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Frank Ford
06-21-2004, 05:27 PM
Anybody out there have a source for information about designing planetary reduction drives using preloaded ball bearings instead of gears? I'd like to come up with 10:1 or better reduction in a housing that measures no more than .750 O.D. by .450 high.

30 years ago a machinist friend made a 9:1 drive that fit within a 1/2 x 3/8 can, but I lost contact LONG ago. I'm just getting started on this, and my first seat-of-the pants attempt yielded a working prototype that's about 6.5:1.



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Frank Ford
www.frets.com

BillH
06-21-2004, 05:47 PM
Hmm, Well, not a reduction drive, but Tamiya sells a Ball differential for their r/c cars that work in a similiar fashion. They act like a bearing between plates, but also drives the plates.

gunsmith
06-21-2004, 07:00 PM
A system used by Paxton as a blower for cars and has been used since the first world war in planes. It was originaly built by McCullach (I'm not sure if I spelled it right but they are the chain saw people). It has since been bought out by Paxton. This same blower is still being used today by hot rodders. Just about bullet proof and bare bones basic ball drive. For your purpose you would use the system as a reduction instead of to increase speed. Since it has been around so long there is for sure complete drawings out there in automotive parts books. It was used by Packard, Hudson, Studabaker and more recently Ford. Hope that helps.

Rich Carlstedt
06-21-2004, 07:10 PM
There is a Japanese maker of such varispeed boxes used in many industrial applications.
Their name slips my mind, but it is a good unit. the balls move inside two nested cones as I recall. Only crital thing is the "OIL" !
Special in that it must lubricate , but no slip...sort of like Fords old auto transmission fluid requirements.
I worked with these about 20 years ago, but saw one recently in a shop.

darryl
06-21-2004, 08:21 PM
Science and Mechanics ran an article years ago on what they called the 'fabulous friction free drive'. It was basically two flat round discs with balls sandwiched in between in specially curved races. I'll see if I can find the article. It claimed a large ratio and potential to handle mucho horsepower. Another device reported on was actually a planetary setup using friction drive, with tapered rollers as 'planets'. These rollers had a larger section on one end which was driven by a smaller tapered drive shaft, in essence a stacked array of planetary gear trains, but without gears. The only bearings were on the input and output shafts. The end result was a claimed ratio of 300-1, IIRC. The whole thing was tapered together, so that axial force on the input shaft kept all the elements under compression and therefore together.
Thanks for the reminder, now that I have machine tools, I will again consider making a mockup of this one, since I found it intriguing. Like I need another project right now-

Dave Opincarne
06-21-2004, 09:17 PM
If the ball drive works the way I assume it does, could someone expalin to me how it could have less friction than properly made gears teath which don't work against each other but roll, or how they can handle more power when the contact point is a ball rather than a line across the tooth face?

wierdscience
06-22-2004, 12:43 AM
Well for starters,the device is in the Ingenious mechanisms book series,it consists of a large ball bearing with the input shaft pressed into the inside race,the face shield/seal of the bearing is removed and the output(supported by another ball bearing)has three or six pins sticking out of the face of a flange axialy which ingages the cage of the input bearing,since the circumfrence of the balls are a fraction of the inner and outer races it does provide for a reduction.
The greater the diameter of the input ball bearing and the larger the ball count the greater the reduction and torque that can be achieved,but the levels of both are still small unless a means of providing increased thrust loading is devised.

As a side note the hydrostatic transmissions use two rows of ball bearings between moveable races,not as direct reducing elements,but as an efficient hydrualic pump motor combination,maybe you could look and see how small they are made.

John Stevenson
06-22-2004, 03:46 AM
Dave, They don't have less friction.
There is usually a stack of belville washers that keep the plates together and these put a lot of force on so they don't slip.
They also generate a hot of heat.
Three of the mixing machines we look after have large drives on the same as these, in fact I threw one in the scrap only yesterday.
When these are running continous they get that hot you can't put your hand on one. We get about 18 months out of a gearbox and then fit a new one as they cost more to repair than new.

The Colchester Chipmaster employes a similar gearbox made by Kopp. Mnay have been taken out and replaced by VFD drives.

John S.