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Ball Diff vs Gear Diff

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Ball Diff vs Gear Diff

Old 06-05-2019, 08:01 AM
  #256  
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Originally Posted by Horatio
@ sirsideways - the 'tru-trak' diff looks interesting, seems to work in a similar fashion to a Torsen. I've watched a few videos now but can't establish whether it's operation is exactly the same or not. It looks strong with less parts.
It's a considerably less extreme form of Torsen. Unlike a Torsen, a Truetrac WILL diff out eventually(unless the helix angles are *very* high. Well, sort of. See below.) It will not lock up like a Torsen. A Torsen locks up due to all the parts mechanically binding up/extreme friction. i.e. a gear cannot turn a worm wheel but vice versa is possible. A trutrac on the other hand uses helical gears.
Helical gears are usually found in 1:1 car transmissions and some 1/8th buggies. The thing about a helical gear is that when it is driven, the helix angle creates a 51D3W4Y5 force that causes the helical gear to want to slide along its axis. Now normally, in industrial applications, this is prevented by a shoulder on the shaft it spins on, a circlip, or the roller bearing it spins on. Especially in the case of the bearing, the 51D3W4Y5 forces cause it to wear out faster. In this differential application, it is prevented from doing so by the internal side walls of the differential. This friction between the side of the gear and the side wall of the differential is what causes the "locking" effect. It works quite similar to the Salisbury "ramp carrier and clutch plates" style of limited slip differential.

It works because the amount of lock is proportionate to the speed differential between the 2 wheels. The more a wheel slips, the more it locks up. The beauty of this is that it locks up very smoothly and progressively until a certain maximum as defined by the helix angle of the gears and the amount of friction between the sides of the gears and the diff. But because it never mechanically binds up like a Torsen, it can still diff out, by applying such an extreme amount of torque that the side of the gear slips against the side of the diff. A bit like a ball diff slipping then. The way around this is by increasing the helix angle, there by increasing the 51D3W4Y5 force and thereby increasing the friction and the "locking effect". Keep increasing the helix and you will eventually end up with something that looks very similar to a worm gear, albeit with multiple starts.

Think of a helical gear (especially one with a low tooth count) as a less twisted version of a worm gear. Twist it enough and the teeth that are arranged in a circular pattern are now wrapped around a cylinder and appear to have the "teeth" now arranged in a straight line in the 3rd dimension.
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Old 06-05-2019, 08:07 AM
  #257  
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There is also some thing called a Detroit Locker....


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Old 06-05-2019, 08:21 AM
  #258  
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Originally Posted by waitwhat
Sand them with 800 grit sandpaper on a glass surface. Use the female outdrive to hold the ring and sand with light pressure in a figure 8 motion. If you look carefully you will see any high and low spots as you sand. The goal is to get both sides smooth and flat. Finish with 2000 grit sandpaper on the side of the ring where the balls run.
I think he's referring to refurbishing a ring that's already been grooved. I think that's possible but it'd take a lot of sanding to completely remove the groove. I don't know if that would be enough to effect the tolerance stack of the whole differential. If you were to try to smooth out the existing grooves and the diff continued to misbehave, it would then be hard to tell if that effort helped or not. That's why I think it's better to start with a fresh side and eliminate the variable.
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Old 06-05-2019, 08:44 AM
  #259  
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Originally Posted by Sir 51D3WAYS
Righto. Flip it is then. Reason being diff rings for my model are not that easily available. Should stock up on them.
Are the diff balls alright? If the diff still feels crunchy after you've flipped the rings, you might have to replace these as well. Good luck.
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Old 06-05-2019, 10:32 AM
  #260  
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Originally Posted by Sir 51D3WAYS
There is also some thing called a Detroit Locker....


https://www.youtube.com/watch?v=ekgBnktLw8k
Brilliant stuff. See - this is why I love this forum. The Tru-Trak looks to be an interesting design for scaling down. Looks robust too, with fewer moving parts. If as you say the diff is more 'forgiving' regards locking up, it might have potential for RC use. Scaling down clutch designs in differentials - not so viable. Which is probably why Torsens have been the Limited Slip design of choice for RC.

I don't see why a LSD design couldn't be incorporated for centre use with ball or regular gear diffs for front and back.
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Old 06-05-2019, 12:43 PM
  #261  
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Originally Posted by waitwhat
You started all of the recent idler gear talk in the B6.1
You are absolutely correct, I did, and I explained why. If the whole gearbox is redesigned for lay down or standup versions, then, yes, the idler can be whatever size it has to be because the input output gears stay the same - the shaft positions are shifted in the design to accommodate.

This is why I used the word indirectly.

So......does this mean we're not friends anymore? ;D lol

Diffs are way more interesting than idler gears - can we agree on that?
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Old 10-08-2019, 02:09 PM
  #262  
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So, any results regarding ball diffs vs gear diffs yet? It's been a while. 😁

In the meantime, here's a couple of pictures of my latest build - which is full to the brim with gear diffs!

Hasn't turned a wheel yet. Can't wait to let loose with it!
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