avs

iTrader: (2)

serpent made a diff for 1/8 (the 1/8 2wd class died maybe 6-8 years back?)
anyways, the general consensus was that a rear diff was overall slower than a spool rear axle. it would make for smoother drives out of corners but overall the car was slower, it would rotate slower and it was heavier. i don't recall any reliability issues.

i never tried it in 1/8 scale but the 1/10 2wd car seemed to run best when the diff felt graunchy and in need of repair. a smooth new diff was slower. i only mention this to indicate that what may seem better isn't always an improvement.

team novarossi

the suspension design we serpent uses dates back from before the vector or is slightly pre vector....
And indeed designed to run with a diff.

The stupid camber change is easy to explain.
If you keep all your 4 wheels planted firmly down tot the racetrack you will have undriveable car because the lack of a diff.
To make it corner better they made the inside rear wheel coming of the ground.

The reason why the 1:8 scene is not using the diff is mostly because everybody follows everybody....and there are a very few people that are not afraid of going outside the box.
The real reason is performance wise...with a diff your car drives better and smoother but it was slower due the mass of the diff your engine had to accelerate.
But that was 10 years ago...or more.
I think it is not so hard to design a lightweigth diff for the 1:8 now.
Just look at the diff of a F1 car, hardly bigger then a football and it withstands 900+ Hp!
so why can't we have it???

squarehead

iTrader: (75)

All reasonable explanations. And I agree completely about technology advancements. There is no reason to not to be able to handle the power of a .21 when diffs can be built for buggies and other R/C cars with a LOT of horsepower and a lot more traction than asphalt.

I don't know a whole lot about these cars yet, but in my limited exposure to the design of the various chassis in this class, it seems to me there are likely other ways of splitting the atom, for sure.


This class is REALLY going to be a lot of fun.



Oh by the way, I received my 12mm hand reamer from J&L yesterday and the wheel fit is much better, but still pretty tight (duh). You'd think the son of a machinist would know that the hole should be slightly oversized from the shaft unless a press fit is required. For anyone buying a reamer for the wheels, I'd recommend oversize from 12mm and buy a .4735" straight-fluted reamer. That should fix the fit issues that all wheels seem to have. I need to pay attention more...




doug

duneland

ApexSpeed,
The coned rear tires simulate a diff (in feel).
If you try to run the tires flat & with little or no camber, the car will want to 'lock' in a straight line and resist turn-in. When the front tires bite enough to establish turn-in, the back-end will break loose and whip around. By coning the tires (and running the appropriate amount of -camber and toe-in), the tires are forced to scrub when running straight. Makes for a smoother transition from straight running to cornering. A differential would give less tire wear and change set-up approach. It would add rotating mass and complexety/probably slow down accelleration.

Rick Davis

During the early days of 4wd I tried diffs a number of times, and if you want something that pushes like a dump truck on power they are they hot tip.

squarehead

iTrader: (75)

Thanks for those explanations, Ron and Rick. I appreciate the input.

So if I am reading into this correctly, as a whole, these cars have so much rear tire that with a properly designed rear end, there is so much rear traction that the cars won't turn. So to fix this, a solid rear axle is run, and the setup of the cars revolves around the idea that a live rear end needs to lever the car (or the inside rear tire) off of the ground to allow the car to tun properly, rendering it essentially a 3wd car.

So doesn't logic tell us that there is WAY too much rear tire?

Would a lighter, narrower, smaller rear tire with a differential and a rear suspension design that kept both tires on the ground through the corner make more sense? Or is this just silly talk?


Patronize me, my brain is like a lotto machine filled with ping pong balls...




doug

ESWLFSE

iTrader: (7)

I think a bigger problem is that a proper limited-slip feature adds enough weight and complexity to the diff to offset any traction gains. An open diff will just lose traction spinning the unloaded tire.

azcau

iTrader: (1)

Then wouldn't we be driving bigger, heavier Touring Cars ???

Nice thread, I'm enjoying it.

squarehead

iTrader: (75)

Not necessarily, but what's wrong with a touring car design if it works? If you have so much rear traction that you are designing cars to lever the inside rear off of the ground to get the car to turn, you may have too much tire. With 4wd, it seems as though there really isn't a need for that much rear tire, but maybe I'm wrong.

Has anyone ever tried narrowing up a set of rear tires slightly and not using as much rear camber?


Just wondering.

duneland

ApexSpeed,
It is not necessary for the inside rear to be off the ground in order to turn.
This happens only in tight corners with high entry speed.
We vary the tire widths to help tuning, but this not an attempt to run flatter tires. You still have the spool and car will still resist turn in, it would just break loose more dramatically.

squarehead

iTrader: (75)

Good to know. Thanks, Ron.


I still think narrower tires, and more traditional rear-end geometry with a gear diff would be an interesting test.

bozla

ISn't a solid rear axle a regulation thing?

squarehead

iTrader: (75)

In the U.S., there are no ROAR or other sanctioning rules that mandate or regulate differentials or rear axle types in any class of R/C racing.

Taylorm

Apex, i've wondered that myself........why not have a diff and run the tires flat?..then you get somewhat even wear of the rear tires.........i just won an old BMT 934 1/8 4WD on ebay and it has a diff in the rear????????........wonder why they (diffs) never caught on........more complexity?..more overall maintenance?.......consistency without having diff losing it's setting???.not that i'm dying for a diff in my 1/8 cars...the last thing i need is more work...

M7H

With a diff. during cornering, you will loose to much traction on the inner, unloaded tire. All the engine's power will be just lost here.

The cornering speed of these cars is so big, together with very little weight, that a solid rear is the way to go.
I even seen 1/8 traction roll.....