[Joe Johnson]

Parallel axis helical gears are stronger and quieter than spur gears of the same size but they are significantly less efficient.

There are 2 main reasons: sliding contact and trusts loads.

There is more sliding contact between the teeth of a helical gear than of a spur gear. This makes the gears quieter but it also makes them less efficient.

The second major factor is that that thrust loads have to be managed. If you put in lousy thrust bearings, you can quickly loose a LOT of efficiency.

I have designed many robots over the years. I have yet to use a helical gear on any of them.

Other folks have other ideas, but for me and mine, I have never seen a case where the pros outweighed the cons.

Joe J.