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  • #31
    All the ones I've dealt with would disengage when the input falls below a certain RPM but none of them would back-drive. They were just a long spring wound around the circumference of a bunch of friction shoes. As I said earlier, it could work if a potential relay cuts out the pony motor when the main idler is up to speed. Clutch on the pony motor disengages when the pony motor RPM drops. Maybe use the wild leg of the RPC for the signal on the potential relay. That way you know they are generating before the pony gets cut out.
    25 miles north of Buffalo NY, USA

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    • #32
      The input RPM can't fall below the engagement RPM when the input is engaged to the output, and the output becomes the driver.
      DZER

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      • #33
        Originally posted by Doozer View Post
        The input RPM can't fall below the engagement RPM when the input is engaged to the output, and the output becomes the driver.
        None that I have dealt with would do that. All of them you could cut the throttle and the clutch would disengage immediately.

        Some of them are straight centrifugal with radial moving shoes and a garter spring, some have pivoted shoes. The pivoted will be pushed out of engagement if the load over-runs the drive. The radial garter spring type always disengaged also, but the disengagement was not as positive.

        None would back-drive.
        4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

        Keep eye on ball.
        Hashim Khan

        Everything not impossible is compulsory

        "There's no pleasing these serpents"......Lewis Carroll

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        • #34
          You are clueless. Read and understand what I wrote.
          DZER

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          • #35
            I believe Doozer is right. In my independent thinking before he joined the thread, I had come to the same solution.

            There are two things I think that would fix the issue
            1. Using say a 2400 RPM engagement clutch but setting the motor to oversync the phase converter. After the pony was shut off, the RPM at the clutch would be under it's engagement speed.
            2. Use a sprag bearing. I'm not 100% sure I'm thinking about it the right way, but I'm pretty sure a sprag bearing would allow it to freewheel. Soo... with the clutch I mentioned in post 19, and a 1750 RPM motor, it might work. I'm not sure how tight the engagement RPM on these motors are. By the time I got the clutch and sprag bearing, I'd be about $100 in. Not the end of the world, but it damn well better work by the time I drop that kind of cash. E: Nope, strike all that. The sprag bearing would engage immediately and prevent the clutch from doing it's job. Still may be useful if the motor has enough torque to start it.
            Someone mentioned lawnmower clutches, and that may work well. I'm not sure if I can get one any cheaper than a car clutch. That is actually where I got the idea though.
            21" Royersford Excelsior CamelBack Drillpress Restoration
            1943 Sidney 16x54 Lathe Restoration

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            • #36
              Originally posted by Doozer View Post
              You are clueless. Read and understand what I wrote.
              You ARE so polite, and explain yourself so well......

              WTF did you mean then? The "engagement" rpm would be the RPM that causes the drive portion to expand and engage the driven part. Above that RPM from the driving side, the parts are linked together. Sort of.

              But, that does not mean the drive side does not disengage. it just takes some friction on the drive side to work. I think you are over-estimating the amount of hysteresis in the system. The driven side cannot provide back drive against any tendency to slow down, as a rule it cannot backdrive any significant power in any I have seen. they are designed not to in the ones I have used. And they obviously were driven to an rpm above the engagement speed.

              The ones I have used were somewhat like a sprag clutch, when they engaged, the friction in the drive direction tightened them. Centrifugal force alone was not enough to produce the needed friction to drive the load. But if the drive power stopped, and there was any significant friction on the drive side, the torque through the clutch in reverse would release that "grab", and allow the drive side friction to slow the clutch to drop out. A belt drive might likely be enough.

              The easy way as I see it is to set up a belt drive so that the pony gets the idler "close enough to" synchronous speed, but not all the way there, and not "over". Then, when the idler gets power, it will accelerate, and "kick loose" the sprag type feature of the clutch. The belt friction should finish the job, because once it starts to slip, it will keep slipping when in "backdrive". It sure worked with the go-karts we built.

              You do not need the motor over synch, you only need it to 70-80% of synchronous speed, which is where the usual single phase start system cuts out. At that point the direction is established, and the motor is going fast enough that once the magnetic field is established, it will have enough back EMF to hold down the current draw. There will be enough accel left to kick the clutch loose.

              I have some around here somewhere, I can take a look at them if I happen to spot them.
              Last edited by J Tiers; 04-21-2021, 12:44 AM.
              4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

              Keep eye on ball.
              Hashim Khan

              Everything not impossible is compulsory

              "There's no pleasing these serpents"......Lewis Carroll

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              • #37
                Now that I think about it closer, you've got a point. The weighted clutch only springs out when inner pieces of the clutch is spun. Not the outer. So once the motor takes over, it may be able to idle back down with the added drag. Hmm. That $70 clutch may be the cat's pajamas.

                Thanks JT.
                21" Royersford Excelsior CamelBack Drillpress Restoration
                1943 Sidney 16x54 Lathe Restoration

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                • #38
                  Originally posted by The Metal Butcher View Post
                  Now that I think about it closer, you've got a point. The weighted clutch only springs out when inner pieces of the clutch is spun. Not the outer. So once the motor takes over, it may be able to idle back down with the added drag. Hmm. That $70 clutch may be the cat's pajamas.

                  Thanks JT.
                  Well,. that's exactly what I think would happen -- the shoes on the type with a garter spring do not stick to the friction surface (the outer shell) by themselves. The only reason they fly out radially and grab, is because the hub is being spun faster than the outer shell. What happens when the hub is no longer being spun faster? The shoes retract. As JTiers says, when you cut the throttle it disengages while the driven part keeps on going. So if you used the generated leg on a relay to cut power to the pony motor, with the clutch hub attached, suddenly the pony motor would be spinning slower than the driven motor -- and the clutch would be disengaged. Lord knows I've picked enough of those clutches out of dead snow blowers. https://www.gokartsupply.com/clutches.htm
                  Last edited by nickel-city-fab; 04-21-2021, 01:23 AM.
                  25 miles north of Buffalo NY, USA

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                  • #39
                    Good discussion (mostly) about clutches, but you really (probably) don't need one... For the few seconds once a day the rpc needs starting, it worked fine for me to just let the pony do it's job and leave it connected. Potential relays and generated legs are just trouble and buy nothing over a timer relay. In my circuit I showed earlier the part numbers I gave are "Grainger", but you can get the them way cheaper elsewhere.

                    Heck, I went down all these paths and was even looking at a tach circuit and mains incoming power phase sync to avoid the big glitch as the rpc rotor syncs with the incoming, but all way way overkill. One day I went... screw it, just bolt the two motors on a plank with two pulleys (I used Poly-vee) and see how well they work with starting from cold. The rpc built around that schematic has been working close to 10 years now.

                    Btw, you don't need to get the main motor fully up to "full speed". Think about it... even a rope pull works, so you can adjust your pully ratios for torque as needed. I went for 1:1 'cos that was what I had. 2:1 will be fine and not subject the pony to more then 3600 rpm Also, in any case full speed of the 1hp driving will not be that of the unloaded RPC motor, so they still have to adjust when power is applied to the rpc (In my case AFTER a short time delay to get the pony spinning up the rpc rotor).
                    Last edited by lakeside53; 04-21-2021, 08:37 PM.

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                    • #40
                      Originally posted by nickel-city-fab View Post

                      Well,. that's exactly what I think would happen -- the shoes on the type with a garter spring do not stick to the friction surface (the outer shell) by themselves. The only reason they fly out radially and grab, is because the hub is being spun faster than the outer shell. What happens when the hub is no longer being spun faster? The shoes retract. As JTiers says, when you cut the throttle it disengages while the driven part keeps on going. So if you used the generated leg on a relay to cut power to the pony motor, with the clutch hub attached, suddenly the pony motor would be spinning slower than the driven motor -- and the clutch would be disengaged. Lord knows I've picked enough of those clutches out of dead snow blowers. https://www.gokartsupply.com/clutches.htm
                      Once the centrifugal clutch is engaged, power flow is bi-directional.
                      The shoes will stay engaged until the RPC motor is shut down.

                      -D
                      DZER

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                      • #41
                        Originally posted by Doozer View Post

                        Once the centrifugal clutch is engaged, power flow is bi-directional.
                        The shoes will stay engaged until the RPC motor is shut down.

                        -D
                        And, the earth is flat, there are thousands of mole children under Central Park, etc. šŸ˜

                        Doozie, it's not that what you suggest is impossible in theory, it just does not happen with real clutches of the types under discussion

                        Do I need to show a picture of one?
                        4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                        Keep eye on ball.
                        Hashim Khan

                        Everything not impossible is compulsory

                        "There's no pleasing these serpents"......Lewis Carroll

                        Comment


                        • #42
                          I'm still down for the clutch idea. I'd be highly interested if someone would be willing to test one before I drop $75 on a new bearing model. That's a lot to ask, but if anyone was curious themselves....

                          At any rate, I'd appriciate it.
                          21" Royersford Excelsior CamelBack Drillpress Restoration
                          1943 Sidney 16x54 Lathe Restoration

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                          • #43
                            You're emoting.
                            When people emote,
                            they don't think clearly.
                            Get calm and
                            Imagine the power flow.

                            -D
                            DZER

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                            • #44
                              Originally posted by The Metal Butcher View Post
                              I'm still down for the clutch idea. I'd be highly interested if someone would be willing to test one before I drop $75 on a new bearing model. That's a lot to ask, but if anyone was curious themselves....

                              At any rate, I'd appriciate it.
                              Use a salvaged Chain saw clutch,machine the drum from a steel slug to fit your Idler shaft 1-5/8ā€ Iā€™m guessing.Take the flyweight hub and adapt to your pony motor two separate components,alignment will be critical.

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                              • #45
                                Silly Doozer. Changing the subject.

                                Think for a moment. You are going by theory, which is a valid approach, except that you have to get all the actions correct. Theoretically, if the speed were above the engagement speed, and it was a binary system, either "engaged" or "not engaged", it might drive in reverse. But it is "unstable".

                                There are a couple types of clutch.

                                One type "goes over center", in other words, it gets to a certain speed, then engages quickly. Ones where the shoe pivots like an old brake shoe, and is forced into the opposite surface by leverage. They are not so dependent on the speed to control the force once engaged, but are sensitive to power flow.

                                Then there are ones that work only by a spring and "centrifugal force". Those have friction that is dependent on rpm. They are not as "positive" engaging, and slip until at a higher speed. That makes them very dependent on the difference between engagement speed and ultimate speed. The reverse side is that any slowing reduces the friction and the chance for reverse drive.

                                The "brake shoe" type would potentially hold in, except that if there is force FROM the driven side, it breaks the force holding the shoe in contact, because that force is dependent on the opposite direction in which torque is applied. (same like the less effective "trailing" brake shoe). That force from the driven side would come when the idler gets power and accelerates up toward synchronous speed, while the pony loses power, and would require torque from the idler to speed it up against inertia. If there is some friction, like a belt drive, it should slow down OK. A lawnmower engine has plenty friction, and works fine.

                                The "speed dependent force" type COULD reverse drive, but again the friction and inertia of the unpowered pony, combined with the sudden increase of speed by the idler as it gets powered, should break it loose. Once the pony slows at all, friction in the clutch begins to drop off, and eventually it should be uncoupled if there is reasonable friction in the pony system.

                                Your real point (and mine) ought to be not that it is a slam dunk to work (or not), but that a proper system needs to be "designed". (we never did that, back then we were not aware of all the details, it just worked)

                                The clutch should have a torque capability vs speed curve. If you WANTED it to back drive, you might be able to find a combination that WILL do it, by choosing a clutch which has a suitable torque curve, considering the engagement speed, and ultimate speed, with the pony friction and available torque.

                                Conversely, there ought to be combinations that WILL NOT back drive in the system, because of the combination of engagement speed, ultimate speed, and torque curve vs friction from the drive side.

                                Once you look at all that, it starts looking good to just let it start, then lever up the pony so that it throws the belt. Or, even simpler, just let the pony spin with the idler.
                                Last edited by J Tiers; 04-21-2021, 10:20 PM.
                                4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                                Keep eye on ball.
                                Hashim Khan

                                Everything not impossible is compulsory

                                "There's no pleasing these serpents"......Lewis Carroll

                                Comment

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