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  • I need a transmission idea

    I have a front cutter bar style walk behind mower. It is an Agria 4300. Great mower for rough grass and weeds.

    The drive mechanism is quite simple. A horizontal crankshaft motor with a double pulley. A belt drives the double pulley on the gearbox. One belt with a tensioning pulley is cable operated to put tension on the belt to drive the mower forward. For reverse the hand lever is squeezed which relaxes the tensioning pulley and pulls a hard rubber ring on another pulley against and into the second vee grove on the pulley on the crankshaft. On the pulley with the hard rubber ring is a belt that goes down to the second vee grove on the gearbox double vee pulley thereby reversing the direction on the gearbox and subsequently the mower goes in reverse.

    Beautifully simple. But the reverse is not very positive and I must pull the mower back most of the time. I would like to come up with a more positive drive for the mower. Either one with clutches or cones or.......??????

    The original drive is just ok for reverse and I need reverse alot. Space is not really a problem. It is a 5hp Briggs & Stratton engine.

    Clear as mud?
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

  • #2
    Here is a picture of what the current drive system consists of.
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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    • #3
      Hi, I assume the reverse used to work when the mower was new and my guess is the friction characteristics of the rubber surface have changed.

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      • #4
        I should be able to work it out, but you need to label the pulleys in your description.

        I have a mower with a much simpler drive. One speed, it pulls a tensioner to tighten the belt when you squeeze the handle. It's hopeless.

        But, I've never even bought a new belt for it. Have you tried new belts ?

        I do admit that my thoughts run along the lines of : it once worked with factory-specced belts, but it will never be as good again.

        If you really want a good job, you need permanently meshed spur gears, and the handles pull clutches back against spring pressure, or push clutches on. It just needs a little ingenuity. One way a wire pull can press a clutch on is to have it pull a lever, the lever attached to a spiral cam, which presses on a similar spiral cam to produce axial pressure, causing an output gear to be friction driven by an adjacent gear.

        You're into the big world of mechanisms. Could be fun, but it's only a mower.
        Richard - SW London, UK, EU.

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        • #5
          I have an old snow blower withthe SAME transmixer. If you dont have the belts adjusted EXACTLY as the little picture shows it wont back up. If you do it will spin the tires in reverse when you hit the car. Dont ask how I know that.

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          • #6
            I assume the crankshaft pulley is the one at the bottom and rotation is clockwise? If so, the one marked II is the friction drive for reversing and moves leftwards (with respect to the diagram) when reverse is selected.

            If you were to reposition II to be closer to the crankshaft (you would need a shorter belt) you could position it so that the driving forces caused II to more closely press against the rim of pulley I. If you moved it too far it would actually jam itself in reverse.

            So, my suggestion, replace the Bowden cable with a lever linkage that will both push it into reverse and positively push it out of reverse and move pulley II closer to the crankshaft. You would then get plenty of friction to get positive drive.

            IMHO of course!

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            • #7
              Its only a mower!!!! Who said that? Where do you live? THat is like the wife saying "it's only a junk of steel. Why are you getting so worked up?" London is not so far away from me. Be careful when you say it's only a mower!!!


              THe top pulley in the picture is the crankshaft pulley.
              Location: The Black Forest in Germany

              How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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              • #8
                Originally posted by Black Forest


                THe top pulley in the picture is the crankshaft pulley.
                Clockwise rotation? If so move that rubber pulley so that it moves, or tries to, under the crankshaft pulley. The way they designed it the hand cable has to provide the pressure that creates the friction, if you move that pulley down a bit the friction will increase the pressure which in turn will increase the friction, sort of like leading shoes on the brakes on your Trabant.

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                • #9
                  The crankshaft pulley turns counterclockwise I believe. And yes the hand lever cable is all that applies the force for the friction. There is a gas shock that pushes the idler wheel over onto the belt for forward travel. THe hand lever cable pulls the ider away for neutral and reverse.
                  Location: The Black Forest in Germany

                  How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                  • #10
                    Originally posted by Black Forest
                    The crankshaft pulley turns counterclockwise I believe. And yes the hand lever cable is all that applies the force for the friction. There is a gas shock that pushes the idler wheel over onto the belt for forward travel. THe hand lever cable pulls the ider away for neutral and reverse.

                    Crappy design, no wonder it does not work.

                    The only solution I can see would be to improve the friction, maybe beef up the cable system (somehow), or improve the friction material on the wheel which I assume is rubber which has gone a bit hard over the years?

                    You could get something like a ring cut from a suitable sized tire inner tube and glue that over the old rubber, that might work for a while.

                    Maybe you could turn a 'vee' in each of the wheels and put a suitable 'O' ring around one of them, I am sure that would be more friction than a flat tire against a smooth wheel.

                    Sorry, those musings are probably not worth much...

                    John
                    Last edited by The Artful Bodger; 10-06-2011, 04:47 AM.

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                    • #11
                      What would be great would be a clutch with a double throw to it. But I don't know of any to look at to get idea's.

                      Maybe the clutch on my STanko lathe would give me some idea's. If I recall it has an inline clutch arrangement to reverse the spindle. Tomorrow I will have to take the top off it and have a look.
                      Location: The Black Forest in Germany

                      How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                      • #12
                        basic clutch

                        Something like this clutch would be nice. The blue disk would be a gear for the reverse direction as would the brown disk that it touches. I just modeled plain round to make it quick.
                        Location: The Black Forest in Germany

                        How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                        • #13
                          If has to be a clutch that can handle becoming engaged while the motor is running so a dog clutch it no good. Likewise using gears they have to be engaged all the time.

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                          • #14
                            I was thinking more of a pressure plate type of clutch.
                            Location: The Black Forest in Germany

                            How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                            • #15
                              Originally posted by Black Forest
                              I was thinking more of a pressure plate type of clutch.

                              If you could mount II so that it did not move you would have a gear on there permanently engaged with a gear on the engine pulley then you could use a pressure plate type of clutch as used on a lot of motor cycles, or maybe an air con clutch from a car (but I think you would need a battery to operate that).

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