Spiral cut vs. Standard diff gears

[simplechamp]

I know the difference between the two, but what are the advantages/disadvantages of each? I notice on many new 1/8 vehicles they advertise spiral cut gears as a selling point. Are they less likely to bind or strip? If so, why?

Thanks!

[Sammus]

they can handle more power for one because the teeth are bigger (longer).

disadvantages include that they need to be line up in two dimensions to get the mesh right, and they can put harder thrust forces on the outdrive bearings and thus has more potential to destroy them (the bearings).

[J57ltr]

Spiral cutting reduces noise, and increases friction, and with the benefit of added strength (more contact surface). The only gear sets I have ever messed with are on real cars, so I am used to setting both ring and pinion, for the proper mesh and backlash.

I hear different things from different people, but it seems to me that setting both pinion depth and ring lateral spacing would be real important since most RC cars out power most real cars in power to weight ratio.


Jeff

[simplechamp]

So it's not like spiral cut is the new big thing making standard ring and pinion gears obsolete... each has advantages and disadvantages that only the individual user can decide what works better for them.

The reason I asked is because I just bought the V3 hybrid diff kits for my E-revo, then I started looking at diffs with spiral cut gears and thought "great, now I need to spend more money to convert the diffs to spiral gears" but I think that would be overboard for now. Haven't even got the E-revo yet and I'm already going broke!

[lincpimp]

I have run both, and find no obvious strength benefit using the spiral cut. The lst and muggy use std cut gears, and I have not seen many who have issues with them. As stated, the spiral cut gears will place alot of thrust load on the pinion bearings, so it would be good to have a spacer that goes between the bearings to spread the load. The lst and muggy have this spacer stock, which would no doubt help other vehicles that use spiral cut and do not have the spacer.

Sikeston38m had bearing issues with his DDD outrunner powered revo using spiral cut gears, Have a look at his threads and there is a bunch of info there.

[MetalMan]

I've only run straight cut gears until recently I acquired a used CRT that came with spiral cut Hot Bodies diffs (10/43). Fact is, if shimmed right straight cut gears can handle just about anything, in my testing they are good for more than 5HP peaks.

[simplechamp]

I think I'll definitely stick with the standard diff gears for now. I mean I haven't even run the thing yet, just wanted to do the V3 diffs right from the start to prevent headaches later. Who knows, maybe the stock E-revo diffs would work fine, but I want something that I know will take some abuse.

[sikeston34m]

Originally Posted by lincpimp

Sikeston38m had bearing issues with his DDD outrunner powered revo using spiral cut gears, Have a look at his threads and there is a bunch of info there.

Yep, I could blow the rear diff in a single run.

I was using the Hotbodies 1/8 diffs in the RCM Revo diffs cases. Was even using the aluminum 1/8th diff cup to eliminate flex at that point.

The setup was shoving a ton of abuse at the rear diff. The weak point was the pinion bearings. I even upgraded to the ceramic bearings. Didn't make a difference.

The spiral cut gears load the pinion ball bearings as if they are thrust bearings. It would punch the center race through the bearing every time.

Little balls everywhere. LOL

The 13/43 straight cut gears proved to be the tougher setup since they load the ball bearings the way they are meant to be loaded.

[simplechamp]

Thanks for the help everyone! Sounds like the standard gears are a proven solution that I'll stick with. Just need to get a full CVD set and the drivetrain will be in good shape.

A little unrelated, but should I keep the locked center spool, or get a center diff? Is it worth it? or just another mechanical part to wear out and break?

sikeston34m: Seeing that pinion gear punch through a nice pair of ceramics has to be heartbreaking! Those babies ain't cheap!

[sikeston34m]

Here's a couple of pictures

The spiral cut gears try to either pull the pinion into the cup, or shove it out of the diff. See the comparison? The only thing stopping it from doing this is the bearings.

[sikeston34m]

Here's a picture of the two ring gears side by side.

[Snipin_Willy]

Originally Posted by sikeston34m

Here's a couple of pictures

The spiral cut gears try to either pull the pinion into the cup, or shove it out of the diff. See the comparison? The only thing stopping it from doing this is the bearings.

Interesting. I wonder if this was part of the intent when they started making them. Hard to imagine an engineer missing this sorta thing then a free body diagram should be the first thing the look at.

[simplechamp]

Spiral cut gears don't seem that great anymore... at least not until there is a good way to remedy all that force applied to the bearings. Not only does it destroy the bearings, but it's force being wasted that could be going to drive the wheels.

[Unsullied_Spy]

I prefer standard cut gears for that reason, I don't like replacing my bearings all the time.

The only time I've ever killed a 1/8th diff was in my Muggy, the plastic case cracked and allowed too much flex under power and the teeth started skipping. Replaced the ring and pinion and converted to aluminum cases and have put over 100 hours on the diffs since and so far I haven't done anything but re-grease the ring and pinion.

[simplechamp]

That's what I'm looking for, low maintenance. It seems steep that I just dropped $200 on diffs, but over the life of the car I think it will pay off. Won't be spending all my money on Traxxas diffs every few runs, and won't be spending all my time rebuilding them.

Now it's just finding/making a REAL center diff. I have been reading up on the one cowboy had created, but the thread petered out long ago and there's been no talk of the hybrid center diffs since. I don't see the point of using the Traxxas one. All anyone seems to do is get it and then try anything they can to lock it up again. Might as well just keep the locked spool until a true solution is found.