adapter on the 44T. 11a and 12a show the entire assembly threaded together - jd
     

    Attached Files:

  8. dearthvader03

    dearthvader03 New Member

    Jd,

    Thanks so much for the info. After reading your post and looking at the photos several times I finally figured it out.

    There's only one more question: Where did you get the male threads (the ones the southpaw sprocket screws onto) that are welded to the flange? Are they pretty common?

    I have a welder so I should have no problem making a flange that will work, I just need to know where to get the threads.

    Josh
     
  9. jdcburg

    jdcburg New Member

    Josh - I used a right side BB cup, the kind that holds the bearings in a non-cartridge cup-bearing-spindle bottom bracket. After you get the Southpaw, take it to your LBS. They probably have a bunch of used cups on hand. The right hand ones have LH threads, but apparently there are 2 styles so you might have to try a few to find one that threads in correctly. The nice thing about these is the center hole is large enough for the BB spindle. But be very careful welding it on - if it's not perfectly square to the flange as well as perfectly centered, there will be excessive runout causing wobble in the Southpaw and the sprocket that attaches to it. If you have access to a threading machine and the right die, you might want to weld a blank nipple onto the flange and thread it afterward - jd
     
  10. dearthvader03

    dearthvader03 New Member

    Thanks so much for the info, jdcburg. I'll definitely be putting it to good use and I'll attach a pic when complete.

    Josh
     
  11. GearNut

    GearNut Active Member

    Thank you jdcburg!
    What you have made is exactly what I have been contemplating recently. I have worked it out in my head, but you have made it, and shown exactly what is needed and where to get the necessary parts. You are awesome!
    Again, I thank you.
     
  12. jdcburg

    jdcburg New Member

    Thank you Josh and GN. I look forward to seeing the images of your builds as they progress and also to hearing about various problems and the work-arounds you develop for them. We just got another coating of the white stuff and more is predicted for the weekend but riding season is coming and I'll be doing more testing and tweaking. One issue with this system is chain alignment - the motor sprocket freewheel pushes everything to the right. As you saw in the video I put an upright post near where the drive chain goes onto the front sprocket. I have since put a roller on that to reduce noise and friction but the post "gives" a little on hard acceleration in 1st gear and the chain has jumped the sprocket a few times. It's not a problem in the higher gears. I have to attach the post more securely or make it more rigid but the determining best fix is going to require road testing. - jd

    ps - Jim at SBP (Ghost0 here) is a great resource for questions regarding their parts and fitting things, etc
     
    Last edited: Feb 26, 2010
  13. GearNut

    GearNut Active Member

    It will be a while 'till I post anything about a new build of mine.
    I plan on doing a Q-Matic with a jackshaft setup. That will take $$$, and I received notice yesterday that the shop I work at will be closing it's doors forever next week.
    I am contracted, so to collect on un-employment I would have to pay myself.
     
  14. roofman6

    roofman6 New Member

    Thanks

    JD,

    Thanks for posting and explaining your bottom bracket free wheel. I've been thinking about motorizing a recumbent, and like the underseat engine design with chain drive to the bottom bracket. You've sure cleared up a lot of my questions.
    Thanks again,
    roofman6
     
Loading...