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# Gears with roller bearings

Increase complexity, reduce friction
 (+1) [vote for, against]

Involute gears are great. They are designed so that the force from the drive gear is always pushing the driven gear in the same direction.

The surface of the drive gear slides/rolls across the surface of the driven gear.

My idea is to stick a roller bearing in between the gear teeth to reduce friction.

The bearing would be actually be a trolley of three bearings connected together as shown in the linked Veritasium video.

The trolley would be attached to a spring. The trolley starts at the bottom of the gear tooth. As the gears move the trolley moves up the tooth, tensioning the spring. When the trolley gets to the top of the tooth it is no longer held between the teeth of the two gears, and the spring pulls it back to the bottom of the tooth.

Instead of a trolley attached to a spring on each tooth, it might be possible to have just a pair of trolleys somehow connected such that they travel from one tooth to the next such that one trolley was always at the touching point between the two gears.

This might be useful in big gears, where friction and wear are significant problems.

 — xaviergisz, Oct 17 2021

Animation of involute gears https://i.redd.it/0aathzyjbwt71.gif
[xaviergisz, Oct 17 2021]

Veritasium video https://youtu.be/yCsgoLc_fzI?t=13m40s
[xaviergisz, Oct 17 2021]

https://en.wikipedi.../Recirculating_ball [pocmloc, Oct 17 2021]

https://en.wikipedia.org/wiki/Ball_screw [pocmloc, Oct 17 2021]

As far as I can remember (been a while since I studied...), the point of the involute is that the surfaces DON'T slide; they roll together smoothly (in a perfect world, of course). Not sure about HELICAL gears. Maybe 3D print a couple of large scale gears to experiment with.
There are similar weird transmissions like the cyclo-drive, that sort-of do this in a different way (all contacts are rollers, IIRC).

With proper lubrication, there is always a thin layer of oil or grease so metal-on-metal contact never occurs between the moving surfaces.
 — sninctown, Oct 17 2021

 I like the idea, but I think there is a detail that will make this not work. When contact first happens (dot on blue double arrow in the first animated .gif link is at the highest position), the surface of the upper gear is moving to the right relative to the lower gear. So presumably a trolley similar to the one in the second link (and the same orientation) could be constructed that would move at the right rate and stay at the point of contact. But wait, as the point of contact moves toward the center, the relative speed of the two surfaces decrease, even though the point of contact continues to move. When the contact point is half way between the gears, there is no sliding, just rolling. As the contact point moves farther right (and down), the relative motion is actually reversed: the surface of the top tooth is moving left relative to the surface of the bottom tooth, so our trolley in the original orientation would want to move left, even though the contact point is still moving right.

I'm afraid you need a trolley with independent rollers top and bottom and some mechanism to move it to keep it lined up with the contact point. This is not impossible since the contact point does move along a straight line as shown in the animation, but it will be a bit more complicated than your idea.
 — scad mientist, Oct 18 2021

That is some fine analysis [scad mientist]. This already overly complicated idea has now been shown to be quite impractical!
 — xaviergisz, Oct 18 2021

It might be possible to salvage this idea by using gears with straight/flat triangular teeth. The trolley acts as an intermediary to keep the force smooth from the driving to driven gears.
 — xaviergisz, Oct 20 2021

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