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Planetary Reduction

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  • Planetary Reduction

    Want to build planetary [have 2 styles] gear reduction [between 6&7:1] for use in "pulling" Garden Tractor, using standard supplier gears, or making making them; finding in use application would be great!!...Horsepower 60-70 range, torque 50-60 ft.lbs..need in as small a package as possible. I have posted other groups/forums,searched gear suppliers and have discovered that 1)the formulas in Machinery Handbook are not that exact,2) one supplier recomemded load is 30% of max load and break load is 2x max load. Need and value all input. If I test for strenth do I put everthing in intended configuration and put a torque wrench to it till it breaks? Thanks to those that have contributed. I can E mail sketches/converse to those interested. Happy Holidays, Seb.

  • #2
    It is not the constant torque that usually does you in, but the peak torque and drive line shock (wheel hook up, terrain, etc.) that kills parts.

    A spur reduction drive box would make more sense (a small gear driving a large gear, has over 95% efficiency (less power loss), cheaper, and less parts to go snafu.

    You could also do this with double roller chain, or heavy roller chain & sprockets.

    These are all standard driveline components available in most civilized areas. You could search on

    btw, an epicyclic gear box is more effecient (+92%) and can take higher loads than a regular planetary (80-92%). Expect really high prices.


    • #3
      Well, a "pulling garden tractor" must be one
      of those things in tractor pulls, right? So
      long term life probably isn't a issue; you just want to keep loads reasonable to keep from breaking things.

      The big sneaky problem is there can be a lot
      of shock loads due to fluctuations in traction and weight transfer, so your peak torque loads can be much higher than the engine power might indicate due to inertial
      loading effects.

      For the cheapest, strongest transmission
      possible I'd use a double reduction roller chain drive. You can use a smaller chain for the first reduction and use larger chain to handle the final drive. Each reduction
      should be on the order of 2.5 to one.

      Since a chain drive's limiting factor is
      chain strength (for shock loads, assuming
      you're using at least 20-odd teeth on the
      smaller sprocket), you can size the drives
      using chain working load limits. If you
      enclose this mechanism to keep the rocks
      out and some oil in, it will last a suprising long time.

      Have you considered a snowmobile torque
      converter? About 2.5:1 reduction at
      stall, over 1:1 at full speed... combine
      this w/ a 4:1 final drive and you'll get a
      lot of speed up in the first part of the
      pull, while still having mucho grunt to keep
      some big tires pulling hard.

      Bart Smaalders
      Bart Smaalders


      • #4
        Thanks, guys..I had wanted to use the planetary as a "clutch" also.There is two types [as far as I can figure] that would work, both need one part to be "fixed", so by using a band to acclomplish this [it would just freewheel otherwise] it can become a clutch too..What is the difference between a regular planetary and an Epicyclic ?


        • #5
          An epicyclic gear is a planetary gear, it is just another name for it. Another type of gear is the epicycloidal, or cyclo gear, which uses cam disks that rotate against rollers. This type of gear has a higher efficiency then a planetary gear since the friction is rolling of the cam disks against the rollers whereas the planetary has sliding friction of the gear teeth. The cyclo gear can also withstand 500% shock loadings since the disks are in contact with several rollers at a time. You can check out this site for a description of how it works