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Old 11-18-2009, 12:07 PM   #1
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Default Why no ball diffs???

Guys, why do the 1/8 buggies/truggies run gear diffs as opposed to ball diffs?....would it be to hard to keep a consistent tune on a ball diff??.....also, what would a buggy/truggy handle like with real thick grease in the diffs (like bearinge/axle grease)...........more like live axles/spool??
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Old 11-18-2009, 12:25 PM   #2
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ball diffs are not strong enough to handle 1/8 scale loads and even if they were it would be hard to keep them consistent.

does not matter if it's oil or grease - the thicker, the less diff action u get
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Old 11-18-2009, 12:29 PM   #3
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Try running your gear diffs empty with NO lube in them.

Then you'll have your answer as to 'why no ball diffs'.
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Old 11-18-2009, 12:33 PM   #4
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1. Ball diffs don't like dirt and grit.

2. Require constant maintainance.

3. Don't like high horsepower.

4. Not as adjustable.


Even many electrics are going the gear diff route. It's just better for everything but carpet racing.
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Old 11-18-2009, 02:19 PM   #5
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i was gonna say they would slip way to easily with the power of a nitro. heck i could never get the ball diff in my losi xx to hold up when i was using a hot motor...it would melt the gear constantly...till i upgraded to a metal gear.
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Old 11-18-2009, 02:25 PM   #6
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Let's put it this way, after melting down several diffs in a 1/10 electric dirt oval sprint car, I put a SC10 gear diff in there. Best move ever. Always smooth, consistent and easy to tune. I can't imagine the nightmare of trying to keep a ball diff together for a long 1/8 nitro main
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Old 11-18-2009, 02:29 PM   #7
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Could you imagine all of the barking that would be going on during a race. With the power the engines are making today, the demands of the tracks, and 3 diffs in 1 car, those ball diffs would be slipping and squealing all over the place. It would be funny though.
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Old 11-18-2009, 02:40 PM   #8
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1/10th nitro on road and offroad vehicles use ball diffs. I'd wager that a 1/10th mod electric carpet car works it's diff as hard as a 1/8th offroad car (ton's of traction, assanine horsepower/torque). The assumption that a ball diff can't take 1/8th weight/power is based on the fact that nobody has developed a ball diff for 1/8th since the 80's when they ran diffs in 1/8th on road cars.

Gear diffs are an easy solution for 1/8th off road and are working well enough but think about a few things:
1. a Gear diff under power is trying to disassemble itself, all the gears are straining to move outward.
2. there are NO bearings supporting the loads mentioned in #1.
3. There are no bearings supporting the outdrives of any of the diffs, just steel on steel bushing surfaces with whatever grease is left a few runs after a re-build.

Ball diffs solve all of the above issues.

Gear diffs work well enough but do you think they could improve?
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Old 11-18-2009, 03:29 PM   #9
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Quote:
Originally Posted by Davidka View Post

1. a Gear diff under power is trying to disassemble itself, .......
2. there are NO bearings .......
3. There are no bearings supporting the .......

Ball diffs solve all of the above issues.

Gear diffs work well enough but do you think they could improve?
and who cares? never seen a diff internals fail on a car with high quality diffs like mugen or Hot bodies hardened. sure stripped gears if someone did not shim them right

My brushless mugen has way more power than any nitro and after whole racing season the diff internals are like new and i dont really rebuild diffs just refill them. and no wear at all. adding more parts to the diff will make it just more prone to fail.

look for example at slipperential (RC Monster invention for Brushless cars combining center diff with slipper clutch) it works great and helps to tame the power of BL motor but it needs lot of care because it is very complex part.

keep the diff simple. just few gears and oil
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Old 11-18-2009, 03:34 PM   #10
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only reason diffs need all that tuning with fluids is b/c its an open diff and therefore naturally a handicap. but u cant exactly call up torsen or quaife and get a limited slip for ur 8ight now can u (dont say smartdiff lol).

a ball diff could be made to handle the 'torque', no1 has done it yet. hell the ball diff was invented for use in a tractor!

is it feasible and warranted, prolly not.

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Old 11-18-2009, 03:51 PM   #11
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Quote:
Originally Posted by Davidka View Post
1/10th nitro on road and offroad vehicles use ball diffs.
Many are now switching to gears diffs for all the reasons I mentioned earlier.


Quote:
Originally Posted by Davidka View Post
I'd wager that a 1/10th mod electric carpet car works it's diff as hard as a 1/8th offroad car (ton's of traction, assanine horsepower/torque).
Much lighter car, no jumps and bumps to deal with. Plus, while old brushed motors made gobs of torque, new brushless motors have much less. Plus again, carpet racing doesn't involve so much grit, dirt and sand.


Quote:
Originally Posted by Davidka View Post
The assumption that a ball diff can't take 1/8th weight/power is based on the fact that nobody has developed a ball diff for 1/8th since the 80's when they ran diffs in 1/8th on road cars.
2wd 1/8th onroad is alive and well in europe. Some cars come with ball diffs, most come with gear diffs and some offer both. Most prefer the gear diffs.

Quote:
Originally Posted by Davidka View Post
Gear diffs are an easy solution for 1/8th off road and are working well enough but think about a few things:
1. a Gear diff under power is trying to disassemble itself, all the gears are straining to move outward.
2. there are NO bearings supporting the loads mentioned in #1.
3. There are no bearings supporting the outdrives of any of the diffs, just steel on steel bushing surfaces with whatever grease is left a few runs after a re-build.

Ball diffs solve all of the above issues.
1. Many of those non-bearing supported components you mentioned do not need to be bearing supported. Drag in the diff is usually a good thing. That's why we use those heavy greases.

2. Ball diffs have a problem all their own. The only thing preventing them from slipping is the friction between hard steel rings and the very small contact patch of hard steel balls. This requires a LOT of pressure and you will still get some slippage when landing those jumps on throttle or powering through a woops section. Power + slip equals rapid wear. There is zero slippage in a gear diff.

3. Ball diffs are great for onroad because the traction and lack of bumps means inside wheel spin is less of a problem. Therefore you want the diff to be as free as possible to maximize the car's turning ability. This doesn't work so well in offroad where forward traction is all important. You need a much heavier (talking about feel here, not actual mass) diff to reduce wheelspin. A gear diff can do this well without all the drawbacks of a ball diff.

I'm not saying they couldn't work, of course they could work. I'm just saying they will require MUCH more maintainance to achieve the exact same result. They will not work better in an offroad environment.
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Old 11-18-2009, 03:54 PM   #12
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Quote:
Originally Posted by ultegrasti View Post
a ball diff could be made to handle the 'torque', no1 has done it yet. hell the ball diff was invented for use in a tractor!

is it feasible and warranted, prolly not.

R
Bingo. Yes it COULD work. No it would NOT be better.

Didn't know about the tractor bit though, might have to look that up
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Old 11-18-2009, 03:54 PM   #13
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MRC use to sell a 1/8th scale truck that was built like a 1/10th gas truck with a TTr .21 2wd and a huge ass ball diff.
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Old 11-18-2009, 05:49 PM   #14
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Many are now switching to gears diffs for all the reasons I mentioned earlier.

Not many, the only serious 1/10th offroad car I am aware of that comes with gear diffs is the new Druango. AE team drivers have tested the SC10's gear diff in the B4 and T4 and unanimously agree that the ball diff is faster.




Much lighter car, no jumps and bumps to deal with. Plus, while old brushed motors made gobs of torque, new brushless motors have much less. Plus again, carpet racing doesn't involve so much grit, dirt and sand.

I disagree, the BL stuff has more torque, along with the new lipo batteries, we're running less powerful motors to arrive at the same amount of power overall.




2wd 1/8th onroad is alive and well in europe. Some cars come with ball diffs, most come with gear diffs and some offer both. Most prefer the gear diffs.



1. Many of those non-bearing supported components you mentioned do not need to be bearing supported. Drag in the diff is usually a good thing. That's why we use those heavy greases.

A bearing supported diff will operate more accurately and free under load, won't it? Nobody's using heavy grease that I'm aware of. Liquid silicone but that's not really that limiting.


2. Ball diffs have a problem all their own. The only thing preventing them from slipping is the friction between hard steel rings and the very small contact patch of hard steel balls. This requires a LOT of pressure and you will still get some slippage when landing those jumps on throttle or powering through a woops section. Power + slip equals rapid wear. There is zero slippage in a gear diff.

This is true but again, a 1/8th diff would presumably have larger/more diff balls. Plus, the only tension the critical parts of a ball diff are under is the spring tension governing the slip, under load all those values stay the same, unlike a gear diff.

3. Ball diffs are great for onroad because the traction and lack of bumps means inside wheel spin is less of a problem. Therefore you want the diff to be as free as possible to maximize the car's turning ability. This doesn't work so well in offroad where forward traction is all important. You need a much heavier (talking about feel here, not actual mass) diff to reduce wheelspin. A gear diff can do this well without all the drawbacks of a ball diff.

I'm not saying they couldn't work, of course they could work. I'm just saying they will require MUCH more maintainance to achieve the exact same result. They will not work better in an offroad environment.

Dirt and grit is a non issue, just like in 1/10th. It must be assumed that a ball diff will be inside a sealed diff case, just like most offroad vehicles.
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Old 11-18-2009, 09:33 PM   #15
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Maybe so. If it's better I would suggest building one. If it really is quicker, people will buy it.

And you are right, brushless does have more torque but the gearing being used to get the best laptimes out of them is actually resulting in LESS torque at the rear wheels. I have driven 1/12th with 19t and 10.5 and while they both produce about the same laptime, the 19t has MUCH more rip off of the corner. Of course, I haven't run electric offroad in years so I have no idea what those guys are doing.
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