Using Pinions as Idlers

[John T]

My project involves a large ring gear (see photo 89) that floats.  It has no axle to rotate around because of other component s that will be added as the project develops.  The ring gear is turned by the pinion in the upper right and will be hand turned with a hand crank.

In its operating position the weight of the ring gear will rests on the lower two pinions.  If I use the GM normal pinions the ring gear naturally rest at the bottom the the pinion gears and binds.  My solution has been the following .

First leave the upper right pinion driver as designed by GM as it is the driver. (Photo 90)
For the idlers that carry the weight of the ring gear I've altered some of the paramters:
The Shift was left unchanged
The Stub was changed from 1 to 0.5
The Width was changed from 0.5 to 0.45

Although not fully tested it looks like this might work although the motion isn't really smooth.  Is there some other way to use pinion idlers and achieve smooth motion?

[ArtF]

Hi :

   Havent hit that problem myself as yet.. but Id thinking doing a profile shift outwards should work as it shifts the pitchline outwards.

Art

[vmax549]

YEP as you have noticed Gear teeth were never designed to support the weight load of the engaged gears

Two Solutions come to mind, go to a very fine took profile that spreads out the load and engagemen t angles

or reprofili ng the tooth tip and root as a constant radius so the tooth tip actually acts as a bearing as it engages the root on both gears.  With large teeth profiles you still may have a bit of bump bump as it rotates and lifts the gear as the root engages the tip.

Just a thought, (;-)TP

[John S]

Instead of one pinion use two pinions side by side, not touching and arrange the centre distance between the two so as one pinion has it's tooth in mesh the other is at the top of the ring gear tooth, this way you have better support as it runs on differnt parts of the teeth.

A bit like a poor man's helical gear but spread out over two gears insted of having a deep gear.

Your design may not allow this though ??

John S.

[John T]

Thanks for the ideas - My design is really flexible and so I was able to try some of the ideas suggested . The pinion depthing remained a critical factor to avoid binding and the more pinions I added the more opportuni ties there were for things to "not cooperate".  Since this project is really only a toy and is intended for children to "hand crank" I have provided a "slide ring" for the large floating gear to work within.

This isn't an elegant solution but is simple and so far at least fool proof.  The internal pinions don't seem to present a problem so I may be on the way.

[bpark1000]

If the design permits, use a high pressure angle involute (up to 45 degrees) for the gear/pinions.  Do not design in the standard clearance s; design to standard "50% thickness" at the pitchline .  The gears will mesh well under pressure without jamming.

Does the outside of your gear need to have teeth?  If not, make that round and use rollers.