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FunwithFox

DT-02 ball diff to spool conversion

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Hello!

I'm currently acquiring some of the last parts needed

for my hopped-up-to-be Street Rover.

After some forum searches I'm still a little unsure, so it's time to ask.

I already have the DT-02 ball diff (53863)

http://www.tamiyausa.com/product/item.php?product-id=53863,

and was wondering if it would accept these bushings (54424)

http://www.tamiyausa.com/product/item.php?product-id=54424

to make it a spool diff?

Has someone this setup in their DT-02 ?

How would you compare the difference in handling to a

  1. DT-02 with a standard diff
  2. DT-02 with a ball diff

On what kind of track surface would/do you run this setup?

Any other comments?

FunwithFox

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the Tamiya DT02 ball diff is a limited slip ball diff, it is designed to slip under load anyway. As the DT02 chassis cannot have a slipper clutch Tamiya made this ball diff to slip.

It is just a case of getting the setting right, it really does work very well. When you built the ball diff you would have seen the concave spring washers .....

those let the ball diff slip as designed.

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Hello and thanks for the reply!

Yes the DT-02 ball diff is a limited slip ball diff, but I was more curious

about how it functions with these bushings (54424)

post-2156-0-46826900-1444700370.jpg
which replace the 3mm balls in the diff.
The drawing for installation:

post-2156-0-38986900-1444700389_thumb.jp

So if someone is using or has experience with this setup,
comments would be helpful for me.
FunwithFox
Edited by FunwithFox

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Locking the rear diff on a 2WD buggy is a recipe for serious understeer, or if you do get it to steer, it will do donuts on most surfaces. There's very little between those two extremes.

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Lots of people have lots of experience with both these types of diffs through racing at the DT challenge. Which had it's third successful event this year :)

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Does spool means just a locked diff? If yes, this should be possible with the regular gear differential.

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No doubt if you use the ball diff as an actual diff then it works great. But if you lock it so it doesn't diff, as he suggests with the 3mm bushings in place of the balls, it should be a challenge to drive. He's proposing the same thing RWD drift cars are doing currently.

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I think these bushings are intended for use in 4WD cars with a front ball diff. Drive out of corners can be improved with a front spool but these put huge loads onto drive shafts if you clip a corner marker which often breaks the shaft. With these bushings the spool will operate as a slipper spool under these shock loads which should protect the drive shafts.

In the rear of a DT-02 would not be a good place for these and the handling would be wrecked as previously described.

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By the way, I don't see where the DT02 ball diff is anything special compared to any other ball diff. The marketing around this diff calls it "limited slip." Big deal! All ball diffs slip to a certain extent. It has a central gear, diff balls, rings, plates, outdrives, thrust bearing, and adjustment screw just like any other ball diff. The cone washers replace the typical coil spring. So what? Pan cars and F1 cars do the exact same thing. In fact, tuning tips for the F103 suggest adjusting the ball diff so it just barely slips to help control power delivery to the tires. So, there's nothing special about its "limited slip" characteristics -- every other ball diff out there acts the same way. I think Tamiya threw "limited slip" in the description of this ball diff just to contrast the "non-slip" characteristics of the kit gear diff.

tamiya_53863_002.jpg

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I can tell you this ball diff does slip and is very good. I use one in my DT02 mod car and my DT03T.

This ball diff some how is nothing like a proper ball diff, non of my TRF ball diff's slip as they are not suppossed to !

My DT02/3 limited slip ball diffs slip wonderfully !!

Without owning one I am not sure you can say without trying one first.

Some how the spring cone washers work very differently to a normal spring.

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Personally I really think the 'limited slip' term is confusing here. Limited slip differentials in general are named that way because they allow a degree of slip between the tyre and the ground, unlike an open diff which sends all of the torque to the unloaded wheel. The term has nothing to do with balls skidding on rings and replacing slipper clutch action. In my opinion you never want an RC ball diff to slip because the margin of error between ok and meltdown is so small. It's metal-on-metal with silicone grease which can not lubricate the interface between the ball and the ring. Is there some constructional difference between the DT-02 ball diff and other ball diffs? Because by the automotive definition, ALL ball diffs are limited slip by virtue of the preload adjustment you can make with them. They are the half way point between an open diff and a solid axle.

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Firstly I must apologise for this post, I tend to offend people with how I try to get things across. It is well known on this web site I am rubbish with diplomacy.

yes, the balls do slip or 'skid' as you put it ........

And you should never use silicone grease on a ball diff.

maybe if people actually have this limited slip ball diff and actually raced with it ............... well you get the point.

The DT02 platform as we all know is used in the massively popular Tamiya fighter cup in Japan. And as we all know the Tamiya super fighter cup is huge in Germany as well.

The DT02 chassis has no slipper clutch option deliberately built in to the chassis so the limited slip ball diff was devised. It is actually the same limited slip ball diff that is in the Top Force.

Being a racer I race my trf502x and my 201 vega and my 201/502 hybrid and these diffs do not slip in anyway as I build them properly. That's why they have a slipper clutch !

Once a trf ball diff starts to slip it is re-build time.

If the trf ball diff slips on power it means it is not tight enough, maybe more people should race their cars.

Ok moving on,

The Tamiya DT02 challenge which I organise every year is hugely popular and ran it's third successful year this year.

In the mod class we run the limited slip ball diff as the 19 turn specs and 10.5 brushless makes the car wheelie with the gear diff.

Having the limited slip ball diff 'slip' the front wheels stay on the ground.

Racing, cannot beat it :D fantastic.

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Hello again!

Edited my second post above a little. The images were not showing, but hopefully that got remedied.

So, a DT-02 ball diff with bushings is the way to go,

if you want a understeering RWD car or for drifting, it seems.

But one possible scenario still comes up to my mind:

Loose sand (slipping tyres) on a beach and a driving style not so much forward,

but sideways like cornering in rallying or on dirt ovals.

So just bashing and sand in the air all around, would it work ? :)

FunwithFox

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FunWithFox: Yes, the sand scenario would be one where a solid axle or ball diff fitted with those plastic bushings might actually be a good set up. You would have to try it out. Certainly the SRB cars with solid rear axle are great to drive on sand. Their shortcomings are clear on harder grippy surfaces though.

Super Gripper: I understand and respect your point of view. I'm a big fan of racing too and do my fair share, including your awesome DT-02 event which I have attended for the past two years. Placed quite well on both occasions. However, running in the standard class I was using the kit geared diff, not the DT-02 ball diff. I haven't ever opened up a DT-02 ball diff but from the exploded view posted I see nothing to suggest this unit should be any more tolerant of balls slipping on the rings than any other competition RC diff such as those in the TRF cars. I have some knowledge of these as I have designed and made several diffs over the years including some that have been very successful in competition.

If I had to guess, I would imagine Tamiya have named this a 'limited slip' ball diff because the type of newcomer most likely to own and run a DT-02 chassis may not be aware of the merits of a ball diff and the fact that their characteristics make them better for racing. However, they may well be aware of an LSD as a car upgrade or performance mod in 1:1 cars so it just gets the point across better for that audience. But, that's just a guess.

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So...

Does spool means just a locked diff? If yes, this should be possible with the regular gear differential.

...since nobody replied yet, I'd like to pose my question again. If this is about locking the diff, how about just pouring hot glue into the gear diff, or locking it with an additional spider gear (if possible)? Instead of trying to lock a ball diff.

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Yes a spool is just a locked diff or solid axle. He already has the ball diff so these bushings provide an elegant way of locking it. You could glue up a gear diff to achieve the same thing, but that's a bit 'cave man'.

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Ah well, so FunwithFox already has got the ball diff as a hop-up and thinks about how to modify it.

I guess his Street Rover kit already came with a gear diff from the start, so he should have two diffs (1 x ball, 1 x gear) now.

My thoughts are:
The DT-02 ball diff is expensive. From the few things I know or heard about it, I guess it uses unique parts. If I'd own one, I wouldn't bother modifying it.
The DT-02 gear diff is inexpensive, and is provided with the basic kit anyway. The diff parts aren't unique since they are found in many other Tamiya kits as well. I would have no problems tinkering with such a common diff.

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Hello...

and thanks all for your input. As I was ordering some parts anyway, I decided to

add the bushings to my order. The Street Rover build will be something for me

to do during the winter holidays. My plan is to hop it up to a DT-02MS standard.

speedy_w_beans and LongRat:

Thank you for your comments on handling, setup pros/cons and the sand scenario.

GregM:

Thanks for your opinion on the gear/ball diffs and your clarifying question about the spool.

The reason, why I was asking about the bushings, was that the ball diff set up with the bushings

would (in my reasoning) be a more fault-tolerant version of a locked DT-02 diff, as it would allow

still slip, when the a shock, a crash or other situation would be hard enough on the locked diff.

Also the fact, that the change (bushings) can be easily reversed back to a normal ball diff,

makes it a no-risk mod. I'm also going to assemble the original gear diff (came with kit)

so that I can compare the handling between the two versions later (and also have a spare).

And yes, I have many times heard, that the normal gear diff is pretty bullet-proof normally.

Have a nice day!

FunwithFox

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