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  1. #41
    Join Date
    Aug 2008
    Posts
    573
    Well somethings wrong with my calculation. I've just modelled it here and get ~32:1

    My instincts are telling me it's a simple matter of differential ratios, but all my head says is 'thump thump thump thump' . Time for an early night
    Bill

  2. #42
    Join Date
    Aug 2008
    Posts
    573
    Here's a quick gif.
    Attached Thumbnails Attached Thumbnails compound planetary box.gif  
    Bill

  3. #43
    Join Date
    Jan 2009
    Posts
    81
    I went back to the traction drive. I belive it could be built with a lathe and drillpress. To build the gear-bearing type i would need a rotary table to broach the internal gears and cut the regular gears!

    The side plates is missing, but will hold the sealed ballbearings to keep the oil in the house and from the floor The housing is 140mm diameter * 90mm long. The ratio is around (i think) 180:1
    Attached Thumbnails Attached Thumbnails traction drive.jpg   traction drive 2.jpg  

  4. #44
    Join Date
    Aug 2008
    Posts
    573
    How do you intend to maintain the pressure on the rolling surfaces? (as it changes temperature and wares the surfaces)

    I've made some progress with the ratio calculation, it is a simple differential ratio, but I seem to get two different ratios from my model (one as per calculation) depending on the frame of reference.

    I.e. if I hold the planet still and allow the ground and output gears to revolve, I get the correct, calculated, ratio. If I fix the ground I appear to get a different ratio. (there could be two reasons i) I could be counting the ratio incorrectly or ii) the model is not working the way it should - I suspect the former).
    Bill

  5. #45
    Join Date
    Jan 2009
    Posts
    81
    I was thinking of a slight shrink fit and using oil to keep the metal from touching.
    As it's for a rotary table i don't think the temperature will be a big problem, but i would use the same material for the rollers and housing to get the same expansion coefficients. What do you think? Will it work?

  6. #46
    Join Date
    Aug 2008
    Posts
    573
    I was thinking of a slight shrink fit
    OK - But I suspect this will mean the contact pressure is maintained by slight distortion (springing) of the outer rings (The end plate fittings should allow this radial movement)

    [edit] You should think about the output ring design; it you use the current drum shaped design, as it flexes it'll do so at an angle to the rollers. What about including an internal ring that connects to the outer at the centre

    It'll need some tight tolerances to work.

    and using oil to keep the metal from touching
    I think this is where traction fluid becomes useful i.e. it lubricates the bearings and low pressure sliding surfaces while maintaining grip on the drive rollers.
    Attached Thumbnails Attached Thumbnails outputdrum.jpg  
    Bill

  7. #47
    Join Date
    Jan 2009
    Posts
    81
    Yes tight tolerances, but thats just fun when you do your own projects

    I found a manufacturer of traction fluid earlier:
    http://www.santolubes.com/santotrac/index.html
    But i think i would try with synthetic oil first anyway.

  8. #48
    Join Date
    Aug 2008
    Posts
    573
    see edit

    [edit]

    But i think i would try with synthetic oil first anyway.

    Rub it on your ****s it'll make you hair curl - Do not use it in a traction drive!
    Bill

  9. #49
    Join Date
    Aug 2008
    Posts
    573
    Another thought; If you used hollow rollers (i.e tubes) , they would distort, instead of the outer rings.
    Bill

  10. #50
    Join Date
    Mar 2006
    Posts
    2712
    Look up the formulas for epicyclical gearing. There are some +1 & -1's in the ratio calculations to compensate for planet rotations, I think. I have it here somewhere. ????

    Dick Z
    DZASTR

  11. #51
    Join Date
    Aug 2008
    Posts
    573
    Quote Originally Posted by RICHARD ZASTROW View Post
    Look up the formulas for epicyclical gearing. There are some +1 & -1's in the ratio calculations to compensate for planet rotations, I think. I have it here somewhere. ????

    Dick Z
    I was trying to work it out from first pinciples (always doomed to failure ).

    +/-1's sounds about right

    Thanks Dick.
    Bill

  12. #52
    Join Date
    Mar 2006
    Posts
    2712
    I think the ratio thing is explained under epicyclical gearing on wikipedia.

    The patent # for gear bearings is US 6,626,792 B2 Sep. 30,2003

    Dick Z
    DZASTR

  13. #53
    Join Date
    Jan 2009
    Posts
    81
    I made a new design of the traction drive with angled rollers and preload with belleville washers. The spacer is a plastic disc with slots for the planets to roll in and is placed between the input and output sun! Think this would work?
    Attached Files Attached Files

  14. #54
    Join Date
    Aug 2008
    Posts
    573
    Quote Originally Posted by Zoidberg View Post
    I made a new design of the traction drive with angled rollers and preload with belleville washers. The spacer is a plastic disc with slots for the planets to roll in and is placed between the input and output sun! Think this would work?
    Good, very compact but...
    With the tapers arranged like that there is a differential ratio across the taper, so there would be sliding friction as the roller turns. (That's why my rough design here looks the way it does).
    Bill

  15. #55
    Join Date
    Jan 2009
    Posts
    81
    Yes i know, but i would need feedback from the output anyway

    Another thing i have been thinking about is to be able to switch between 1:1 and 60-100:1 to be able to do turning and indexing on the same spindle/setup. But dont know how to to do it and to keep the indexing backlash free.

  16. #56
    Join Date
    Aug 2008
    Posts
    573
    Another thing i have been thinking about is to be able to switch between 1:1 and 60-100:1 to be able to do turning and indexing on the same spindle/setup. But dont know how to to do it and to keep the indexing backlash free.
    How about some sort of clutch to connect the input to the second stage planet, and a mechanism to disconnect the first stage planets from the outer ring? (i.e. remove the pre-load?)
    Bill

  17. #57
    Join Date
    Jan 2009
    Posts
    81
    Hmm, perhaps i could disconnect the grounded annulus from the housing so it could rotate free and lock the rotation of the planets!?

    Check my sketch for another possible simple solution. The problem with that is it would have to be manual to be resonable.
    Attached Files Attached Files

  18. #58
    Join Date
    Mar 2004
    Posts
    439
    Not to throw a wrench into the works, perhaps someone has already mentioned this, but I had used one of these a long time ago on a extremely high accuracy (±1 arc sec) air bearing rotary table:
    http://www.onviollc.com/dotnetnuke/C...1/Default.aspx
    It worked very well for the application, and I was wondering if it could be recreated in a home shop with low cost roller bearings or ball bearings.

    Keith
    NEATman

  19. #59
    Join Date
    Jan 2009
    Posts
    81
    Actually i was reading about a DIY version of a DIY cycloidal reducer (for use with a telescope) yesterday! Interesting stuff, well worth to check into further!

    http://www.telescopeshop.co.za/telescope_drives.htm

  20. #60
    Join Date
    Jan 2009
    Posts
    81
    I made a test to see what happens with the gearing ratio when i lock/release certain parts of the assembly! I used gears to see that the gearing is correct.

    When i lock the input annulus to the housing i get about 197:1 ratio.

    When i release the input annulus i get about -5:1 ratio, but then i would need to lock the planet carriers orbital rotation to transmit any torque if i'm thinking correctly!?
    This should be easy with 2 brakes, 1 for the Input annulus and one for the planet carrier that you switch between.

    If i would release the input annulus and lock the planet rotation i should get 1:1
    But that is a little harder to acomplish! Got any ideas?

    Edit: I got an idea! What if you release the input annulus from the housing and connect it with the output annulus, the difference in gearing should lock up the hole assembly and give 1:1!?
    Attached Files Attached Files

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