Differences in 6s straight vs spiral cut diff gears? Questions galore ahead

MrTitanium

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Ordered two sets of new Typhon 6s differential assemblies from JenRC... for my Infraction. I stripped everything down and threw it all in the ultrasonic cleaner. Now... I noticed that the Typhon diff gears are spiral cut but my Infraction are straight cut. Both designs carry 43 tooth count.

Why did Arrma do this? Are there perks when running one gear design over the other? Which design is stronger? Should I stick to the straight cut gears in my Infraction, or switch to spiral design?
 

chevys10zr2003

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Straight handles more power and torque because the surface areas of the gears in contact with each other are greater than that of helical/spiral

oh and no don’t use helical cut instead of straight cut.
I always thought that the helical gears did better with more power because of the greater surface area between the teeth and the straight cut gears were more efficient.

I also thought that the Typhon and Senton always had straight cut gears while the Kraton, Talion and Outcast had spiral cut gears.
 

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I always thought that the helical gears did better with more power because of the greater surface area between the teeth and the straight cut gears were more efficient.

I also thought that the Typhon and Senton always had straight cut gears while the Kraton, Talion and Outcast had spiral cut gears.
Nope. The straight cut has more contact area. Hence Motorsport uses straight cut gears. The only downside is noise. Straight cut gearboxes are loud which I love!!
 

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I always thought that the helical gears did better with more power because of the greater surface area between the teeth and the straight cut gears were more efficient.
I always thought the same thing, to be honest.


Thanks fellas. Valuable lesson learned. Guess those Typhon diffs are going in the parts bin. JenRC... here I come again!
 

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I always thought the same thing, to be honest.
A simple way to look at it is use your fingers and pretend they are gears. Now interlock them opposite each other and you have maximum contact area. Now move them about 45 deg and you’ll have way less contact area.
 

chevys10zr2003

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Nope. The straight cut has more contact area. Hence Motorsport uses straight cut gears. The only downside is noise. Straight cut gearboxes are loud which I love!!
How does the straight cut have more contact area? The shortest distance from point to point is a straight line, so if have straight cut gears the tooth itself would actually be shorter than a spiral cut gear. I'm not 100% sure but that would make sense to me.
 

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How does the straight cut have more contact area? The shortest distance from point to point is a straight line, so if have straight cut gears the tooth itself would actually be shorter than a spiral cut gear. I'm not 100% sure but that would make sense to me.
Another way to try this is get two gears and mesh them together normally. Now turn one gear to 45 deg and the contact area drops drastically.
Look at your RC car. Your pinion and spur gears are straight cut and in constant mesh - 100% contact area. Turn one of them to 45 deg and then see how much of the tooth is contacting the other tooth.
 

chevys10zr2003

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Another way to try this is get two gears and mesh them together normally. Now turn one gear to 45 deg and the contact area drops drastically.
Look at your RC car. Your pinion and spur gears are straight cut and in constant mesh - 100% contact area. Turn one of them to 45 deg and then see how much of the tooth is contacting the other tooth.
That's not really the same thing though since doing that with straight cut is doing something they aren't really designed to do. Spiral cut gears are designed to have consistent mesh with the gears angle cut.

I did a google search and everything I have read is saying that spiral is stronger. Now it is the internet and not everything is true on the internet, but I didn't find one bit saying that straight cut was stronger.
https://clr.es/blog/en/spur-gears-helical-gears/
 

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https://bit.ly/2Ukq0tk is what I looked at just now. I've read that Typhon uses helical though and I think maybe the only vehicle that does from Arrma. I see the guys that jump big change to outcast diffs too. The article states noise and power transfer dependability
 

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That's not really the same thing though since doing that with straight cut is doing something they aren't really designed to do. Spiral cut gears are designed to have consistent mesh with the gears angle cut.

I did a google search and everything I have read is saying that spiral is stronger. Now it is the internet and not everything is true on the internet, but I didn't find one bit saying that straight cut was stronger.
https://clr.es/blog/en/spur-gears-helical-gears/
They can’t handle the loads that straight cut gears can.
 

chevys10zr2003

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They can’t handle the loads that straight cut gears can.
In the link that I posted they state that spiral can handle higher loads though.
https://bit.ly/2Ukq0tk is what I looked at just now. I've read that Typhon uses helical though and I think maybe the only vehicle that does from Arrma. I see the guys that jump big change to outcast diffs too. The article states noise and power transfer dependability
According to the owners manuals the Typhon has AR310441, which is straight cut and used on the Typhon, Senton, Limitless and Infraction and the Kraton has AR310497, which is spiral cut and used on the Talion, Mojave and the Outcast.
 
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suchtragedy

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Nope. The straight cut has more contact area. Hence Motorsport uses straight cut gears. The only downside is noise. Straight cut gearboxes are loud which I love!!
Not accurate, it has less contact area. Straight cut is more efficient because it wastes less energy.

Here's what I know based my experience with automotive wrenching/mechanics and racing, reaffirmed by Google so I don't get it wrong trying to explain.

Straight cut:
- cheaper to make
- more efficient power delivery (less friction, all energy is going in parallel with shafts)
- no axial force on shafts (all energy is being moved in parallel directions, not in two perpendicular directions like in helical)
- torque hits instantly so not smooth feeling during gear shifts
- loud af
- higher wear over time due to loads spread across less teeth at any given time when compared to helical with same load (more teeth in contact at any given time in helical)

Helical:
-quieter
- smoother transitions during gear shifts as gears glide together into place
- more expensive to make due to design/added manufacturing complexity
- better than straight cut in high load scenarios (load is spread across more teeth compared to straight cut at any given time)
- Can deliver power to either parallel or perpendicular shafts
- power loss/less efficient due to design (gears pushing away from each other causing axial drive force which is wasted energy, friction/heat generated as gears slip along their face, also more surface area contact overall compared to straight cut aka higher friction coefficient)
- axial drive force adds strain on shafts and bearings

Drive a race car with a straight cut gear transmission and feel how harsh the shifts feel and how loud the gears are and you'll know why modern everyday automobiles use helical gears instead despite being less efficient. The disadvantages of helical gears come at the compromise of comfort, convenience, and durability over time. But for straight up efficiency/performance straight cut wins.

I'm not an RC expert but based on all of this and what I've seen, in general RC applications you should see straight cut for main drive gears most always due to cost/simplicity and efficiency, and bevel gears when you need to transfer the energy in another direction (differentials). I am not sure where a helical gear would be appropriate in RC but as I said I am not an RC expert and this is all based on what I know from my observations in RC and my automotive knowledge in general.
 

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The shops I’ve worked at we always installed straight cut transmissions for performance and racing purposes. They can handle the punishment given but downside is noise. My own personal car had a quaife straight cut gearbox which was made for rallying and racing purposes. No matter what I did to it I couldn’t break it.

Like you said RC cars could be different, but from my experience we used straight cut for a reason and it’s the go to setup in many variants of Motorsport.
 

chevys10zr2003

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The shops I’ve worked at we always installed straight cut transmissions for performance and racing purposes. They can handle the punishment given but downside is noise. My own personal car had a quaife straight cut gearbox which was made for rallying and racing purposes. No matter what I did to it I couldn’t break it.

Like you said RC cars could be different, but from my experience we used straight cut for a reason and it’s the go to setup in many variants of Motorsport.
From what I have read it's because they can make the gears and teeth bigger to overcome the weaker design but since there isn't any axial loading they can make the bearings and houses significantly smaller and lighter making for great weight savings. Then when you couple that with the greater efficiency it makes it ideal for racing applications. I'm not an engineer by any means so all I can do is go by what the internet says.
 
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