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Old 07-01-2008, 11:39 AM   #1
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Default Anyone ever run a live axle?

I'm going to try taking the diff balls out of my old t3 (race my t4) and see how it does on the track. Has anyone tried it? I figure if it's good enough for all the racing quads (yamaha/suzuki/honda/arctic cat/kawasaki) on the market then why not r/c.
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Old 07-01-2008, 12:30 PM   #2
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No more corner entry steering, nor corner exit grip, it blows.
I tried on my T CR once.
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Old 07-01-2008, 12:35 PM   #3
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Had one in my xxxt and its not great... ok for bashing if thats what you do. I hate ball diffs, with brushless/lipo I went through a bunch and had to run them crazy tight so it acted closer to a locker. Desert truck gear diff was the answer. Man, what a difference in turning, it real tough, no maintenance.
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Old 07-01-2008, 01:27 PM   #4
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Makes sense it would break loose it turns. I kind of favor that driving style. I would think a live axle would be faster out of a turn and on the straight but would suck in twisties and on sweepers. I also think a live axle would recover from slides much easier then diff cars. I'll put it to a test on the track.
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Old 07-01-2008, 03:53 PM   #5
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It's called a spool and it usually only used to replace the front diff. Popular in touring car onroad with rubber tires on asphalt, but not so much offroad.
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Old 07-01-2008, 05:47 PM   #6
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Off-Road races are won in the corners and by staying on all 4 tires headed in the right direction. If you aren't doing this you are slipping behind.
So..
If your car pushes, you are losing time.
If your car is loose, you are losing time.
If your car is in the air and the arc distance is longer than you can drive in the same time.. you are losing time.


Ergo
if you have a hairpin turn, generally you want to be within 1 foot of the corner. The rough distance you will cover can be determined with the circumference formula. 2 x Pi x r. at 1 foot (12 inches) 2 PI 12 = 75.39... except you are only going a half circle so divide by 2. 37.7 inches. if you are 3 feet from the corner because your car wont turn or you just blew the corner.. 2 pi 36 = 226.19 / 2 = 113. Guess what.. 113 - 37 = 76 .. which equals about 6 car lengths. remember this is an example.


So pay attention in math class.

I think you'll find out with your test that the live axle isn't useful for turning left and right. I know of no one running a live axle in a regular road coursey racing series. Only nascar runs it at the 2 or 3 road events a year.
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Old 07-01-2008, 05:59 PM   #7
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Uhhh...yeah... If you're gonna try and look like a braniac, you should really have your terms straight.

A "live axle" is a rigid axle. And there are many, many "turning" style automotive classes that run them. Virtually all the bigger off-road vehicles (all the pro CORR classes and the larger SCORE trucks) and NASCAR run live axles.

I was just BS-ing with my friend (CORR crew chief, who's #1 in points ATM) about R/C stuff vs. 1:1 and he was wondering why we didn't run live axles.

http://www.google.com/search?hl=en&c...ition&ct=title

Stringcheese is talking about a locked diff or spool...and I think that's what you were referring to as well.


Quote:
Originally Posted by Mason View Post
Off-Road races are won in the corners and by staying on all 4 tires headed in the right direction. If you aren't doing this you are slipping behind.
So..
If your car pushes, you are losing time.
If your car is loose, you are losing time.
If your car is in the air and the arc distance is longer than you can drive in the same time.. you are losing time.


Ergo
if you have a hairpin turn, generally you want to be within 1 foot of the corner. The rough distance you will cover can be determined with the circumference formula. 2 x Pi x r. at 1 foot (12 inches) 2 PI 12 = 75.39... except you are only going a half circle so divide by 2. 37.7 inches. if you are 3 feet from the corner because your car wont turn or you just blew the corner.. 2 pi 36 = 226.19 / 2 = 113. Guess what.. 113 - 37 = 76 .. which equals about 6 car lengths. remember this is an example.


So pay attention in math class.

I think you'll find out with your test that the live axle isn't useful for turning left and right. I know of no one running a live axle in a regular road coursey racing series. Only nascar runs it at the 2 or 3 road events a year.
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Old 07-01-2008, 06:22 PM   #8
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In that case, you'd want to race an old Tamiya Grasshopper. The reason we don't use solid rear axle tubes is a) too much unsprung weight and b) not enough articulation to handle the bumps and ruts. Keep in mind the scale we are running. A 2 ft high jump that launches your car 5 ft in the air, would be a 20 ft jump that launches a CORR truck 50 ft in the air. What a CORR truck would consider a rough track would be a glass smooth track to us.

The only RC cars that use what you could call a live axle would be 1/10th and 1/12th pan cars. They DO run on glass smooth tracks and would rather have the very low overall car weight that the rear pod type setup allows.
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Old 07-01-2008, 06:29 PM   #9
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my terms are right.

corr rules (pro 2) limits rear suspension to live axle only. suppose to be like production vehicles so people can 'associate' with them. doesn't mean its faster.
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Old 07-01-2008, 07:32 PM   #10
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Quote:
Originally Posted by Mason View Post
my terms are right.

corr rules (pro 2) limits rear suspension to live axle only. suppose to be like production vehicles so people can 'associate' with them. doesn't mean its faster.
I know YOU think IRS is faster...but you don't actually build race cars, do you?

Oddly...a guy who does build them for a living...has an actual engineering degree AND IS CURRENTLY LEADING IN POINTS in the top CORR class says differently. That's why he was wondering why we didn't use them. EVERY Pro class in CORR uses them, Pro-Lite, Pro-2 and Pro-4.

And you did have the terms backwards. Go re-read your post.
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Old 07-01-2008, 08:38 PM   #11
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Some advantages of IRS are suspension alignment related, allows for things like rear toe, camber, and camber and toe gain/loss, adjustable roll center, yada yada, through various suspension changes. Both body roll and ride height changes. And the lighter unsprung weight that was mentioned.

Not sure about CORR rules, but offhand I’m not aware of any race cars that don’t use IRS when it’s allowed. Even on reasonably smooth onroad surfaces, F1 and Indy for example. Or road cars when cost or load carrying capacity (ride height considerations) is not a significant factor.

Remember several years ago in NASCAR, I think it was early mid ‘90s, there was a rash of broken axles. They were bending the solid live axle a little to get some camber for cornering. Relying on the splined connection of the half shaft (they use “live” half shafts unlike normal road cars they are derived from for safety, i.e. they do not hold the wheel on with the half shaft) to absorb the angled drive. Which it didn’t do very well, thus the breakage problem. NASCAR does require live axles by rules.

Of course ya got to define what fast is, IRS only helps when you are talking cornering speed and bumps. Live would be the best for Bonneville I suspect, straight ahead and hammer down. But not sure, I don’t have that experience. I do have the fancy sheep skin and several decades of suspension design/application/development experience, have studied and worked with virtually every suspension design out there, including historical examples and their development. And tire dynamics, which is where everything is aimed at. Including experience with NASCAR live axles. For what’s it’s worth, which I recognize ain’t much here. Just call it my hunch if you will.

Back to the diff issue, in my experience with RC a locked diff/spool doesn’t even work all that well down the straight in off road. Any loss of traction tends to send the rear end wiggling. A diff allows one wheel to help maintain tracking when the other encounters traction difficulties. Not to mention the problems getting into and around the corner. Of course, that could just be my lack of driving skill!

Right, wrong, or indifferent, Cheers to all.

Last edited by Dave H; 07-02-2008 at 06:34 AM.
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Old 07-01-2008, 09:01 PM   #12
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In the race class that I ran you must run the stock setup that your car left the factory with, so if you had a live axel you where stuck with it. And its time has come and gone. You have to deal with watts links, panhard bars and the like to keep them where they are supose to be.....they flat suck. And I can't think of a car that still uses them off the top of my head other then the crown vic.

So what people did to be legal was to....ahhh....warm up the axel tube then....ahhh....opps drop it. This would alow you to change the camber on the rear wheels. It is a little hard on axel bearings. I am talking about older cars like RX7's and the like.

I have not seen an RC car with a live axel in a very long time. And the only reason to run one is because the rules make you.

If I understand what you are talking about is locking the diff, and doing it the quick and dirty way like welding the diff on a real car. It will help in some areas and hurt in others. In the vintage sports car world and in classes like SCCA prod classes it is a common practice. Expecially if you have a odd ball car that it is hard to find a real LSD for.
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Old 07-01-2008, 09:08 PM   #13
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Quote:
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And I can't think of a car that still uses them off the top of my head other then the crown vic.
You're close, but don't forget my Mustangs! Which are for 2 reasons, cost and drag racing. Well, only cost in my case, I haven't tripped the lights for nearly 30 years myself. And that was usually only with one driven wheel.
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Old 07-01-2008, 09:52 PM   #14
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You're right Joe. When somebody asks one question in the thread topic and states a different one in the body of the message, I'll never be right.

He's going to have wear problems with the diff moving around in the case unless he shims it a bit.
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Old 07-01-2008, 10:07 PM   #15
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Quote:
Originally Posted by Mason View Post
You're right Joe. When somebody asks one question in the thread topic and states a different one in the body of the message, I'll never be right.
Quote:
Mason said:
I think you'll find out with your test that the live axle isn't useful for turning left and right. I know of no one running a live axle in a regular road coursey racing series. Only nascar runs it at the 2 or 3 road events a year.
You confused a live axle and a spool. You made a mistake and internet rules require that you have your balls busted for it. No biggie...happens to everybody at some point or another.

The point was, that contrary to what you said, NASCAR runs a "live axle" at every event, but a "spool" only occasionally. CORR uses them at every event and SCORE Trophy trucks use them.

I can't find anything in the rules that requires live axle in Pro 4...and unless they required IRS, they aren't gonna use it, because it doesn't handle as well. Well...at least according to the guys who make a living doing it. There may be some places where it's preferred, but it isn't in CORR. Again, that's why he was asking why we DON'T run a live axle instead of IRS.

http://corracing.com/getfile.asp?tid...+2008+Rulebook

I'll check in the morning to see if they're required...but I know which one is preferred. We just had the conversation a few days ago. IIRC, it was because you can keep the weight where you need it.

Last edited by Turbo Joe; 07-02-2008 at 08:23 AM.
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