Manual clutch equivalent of a std centrifugal?

Discussion in 'Spare Parts, Tools & Product Developement' started by svejkovat, May 18, 2009.

  1. svejkovat

    svejkovat New Member

    I did try googling this for a while. Maybe I'm not wording it right. I'm guessing that it must exist. The fairly ubiquitous little centrifugal clutches for minibikes and karts, the things that just slide right onto the engine shaft.... is there a manual equivalent? I'm picturing something similar looking, with sproket, except that it has an arm leading off of it, similar to that on a coaster brake, to bolt stationary, and a cable leading to a handlever.

  2. HI,

    I've wondered about that too and I have actually searched quite a bit for a manual conversion like you are thinking about BUT I had no luck in finding one....I think it would be
    difficult to make...

    I think a crude way to make a "manual clutch" would be to use a belt and pulley system and a manually activated idler to apply tension to the belt to "engage" the system...

    The other way I thought would be to use an electric clutch like those found on zero turn lawn mowers BUT those are more or less on/off plus belt not chain....

    Maybe somebody else had better luck researching this?

  3. svejkovat

    svejkovat New Member

    I spent another couple of hours searching last night and found nothing. The fact that nothing like it exists on some very complete parts vendor's sites for all things minibike and gokart makes me wonder if, like you suggested, it might be too complicated to build to compete with the centrifugal clutch (at least for minibikes and gokarts). Centrifugal clutches can be pretty darn sophisticated, with a range of rpm curves and lockup rates, they fit the bill nicely enough for even the most technical racers. For these single ratio transmissions a manual clutch probably wouldn't offer the rider/driver any real advantage since the power curves of the motors/transmissions are pretty calculable and constant.

    But for motorized bicycles it would be fantastic. I'm looking at that shift kit from sickbikeparts and dreaming of putting a little manual clutch if one were available as I described on the right hand side of that jackshaft. As such, you could dispense entirely with the centrifugal clutch at the motor, and as a bonus, the entire motor drivetrain would be isolated while pedaling with the motor off.

    I don't know.. two sections of a clutch locked separately to a shaft with an idling sproket between them. One of the plates is fixed via arm to motor or mount, and within is a round pressure plate that is driven into the idler (both having thrust bearings) via coarse threading or multiple ramps around the plate. When a plate is rotated with the cable, it is pushed away from the other plate into the idling sproket/clutch face. Easy enough to imagine. Kind of suprising that it doesn't exist in some fashion out there.

    Heck, the blade disengagement clutch under my honda push mower is extremely close to what I've described, but about 2/3 overscale and overweight to put on a little trimmer motor. It engages and disengages with a manual cable (unlike 99percent of the riding mower blade clutches out there that are 12vdc). So I know the concept is valid. I have a hunch that it exists on some product out there. I just can't picture the application. Economies of scale can be a real boon to experimenters, if you know where to look. When something already exists as an automotive part or home durable goods part it's going to cost 1/100th of the price of something needing to be custom built. Often, it's just a matter of figuring out where that part is already in use.
    Last edited: May 19, 2009
  4. srdavo

    srdavo Active Member

  5. svejkovat

    svejkovat New Member

    I really don't understand why he would use the idler pulley arrangement when a centrifugal would have been much nicer for is needs. Guess it looks a little more 'harley' like. The idler pulley clutch dates back to steam engine hay thresher days, and probably even back to DaVinci's time.

    It would really be an eyesore for what I have in mind, would still induce too much drag on the pedals when "loosened" This is more what I had in mind...
    Versions in single and multiple discs, three to sixty lbs unit weight. Perfect. But unfortunately the application is so rare (inexplicably) that these cost many many hundreds of dollars.

    I'll have to keep looking.

    Attached Files:

    Last edited: May 19, 2009
  6. svejkovat

    svejkovat New Member

    Ok, the salesguy told me the version that I asked about is over 2000USD.
    I've pretty well exhaused all leads now. An affordable version does not exist on this planet. The picture above, all but a sprocket in place of the pulley, is uncannily like the image I constructed in my head late last night when I was putting this thing together. The cutaway describes something that is waaaaaaay beyond my shop skill. I am determined however to arrive at a xmission that will allow pedaling and motor drivetrain to be (almost) completely independant upstream of the crank. Without this manual clutch, that means having to have a freewheel on the jackshaft and a centrifugal clutch on the engine shaft,, which, for std four cycles, means pull starting.

    Anybody have any other ideas for starting using this arrangement? Pull cords just seem like such a defeat. A motorized bike is already almost pegging the dork-meter even without having to pull start the **** thing.
  7. Junster

    Junster Member

    Try looking up Jabsco marine pumps. They use a manual clutch very similar to a electric auto AC clutch.
  8. svejkovat

    svejkovat New Member

    A jabso pump is generally fractional hp and not positive displacement (they're centrifugal pump rotors). Any clutch that is driving one of these rotors is going to be very very light duty.
  9. Junster

    Junster Member

    All the Jabsco pumps I used in Alsaka were rubber impeller pumps run as auxillery pumps on large diesel engines with 2" output and could put out serious (read FIREHOSE) water volume and pressure. They were available with electric or manual clutches and I never had any problems with any of the manual clutches on them.
  10. svejkovat

    svejkovat New Member

    Sorry about that. I never realized that they made larger pumps. I've only ever seen their small series for home and watercraft stuff. I'll have to give it a look.
  11. Junster

    Junster Member

    No biggie I still have no idea if the clutch would be adaptable anyway. Plus after thinking about it a 2" Jabsco goes for about $320 retail. The separate clutch parts would probably be cost prohibitive anyway. I've only changed the impellers. Never had one of the clutches apart.
  12. HseLoMein

    HseLoMein Member

    I just feather (very slow release) the clutch while revving high, it acts just like a centrifigual clutch and i can take off from standstill
  13. svejkovat

    svejkovat New Member

    Here's another.


    Models available down to 1hp input in torque ranges we're talking about. Spec sheet lists ratings @100rpm, well within where I need to be at the output of a gearbox. Probably waaaay too expensive once again for this project (i don't know yet) but at least my search is getting warmer.

    Driven discs are separated by wave/spring washers and drag induced while idling /disengaged is "negligible" according to the product description. Whether negligible in an industrial setting, or from a bicycle rider's experience may be a reckoning point.

    So.. Can someone please disabuse me of the concept generally?

    A motor, connected to the crankset via three reductions. 1st is timing belt to compact gearbox. 2nd is the gearbox itself (prob a compact planetary from this site... 3rd is chain from gearbox to inner chainring on the White industries heavy duty crankset freewheel from Sickbikeparts. Outer chainring drives rear derailleur. Motor is connected direct to gearbox with no centrifugal clutch. A hand operated clutch similar to the one shown above is on the output shaft of the gearbox (notes on the clutch website indicate that it will accept a sprocket directly.

    This is the only way that I can imagine, without a sloppy carriage of v-belts and idler pulleys, to fit all three needs..
    ..ability to start the engine while pedaling (via the hand clutch)
    ..ability to engage/disengage the motor and transmission either while pedaling with motor off, or when stopping/idling.
    ..overrunning isolation of the pedals from the motor and motor xmission and vise-versa. Motor never actually runs the bicycle crank, only the freewheel attached to it. Pedals cannot overrun the motor in this setup, but that's not likely to be a problem (i think).
    ..pedals are not spinning the motor xmission while the motor is off.

    What's not to like?
    Last edited: May 25, 2009