68 replies to this topic

[NeilR]

Assuming the same braking power, what is the disadvantage is a single rear disc acting on a helical diff housing, vs twin discs acting on the driveshafts? IS there a potential cross axle issue in rear braking in a turn?
The car will be a very simple, 350kg, 750cc bike engined single seat hillclimb car with wings and it is unlikely that it will lift a rear wheel as rear roll will be soft and rear travel generous at 80mm. Speeds will be up to 175kph and we had planned to use front motorcycle calipers and 260mm diameter 5mm thick discs all around - two on the front and one on the rear. Grip will be limited by the fact that we initially plan to use used Formula Ford rubber...and then will switch to Hoosier R25 crossply slicks on 6/7" rims.

Edited by NeilR, 15 January 2010 - 23:00.

[Lee Nicolle]

Assuming the same braking power, what is the disadvantage is a single rear disc acting on a helical diff housing, vs twin discs acting on the driveshafts? IS there a potential cross axle issue in rear braking in a turn?
The car will be a very simple, 350kg, 750cc bike engined single seat hillclimb car with wings and it is unlikely that it will lift a rear wheel as rear roll will be soft and rear travel generous at 80mm. Speeds will be up to 175kph and we had planned to use front motorcycle calipers and 260mm diameter 5mm thick discs all around - two on the front and one on the rear. Grip will be limited by the fact that we initially plan to use used Formula Ford rubber...and then will switch to Hoosier R25 crossply slicks on 6/7" rims.

Presuming you are using a solid axle in theory it will work fine. But for some reason it will never work as well as two rotors and callipers of the same thearetical braking power. The rotor will have to be on or near centre or you will get steer from the rear under braking.
Some road race karts use a single rear rotor but from my limited experience the fast one pay the weight penalty with two.
On sprintcars they normally use a 11 or 12" inboard disc on the left side of the diff with a 4 piston calliper. On the R/R they normally usew a small rotor and tiny calliper outboard. This system pulls them into the corner [turning left at all times]

[SteveCanyon]

No, Neil, use two brakes on the rear if you have any kind of diff on the rear axle. You're just asking for lots of spins under brakes if you don't.

Billzilla

[NeilR]

Many british HC cars use a single rear disc, but FSAE have moved away from it, hence my question.
Why the spins Bill?

[gruntguru]

Many british HC cars use a single rear disc, but FSAE have moved away from it, hence my question.
Why the spins Bill?

Are the FSAE teams moving from single to twin discs the same ones who are changing from a spool to a diff?

Edited by gruntguru, 16 January 2010 - 03:26.

[SteveCanyon]

Many british HC cars use a single rear disc, but FSAE have moved away from it, hence my question.
Why the spins Bill?

You're going to be hill climbing the car, and I suspect it'll be going a lot faster than the SAE cars do.
It also means a lot of downhill stops so the rear end will get rather light. You don't have to lift a wheel off the ground to get it to lock-up, only enough for the brake torque to overcome the frictional forces generated by the tyre. So, if on rear tyre locks then you are faced with getting off the brakes enough to unlock it, or going off-track, or spinning.
And as I'm fond of saying, the better set-up the car, the more rear brake you can carry so if you start locking rears then you're going to increase your chances of something undesirable happening.

Billzilla

[NeilR]

OK will investigate machining CV cups so as to add dogs/rear discs.

[cheapracer]

There is something that uses the setup of a torsen style diff with sprocket one side and disc the other side for bike engine race cars - maybe Quaife?

Keep looking, it's somewhere

..if you start locking rears then you're going to increase your chances of something undesirable happening.

All that time in FWD is turning you gay you know?

Edited by cheapracer, 16 January 2010 - 07:59.

[NeilR]

http://www.westhouse...chaindrive1.htm

[SteveCanyon]

All that time in FWD is turning you gay you know?

Yeah yeah me love you love time pretty boy!

Steve.

[gruntguru]

You're going to be hill climbing the car, and I suspect it'll be going a lot faster than the SAE cars do.

I would suggest the opposite. A good SAE car with restrictor removed will have more power and only 60% of Neil's target weight. Aero may be the only downfall for SAE cars not equipped with wings, and only on faster tracks.

Edited by gruntguru, 16 January 2010 - 10:04.

[SteveCanyon]

I would suggest the opposite. A good SAE car with restrictor removed will have more power and only 60% of Neil's target weight. Aero may be the only downfall for SAE cars not equipped with wings, and only on faster tracks.

How much power do the SAE cars make?
A reasonable 750cc bike engine will be over 100hp no problems.

Billzilla

[gruntguru]

How much power do the SAE cars make?
A reasonable 750cc bike engine will be over 100hp no problems.
Billzilla

Less than that with the restrictor. Without the restrictor you can just compare stock bike engine specs. The hot 600's are built for production 600 racing so most of them make about 120hp stock.

[NeilR]

I have a GSXR 750 engine at 128bhp and 82nm at 10,000rpm. A 2005 600GSXR is 108bhp and 63nm at 11200rpm. So there is a reason to go for the extra 150cc.
The lightest 1000cc HC cars are spot on 220kg wet. However we are trying to make a simple version...an L plate single seater that 2-3 guys can drive on the day. It will start, idle, handle an 'off' across the ripple strips and will be as safe as possible. FTD is not our focus.

Edited by NeilR, 16 January 2010 - 11:46.

[Fat Boy]

Assuming the same braking power, what is the disadvantage is a single rear disc acting on a helical diff housing, vs twin discs acting on the driveshafts? IS there a potential cross axle issue in rear braking in a turn?
The car will be a very simple, 350kg, 750cc bike engined single seat hillclimb car with wings and it is unlikely that it will lift a rear wheel as rear roll will be soft and rear travel generous at 80mm. Speeds will be up to 175kph and we had planned to use front motorcycle calipers and 260mm diameter 5mm thick discs all around - two on the front and one on the rear. Grip will be limited by the fact that we initially plan to use used Formula Ford rubber...and then will switch to Hoosier R25 crossply slicks on 6/7" rims.

Running a single disc just doesn't work well in practice. The cost/complexity of doing one per side is pretty minimal. Go with 2. There's a reason why you don't see any proper racecar running a single disc setup.

I'd also shy away from the R25's. That is a very soft compound that is difficult to really get the best out of. The idea of FFord rubber (DoT?) is a good one. A harder slick, maybe the R50 or so, would probably be a better all around choice.

[NeilR]

Ok, twin disc it is.
R25 may not be too soft. The track is as per this clip:
Runs are ideally less than a minute and getting heat into the tyres is a challenge, hence the use of uncut dunlop wets, avon hillclimb tyres or the softest F3 slicks people can get. The R25's are also lighter than a radial and cheaper, but you are right that the used FF tyres will last for a long time as long as we don't flat spot too many! Why do you think the R25a bias ply is tricky?
We're also in a quandary re suspension in such a small light car...any hints?
BTW I don't suppose you know of any teams that want to sell off some old steering racks?

[Lee Nicolle]

Ok, twin disc it is.
R25 may not be too soft. The track is as per this clip:
Runs are ideally less than a minute and getting heat into the tyres is a challenge, hence the use of uncut dunlop wets, avon hillclimb tyres or the softest F3 slicks people can get. The R25's are also lighter than a radial and cheaper, but you are right that the used FF tyres will last for a long time as long as we don't flat spot too many! Why do you think the R25a bias ply is tricky?
We're also in a quandary re suspension in such a small light car...any hints?
BTW I don't suppose you know of any teams that want to sell off some old steering racks?

The problem with the Hoosiers [and most American race tyres] is that every heat cycle makes them harder and they are usually unuseable well before they wear out.
I sugest maybe the Dunlops will be better as you will get more useable consistent life from them.

[Pat Clarke]

Hi Neil,

I haven't been here for a little while, so I have only just seen your post.
In the early days of FSAE, a few things conspired to make the single rear brake across a Torsen popular.
The Torsen people were (are) sponsors of the event, so most teams took advantage.
The cars had a short wheelbase as part of the genesis of the sport being Autocrossing, and some of the better teams (like Cornell) were using a single rear brake.
The 'monkey see, monkey do' syndrome saw that become pretty well standard practice.
What that setup did was ensure the cars had lots of trail braking generated corner entry understeer.

When Wollongong Uni hosed them off in 2003 with twin rear brakes and no understeer, there started a drift away from single brakes.

Similarly, spool rear ends were only used by poverty teams until Uni of Queensland had a diff lock up at FSAEA in 2002. They figured out how to make it work pretty well (with advice from Carroll Smith and some other guy I know), to the point where their subsequent cars were very quick with a spool and a single brake. The team took that package to the first Formula Student event in Germany and were fast enough to win all the dynamic events. This raised the profile of that setup and we are seeing more of them, possibly 5 or six at FSAEA 2009.

In 2009, Monash University cleaned up in FSAE-A with a spool, their first time with that setup.

For your 'Social Climber' project, perhaps a spool with a single disc is worth considering? It would certainly reduce the cost and complexity of the project, reduce total and rotating mass and give better off the line traction.

The construction is sanitary and relatively to make, the spool simply supporting the disc on one end and the sprocket on the other.

There is now a pretty good pool of knowledge in Australia about how to make such a car work well. A spool is not necessarily a shortcut to understeer. In Hockenheim in 2006, the Germans were lined up on the fence, jaws on the ground, trying to figure out how the heck the banana benders were going so quick :-)

Cheers

Pat

Edit.

Take a look at this. http://www.youtube.c...feature=related.

It is Stuttgart Technical University running at a hill climb in Europe. This car certainly uses a LSD (Drexler) and 4 wheel brakes. It weighs in at about 225kg wet and by the sound of it, has the restrictor removed. The engine is a late model Japanese 600/4 of some description.

PC

Edited by Pat Clarke, 20 January 2010 - 05:43.

[Fat Boy]

The problem with any race tire is that every heat cycle makes them harder and they are usually unuseable well before they wear out.

fixed.

Edited by Fat Boy, 19 January 2010 - 20:40.

[Fat Boy]

I do understand what a hill climb is. The R25 would probably be a good tire to run if you were going for FTD. Judging from the build of the rest of the car, you aren't. That's why I think a harder tire would be a more consistent option.

Pat raises a good idea. Spools weren't invented in Oz, as he might have you think, though! There have been several successful spool cars at FSAE, perhaps prior to his tenure, however. I remember a beam front and rear from Illinois one year that was very competitive. Imagine that!

A spool would be a very good option for the car you're proposing. It's light, strong and if done properly has now vices that are unsurmountable. It's a narrow tracked car around reasonable radius corners. The cornering load alone will be enough to lift the inside rear and allow the car to turn. The driver just as to learn to not apply throttle and steering lock at the same time. Once he learns this, he'll be fine. It would take you back to a single disc and would eliminate a lot of headaches concerning a diff.

Good food for thought.

[Lee Nicolle]

fixed.

I will stand by my original statement, having used Hoosiers and Goodyears on both road race cars and dirt speedway cars they are really good for one meeting alone, after that they are junk. Having used Dunlops, Bridgestone, Yokohama and Avons all were more consistent, sure they go away 1/2 a second but the Yank tyres are 2 or 3 sec or worse.Particularly Goodyear.
Great when new though.
I have found American Racer [Mcreary] far more consistent on dirt though are probably slower originally

[NeilR]

Pat thanks for your reply. If you have read the social climber posts on Race Mags website you will know that it was a question you raised in one of your FSAE blog spots that made us query the idea of a single disc. With respect to costs the Honda helical LSD we have costs $500 delivered from Japan and we could make a spool to the same dimensions so it could be swapped in/out as required. Within the overall design we were trying to minimise machining/fabrication to try to control costs and skills required. Having said that I can see that we could save around $300 per car going this way. The 'headaches' re the diff are not that great in most respects. The diff housing requires four this welsh plugs in one side and then a housing to control the oil, which we had planned to make from 4mm spun ali, but now it does not have to take a braking load may as well be made from FG/carbon with a vynalester resin. Chain tension is what we need to work out and we were wondering why no one bothered to use the chain tensioners like the ATV's use or as per a camshaft chain?
Fatboy no offense was intended regarding your knowledge of motorsport. I still tend to think of hillclimbs as a eurocentric motorsport, though I am aware that some do occur in odd spots of the USA. I do see your point re the R25's. Our plan was to use used FF tyres at the start as noted, as no doubt we will flat spot a few here and there...they will be hard, but good enough. Also FTD in class is possible...750cc formula libre is virtually unpopulated so if we go with 3 cars and 6 drivers we may well make up the whole class!

[Fat Boy]

Pat thanks for your reply. If you have read the social climber posts on Race Mags website you will know that it was a question you raised in one of your FSAE blog spots that made us query the idea of a single disc. With respect to costs the Honda helical LSD we have costs $500 delivered from Japan and we could make a spool to the same dimensions so it could be swapped in/out as required. Within the overall design we were trying to minimise machining/fabrication to try to control costs and skills required. Having said that I can see that we could save around $300 per car going this way. The 'headaches' re the diff are not that great in most respects. The diff housing requires four this welsh plugs in one side and then a housing to control the oil, which we had planned to make from 4mm spun ali, but now it does not have to take a braking load may as well be made from FG/carbon with a vynalester resin. Chain tension is what we need to work out and we were wondering why no one bothered to use the chain tensioners like the ATV's use or as per a camshaft chain?
Fatboy no offense was intended regarding your knowledge of motorsport. I still tend to think of hillclimbs as a eurocentric motorsport, though I am aware that some do occur in odd spots of the USA. I do see your point re the R25's. Our plan was to use used FF tyres at the start as noted, as no doubt we will flat spot a few here and there...they will be hard, but good enough. Also FTD in class is possible...750cc formula libre is virtually unpopulated so if we go with 3 cars and 6 drivers we may well make up the whole class!

Hillclimbs I think of as eurocentric as well, but they resemble our autocrosses. The difference is they're cooler and generally faster.

Let's say you go out and set a time on the FF tires and then bolt on the stickies. Now running the FF tire times will be easy, but that is not the same as getting the most out of the stickies. Really getting the most out of a qualifying tire is a hell of a chore that isn't necessarily as fun as driving a lower performing tire like a hooligan, especially for an amateur. In general, to get the most out of a qualifying tire, you have to really explore the corners of the envelope. That means big hits on the brake pedal to compress the brake zones, _really_ pushing on corner entry and still getting the throttle on early. Is that really what you want your paying drivers to be doing? Probably not. The entertainment bang for the buck just isn't there and the chance of hurting the cars goes up quickly. That's why I say what I do about tires.

Also, if you make up the entire racing class, then you damn well better set fast time!

Good luck whatever you decide.

[Fat Boy]

I will stand by my original statement, having used Hoosiers and Goodyears on both road race cars and dirt speedway cars they are really good for one meeting alone, after that they are junk. Having used Dunlops, Bridgestone, Yokohama and Avons all were more consistent, sure they go away 1/2 a second but the Yank tyres are 2 or 3 sec or worse.Particularly Goodyear.
Great when new though.
I have found American Racer [Mcreary] far more consistent on dirt though are probably slower originally

I'm not particularly a fan of Goodyear or Hoosier, having had to run both at times. Bridgestone/Firestone is a yank company that produces some damn fine tires and they're just across town from Goodyear. Nationality isn't really the issue. FWIW, the Goodyear in the Formula Mazda series gets generally high marks for longevity. Apparently, even they can get it right at times.

[Pat Clarke]

Quote the Corpulent Lad...

"Spools weren't invented in Oz, as he might have you think, though! There have been several successful spool cars at FSAE, perhaps prior to his tenure, however. I remember a beam front and rear from Illinois one year that was very competitive. Imagine that!"

Hey, I never claimed the Aussies invented spools, only that in recent years the Aussie teams have been making them work better than most. I had commented that it was usually (always?) the low buck teams that used them for budgetary reasons. We are now seeing teams select a spool for it's advantages.

Oh, and I do recall the beam axle cars (more than one from more than one team) the DeDions, the Macpherson struts , the semi trailing links and the swing axles and Lancaster links and others that slip my mind right now. I don't recall any of them being what I would call 'competitive' (To my mind 'competitive' means being in there with a chance to win), Rather they were serviceable, in that they were able to compete.

I have been involved with FS/FSAE since 1994 and prior to that I was on the CIK committee in Paris for far too long.

Last words here

Were I building a car under the same parameters as Niel's 'Social Climber' it would have a spool and single rear brake. It would also probably be a 'sidewinder' with the engine beside the driver. I doubt frontal area would be a big deal in a social hillclimber.

Pat

Edit: Spelling =]

Edited by Pat Clarke, 20 January 2010 - 09:38.

[Fat Boy]

Oh, and I do recall the beam axle cars (more than one from more than one team) the DeDions, the Macpherson struts , the semi trailing links and the swing axles and Lancaster links and others that slip my mind right now. I don't recall any of them being what I would call 'competitive' (To my mind 'competitive' means being in there with a chance to win), Rather they were serviceable, in that they were able to compete.

I have been involved with FS/FSAE since 1994 and prior to that I was on the CIK committee in Paris for far too long.

Last words here

Were I building a car under the same parameters as Niel's 'Social Climber' it would have a spool and single rear brake. It would also probably be a 'sidewinder' with the engine beside the driver. I doubt frontal area would be a big deal in a social hillclimber.

Pat

Edit: Spelling =]

Pat,

I had to check the results. In '94 and '95 the Univ. of Illinois #54 was 10th and 7th respectively. If I remember correctly, that was the beam front and rear sidewinder car. Now, maybe that's not high enough for you to consider it competitive, I don't know. I do know it got plenty of people's attention.

For the record, my first FSAE was '92. I haven't been involved every year, but many. My condolences on the CIK appointment. That must have been painful.

I agree with your premise. A spool, single brake and possibly a sidewinder (although I would probably tend to go for a little longer wheelbase knowing the speeds they are liable to see) would be good options.

[Pat Clarke]

Thanks for the CIK condolences, that is appreciated!
I had no idea how bent the whole thing was until I arrived in Paris, bright eyed and bushy tailed and reported for business to that old rogue Ernst Buser.
When my time was up, I happily stepped away and formed an alliance with FSAE =]

Pat

Oh, and, yes, a longer wheelbase would be in the works. That would enable to move my feet behind the front axle line and the steering rack.

[NeilR]

Thanks for the CIK condolences, that is appreciated!
I had no idea how bent the whole thing was until I arrived in Paris, bright eyed and bushy tailed and reported for business to that old rogue Ernst Buser.
When my time was up, I happily stepped away and formed an alliance with FSAE =]

Pat

Oh, and, yes, a longer wheelbase would be in the works. That would enable to move my feet behind the front axle line and the steering rack.

I think a sidewinder car, given the variable driver weights, might not be the best solution, but I will mention it to the others.
Feet will be behind the front axle line and there will be a crush box on the very front of the car and something on ther rear too, plus side pods of some sort.
We may have found a solution for the steering racks in the buggy racks, but they will need some modification to support the ends of the rack itself.

[Lee Nicolle]

With a chain drive car simply build/buy an axle like a kart. With hub carriers mounting radius arms and shocks. [And the bike ones would be a good cheap start]Simple, bullet proof and do your sums right with the mountings and you will never have a chain problem with small suspension travel. Or a simple sprocket in a solid carrier in the middle and some simple small driveshafts on radius rods.

[SteveCanyon]

With a chain drive car simply build/buy an axle like a kart. With hub carriers mounting radius arms and shocks. [And the bike ones would be a good cheap start]Simple, bullet proof and do your sums right with the mountings and you will never have a chain problem with small suspension travel. Or a simple sprocket in a solid carrier in the middle and some simple small driveshafts on radius rods.

+1

I'd highly recommend something like this ->


With this combination, all your concerns about what brakes & diff to use are no longer a major worry - Right foot controls everything.;)

[cheapracer]

There is now a pretty good pool of knowledge in Australia about how to make such a car work well. A spool is not necessarily a shortcut to understeer. In Hockenheim in 2006, the Germans were lined up on the fence, jaws on the ground, trying to figure out how the heck the banana benders were going so quick :-)

Smoke and mirrors, while they were all staring at the spool they didn't see the nitrous bottle

I've said it before, I have run many a locked diff due to my children needing shoes and I never suffered understeer with a good chassis setup (and a bit of aggresive driving ;) ).

Worked for numerous and unbeatable Porsches too such as the 956, 962 and 917 oh and we should mention that V8 Supercars have to run a locked diff by the rules (unless they changed it) which at one point led to slipping devices at the wheels themselves (torrington bearing maybe?)

Edited by cheapracer, 21 January 2010 - 10:55.

[Fat Boy]

+1

I'd highly recommend something like this ->


With this combination, all your concerns about what brakes & diff to use are no longer a major worry - Right foot controls everything.;)

It appears they've lost none of the handling prowess of the original MBA chassis.

[NeilR]

actually two 750cc karts are the usual entrants at the australian hill climb championships. To say that they are exciting to watch is not overstating it. The in-kart video is frankly scary as they go over the bumps and have to deal with the camber changes etc.
Cheapy I'd never use the V8's as a guide to handling...they are a very odd beast. However the die is cast, we will continue with the honda diffs and will make a spool for those who don't want to stump up the money and maybe we'll try it in the future.

[Lee Nicolle]

actually two 750cc karts are the usual entrants at the australian hill climb championships. To say that they are exciting to watch is not overstating it. The in-kart video is frankly scary as they go over the bumps and have to deal with the camber changes etc.
Cheapy I'd never use the V8's as a guide to handling...they are a very odd beast. However the die is cast, we will continue with the honda diffs and will make a spool for those who don't want to stump up the money and maybe we'll try it in the future.

Ther seems to be a few bike engined 'specials' in Aussie hillclimbs. And seem to be damn quick. There was a couple at Collingrove last year.
Plus some that have been around forever like Dean Richards Ragno.

[cheapracer]

Cheapy I'd never use the V8's as a guide to handling...they are a very odd beast. However the die is cast, we will continue with the honda diffs and will make a spool for those who don't want to stump up the money and maybe we'll try it in the future.

Oh I was just pointing out that just because one has a locked diff the world isn't going to end the first corner you come to.

I wonder what Mark Donahue used in his F1 car being a user of locked diffs for most other occasions.

[NeilR]

Lee quite a few of the VIC guys go to SA for the champs etc. Colingrove's 'dip' after turn one often shows up cars with a lack of droop travel.
Donohue used a locked diff. I believe.

[Fat Boy]

Still merrily traveling off topic....

On FSAE I spoke to last year decided against a spool specifically because of rain. Apparently, they were very happy with the dry performance, but after running in the rain they decided it was too difficult to drive. They had a point If you take away 1/2 of the lateral ability of the car, then all the sudden that inside tire is a hell of a lot more stuck than it was in the dry. Karting in the wet with a dry setup is absolutely no fun and about as frustrating as can be. I guess they felt the same way.

You could set the car up around the spool and then wager it was going to be dry, but that's a costly wager to get wrong.

[SteveCanyon]

Still merrily traveling off topic....

On FSAE I spoke to last year decided against a spool specifically because of rain. Apparently, they were very happy with the dry performance, but after running in the rain they decided it was too difficult to drive. They had a point If you take away 1/2 of the lateral ability of the car, then all the sudden that inside tire is a hell of a lot more stuck than it was in the dry. Karting in the wet with a dry setup is absolutely no fun and about as frustrating as can be. I guess they felt the same way.

You could set the car up around the spool and then wager it was going to be dry, but that's a costly wager to get wrong.

I haven't run a kart in the wet, but I've driven a Mitsubishi Lancer rally car (early 80's sort of thing) and it was pretty good to drive most of the time .... but I found out rather quickly that you never ever ever back off halfway around a corner.
As long as you kept your right foot into it, it was quite predictable.

[Lee Nicolle]

Having raced tintop type cars with some success for 40 years with locked diffs i often wonder about some peoples objectivity with them.
Reading an oil companys blurb about different oils to change the chararistics of LSDs. Why??
The few cars I have driven without were interesting, I tried an LSD in my rallycross car in the late 70s. It was freshly reclutched by an expert, best oil advaiable [then] and it wore out in 3 heats. I then refitted the locked diff for the finals[which I won] and the car was quicker and more positive.
I also drive a strong V8 Sports Sedan with a Detroit locker, that was bloody awful. On trailing throttle the thing was clunking and banging in the back and the car is flopping all over the tyres.And it broke 31 spline GT axles fairly regularly. The prep people subsequently talked him into putting a spool in it. He complained about it being harder to drive but it was consistently faster and did not break axles anymore.
In a proper open wheeler or Sports car a proper race type LSD may have its advantages but otherwise most people are outtricking themselves. Learn to drive and set the car up around a locked diff and you have a reliable car with one less variable.

[Pat Clarke]

Well said Lee!

Big Boy, karting in the wet is horrible if the setup is not correct..It gives a whole new meaning to the word 'understeer', but with the correct setup and a knowledgeable (experienced?) driver, then not so bad. I have had some painful drives in the wet and I have had some blinders...The trick was to figure out why (And then there is no trick...see my signature)

The best way to understand how a spool works is to understand the effect of differing slip angles across the car. It is never so crude a 'picking wheels up'

Cheers

Pat

[cheapracer]

Having raced tintop type cars with some success for 40 years with locked diffs I often wonder about some peoples objectivity with them.

Simple, they haven't driven them and listen to other people who also haven't driven them.

[Catalina Park]

I had quite a bit of fun at Oran Park in in the early 90s in a VE Valiant with a locked diff, 500hp and 6" wide road tyres.
Some people just don't know what they are missing.

[murpia]

Joining this one late...

A single rear disc will work with a spool, but don't neglect the fact that you are now transmitting brake torque through your CVs (tripods) and that means they'll need to be stronger (heavier) that if they only had to transmit engine torque.

A single rear disc will also work with a completely open diff, as the rear contact patch torques should always be equal. I doubt you want to use an open diff, though...

With any kind of torque biasing diff (torsen, plate, helical etc.) then you'll get inconsistent handling under braking, as the variation in tyre slip ratios as grip changes will interact with the torque biasing and introduce all sorts of varying yaw torques.

Not sure what happens with a viscous coupling, need to think about that...

A fully active diff (but not a torque vectoring diff) can be programmed as follows: straightline braking = spool, initial turn-in = fixed torque bias, apex = slip ratio control based on corner radius, early exit = slip ratio OR fixed torque bias (depends on interactions with traction control), straightline exit = spool again, straightaway = open (low drag). Straightline exit vs. straightaway is defined by throttle opening (100% = straightaway).

Regards, Ian

[gruntguru]

Joining this one late...

A single rear disc will work with a spool, but don't neglect the fact that you are now transmitting brake torque through your CVs (tripods) and that means they'll need to be stronger (heavier) that if they only had to transmit engine torque.

Not really. Traction limit braking will produce less torque than a traction limit launch due to weight transfer.

A single rear disc will also work with a completely open diff, as the rear contact patch torques should always be equal

Rarely equal once a tyre breaks traction.

With any kind of torque biasing diff (torsen, plate, helical etc.) then you'll get inconsistent handling under braking, as the variation in tyre slip ratios as grip changes will interact with the torque biasing and introduce all sorts of varying yaw torques.

How is that worse than a two disc setup with one tyre locked and therefore less retardation than the other?

[NeilR]

Interesting, as I had not expected such support for a spool. Thanks to the wonders of sports-compact racing (whatever that really is) we have found a commercially available spool that takes the place of the Honda LSD and one of the builders is keen to go this way. Given my local track is in Gippsland and prove to wet weather I think I'll stick with the helical LSD. We have had the inboard vs outboard brake discussion recently. The plan was to follow UK and FSAE practice in using the bearing blocks as caliper mounts and use a flange mount on the CV cup to hold a rear motorbike disc (250mm x 5mm thick) and 4 pot radial mount motorbike caliper. This has met a surprising amount of resistance and suggestions of impending doom as driveshafts let go and we all follow Ayrton Senna to our doom! Frankly I cannot see rear brake torque from a 7" slick worrying a Honda civic driveshaft, but there you go. We'll investigate an outboard setup as an option, but I must admit the armchair enthusiast in me likes the idea of a 6kg loss of unsprung weight (11kg over the production brakes used on the uprights we have).

[Pat Clarke]

Quote NeilR
"We may have found a solution for the steering racks in the buggy racks, but they will need some modification to support the ends of the rack itself".

Neil, are you still thinking about rack designs?

I have been giving this some thought. Years ago I had a design idea for steering using a modified production rack, but with adjustable steering rate and adjustable Ackermann.

I have lost the design, it died in a hard drive many years ago, but scratching around the brain cells, I'm pretty sure I remember how it worked.

If you like, I will sketch it up and email it to you? Give me a day or two

Cheers and Happy Australia Day (Also my 16th Australian birthday as I was 'neutralised' in 1994) =]

Pat

Edit:

PS, you won't break axles with inboard brakes unless you do something really silly in design. You can have both dual inboard brakes and a sprocket drive but the design will get a bit fussy. A benefit of inboard brakes is it is much easier to react the brake torque, whereas outboard brakes need to react the forces through the suspension components.

Another option would be to run the brakes inside the upright as seen on the UoWA 'World Champion' car. This usually limits the rotor diameter, but that's probably not such a big deal at the rear.

I still think a single brake on a spool has it's merits, even on a cold wet Gippsland hill =]

Edited by Pat Clarke, 25 January 2010 - 12:34.

[cheapracer]

I have been giving this some thought. Years ago I had a design idea for steering using a modified production rack, but with adjustable steering rate and adjustable Ackermann.

Oh please share here Pat

[cheapracer]

Given my local track is in Gippsland and prove to wet weather I think I'll stick with the helical LSD.

Locked/spool is great in the wet, allows the inside tyre to slip a bit easier in the turn and gives great braking stability.

I'm getting tired of my spell check (auto in Google Chrome) telling me tyre is wrong.

[NeilR]

Pat I would be interested to have a look, it seems we share a birthday too, though I'd prefer a term that did not imply 'neutered'!
I have Monash's FSAE car in the next issue of Race magazine and the NZ team promised something too, so two of the five Uni's invited got back to me, which is a better than average response from student at the end of the year (what magazine can compete with holidays, beer and sex?). Naturally I have a load of images from the event, but haven't got around to an article on the actual event itself.
We have discussed torque reaction. The only real challenge for us how to attach the brake disc mount to the CV cup, which is presumably case hardened, cast steel. I proposed three dowels/bolts into the most solid lobe section of the CV cup. The issue is to weld/braze/shrink fit as the other fixing method.

[Fat Boy]

Well said Lee!

Big Boy, karting in the wet is horrible if the setup is not correct..It gives a whole new meaning to the word 'understeer', but with the correct setup and a knowledgeable (experienced?) driver, then not so bad. I have had some painful drives in the wet and I have had some blinders...The trick was to figure out why (And then there is no trick...see my signature)

The best way to understand how a spool works is to understand the effect of differing slip angles across the car. It is never so crude a 'picking wheels up'

One thing I often do with a new driver in the rain is send him out with no changes to the car and tell him to get on with it. Sometimes you don't have time for a big rain change-over and they need to know what to expect. Then I'll go in steps to a wet setup. Well, one day I was karting and we had a short rain. I thought, I'll do the same with myself as I would with any driver. Take the dry setup and figure out how to drive it. Well, in a kart, that idea sucks. Like Pat says, it gives a whole new meaning to the word understeer. It's not a driver control thing. Sometimes the kart will simply not negotiate the corner regardless of the speed. I would have the thing going 5 mph driving straight off the track. They should make prisoners drive that.

Pat doesn't like the terms 'picking up wheels'. While I agree it's crude terminology, it's also descriptive enough to get the point across. The inside of a locked rear has to operate at a higher slip ratio and slip angle than the outside or you're not turning. Steering geometry has a lot to do with this, but so does lateral load transfer and roll-couple distribution. Why many sedans and saloon cars operate well with a spool is that they have a high enough of a C.G. that the inside tires (front or rear) have very little weight on them and achieving the necessary slip without inducing a large moment resisting the turn. Getting everything set right to conspire to let a spool car turn can vary from quite difficult to nothing at all depending on the car.

There are some nice traits in a spool. It doesn't wear out. It always operates the same. Tuning is 'done'. They're pretty good at putting a large amount of power to the ground. Having said all this...they ain't magic. In slick conditions, they don't tend to do a very good job of putting power down. It's a bit of a paradox, but as the track gets slick, you're better off allowing _some_ inside wheelspin to make for more controllable breakaway characteristics. If you're on a very slick track and at 20% throttle you are spinning both rear tires, then your throttle control has to be quite precise. Also, because in these situation, cornering loads are reduced, the inside rear produces more of an understeering moment. The kart was the worst scenario of this going from 'can't turn the damn thing' to '****, I'm gonna spin' in about 0.001 seconds.

The best situation for a spool is a narrow car with a relatively high CG operating in consistent conditions. I think the 'Weekend Warrior Hill-climb Car' meets this enough to be a reasonably good match.