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I've heard that slanted gears are better then straight gears . One reason because slanted gears run quieter then the straight ones, so I've heard . Is there any other reason why slanted gears are better then straight? Second question; If you run the same motor pinion gear and the same main gear and the throttle curves stay the same, does the slanted gear runs a little higher RPM then the straight gear?

No. But they are quieter and the contact between the pinion & gear is better.

Better is subjective.

They do tend to be quieter due to the sliding engagement/disengagement of the gears and spreading the contact forces out along a longer "line" on any given tooth. Due to the greater contact face in the mesh, they transfer power more efficiently.

Of course, there are drawbacks. Due to the slanted engagement faces, there is an axial force generated so there is "wasted" energy and if the axial force is great enough, it can lead to binding at the gear hubs or need to be handled (thrust bearings or maybe doubled or tripled up radial bearings, for instance). The axial force can also cause the main gears to bend/warp and go out of alignment under load, leading to uneven wear and reducing the contact mesh, negating some of the power handling benefits being sought. So slanted gears, at least in high torque applications, usually will be CNC milled out of high strength materials and designed specifically to resist bending and warping under load. All this means they tend to be significantly more expensive than straight gears.

As to RPM difference: no, assuming same tooth counts and setup, switching from straight to slant tooth should not impact RPM.

What Paul said! Good explanation!

+1 on Paul:) Also the lateral force can generate greater stress on the bearing so less life of the bearing:( Generally quieter:) But that means your heli sounds like a Mini instead of a Mustang:)

We... My E7SE does NOT sound like a mini... But it doesn't sound like a Harley either! Lol

Thanks Paul for that information. I appreciated it.