Reply with QuoteHere's a quick gif.
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
Here's a quick gif.
Bill
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 floorThe housing is 140mm diameter * 90mm long. The ratio is around (i think) 180:1
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
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?
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)I was thinking of a slight shrink fit
[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.
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.and using oil to keep the metal from touching
Last edited by BillTodd; 01-29-2009 at 08:38 AM.
Bill
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.
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
Another thought; If you used hollow rollers (i.e tubes) , they would distort, instead of the outer rings.
Bill
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
I was trying to work it out from first pinciples (always doomed to failureOriginally Posted by RICHARD ZASTROW
).
+/-1's sounds about right
Thanks Dick.
Bill
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
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
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.
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?)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.
Bill
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.
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
Actually i was reading about a DIY version of a DIY cycloidal reducer (for use with a telescope) yesterday!
http://www.telescopeshop.co.za/telescope_drives.htm
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!?
Last edited by Zoidberg; 03-19-2009 at 07:17 PM.
Posting Permissions
