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Question about planetary gears

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  • Tom Capon
    Hi guys, I m working on the design for my Tri-Star vehicle, and I need to do some research on the workings and design of planetary gear systems used as
    Message 1 of 7 , Aug 31, 2004
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      Hi guys,
      I'm working on the design for my Tri-Star vehicle, and I need to do some
      research on the workings and design of planetary gear systems used as
      differentials. I will be building my own planetary gear systems into the
      meta-wheels to divide power between the true wheels and the
      meta-wheels. Does anybody have any ideas where I should start? Websites?
      Books? Thanks a lot. --Tom Capon
    • Tom Capon
      here is my website. I haven t got the meta-wheel info up yet but it is coming soon. www.destructonet.org/tom
      Message 2 of 7 , Aug 31, 2004
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        here is my website. I haven't got the meta-wheel info up yet but it is
        coming soon.

        www.destructonet.org/tom


        At 06:02 PM 8/31/2004 -0400, you wrote:
        >Hi guys,
        >I'm working on the design for my Tri-Star vehicle, and I need to do some
        >research on the workings and design of planetary gear systems used as
        >differentials. I will be building my own planetary gear systems into the
        >meta-wheels to divide power between the true wheels and the
        >meta-wheels. Does anybody have any ideas where I should start? Websites?
        >Books? Thanks a lot. --Tom Capon
        >
        >
        >
        >Visit the SRS Website at http://www.seattlerobotics.org
        >Yahoo! Groups Links
        >
        >
        >
        >
      • Dave Hylands
        Hi Tom, I m not sure I understand why you need to divide the power. If you just build a gearing system like this: http://www.visi.com/~dc/tristar/ When one of
        Message 3 of 7 , Aug 31, 2004
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          Hi Tom,

          I'm not sure I understand why you need to divide the power. If you just
          build a gearing system like this:
          http://www.visi.com/~dc/tristar/

          When one of the "true" wheels (I assume by this you mean the smaller
          wheels with the rubber on them) stops, then this forces the "meta" wheel
          (whole assembly) to rotate.

          I can understand having a differential between the two sides (which is a
          more conventional use).

          --
          Dave Hylands
          Vancouver, BC, Canada
          http://www.DaveHylands.com/

          > -----Original Message-----
          > From: Tom Capon [mailto:robot@...]
          > Sent: Tuesday, August 31, 2004 3:07 PM
          > To: SeattleRobotics@yahoogroups.com
          > Subject: Re: [SeattleRobotics] Question about planetary gears
          >
          >
          > here is my website. I haven't got the meta-wheel info up yet
          > but it is
          > coming soon.
          >
          > www.destructonet.org/tom
          >
          >
          > At 06:02 PM 8/31/2004 -0400, you wrote:
          > >Hi guys,
          > >I'm working on the design for my Tri-Star vehicle, and I need to do
          > >some research on the workings and design of planetary gear
          > systems used
          > >as differentials. I will be building my own planetary gear systems
          > >into the meta-wheels to divide power between the true wheels and the
          > >meta-wheels. Does anybody have any ideas where I should start?
          > >Websites? Books? Thanks a lot. --Tom Capon
        • Tom Capon
          Exactly. The gearing system *is* what distributes the power between the true wheels and the metawheels. I ve looked at Doug s page before, and this design
          Message 4 of 7 , Sep 2, 2004
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            Exactly. The gearing system *is* what distributes the power between the
            true wheels and the metawheels.

            I've looked at Doug's page before, and this design does use a differential
            connected with outputs going to the true wheels and the metawheels. This
            distributes the power evenly between the two, just like it does when it is
            between the left and right wheels on a car. If there is some but not total
            resistance in the true wheels, then part of the power will be transfered to
            the metawheels to overcome the slight obstacle. This also causes a
            smoother transition between true-wheel power and metawheel power when going
            over a large obstacle (such as a step).

            The planetary gears are configured to have the same function as the
            differential that Doug uses (he actually suggested the idea on his
            site). I am using them because the implementation without LEGO will be
            cheaper and easier to construct (differentials can get expensive, and this
            way I don't have to have concentric axles). I'd just like to learn more
            about how the planetary gear system works, so that I can modify it if
            necessary.


            At 03:39 PM 8/31/2004 -0700, you wrote:
            >Hi Tom,
            >
            >I'm not sure I understand why you need to divide the power. If you just
            >build a gearing system like this:
            >http://www.visi.com/~dc/tristar/
            >
            >When one of the "true" wheels (I assume by this you mean the smaller
            >wheels with the rubber on them) stops, then this forces the "meta" wheel
            >(whole assembly) to rotate.
            >
            >I can understand having a differential between the two sides (which is a
            >more conventional use).
            >
            >--
            >Dave Hylands
            >Vancouver, BC, Canada
            >http://www.DaveHylands.com/
            >
            > > -----Original Message-----
            > > From: Tom Capon [mailto:robot@...]
            > > Sent: Tuesday, August 31, 2004 3:07 PM
            > > To: SeattleRobotics@yahoogroups.com
            > > Subject: Re: [SeattleRobotics] Question about planetary gears
            > >
            > >
            > > here is my website. I haven't got the meta-wheel info up yet
            > > but it is
            > > coming soon.
            > >
            > > www.destructonet.org/tom
            > >
            > >
            > > At 06:02 PM 8/31/2004 -0400, you wrote:
            > > >Hi guys,
            > > >I'm working on the design for my Tri-Star vehicle, and I need to do
            > > >some research on the workings and design of planetary gear
            > > systems used
            > > >as differentials. I will be building my own planetary gear systems
            > > >into the meta-wheels to divide power between the true wheels and the
            > > >meta-wheels. Does anybody have any ideas where I should start?
            > > >Websites? Books? Thanks a lot. --Tom Capon
            >
            >
            >
            >Visit the SRS Website at http://www.seattlerobotics.org
            >Yahoo! Groups Links
            >
            >
            >
            >
          • Dave Hylands
            Hi Tom, ... Ahhh. This make sense now :) I hadn t seen the planetary gear section on Doug s web site before. I ripped apart a cordless drill once, and they
            Message 5 of 7 , Sep 2, 2004
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              Hi Tom,

              > I'd just like to learn more about how the planetary
              > gear system works, so that I can modify it if
              > necessary.

              Ahhh. This make sense now :) I hadn't seen the planetary gear section on
              Doug's web site before.

              I ripped apart a cordless drill once, and they typically use planetary
              gears. That is a great way to learn how they work. You can pick up a
              cheap cordless drill at Harbor Freight if you want to experiment.

              This site has some useful information on it:
              <http://www.du.edu/~jcalvert/tech/planet.htm>

              The planetary gearbox basically has 3 "shafts", one connected to the sun
              gear, one connected to the planet gears, and one connected to the ring
              gear. Normally, one of the shafts is an input, one of them is an output,
              and the other one is fixed. However, by having the two non-input shafts
              used as outputs, you essentially have a differential with gearing, where
              the outputs are driven at potentially different gear ratios, with power
              being transferred between them.

              This PDF has great pictures of the inside of a cordless drill:
              <http://psdam.mit.edu/2.000/administrative/handouts/planetary-gear-train
              s/Planetary-Gear-Trains.pdf>

              I also discovered that electric/gas hybrids use a planetary gear system
              with the electric motor on one shaft, the gas motor on another and the
              3rd as an output.
              <http://www.personal.psu.edu/users/n/j/njf118/tech%20art.pdf>
              <http://home.earthlink.net/~graham1/MyToyotaPrius/Understanding/PowerSpl
              itDevice.htm>

              The bottom of this page has a bunch of the match behind calculating
              ratios and such:
              <http://www.mech.uq.edu.au/courses/mmme2104/chap06/s1.htm>

              --
              Dave Hylands
              Vancouver, BC, Canada
              http://www.DaveHylands.com/
            • Tom Capon
              Thanks! This gives me a great jumping-off point; I didn t find those sites when I searched. They also verify some of my own calculations. Now I ve just got to
              Message 6 of 7 , Sep 2, 2004
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                Thanks!
                This gives me a great jumping-off point; I didn't find those sites when I
                searched. They also verify some of my own calculations.
                Now I've just got to do something with the calculations I made:
                When the ring gear is stationary:
                (angular velocity of sun gear) = (angular velocity of arm) x ( 1 + [ (pitch
                radius of ring gear) / (pitch radius of sun gear) ] )

                When sun gear is stationary:
                (angular velocity of ring gear) = (angular velocity of arm) x ( 1 + [
                (pitch radius of sun gear) / (pitch radius of ring gear) ] )

                The radius of the planet gears does not come into play, but that is
                dependent on both the radius of the sun gear and the radius of the ring gear.


                I guess hybrid cars use the planetary gear system as a differential too,
                only in reverse. The output is the sum of the input speeds.



                --Tom Capon


                At 03:07 PM 9/2/2004 -0700, you wrote:

                >Hi Tom,
                >
                > > I'd just like to learn more about how the planetary
                > > gear system works, so that I can modify it if
                > > necessary.
                >
                >Ahhh. This make sense now :) I hadn't seen the planetary gear section on
                >Doug's web site before.
                >
                >I ripped apart a cordless drill once, and they typically use planetary
                >gears. That is a great way to learn how they work. You can pick up a
                >cheap cordless drill at Harbor Freight if you want to experiment.
                >
                >This site has some useful information on it:
                ><http://www.du.edu/~jcalvert/tech/planet.htm>
                >
                >The planetary gearbox basically has 3 "shafts", one connected to the sun
                >gear, one connected to the planet gears, and one connected to the ring
                >gear. Normally, one of the shafts is an input, one of them is an output,
                >and the other one is fixed. However, by having the two non-input shafts
                >used as outputs, you essentially have a differential with gearing, where
                >the outputs are driven at potentially different gear ratios, with power
                >being transferred between them.
                >
                >This PDF has great pictures of the inside of a cordless drill:
                ><http://psdam.mit.edu/2.000/administrative/handouts/planetary-gear-train
                >s/Planetary-Gear-Trains.pdf>
                >
                >I also discovered that electric/gas hybrids use a planetary gear system
                >with the electric motor on one shaft, the gas motor on another and the
                >3rd as an output.
                ><http://www.personal.psu.edu/users/n/j/njf118/tech%20art.pdf>
                ><http://home.earthlink.net/~graham1/MyToyotaPrius/Understanding/PowerSpl
                >itDevice.htm>
                >
                >The bottom of this page has a bunch of the match behind calculating
                >ratios and such:
                ><http://www.mech.uq.edu.au/courses/mmme2104/chap06/s1.htm>
                >
                >--
                >Dave Hylands
                >Vancouver, BC, Canada
                >http://www.DaveHylands.com/
                >
                >
                >
                >Visit the SRS Website at http://www.seattlerobotics.org
                >Yahoo! Groups Links
                >
                >
                >
                >
              • Juan Lozano
                ... Hi There are some pages on www.howstuffworks.com that touch the subject of planetary gears, particularly: http://home.howstuffworks.com/inside-sd.htm
                Message 7 of 7 , Sep 2, 2004
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                  --- Tom Capon <robot@...> wrote:
                  > I'd just like to learn more
                  > about how the planetary gear system works, so that I can modify it if
                  > necessary.


                  Hi

                  There are some pages on www.howstuffworks.com that touch the subject of
                  planetary gears, particularly:

                  http://home.howstuffworks.com/inside-sd.htm (diss. of an electric screwdriver)
                  http://science.howstuffworks.com/gear-ratio4.htm (scroll down a bit)

                  There's also a description of automatic car transmissions (they use a lot of
                  pl. gear sets), but what you'll find more interesting are these 2 I mentioned.






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