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RPC with Centrifugal Clutch on Pony Motor

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  • #16
    Originally posted by Tundra Twin Track View Post
    I will try to explain the Back-Driving I’ve experienced many times on Snowmobiles in the Mountains.When dropping off very steep slopes 50-85 deg. the Belt will grab the disengaged Primary Clutch and over rev the Engine,only way to stop that is hit the Brakes or Hit the throttle on a already over reving engine.I know it sounds impossible but have experienced many times in last 36 years.
    Thank you, I was wondering WTF that was all about with "primary clutch" and "Back driving". All of my experience with centrifugal clutches have only the one clutch, and back driving is impossible. Said applications are on chain saws, go-karts and mini-bikes. And the occasional snow blower.

    On those machines, the only way to engage the drum is to spin the hub at a fast enough RPM. Once the hub RPM drops, it disengages.
    25 miles north of Buffalo NY, USA

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    • #17
      Nice job! Never thought about using a centrifugal clutch on an RPC. I did build one with a recoil start from an old Briggs engine that worked well.
      I just need one more tool,just one!

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      • #18
        Originally posted by Tundra Twin Track View Post
        This Pony Motor only runs for 2 seconds and doesn’t even get Idler up to 1740 rpm,Bump start it could be called.
        thats exactly what it is, bump starting the engine.

        On the Example I talked about was a four cylinder engine reving up to what sounds like demolition to crank an Old Diesel engine up.

        Think about old tech were electric starter motors just were not up to the need, or if your batteirs were dead. Four banger getting all raspy then Bang!, Throw the clutch on the Cat Engine, out of gear and hope she lights. M

        Might take a few go arounds then the Big Diesel is lit. Four bnger was just a big starter engine.

        Bump Start/// JR.

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        • #19
          Originally posted by wierdscience View Post
          ... RPC. I did build one with a recoil start from an old Briggs engine that worked well.
          Clever - I like it!

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          • #20
            Originally posted by nickel-city-fab View Post

            Thank you, I was wondering WTF that was all about with "primary clutch" and "Back driving". All of my experience with centrifugal clutches have only the one clutch, and back driving is impossible. Said applications are on chain saws, go-karts and mini-bikes. And the occasional snow blower.

            On those machines, the only way to engage the drum is to spin the hub at a fast enough RPM. Once the hub RPM drops, it disengages.
            Hmm. Not sure this is true. Seems to me that a centrifugal clutch will remain engaged as long as the rpm is high regardless of input versus output direction. I think back driving is possible.

            As soon as rpm drops or there is some slippage in a back driven scenario the clutch will release. High rpm and no slippage it will remain engaged.

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            • #21
              Originally posted by strokersix View Post

              Hmm. Not sure this is true. Seems to me that a centrifugal clutch will remain engaged as long as the rpm is high regardless of input versus output direction. I think back driving is possible.

              As soon as rpm drops or there is some slippage in a back driven scenario the clutch will release. High rpm and no slippage it will remain engaged.
              Never seen it happen that way, though. Think "chain saw clutch" after you cut the throttle the chain is still moving but the drum is disconnected. It's just coasting down. After all, there's nothing connecting the drum solidly with the hub. So if you spin the drum up to 3600 RPM the hub will just sit there, the shoes are not connected to the drum they are connected to the hub and held back with a spring.

              If you spin the hub up to 3600 RPM then obviously the clutch will grab like its supposed to. Cut the RPMs below the set point and it lets go. And in this case he has the pony motor on the hub, so when the pony motor RPM drops, it lets go.
              25 miles north of Buffalo NY, USA

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              • #22
                Originally posted by nickel-city-fab View Post
                when the pony motor RPM drops, it lets go.
                Exactly. But the pony rpm won't drop until the clutch lets go...

                You said "impossible". I think it can happen if the speeds are well above clutch engagement speed.

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                • #23
                  Originally posted by nickel-city-fab View Post

                  ... Think "chain saw clutch" after you cut the throttle the chain is still moving but the drum is disconnected. It's just coasting down. ...
                  "Coasting" yeah, but with considerable drag. The momentum of the chain is not enough to keep it coasting very long. Even unconnected to the clutch, the chain will not coast very much at all. Unlike a snow mobile going down a slope where its velocity keeps the clutch & engine rpm high & keeps the clutch engaged.

                  Here's an "easy" experiment: connect a clutch (chain saw or similar) to 2 shafts (input & output). Have a motor connected to each shaft. Turn on the input motor to engage the clutch. Then turn on the output motor & turn off the input one. The clutch will either disengage or not & finalize this discussion. We await your report on the results 😀


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