Centre diff in a FS

[baw888]

So I was tinkering away with my FS the other day, and it hit me how easy it would be to convert the FS slipper to a centre diff.
You may ask why? Well our local track is 50/50 astro turf and loamy dirt. If the slipper is too loose its great on the dirt and turns well, but looses out on the astro turf trying to clear the jumps. If its tighter then steering and onpower stability starts to suffer on the dirt.
So within a few hours and 8 x 5/32 ceramics balls, the slipper was now a centre diff.
Now it turns on a dime. Doesnt step out when under power out of turns and it very settled in the bumps. Drive on the high grip sections is crazy good.
The next race I ran a a PB by more than .5 sec. So it seems to work.

Has anyone else over the years used a centre diff? I know one of the previous lazers had a centre diff but the FS design ends up without a thrust bearing and this seems to bind the front to rear bias perfectly. The slippers spring adjustment give a great variation in drive.. Id post a photo but it looks like the slipper, just with a white spur instead.

Brad

[Gayo]

Wow, interesting. So you don't loose drive on high grip parts?
What brand of spur and diff ring do you use?

Pics please!

[baw888]

No, the drive on the high grip sections is better, the front wheels dont spin if the traction is there.
On the dirt the front does spin if the diff is set too loose, but it is very easy to dial out.

Parts taken out are spur and slipper pads.

Parts used were: 78 tooth Kimbrough spur, the ones for pan cars.
Drilled out ball holes to accept 5/32 ceramic balls instead of 1/8.
Bearing inside of spur is a B4 idler gear bearing.
Diff rings are Tamiya, from an old on road solid axle rear end, also found that original rc10 'six gear' diff rings are large enough as well.

Method was simple, mount a slipper disc on a bolt, spin them in my drill press at high speed. Use a sharp drill bit tip to carve out a groove to hold the diff rings. Works very well surprisingly.
Put together with minimal lube on the balls.
Lots of black grease where the thrust bearing would nomally be.

I'd believe that this would greatly increase the handling of a stock class racer, probably more that a mod driver.

I'll get photos next week but it really is very simple.

Brad

[fastinfastout]

I dont have an FS, I have never owned a 1/8 scale buggy/truck which has a center diff......but whats the purpose of a center diff?

[Dyna]

This is back to the days of the Tamiya Egress & Kyosho Lazer ZX

Would be nice to compare them ( the normal set up and then centre diff ) back-to-back at the track to see exactly what difference there is - nice work though

[dodgydiy]

i have a homebrew micro which is based mainly on tc parts, have run this with and without centre diff. set as slipper it works better on low grip as it has less tendency to snap and spin without warning. in high grip it drives and turns better with the diff, or seems to anyway, but can be a bit unpredictable when pushing it a bit. this car is small and light so it may well work better in a 1/10 which is a bit less of a handful anyway

[baw888]

Originally Posted by Dyna

This is back to the days of the Tamiya Egress & Kyosho Lazer ZX

Would be nice to compare them ( the normal set up and then centre diff ) back-to-back at the track to see exactly what difference there is - nice work though

Thats the next step for me. The best bit is that it converts back to a slipper, just swap spurs/balls, for a spur/pads.

It think the difference from the old days might be that it doesnt use a thrust bearing. It gives a good limited slip action.

In its firt race weekend it was half a second faster, but then again everyone else was too, being a state titles.

[bender]

Hi Brad,

Looking forward to having a look at your car next time i'm out at Redbank.

Had a similar idea with the Durango a little while ago but haven't worked out a way to implement it yet (the Durango slipper units is very narrow).

Top 1/8 buggy driver Joe Quagmire (spelling) said in one of his blogs a while ago that when he had to run electric buggy he mentioned with all the power we have now that the car could have really benefited from a third diff.

[baw888]

Originally Posted by fastinfastout

I dont have an FS, I have never owned a 1/8 scale buggy/truck which has a center diff......but whats the purpose of a center diff?

Have you ever owned a 1/8 buggy/truggy? All of them usually have a centre diff.

[fastinfastout]

Originally Posted by baw888

Have you ever owned a 1/8 buggy/truggy? All of them usually have a centre diff.

no.....

[c0sie]

Im led to believe, rightly or wrongly, that the centre diff allows you to tune which end of the car the power goes too...

A tighter oil in the centre will allow the power to transfer to one set of wheels (front or rear) whereas a lighter oil will all the power to transfer the opposite way.

As it stands in electric 10th the power seems to flow more towards the front (there is a great photo of Griff's 4WD from the oOple race somewhere on the forum drifting around a wet concrete bank..his rear tyres planted and his fronts lit up).

Surely if you use the centre slipper in a car such as the DEX410 as a centre diff with diff balls you loose the slipper eliment which will ultimately feck your driveline after a while?

[Neil Skull]

I fully understand Diffs in 1/8th as Cosie mentuions it gives you the ability to change the car by giving more or less traction to the front or rear of the car.

To me and please correct me anyone, the FS will run approx equal power to the front and rear i guess maybe a little extra to the front as it has a short prop shaft as opposed to the long one to the rear.
The slipper simply allows the driver to adjust the amount of power to all the wheels adjustable depending on track conditions.
Too loose and you will lose acceleration due to the slipper not producing maximum power to the drivetrain.
Too tight and the car can wheelspin losing accelration due to loss of traction. A good driver could in theroy drive with no slipper or with it locked which i guess should be how you run on high grip.

The Slipper mod by our friend is nothing more than a slipper to me which is likely to be quite loose, therefore on slippery conditions could prove to be very helpful.

Feel free to correct me.

[c0sie]

Ideally you need a slipper that slips to some extent to save your driveline when coming down from jumps etc, rather than killing your ball diffs after afew runs.

The centre diff, I think, would have to be a geared diff so that there is no loss of power transfer (as per the original slipper) yet allows the front and rear to operate independantly where required?

[DCM]

If he has done it with a Dual Slipper unit, then it could work, if he was done it with a normal slipper, where the front and rear outputs are joined, then he has made a very progressive slipper unit...

[Si Coe]

But a dual slipper acts in a similar way to a centre diff itself, or rather can be made to. The dual slipper on the XX4 for example is specifically designed to run different slipper pads front and rear, which effectively alters front/rear power transfer

[mattb]

Originally Posted by Si Coe

But a dual slipper acts in a similar way to a centre diff itself, or rather can be made to. The dual slipper on the XX4 for example is specifically designed to run different slipper pads front and rear, which effectively alters front/rear power transfer

you put different slipper pads in the fs si red or white one slips easier than the other

[baw888]

Some comments.

Having a short font shaft compared to a long rear shaft doesn't effect power transfer.

Yes its done with the original FS slipper setup, very similar like the XX4 duel slipper.
But a slipper will only limit torque applied to the wheels. Its doesnt matter how much grip the tyre gets. When it hits a certain level the slipper gives in.
On tracks with vering levels of grip this becomes a problem.

A diff keeps the torque the same at the front and rear. They might be doing differnet RPM , but the diff will try to kee the torque level the same. Equals a balanced car!

So if the grip level is high. The car will squat rear ward, the rear will untimately have more traction so the front wheels will loose traction first. But this has happened at the point of maximum traction available, not the level on torque the slipper is set to. This means the car will start to understeer under hard acceleration, not step the rear out, it makes it very easy to drive.

If the grip level is low, the front wheels will spin earlier, still providing understeer on corner exits, and not over steer.

Why is it different to a normal ball diff?
Unlike dropping in a standard ball diff, which is very light in its action, (would cause the front wheels to spin like crazy), the diff has no thrust bearings, just like the FS slipper, so you can adjust the diff action, from very light-to very stiff, just like changing the oil in a 1/8 gear diff.

Why I think its better than a slipper unit? Its seems better when on track with inconsistant grip levels. From loose dirt to sections of astro turf.
Has the drivability of a loose slipper in the low traction sections.
Has the direct drive acceleration of a tight slipper on high traction sections.

Brad

[Neil Skull]

Hi Brad,

Thanks for the explanation.
That makes it easier for to understand.

It is a novel idea for sure and i am glad it is improving you lap times.

[baw888]

Ver 2.0 is well under way. A slipper is being added to smooth it all out.

[Mr. Pink]

Tried my very crude centre diff mod yesterday.
Drilled out 8 4mm holes in a original spur-gear with 5/32 balls directly against the slipper plates.

My home track is high grip astro and I found it very easy and smooth to drive. But I had problems to get the car quickly around hair pin turns that is no problem with regular slipper. On medium turns and high speed turns it felt very smooth and stable. I am quicker with standard slipper on this track but it will be tested out on loose surface as well...

One thing that is affected is braking, as you can not brake as hard but on the other hand it is more stable under braking.

My mod did not allow any slip at all (soft alu slip plates directly against diff-balls). so it was the front wheels slipping instead, under-steering on power.