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Helical vs. straight cut diff gears???.....

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Helical vs. straight cut diff gears???.....

Old 05-26-2011, 06:13 PM
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The spiral cut bevel gears are smoother and quieter than the straight cut bevel gears. I don't believe there is an advantage as far as strength.
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Old 05-26-2011, 06:14 PM
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true, when the spiral cut are not meshed right they slip and round off. the straight cut seem to just snap off teeth if they go. as long as they are shimmed right and the bearings are good either should last a long while.
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Old 05-26-2011, 06:21 PM
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The MP9 has straight cut gears and arguably the best drive train that has ever been produced. Just spin somebodies MP9 even with the wheels off, it's pretty amazing. The ST-RR uses spiral cut, and you definitely have to mesh it just right and limit the front brake.
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Old 05-26-2011, 06:59 PM
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I run Grease on my ST-RR Spiral gears. Do you treat Straight cut gear the same?
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Old 05-26-2011, 07:02 PM
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My eight-t with the straight cut gears I would go through a pinion shaft every half a gallon on the front and rear and had to make sure the mesh was good and shimmed properly. On my D8 and D8T the spiral cut gears I put them in and the only time I took them out was when I was changing the diff fluid out, never found any filings come off of them and haven't changed them since I got the new buggy and truggy. I imagine maybe I may have done something wrong with the straight cut gears but even the other guys at the track helped me with shimming and setting it up but that didn't make any difference in the wear. I like the gear mesh of the spiral cut gears maybe I just have bad luck with the straight cut gears.
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Old 05-26-2011, 07:59 PM
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Talking about full size car, here's a picture of a Porsche Cayenne's diff, note the helical/spiral cut gears...

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Old 05-26-2011, 08:07 PM
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You do a helical style cut of a gear to reduce noise pretty much. these days you have to be conscious of passenger comfort in our little cars.

I wish those manufacturers would drop the sexy looks and increased drag of a helical cut and go straight cut, they are not doing us any favors me thinks. Race cars are straight cut.
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Old 05-26-2011, 08:12 PM
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i like helical cut diff gear better than the straight cut on my rc8t i just used 1 shim on each side" like the manuel says and its good no failures and man is it smooth and it spins pretty free !

now the helical cut diff gear is harder to clean though if needed.
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Old 05-26-2011, 08:19 PM
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If it works for pencils then its good enough my my diffs
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Old 05-26-2011, 08:52 PM
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Originally Posted by johnny t View Post
You do a helical style cut of a gear to reduce noise pretty much. these days you have to be conscious of passenger comfort in our little cars.

I wish those manufacturers would drop the sexy looks and increased drag of a helical cut and go straight cut, they are not doing us any favors me thinks. Race cars are straight cut.
+1.
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Old 05-27-2011, 12:05 AM
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I don't understand this but real race cars use straight cuts to the diff and the ring gear? I have looked through nascar, indy and formula one teams pages and looking to see this for myself and they had cut away sections of where the shaft and the pinion gear go to the ring gear and they were all helical or spiral gears but got sick of looking after looking at over 40 pages and couldn't find one with a straight cut pinion to diff ring gear. If a Porche has runs spiral or helical gears it can't be that inefficient and the Germans don't do it if it's a waste of time but more likely it's more efficient and probably a better mesh. I don't know. OOOOOOOOOOOOOOHHHHH WELL!!!!
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Old 05-27-2011, 04:04 AM
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The reason behind helical cut gears is more surface area per gear tooth than straight cut gears and they are quieter than straight cut. You guys keep talking like it's something from another planet
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Old 05-27-2011, 07:05 AM
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That Porsche gear looks like it might be a hypoid gear (the two gear axis don't intersect). Given the same width, the helical gears will be stronger, the running tooth width is wider giving it more strength. Helical gear teeth 'roll' or ease into mesh and out of mesh, this makes them quieter and smoother. Straight cut teeth go into and out of mesh all at once. This creates a bit more noise and vibration because the contact of the tooth width happens all at once. Efficiency, I don't know. I've seen Kyosho, Losi, and Serpent cars free spin very well and they have straight gears. I've seen my HB car spin very good with helical gears, but not as good as the Serpent I saw. Efficiency under load when the car is on the track could be a different ballgame but I think the gear cut style for r/c cars for the end user realistically only comes down to durability (how often you replace gears or gearboxes to keep the gears from skipping).
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Old 05-27-2011, 10:36 AM
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Originally Posted by duck7604 View Post
The reason behind helical cut gears is more surface area per gear tooth than straight cut gears and they are quieter than straight cut. You guys keep talking like it's something from another planet

We keep talking whether its a technology even beneficial to an RC car. I would say no, helical gears only slow our cars down. MP9s and 8ights proved that to me.
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Old 05-27-2011, 11:20 AM
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tbf its not as easy as saying the losi or mp9 is faster than a helical diffed car, there are to many variables to even consider, bearings, mesh, options fitted, drive ratio etc will all make a substatial difference to how a car free wheels and accelerates.

is there a difference who knows, I went from the MBX5R to the 6 and didnt notice any real difference tbh, they both are very reliable when shimmed correctly, however i must say i never ever shimmed my MBX5 Prospec for about the first 3 years just let them rattle around in the diff till someone told me i should, did i ever break a diff gear no never.
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