Nicadrauspro4

Sir 51D3WAYS

No, it's because it would be technologically impractical. The individual balls would have to be the size of bowling balls, the manufacture/maintenance would be a nightmare, you'd have to rebuild it like every 10K miles lol. Neighbourhoods every where would be filled with dudes rebuilding their diffs on their driveway every weekend.....
If you want a similar limited slip effect, get a clutch type LSD with a relatively low lock %.

A ball diff is supposed to diff, not be a slipper clutch although inevitably that happens as well. I've driven an old skool buggy with a slipper, shaft drive and ball diffs at both ends. (Yes such things exist) While it handled way above my pay grade, balancing the slipper with the ball diffs was a nightmare. Then there was the other nightmare of maintenance....

Wrong again. Ball diffs do provide an increasing resistance as the speed difference between the 2 tyres increases (NOT forward speed), albeit in a very mild and linear manner. Fluid filled gear diffs do the same, but in a somewhat exponential/logarithmic manner.

Ball diffs can be tightened to produce a resistance very roughly in the 20-30K cSt oil range, depending on how well it is engineered, albeit at the expense of lifespan. (I've done this before) 30K is emphatically not the thinnest of fluids, I assure you. The one thing ball diffs cannot do is simulate near spool conditions, like a gear diff with say 500K or 1 mill cSt oil in it.

Dan

iTrader: (75)

Lol!! Man, I can admit when I'm wrong and have no problem doing so but fyrstormer just doubles down.

Ball diffs cannot be tightened down to the thinnest gear diff oil? I have a SkyRC diff analyzer and can easily and consistently get a ball diff to read higher resistance than one of my gear diffs with thinner oil.

Raman

iTrader: (94)

He desperately needs to prove he has one up on all of us, majority of whom have been running and racing RC cars for the last 40 years. The slipper clutch to him is the greatest invention in RC.. he clearly can not stop talking about it. Its either that or he has some peculiar fetish.. maybe the words slipper and clutch make him feel tingly inside 🤣

gigaplex

iTrader: (2)

They're clearly wrong but there's no need to mock them like that.

Nerobro

iTrader: (2)

Drivetrains have different loads as a total beyond just one wheel to the other. And I'm not talking about the clamping force on the diff rings. When there's load on the drivetrain, the balls are forced against the spur gear. What's gonna happen when a spinning ball pushes against a fixed nylon surface? How about when you press it really hard against against the nylon? How about when you don't press against the nylon at all... like.. when you're holding the diff in your hands.

Gear diffs don't change behavior based on drivetrain load. Ball diffs do. As opposed to clamping force, which isn't drivetrain load.

Didn't see your post before I made my reply, I think you did better. I decided not to go down the ball diff thing, I can do the math, show the size ratios they'd need.... That originated with team associated didn't it? But I know ball based thrust bearings have been around longer than that... I'd need to do some research.

I appreciate it. :-)

bertrandsv87

iTrader: (2)

Calm down guys....The traditional way of building ball diffs will not allow you to build a ball diff as tight as a gear diff with thick fluid in it, but if you add sticky silicone fluid(ofna diff lock lube or rodent glue) to the available surfaces, other than where the steel balls ride, you can get near spool stiffness with alot of experimenting without any guarantee of consistency or repeatable performance...The sticky fluid needs to contact the ring gear and both diff outdrives with alot of pressure to slow down the speed differences among the three enough to help stop the ball diff from slipping or diffing out when a wheel goes up in the air...It is not easy to get the mouse trap glue in the ball diff exactly where it needs to be...Gear diffs are much less of a pain and will not slip...

Dan

iTrader: (75)

If the XV-02 is 2.6 internal ratio. And 70T (tamiya 06 module) is the center diff spur.....Tamiya only makes a 29t 06 module pinion (as its largest) giving it 6.28FDR if it even physically fits... Not so good for our group wanting to run 17.5 but might be okay for a tiny rally course...

I'm betting the stock direct center spool will allow easier spur options but you don't have the advantage of the center diff. =/

fyrstormer

iTrader: (1)

The friction between the balls and the nylon spur gear is minimal. Nylon is used as a bushing material for a reason; it doesn't drag much as long as it has even a tiny amount of lubrication applied. Additionally, the contacting area between the balls and the spur gear is minimal, equivalent to the head of a pin when you combine the contact areas of all the balls together.

Of course gear diffs change behavior based on drivetrain load. When loaded, the spider gears all try to push away from each other (as all gears do under load), and as a result of that the spider gears are jammed against the sides of the diff housing, which causes the spider gears to drag against the housing under heavy load. Primitive limited-slip differentials are specifically designed to take advantage of this effect; it just so happens that thick silicone oil is an easier and more tuneable approach.

fyrstormer

iTrader: (1)

Okay, I concede that there is a tiny amount of increased resistance under load in a ball diff, but as you say it's very mild and linear, to the point that I simply don't think it matters in any context where the XV-02 (or any non-track car) will be driven.

20k-30k cSt? Definitely not. As you mentioned above and I mentioned before, ball diffs can't generate the kind of exponential increase in drag as they start diffing-out faster and faster. That exponential increase in drag gives gear diffs a massive advantage in taming high-speed wheelspin in low-traction situations (such as, you know, rallying on dirt) that ball diffs simply cannot match.

Also as you point out, the tighter you run a ball diff, the faster it wears out, which is...well, I guess there are some people who don't care about that. I guess some people are content to crank-down the thrust springs on their ball diffs at the expense of having to rebuild them every few runs instead of just using gear diffs. I'm certainly not one of them.

fyrstormer

iTrader: (1)

I can say the exact same thing about most of the people in this thread repeating the words "spool" and "ball diff" over and over. Maybe you're unaware, but these terms are relevant to the topic of RC in general, so they get used a lot. If you'd like to stop seeing them used so much, perhaps you should take up knitting.

Papi

There will be optional bevel gears for 2.43 ratio, that'd give 5.87 FDR.

Nicadrauspro4

Yes it is possible. Why? In my FF-03Pro-R (on-road), I'm using gear diff (steel gears) with 30k oil. In my FF-03RR (rally FF), I'm using ball diffs with aluminum outdrives and used AWG instead of ball diff grease. The effect is having almost the same resistance as the gear diff with 30k oil.

So yes it is possible because I've been running both cars on a regular basis for over a year with that set up and no problems (and no slipper clutch) at all.

Nicadrauspro4

Not as many times or frequent as you mentioned "slipper clutch" and kept insisting that it is a must/necessary on every XV-01/02 and even FF-03.

I never used slipper clutch in any of my XV/FF cars and they run great. Stop insisting what does not apply to others. If it works for you, then fine. But it doesn't mean it will and should work for everyone. Different cars and drivers have different set ups and driving characteristics. So stop being a know-it-all.

MatsNorway

I get a fishing warning from that link Kentech :P