Sun-Planet Engine

Discussion in 'Plans' started by vederstein, Jan 12, 2020.

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  1. Jan 20, 2020 #21

    vederstein

    vederstein

    vederstein

    Must do dumb things....

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    I thought about it and for the system to work, the sun and planet gears must be a 1: 1 ratio. Anything else will bind. If there was a ring gear, then different gear ratios are possible. The ring gear would constrain the planet and then the connecting rod wouldn't need to be "fixed" relative to the planet.

    I wanted the sun-planet gearing to be on the side of the engine, prominently displayed. The gearing in the middle is where I'm not thrilled where it's going. I'm not done, it just needs for design work.

    ...Ved.
     
  2. Jan 21, 2020 #22

    Peter Twissell

    Peter Twissell

    Peter Twissell

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    Hi Verdestein,
    I probably didn't explain my suggestion clearly.
    First, whatever the ratio of the sun and planet gears, the crank rotataes once for each complete cycle of the piston. My suggestion is to fix the cam directly to the crank.
    Second, I think you can have any ratio you like between the sun and planet gears. A large planet gear and a small sun gear will give you more shaft and flywheel speed. There should be only one rotational constraint between the crank and the shaft, so there is no reason why the system should bind.
     
  3. Jan 21, 2020 #23

    vederstein

    vederstein

    vederstein

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    True. But what I think you're missing Peter is that in Watt's design the big end of the connecting rod doesn't rotate relative to the planet gear. Re-watch the video of the 1785 engine. Notice that the planet gear doesn't rotate on its axis. It rotates around the sun, but relative to the con-rod, it doesn't rotate. If the two gears were different sizes this "fixed" relationship fails and a constraint would need removed.

    Removing the constraint between the con-rod and the planet would then allow the system to freewheel and depending on the internal forces may or may not transfer the torque to the flywheel or it just may go to top or bottom dead center and get stuck. The addition of a ring gear on the outside would eliminate the freewheeling and still allow for the planet to rotate on its axis relative to the con-rod, but I don't have the tooling (or any desire) to make a ring gear.

    I built this a few years ago, so I have some insight on actually working with sun-planet gearing systems.



    It's been some years since I got my mechanical engineering degree, but I did specialize in kinematics when I was there. I believe your half way there. I just think there's one part you're missing that would prevent the system from working. (Or perhaps vise-versa and there's something I over analyzing.)

    ...Ved
     
  4. Jan 21, 2020 #24

    Peter Twissell

    Peter Twissell

    Peter Twissell

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    To take your example: If the planet gear is freed from the connecting rod, the shaft and flywheel can spin freely while the rod stays fixed and the planet gear spins on its axis. This remains true for any ratio between the sun and planet gearss. If the planet gear is constrained to anything (whether it be the rod or a ring gear) then it will drive the sun gear.
    I never completed a degree, but I'm not concerned with who is qualified or who is right. If any of us arrives at the correct answer, we all benefit from the knowledge.
     
  5. Jan 25, 2020 #25

    vederstein

    vederstein

    vederstein

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    After some consideration, I thought that inverting the engine would make it more visually appealing.

    After also making the engine single acting (no crosshead) it looks much better. So at this point it's not a design to be junked (yet).

    Capture.JPG

     
  6. Jan 25, 2020 #26

    johnmcc69

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    Looks good Ved! It looks much better this way. Do you think you still need to support the outboard shaft of the flywheel though?
    How big/small is this going to be?

    John
     
  7. Jan 25, 2020 #27

    Peter Twissell

    Peter Twissell

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    Looks good that way up.
    Presumably, with the planet gears fixed to the connecting rod and the rod motion, the motion of the piston will be somewhat non sinusoidal at constant flywheel speed. This might give an advantage in changing motion ratio, smoothing the output torque.
     
  8. Jan 25, 2020 #28

    davidyat

    davidyat

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    Ved,
    Just let me know when the plans are ready. I need a new project after I finished with the Camgine.
    Grasshopper
     
  9. Jan 26, 2020 #29

    vederstein

    vederstein

    vederstein

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    John,

    I already thought about the flywheel. The flywheel (about 5" diameter) is huge for this engine. The reasoning for such a large flywheel is explained below about having enough energy to exhaust the gasses. The crankshaft is only 1/4" diameter. I could have gone bigger if I had a different set of gear cutters, but the only set I have is MOD 0.8 which is a 0.8mm gear pitch. You cannot see it from the picture/video, but there is an outboard ball bearing to support the flywheel. Also on the cam end, there are two ball bearings pressed into the same housing. That's why the bearing housing are thicker than they really need to be.

    Currently the engine has a 1-1/8" bore and a 24mm stroke, making it a bit over square. The stroke is more or less set (again due to the gear cutters I have). The bore is still under consideration. I think if I make the bore under square, the relative longer stroke will give more "time" (percent volume vs percent of stroke) per stroke to let the gasses out.

    On my last single acting engine, (https://www.homemodelenginemachinist.com/attachments/dsc01970-jpg.95019/) I made the inlet/exhaust porting too small. The engine would run, but much of the energy put into the engine was wasted getting the exhaust out. I don't want to make that mistake here.

    Bore to stroke is a balancing act though. If I make the bore much smaller, the connecting rod will interfere with the frame and/or cylinder bore.

    It's all part of design.

    ...Ved.
     
  10. Jan 26, 2020 #30

    vederstein

    vederstein

    vederstein

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    David,

    As always, I highly suggest one waits until I actually build the first one. I have a book of Rudy Kouhoupt designed engine plans I can loan you if you're looking for a proven design. This way you can have a project and can wait the three to six months it will take me to build this engine. There's always changes I make on the fly and ideas that looked good on a computer screen suck in actuality.

    The single piston on the Camgine! is an example. After I actually built it, I realized no matter how careful I was, there was no way I wasn't going to have the thing bind up. Hence I came up with the three piece piston. Also the plate on the back of the spherical bearing was added that wasn't in the original design.

    I expect some issues with this design here.

    If you really want the first issue of the design, I can send you the files outside of this forum (email or in person). Since we only live six miles apart, we can discover the design problems together! The choice is yours.

    As usual with my designs, I'll post them here to the forum after I build the prototype for no charge.

    BTW: (I think it's going to be named Contessa in tribute to my mother in law, Connie)

    ...Ved
     
  11. Jan 26, 2020 #31

    vederstein

    vederstein

    vederstein

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    I think I got the design more or less figured out. The cylinder turned into a casting, but that's ok with me.

    The spool valving on Camgine! worked well, so I'm using a modified version of it here.

    Next up is drawing set and bill of materials creation. But I'll do that another day.

    ...Ved.



    Capture.JPG
     

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