600RR Slipper Clutch on an F4i

[DH]

Hello,

Does anyone know if a 600RR slipper clutch can be used or adapted for an F4i? Or does any team maybe have the clutch shafts/assemblies visible at the moment to compare the two?

Thanks,

Dan

[KU_Racing]

slipper clutch?!? why!?! dont know if they are the same, but knowing honda design efficiency, id guess they are.

Here is the number of honda shop that gives us parts:
(989) 624-2160 Birch Run Powersports, Birch Run MI.
Very knowledgable, and very nice. They might be able to help, but no guarantees.

[Alan]

Originally posted by KU_Racing:
slipper clutch?!? why!?!

Wouldn't a slipper clutch get rid of a lot of that rear end chatter a lot of cars seem to have under braking? Please correct me if I'm wrong.

[Bill Kunst]

Properly balanced brakes and quick shifting(and rpm matching) on the downshift will take care of that problem. A slipper clutch is designed for a racing bike where, on braking, a rediculous amount of load transfer takes place(near 100%) and mere engine braking causes a virtual "locked" rear wheel (its actually slowing down faster, from engine braking, then the bike is).

So, if you are recieving this type of weight transfer, with the rediculous power output of a race bike, yeah it might help. But a longer wheel base, or better weight distribution, might add some benefits as well.

Don't be offended by my reply, I just don't think it is necessary unless the two aforementioned problems are solved and the problem still exists.

Bill

[BeaverGuy]

It allegedly does. Around the time I graduated a guy was retrofitting a slipper clutch from a ZX6RR onto an '01 ZX6R engine in our '05 car. From the limited info I've heard it significantly reduced the chatter during engine braking.

[Alan]

I am not offended. What you said makes sense now that I think about how little braking the rear tire on a bike does when compared to a car. But even still, it seems like a lot of cars with manual shifters have this problem. But I guess fitting a slipper clutch would just mask some braking or shifting deficiency.

[VFR750R]

Cars benefit from slipper clutches. IMHO it does two things. Allows a more consistant brake balance regardless of speed or gear. It allows the driver to not think about it. If the driver knows that the tires chatter or overbrake sometimes, that's some time too much.

[Bill Kunst]

OK,
I have an unrelated question. Does IMHO mean "I'm a ho." or some other computer jargon? I guess I am stupid when it comes to abbreviating whole sentences. I think we had a Vanna White topic on buying a vowel. J/K

I Agree, VFR, but I also think that the two issues I brought up must take priority over a slipper clutch. I will also add some

1. A shifter that reduces large rpm variances.

2. Good weight distribution

3. Good wheel base length

4. Eliminating drivetrain slop
A. Low amounts of lash
B. Strong frame and mounts
C. Good drivetrain torsional stiffness
D. Maybe most effective, 2 outboard brakes

5. Proper dampening

6. Proper brake balancing


Okay, this is lengthy, I know. But I think that if you are meeting the design elements in the competition, these are things that will be addressed. In addressing these, I feel that you will virtually (that is a qualifying word) eliminate the problem. Not only that, you will have a better car.

If at the point of having a better car, you still have wheel hopping, then put a slipper clutch in. I just feel that you could end up masking one of these problems before "tuning" that issue out of you design, leading to a car that does not perform as well as it should.

Bill

P.S. I really appreciate these discussions with all of you. I am just trying to present another opinion that could help in your quest.

[KU_Racing]

I think Bill really said what I was thinking when i wrote my initial reply. No offense to teams using a slipper clutch, but in my opinion tire chatter during braking is the result of the driver not having enough seat time, or one of the things that bill mentioned being out of order. In my opinion, a slipper clutch would just be a 'band aid' solution to solve a problem related to an entirely different system.

[Maverik]

I agree with everything I have read but wanted to chime in anyway... It was mentioned that drivers with enough seat time will drive the car properly (without chatter was the assumption.) But why would a driver have to compensate for a condition that could be taken away? I know driver's who have had 4-5 years of seat time in very similar formula cars throughout the years that will still get the chatter coming hot into a sharp corner. Sure there are probably some weight transfer issues that can be tuned out in chassis and suspension design which will ultimately make the car better, but at what point can you say 'our weight transfer and vehicle balance are perfect'? I don't see any harm in using a slipper clutch as long as you have a good fundamental vehicle design and understand what is happening. It adds minimal weight (albeit rotational) and *should* let the driver focus on driving and not being so nice to the car.

[Bam Bam]

Yeah a good driver will not benefit from a slipper clutch,

You guys know any of those?
Cause I sure as hell don't.

Rev matching throttle blipping and heel toe shifting are great skills as well as being able to keep a car in a narrow powerband

But when you have different drivers every year, (That's right people from good school's actually graduate and get a friggin job) and you have to build a new car every year, Then you wanna make the damn car as easy as possible to drive.

That might mean putting a little bit more roll into the car than what is optimal so that the driver can feel the car respond cornering.
It might mean having an electro pneumatic shifter, or a fat flat torque curve or a slipper clutch.

in our cases typically anything that makes the car easier to drive is going to make it faster.

Yes the driver can compensate, and in this dudes case your right, the time spent adapting an RR slipper to an F4 could probably be better spent finishing the car earlier so the driver can get more seat time.

However, IF he's got the engine apart and the RR clutch would bolt right up, and they have the resources than it's a good idea

[Bill Kunst]

I was merely pointing many of the issues surrounding chatter, or wheel hop, that should be addressed.

On a street car, there is far more forgiveness in the drivetrain. But wheel hop does occur for a few reasons, chatte doesn't.

Chatter is from all the solid mounting and metal-metal interface (no rubber) on our cars along with a phenomenom known as chain slap. Get the megamo (high speed camera) and film the car entering a braking run where chatter occurs. Cookies to doughnuts you will see the tire load, turn, release, turn opposite or stop, and reload. This should not happen.

On a street car where there is over compliant tires and suspension, it is merely loading these components until they overload and release, causing bouncing. Something to do with traction curve of tire? I think so. Also, big sidewalls. Take the same car, put on stiff suspension and bushings, better balanced brakes, low pro tires, and no more bouncy.

So, the question would be why are we chattering, or bouncing, with a race car? One or more of the designed areas affecting this is compromised from a design standpoint.

Will a slipper help this car be faster? I am sure that it could. Why do they put it on bikes? So the guy riding doesn't brown up the seat on corner entry. I am sure, though, that an under developed team could benefit. So much so that I am willing to stake all of $1.50 on it.

Bill

[DH]

Thanks for all the responses - this is very similar to the discussions we have had within our team regarding slipper clutches.

There is no question that our driving skill is below where it needs to be, and we are trying to keep our cars running and in good driver training form year to year to help that. However, our testing time up here in Edmonton is severely limited - we'll get late March to early October if we're lucky.

The biggest reason we have for the slipper clutch is to eliminate downshifting. Any of the endurance drivers from West will be able to tell you that the track required a lot of shifting - and no matter how much seat time we get it will be beneficial to make the car more driveable. My opinion is that it is an engineering competition first, and a driving competition second. A more driveable car is more marketable as an autocross car for the potential customers that would want it (after all, if someone can REALLY drive they might think about A-mod, DSR, or other sponsored and more competitive formulae).

Putting in the slipper is not going to be terribly difficult once the engine is on a bench.

Thanks for all the discussion, and if anybody has done this or knows that it can be done please chime in.

Dan

[VFR750R]

Sorry dude, IMHO mean 'in my humble opinion'.

and in my humble opinion, if F1 drivers are faster with computer controlled heel toe shifting and computer controlled engine braking so would I.

Necessary no, beneficial yes. Can you make a car go fast with a solid rear axle...yeah, but ultimately it's a compromise where a limited slip rear end is better.

There was a time when motorcycles were stable without a steering damper and they were put on to 'tame' a poor handling bike and now there are computer controlled steering dampers on CBR1000RR's. Does that mean that the handling of a CBR is poorly designed? No, they used all the tools available to make the fastest bike they could. Just cause theoretically you don't need one doesn't mean that you shouldn't.

[absolutepressure]

Like Bam Bam and DH said, we are developing this car to sell to a company who will inturn produce and sell it to the unprofessional weekend autocrosser, correct? I think driveability is a major factor if we are to stick to the intent of this design competition.

[Bill Kunst]

agreeable on all points, all those speaking.

The things that I pointed out include everything you have said. A well designed shifter (computer controlled pneumatically controlled w/engine cut) is by far a better answer. One with throttle blips by computer would be great, but against the rules. I merely want to make sure that everything is known about this problem and how to remedy it.

Also, I can't believe that a slipper clutch will eliminate downshifting. And at $800 for a 600rr slipper, and then the cost of a raceable clutch set, I wonder about the cost. This also increases wear on the clutches significantly rather than wearing the tires=more cost. Increase in friction=hotter engine.

I guess that if this is okay with your team's budget, and it will solve wheel hop problems (whether related to traction itself, or design), then, and only then, is this okay. BUT, FOR THE COST, I AM SURE THAT AN EE COULD BUILD A ELECTRO-PNEUMATIC SHIFTER AND THEN SOME.

I am trying to get this out in the air. YES, this is an engineering comp. That is why the issues I mentioned earlier need to be addressed. AND, if addressed properly, they could do just as much for your lap times as the slipper clutch, BUT will do more for your design portion of comp then the slipper. Help me if these statements are completely, or even slightly, unrealistic or true.

Great discussion,
Bill

[KU_Racing]

I guess my argument involves the purpose of a slipper clutch- to prevent the drivetrain of a racing motorcycle (or streetbike these days) from loading up the suspension , locking the tire, or generally killing the rider under engine braking. My argument would be that unless your car has a swingarm in the rear (possible.. but unlikely) a slipper clutch will not provide any performance benefit from a mechanical standpoint. Anytime you brake a tire on rough terrain under varying load conditions, it will chatter. I guess you could say that a slipper clutch is just another technological device you can use to your benefit, but I also would contest that there is no professional touring or open wheel racing car on planet earth that uses a slipper clutch.

Plus, race engines almost always sound SWEET under engine braking. Who wants to quiet that sweet music? Not I.

[VFR750R]

There are many ways to limit engine braking including a slipper clutch. I would venture a guess that any engine management system with an electronic throttle limits engine braking with that throttle ie F1. I don't have proof of that but I can't see why not. Along those lines, you could 'tune' your engine braking somewhat with idle speed.

[MSJ]

This is a great discussion, and I haven't posted in a while so I thought I'd enter my $0.02

I had a similar discussion with our team captain. We experience chain slap on our car from time to time when driving it hard. I was asked if I had ever ridden a bike with a slipper clutch (I come from a motorcycle background which helps and impedes in some areas of driving a formula car).

My experience from riding bikes with slipper clutches, is just that you can be alot more careless about how you're downshifting, and if you're not experienced, you can dive into the corner a little bit easier than if you really want to rev match properly.

But these are not motorcycles, they're formula cars. Nevertheless, the idea is the same.

From my experience, abrupt and jerky riders might be faster than smoother riders at the beginning, but I've always seen smoother riders get faster, and pass unsmooth riders. I was always taught to try and be as smooth as possible.

The goal should be to be smooth. Speed is a byproduct. That being said, I'm no superstar rider/driver.

So do you need it? No.
Would it be cool? Yes.
Can it be done? I'm pretty sure it can be, but not 100% sure.
Was my post helpful? Probably not. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Alan]

I'm glad someone brought this up again because a couple of things have been bugging me about this topic and hopefully somebody can clear up some stuff for me.

Bill Kunst, in one of your posts you say, "mere engine braking causes a virtual "locked" rear wheel (its actually slowing down faster, from engine braking, then the bike is"

Can you elaborate? I am not sure I quite understand this because for any braking to be taking place, the wheel has to be slowing down faster than the bike (no matter if the speed differential is coming from the brake friction or engine friction). Also, does a slipper clutch make any difference to smoothness in braking if there is no downshift?

KU_Racing, in one of your posts you say, "...the purpose of a slipper clutch- to prevent the drivetrain of a racing motorcycle (or streetbike these days) from loading up the suspension ...unless your car has a swingarm in the rear (possible.. but unlikely) a slipper clutch will not provide any performance benefit from a mechanical standpoint."

Can you elaborate? What does this have to do with "loading up the suspension" or whether it's a swingarm. The way I am interpreting this is that if you just let off the throttle and don't apply braking, somehow the swingarm load is affected (irrespective of load transfer). Is this what you are saying?

I guess I thought a slipper clutch was merely a one way clutch which prevents the tires from driving the engine. The benefits being a)you can't overrev the engine and b)the braking system will not see the sudden (albeit brief) change in inertia when the drivetrain passes through neutral. This in turn prevents the brakes from being momentarily over applied which puts the tire in a different part of the mu/slip curve, which creates the initial lock up that puts the chassis in a pogostick mode, which creates the stick/slip cylcle. Can someone tell me if there is something I am misunderstanding?

[Bill Kunst]

Okay,
Sit down and watch MotoGP bike racing. They enter corners with so little respect for human fraility. AS they enter, they have a fistful of front brake, which lifts the rear tire. The engines are so rev happy that they graciously slow down the rear tire faster then the bike slows under stupid heavy braking. Can you say switching ends (if RPM is not matched on shifts). A slipper allows a daft idiot, or someone with disregard for safety (MotoGP rider http://fsae.com/groupee_common/emoticons/icon_biggrin.gif) to downshift without matching rpms.

Lets not forget the HP to weight ratio, the ability to rev, and the lack of weight on the rear tire under braking all play a role in why a slipper clutch is necessary.


Also, about no engine braking. NOT true, they grip LESS.

Bill

[kwancho]

So... does that mean if you have something like an electronic shifter, you can bash it into a downshift and have the clutch take most of the difference in speeds? i.e. no throttle blipping required and much faster shifts?

[KU_Racing]

Sorry bill, but no. the purpose of a slipper clutch is not to allow the rider to downshift without matching revs. On any motorycle with a chain drive, the forces acting on the chain are a very significant part of how the rear suspenion reacts to the ground. The chain adds force into the suspension in the y axis, either positive or negative depending on where the swingarm pivot is located relative to the axis of the front sprocket.

Yes, Alan, if you are on a bike that does not have a slipper clutch and you close the throttle, the reversed load on the chain will feed force into the swingarm, loading the suspension up. on most streetbikes, because of their geometry, the chain will tend to pull the suspension into bump under the 'engine braking' load. This doesnt really sound bad, until you hit a bump and there is a significant force trying to pull down on the swingarm. This can and often will cause the suspension to oscillate because of the opposing forces of the spring/damper and the chain. The oscillation will prevent the bike from braking or cornering at full potential, and if it is large enough can high-side the rider.

basically, to sum it all up: on a racing motorcycle, the slipper clutch is put in place as a suspension tuning device- not for the drivetrain. Unless your sae car is using motorcycle suspension, my opinion is that you dont need one.

Yes Alex, you can downshift with no throttle with a slipper. But you lose the benefit of engine braking, which for me and the way I drive, is extremely useful for balancing the car.

[MSJ]

KU_Racing is absolutely correct. MotoGP rides DO NOT ride like that. Why do you think they're riding those bikes? Because they're the best in the world. They are THE SMOOTHEST riders in the world.

What you see as entering a corner as reckless abondonment grabbing a handful of brake, is just their skill level. They are always rev matching and downshifting.

Again, KU_Racing is correct. The slipper clutch is an absolutely useful tool in preventing high-siding. Which I can speak from experience, really sucks and hurts!

When you do silly things like dump the clutch on a downshift, it upsets the suspension, causing unbalanced corner entry and if your suspension isn't setup right oscillations can occur.

Anyways, I think we've strayed a bit off of course, and I don't want to start a discussion on driving techniques, heh.

[KU_Racing]

Thanks MSJ.

From the website of Sigma Performance, a slipper clutch manufacturer:

"The MV Agusta's we were watching were making beautiful emotive noises, like hollow rolling thunder; noises that came from the rear wheel turning over the engine; engine braking. The noise was fantastic but the effect was for the chain to jerk the rear suspension around, the bigger the pistons and the higher the compression; the worse the problem. It was bad enough to be a significant disadvantage with a 500 four like the MV; with the lumpy great 500cc pulses from a 996 Twin like a Ducati Desmo it is sheer poison, the same with big fours, as soon as there is any decent engine compression there is going to be a lot of engine braking interference with the rear suspension. Even worse, to try and control the pulsing the rear suspension damping is normally set very stiff so compromising the suspension's ability to float over bumps elsewhere on the circuit.

Riding fast on a circuit, or for that matter on the road is all about smoothness, it is about loading up the tyres to their limit of grip (or controlled slide) and holding them there at that fine margin of grip; just before they really 'let go'. All the suspension and chassis set up effort goes into helping this situation be predictable and accurate. What you do not want is the big pistons hung off the other end of the chain jerking the swing arm about, either while floating into a high speed corner or coming into a slow, hard braking corner. To go fast and maintain grip you need smooth progressive deceleration as you roll off the throttle and no jerks that would result in a movement in the swingarm. "

[VFR750R]

I gotta back up Bill here. If you're trailbraking any motorcycle at the limit of grip, engine braking becomes a considerable precentage of rear braking available and it changes with rpm and gear ratio.
It is also true that it will have an effect on the suspension, and you can't ignore either. Slipper clutches help both! Regardless of the design intent, they remove unwanted suspension input AND variable rear braking.

The reason it would help MORE in an FSAE car is a motorcycle rider is able to have infinite adjustment of front:rear braking bias through his right hand and foot. A formula cars braking bias is fixed and is a compromise of all the braking the car will do. If you remove the engine braking effect, braking will be more consistant under all speeds.

[DH]

Interesting stuff guys. It sounds like the slipper will make a bad driver look good and a good driver slower.

I guess the question now is do we have any good drivers, or the time to make our bad drivers good?

Anyway, thanks for the discussion and insight.

DG

[Bill Kunst]

http://en.wikipedia.org/wiki/Slipper_clutch

http://www.sigmaperformance.com/slipper-clutch-faq.html#11

http://www.speedwerks.com/catalog/c241m0bm0b0s1pn1p4582np0

Well, KU, then why would they suggest that it takes the scare out of downshifts and matching revs on high compression bikes? Ask MSJ, he says it in his post.

And yeah, they are reckless. They ride to a limit we can't understand, and at any moment, are within one riding element of crashing. I couldn't do this, but it doesn't mean that it isn't reackless cause they can. They are absolutely amazing to watch!

If you want to do it the cheap way, push in the clutch when you hit the brakes http://fsae.com/groupee_common/emoticons/icon_wink.gif that should be cheaper then the slipper and the money you will spend on replacement clutches.

The sites above should answer questions about the clutch, one even is a proponent for it on four wheeled motocycle engined vehicles.
Bill

[MSJ]

This is a great discussion! http://fsae.com/groupee_common/emoticons/icon_smile.gif

Lets look at this from two perspectives.

1. This is a design competition.
With a design competition, you want to market your product. Why do bikes have slipper clutches? Do they really absolutely need them? Not really, but it sure helps the buy make up his/her mind if bike A has one for the same price that bike B doesn't. But with bigger more powerful engines, they are probably going to save alot of inexperienced people from crashing.

Same idea holds here for our presentations at competitions. We are marketing these cars to the weekend auto-x enthusiast. More features (safety or performance) for the same "price" the better.

2. This is a driving competition.
When I first started riding harder, I learnd to slip the clutch myself and rev match, to be smooth. You can do this too. Or, you can let the slipper clutch do it. The fact remains that our engines are not nearly as powerful as the bikes that actually really benefit from slipper clutches. We don't have 180hp like an R1 or 220hp+ like a MotoGP bike. Our car has a peak of 76hp, it hardly seems necessary.

In the end. Its both. Do what you feel is best. I don't think we'll take the time to do it. I'd rather spend more time being slow and thinking about the way to drive, and becoming fast later through smooth technique. But thats just me. I would say it will change your driving technique alot if you have a slipper clutch. It would be nice to drive two identical cars and feel the difference though.

Lastly, IMHO, it could help, I just don't think its needed. I'll leave it at that as I think we've all made some good points here.

Bill, I still wouldn't call it reckless. I just call it racing :P

[KU_Racing]

It takes the scare out of braking into a corner because the slipper prevents the suspension from moving in an unpredictable way... read it again.

I dont necessarily disagree with VFR on the trailbraking point, but I also know for a fact that most sport bikes will stop fastest in a straight line with the rear tire off the ground.

My other argument against the slipper is this:
When you are racing a motorcycle, the front and rear brakes are individually adjustable. This means that mid-corner you can adjust the balance of the bike by changing the brake balance. From my experience and what most people I have talked to have told me, the common technique is trailing the front brake and adding or subtracting rear brake via the rear brake lever to adjust the balance and line of the bike as the rider sees fit.

In a car, you do not have the option of braking the rear wheels and front wheels independently. The way that the balance of the car is adjusted is using the throttle. I know that when I drive (I am no Raikkonen... I know everyone is different) I often use the extra braking force provided by engine braking to change the balance of the car. When I try to imagine driving a car where no rear braking force is supplied by lifting the throttle, it seems like it would be unnatural, and more difficult to be fast.

VFR is probably right that the car would brake more consistantly WHILE GOING STRAIGHT. My concern is that the slipper will remove some of the driver's feel and control over the car. I think the line about a slipper making a mediocre driver quicker and a fast driver slower is pretty accurate.

On the topic of Sigma recommending slipper clutches for motorcycle-engined race cars, lets not forget that Sigma's main purpose in this world is to sell slipper clutches.

I would like to point out again that there is no major racing series on planet earth (someone correct me here if I am wrong) where a slipper clutch is used. Most series whos rules I understand have not outlawed a 'back-torque limiting' style of clutch, and still no one uses them.

[Ian M]

WOw, this is an amazing post. Wish I could add some knowledge, but I don't know a whole lot about them. So are you saying that a slipper clutch provides absolutely NO engine braking? I thought it just slipped on downshift and allowed the revs to match instead of locking the rear wheel for a second. Wish I knew someone with a bike that had one. The new R6 has one right?

[KU_Racing]

yeah- standard issue on the new R6. The slipper prevents and torque transfer from the wheel to the engine, so yes, no engine braking. The clutch does not fully disengage, it basically just opens up to the point where the torque going in from each end is the same. In other words, when the wheel moves faster than the output shaft of the tranny, the clutch opens up until the torque transmitted by the wheel is equal to the torque being transmitted by the slowing of the engine.

[Bill Kunst]

Okay, you get a little engine braking. It "limits" but doesn't remove engine braking entirely. I highly suggest that you watch motoGP because when they do the onboards you can hear the engine. It sort of holds a pretty steady rpm in decel.

Think of it like a rope type tie down, one direction it tightens, the other it slips. If you look closely at the pictures, you can see the ramps. As pressure is applied through the trans to the clutch, it couses the clutch housing to ride up the ramps and release pressure, the other direction it doesn't and you get normal clutch pressure.

I think it is important to llok at this from a wear and heat aspect. How fast do they wear the clutch, and how hot do they get? I don't know, but wouldn't mind knowing.

Bill

Oh, and bullshit on the matching revs crap. If you don't match revs at 18,000 rpm, you are off track. Add slipper clutch, problem solved. If you can assure me that everytime they downshift that they perfectly match revs, then I will say you lie. Sure, you can't drop it in at 18,000rpm (gearing) and 3,000rpm(engine), but if you are 2,000rpm off, itwon't matter(unless the slipper is not working like it should).

[Bill Kunst]

OK, quick 411.

Imagine my posts as us sitting in a bar talking. I am arguing in a friendly way. Please don't take it personal when I say bullshit or the likes.
Bill

[MSJ]

Bullshit on the rev matching? Really now...

I've seen some damn fine riders, that aren't anywhere near the skill level of MotoGP riders, rev match and downshift so smoothly, while braking deep into the corner, on bikes with no slipper that it makes you really KNOW that its possible.

Using MotoGP technology to compare really isn't fair. They are big bore bigs with tons of power, and their riding techniques are not of this world.

[Chris Allbee]

As far as the comment on what its like to drive a car that lifting the throttle doesn't add to rear braking force...try racing an automatic front wheel drive car. It can be done, it just requires a different technique than rear-wheel drive manual.

bringing this back to the FSAE side of things, its a monumental pain in the ass to teach amateur drivers to rev-match downshift on an autocross course, especially one as tight as the FSAE courses. A slipper clutch is a big honkin' band-aid, but so what? So is traction control and adjustable suspensions for that matter. Its all about making the driver fast in the vehicle, not making the vehicle faster than the driver.

[VFR750R]

Ok, time to switch it up. How bout drag racing type clutches like in use in Pro-stock. They have very little spring pressure, much of the clamping load is applied with centrifugal weights. Actually it's like top fuel too. When a pro-stock car shifts it slips the clutch just enough so the engine doesn't bog or spin the tires.
My boss runs a Comp eliminator car and i've seen graphs of the clutch vs engine speed and it's sick. Think of it as a mechanical traction control. It has to be tuned in but it limits impact load on the tranny and keeps from braking traction. No lift shifts!!

And you can go a bunch of races on the clutch, it's not a one run deal.

[Bill Kunst]

My point has always been that it isn't worth the money if it can be used somewhere else.

Secondly, besides being superhuman, no one, period, is going to match every single shift perfectly 100%. As any racer is riding at the edge of slip vs. grip, this shifting can be the scariest part of a turn. And this is the assurance that a slipper gives. If you could, you might be called Duhamel, or something like that.

I think we might have beat this thread dead. If you have mucho dinero sitting in your wallet and want one, you'll buy it. If you are practical, you will do with out.

Bill

[MSJ]

I completely agree Bill. I thought that was the point I was trying to get to also? http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Dan Nauts]

From an engine braking standpoint, we work on the assumption that the driver has much, much more control on the braking and vehicle balance at the limit when decel is modulated with braking alone.

A late braking, rev-matching downshift manuever where smoothness is required, is just too much to ask for from the average FSAE driver (consistently).

I agree that the slipper clutch would be a crutch for the less than stellar driver, and an un-noticed device for the experienced driver.

And if reduced wheel-hop and smoother downshifts during high rate changes in off-throttle events is the goal, a slipper clutch may help the 'symptom', but not solve the problem (driver smoothness, compliance,...).

Something that was also mentioned was suspension compliance. Last year's car had horrible wheel hop problems under braking during initial testing. Ultimately, replacing the a-arms with much stiffer units, and working on the rear suspension/diff box stiffness solved the problem twofold. Suspsension "wrap-up" was eliminated. And, flex between the motor and diff was eliminated, which was causing chain slap (slop) which in turn was shock loading the drivetrain. Both solutions together cost WELL under the cost of a slipper clutch.

[Bill Kunst]

Thanks, Dan, for a real life solution. We have been talking about alot of theory for quite some time. Addressing wheel hop is very important, and finding the problem can make a big difference as you have said.
My other question that has arose is how would a slipper clutch effect yaw under trail braking. If it would allow the wheels to keep up with the road, would it get the same effect?

Just more questions on the effects of the slipper,
Bill

[Chris Boyden]

Everyone talks about the increased cost...
If you just run a 600RR or one of the kawasaki
engines that come with a slipper clutch...
you're ready to run out of the box...not to mention the higher out of the box compression ratios with the kawasaki engines, and since engines in the cost report are on a per cc basis and you didn't add it/retrofit to a different engine, it's basically a free option.

[Dan Nauts]

Originally posted by Bill Kunst:
My other question that has arose is how would a slipper clutch effect yaw under trail braking. If it would allow the wheels to keep up with the road, would it get the same effect?

An easy (or intuitive) answer to your question would be that the best benefit of a slipper clutch in an FSAE application would be to slow down the yaw rate changes the chassis "feels" as a result of gear changes as a load input to the suspension and tires.

In the example of corner entry: Say an ideal driver can late brake into a corner (w/o shifting) at the traction limit,... i.e., initiate yaw with steering input, and control yaw moment with braking input such that the car is positioned ideally for the next stage of the corner.

Take the same driver and situation and add shifting. Now the driver must work harder to control yaw moment by both "smoothing" out the shifts, as well as modulating brake input to account for the increased decel load the tire sees from the engine. IMO, a very experienced driver can do this intuitively, and find how the car needs to be handled to negotiate the best way around a corner.

Realisticly [sp?], drivers are way less than ideal, and no two corners are the same. I myself prefer a car with alot of rear brake bias, and tend to drive without high rpm downshifts during braking. I'll use the combination of yaw initiation (steering input) and then late, sharp input braking, to "rotate" the car into a corner, and at the end of corner entry will drop as many gears as possible all at once.

Also note, gear changes (up or down) at any point during a corner (entry, mid, exit) present the opportunity to first change the longitudinal load into the tire, and consequently change the yaw of the chassis. If your not at the traction limit, it shouldn't matter that much. If your allready at the limit, your car will "squirrel" around at the best case, and spin out at the worst.

[KU_Racing]

I sort of agree with Dan- but I still think that for many drivers the feel and reaction of the car when the throttle is lifted is pretty vital to how they drive. I guess as usual, it comes down to personal preference.

also, Bill, I definately dont take the stuff on the forum personally- in fact i really enjoyed this discussion. This is exactly what I joined the forum for, and to be honest ive been getting tired of the 'how much ackerman should I run when I havent designed a chassis or picked tires yet' questions on this board.

[JHarshbarger]

Correct me if I'm wrong, but wouldn't you get same effect from lifting the throttle on a slipper and a non-slipper clutch? You still get a decent amount of engine braking with a slipper clutch(the same amount of braking when revs are matched), but it just "slips" when the rpm of the engine is lower than the rpm of the transmission.

Again, could be wrong on this. Just based on what I've heard and read.

[Dan Nauts]

Originally posted by JHarshbarger:
Correct me if I'm wrong, but wouldn't you get same effect from lifting the throttle on a slipper and a non-slipper clutch? You still get a decent amount of engine braking with a slipper clutch(the same amount of braking when revs are matched), but it just "slips" when the rpm of the engine is lower than the rpm of the transmission.

Again, could be wrong on this. Just based on what I've heard and read.

As I understand how a slipper clutch works, you get the same amount of engine braking as you do without. The slipper clutch appears to give the same result as tangential springs on an automotive clutch plate,... it just slows down the initial "de-application" of the clutch, therefore reducing the amplitude of "chatter" from the clutch system.

I'd also bet that with or without a slipper clutch, throttle lifts aren't appreciably different. Only the load shocks from faster gearshift events are different from one system to the other.

[MSJ]

Ok, these are my experiences.

On decel if you simply let off the throttle, the slipper doesn't engage and you essentially get the same amount of engine braking as you would with a with a non-slipper.

However, with a slipper clutch, if you don't perfectly rev match, and under a downshift, you can save yourself from wheel hopping, or even worse, rear wheel spin when entering a corner. Spinning the rear on the motorcycle can cause you to high side when the tyre "hooks up" again. Like I said before, it sucks.

I'm impressed by Dan's post in showing diffent solutions to the same problem. Your driving style is also interesting.

[VFR750R]

So just for clarity here and for myself. In one direction (power) it holds maximum torque for the clutch plates and springs combination. On the decel side, you can set the max torque the trasmission sees from engine braking. So in effect, your going to slip the same amount for the rpm (engine braking torque) in each gear but the effect at the rear tires is similar to the difference without a slipper in the different gears. That's why MotoGP bikes seem to hold a constant RPM on decel?? By adjusting this clutch, you'll effectively change the 'constant rpm' of the engine under decel conditions (assuming same throttle position) and thus engine braking. Down shifting above this rpm would still increase engine braking at the wheel but engine rpm would stay constant. So with every downshift you would still have more engine braking, it would just be less then without the slipper. Of course at the limit, there would be no engine braking, and then no change in braking gear to gear, but what happens when you get back on the throttle. The engine would be barely above idle but at your speed and gear, you could be at 7000rpm 'locked'. So now...you'd get a spike in torque when the clutch locked back up again? Soooo...is the reduced spike in decel worth the spike in accel?

[KU_Racing]

No- the slipper clutch does not hold an engine at a set RPM. It just disengages when the engine is trying to spin slower than the tire- its very simple.

[VFR750R]

So it is the zero torque case, in which a driver would have to be careful reapplying throttle since it would allow the engine to go to idle on decel.

[Boston]

If the clutch disengages when the wheels try to spin faster than the engine, then how can it perform engine braking? My understanding is that a slipper clutch is simply a clutch with an additional sprague clutch which eliminates engine braking by disengaging as the wheels spin faster than the engine...

[Bill Kunst]

if you check back in my posts, I gave a couple of sites that could help with this. It is not a sprague, just two ramps. In applying torque, the backs of the ramps hit, on decel the ramps hit and the more they ride up, the less engine braking there is. Search it on the net, or look at my links.
Bill

[Chace]

The slipper clutch does not disengage during engine braking, it slips, hence the name "slipper clutch". This lets the wheels rotate slightly faster than the tranny. The friction in the clutch is what adds to the breaking. Motorcyle racers use them so that they can dump from 6th gear to 2nd gear without worrying about the back wheel sliding out. You had better hope that you can rev match while dumping the gears or be able to grab some clutch, otherwise this won't work for you.

[Roach]

Hi all ... happened to stumble across this thread because of the link to our site.

My name is Brian Roach from SpeedWerks. We spend a lot of time building and racing motorcycles, and use the yoyodyne slipper clutches in our bikes as well as sell/install them.

The slipper clutches in motorcycles are ramp or ramp and ball. When the input shaft of the tranny is spinning faster than the output shaft of the motor (inner and outer clutch baskets) the clutch disengages the same as if you had manually pulled the clutch lever - the clutch hub is ramped outward by the force. They are designed to reduce or eliminate engine braking.

The stock units in some of the newer model bikes are "ok" ... they are ramp on ramp and reduce enigine braking and wheel hop.

The after-market units like the Yoyodyne or STM can be set up to completely eliminate engine braking. They are ramp and ball, offer more adjustability, and are much smoother actuating due to the balls riding on the ramps. You can tune them for the amount of engine braking you want.

Having gone to a 600cc inline-4 4-stroke from a two-stroke 250GP bike last year, I couldn't deal with the engine braking / rev matching. I hadn't riden a 4-stroke in about 5 years. Installed the yoyodyne unit and by setting up the springs and clutch pack thickness on my R6 the way I want it, I can go from 6th gear to 2nd, no rev matching, no engine braking. Grab brakes at 160mph, click off 4 downshifts, dump clutch, turn bike. No drama. Basically it acts just like my 250GP two-stroke. Once you get back on the throttle, the clutch ramps back together and engages.

- Brian Roach
SpeedWerks.com

[MSJ]

Originally posted by Roach:
Having gone to a 600cc inline-4 4-stroke from a two-stroke 250GP bike last year, I couldn't deal with the engine braking / rev matching. I hadn't riden a 4-stroke in about 5 years. Installed the yoyodyne unit and by setting up the springs and clutch pack thickness on my R6 the way I want it, I can go from 6th gear to 2nd, no rev matching, no engine braking. Grab brakes at 160mph, click off 4 downshifts, dump clutch, turn bike. No drama. Basically it acts just like my 250GP two-stroke. Once you get back on the throttle, the clutch ramps back together and engages.

- Brian Roach
SpeedWerks.com

Interesting. I haven't ridden a bike with an aftermarket slipper. Its interesting that you can totally eliminate engine braking with them and model the down shifting like that of a two-stroke GP (i miss my 125 some days). I guess the art form of rev-match downshifting is quickly disappearing. But, first thing you're taught is that the engine isn't for braking, the brakes are for braking. So, in that regard, I guess its better.

So it brings us back to using them on a FSAE car. I would find it very odd to drive (or ride for that matter) a machine with little to no engine braking. But it certainly would eliminate the chain chatter problem as a fix.

That being said, Brian...how much do these units typically go for?

[Roach]

Interesting. I haven't ridden a bike with an aftermarket slipper. Its interesting that you can totally eliminate engine braking with them and model the down shifting like that of a two-stroke GP (i miss my 125 some days). I guess the art form of rev-match downshifting is quickly disappearing. But, first thing you're taught is that the engine isn't for braking, the brakes are for braking. So, in that regard, I guess its better.

And that's really what it comes down to - your riding/driving stlye and what school of thought you subscribe to. I've been racing two-strokes exclusively since 2000, and you learn very quickly not to rely on the engine to slow you down. To me, it now just makes sense - you're eliminating variables. I use the brakes to slow down, and the throttle to go faster.


So it brings us back to using them on a FSAE car. I would find it very odd to drive (or ride for that matter) a machine with little to no engine braking. But it certainly would eliminate the chain chatter problem as a fix.

A lot of guys have a hard time with it. The first time you expect the thing to be slowing down and it isn't, your brain has a little conference in the back room trying to figure out what to do next http://fsae.com/groupee_common/emoticons/icon_smile.gif

The thing is, you can tune the amount of slip (and that is really what it is - with the wet multiplate clutches in bikes, they're pretty much always "slipping" to some degree when the clutch is disengaged) you want by adjusting the stack thickness, clutch spring rate, and clutch spring pre-load. For example, if you wanted less slip, you could simply substitute 2 barnet heavy springs for 2 of the stock ones. If you wanted to change how much force was required before the clutch started to slip, you could pre-load the clutch springs.


That being said, Brian...how much do these units typically go for?

The yoyodyne units are $800. It's a drop-in replacement for the inner basket and pressure plate - you use your stock clutch plates, springs, and outer basket. I don't really have any experience with the STM units, but they look to be pretty much the same thing but cost a bit more.

- Brian Roach

[Mike Hart]

We're currently trying to work out whether to go for a slipper clutch on our car to reduce the complexity of an auto downshift system and it's interesting reading peoples opinions here. I'm also one of the main autocross/endurance drivers and in my opinion you want to eliminate engine braking in a race car as much as possible. I find it bizarre that some people on here are saying you want engine braking and then in the same post talking about rev matching. The whole point of rev matching (ie heal and toeing or throttle blipping if you're car only has two pedals) is that you are matching the engine crank speed to the wheel speed and hence negating engine braking. Admittedly once the clutch is re-engaged and the engine starts to slow it will cause some degree of engine braking but as far as I'm aware this should still happen with a slipper clutch. To get zero engine braking the engine would have to be completely disengaged from the transmission which, as already concluded, doesn't happen as the clutch slips until engine speed and wheel speed are the same, at which point the clutch re-engages. I know there are teams out there that have used them (it's how I found out about them in the first place), but I'd be more interested to hear some info about wear rates and heat issues.

[Steve O]

First of all I will warn you, get food if you are hungry or use the facilities if necessary, this is kind of long winded.

I have to agree with Mike; If you are an experienced driver you will be matched perfectly into the corner and will not be getting very much engine braking. At that point the only thing that will confuse you is if you go to look for your clutch and it isn't there.

The other thing is with a torsen rear end, like most are using, the ability to apply some brake pressure (meaning your foot is not on the clutch for shifting or other purposes)on accel/corner exit would help your lsd lock up on corner exit and not allow wheel spin as easily. This is a common pro driver technique as applying brake pressure creates a simular effect to a clutch diff since there will always be torque through that drive axle. Even during zero traction conditions( ie. ICE)the diff will still be able to transfer the torque to the other wheel under whatever multiple the diff is set at.

ex: 5:1 diff applies 5x's as much torque to higher traction wheel under locked condition. Zero traction = zero torque 5 x 0 is still 0 so both wheels go nowhere apply braking torque and this solves that problem. Note: this won't work if you have an inboard rear brake.

On the topic of slipper clutches and inboard brakes the slipper clutch helps chatter so much because your brake is directly slowing down the sprocket itself on the rear axle which is causing the chain slap to be so dramatic because there is no slippage between the brake and the motor. Outboard brakes transfer the force through the diff first allowing the impact time to be longer by a few fractions of a second (recall that time is a huge factor in energy transfer!). Most teams with bad chatter problems have rear inboard brakes...check it out. A slipper will eliminate this problem and allow for the single inboard with far less rotational mass and unsprung mass. (Although we do it without a slipper despite the above fact)

As far as my experience with driving all of this I can say I have driven an FSAE car with a regular clutch and a shifter cart with both a regular clutch and a slipper clutch. The shifter cart had similar power (actually higher power/weight), just a spooled rear end and no suspension. That said, I can say from experienced that when cornering if you are where you should be with RPMS you do not feel a difference except for when you look for the clutch and dont have it or it feels funny when you apply it. Some slipper clutch manufacturers though have even gotten to the point of eliminating perch adjusters and allowing the stock clutch lever to act as normal allowing full disenguagement at any RPM (and feel normal as well). As Brian Roach had said, as well, they now allow for full adjustment with a high end one to the point where you could add drag for driver feel and keep a clutch in the cockpit for driver feel and allow the slipper clutch to just compensate for driver error.

The other benefit to a slipper clutch is the ease of power assisted shifting as Mike had mentioned. You don't need a kill box, although it would still help for a very quick shifter device.

For a final verdict on whether or not it is worth it... on a production motorcycle motor I wouldn't bother, too expensive and most of the time not enough adjustability, not to mention the clutches are not meant to take constant clutch slippage... the ones for street bikes aren't meant for racing, just to save a few idiots on crotch rockets(I mean idiot in the way of doing stupid things that will get you killed;I did it when I had a crotch rocket too, so don't take offense!). If you happen to be a team using a moto-x or ATV racing engine you are in luck. These ones are more affordable for top of the line as the slippers in these were initially intended for motors of this size (as opposed to the street copy's of the original motoGP mentioned earlier). ALSO, the clutches are more intended for clutching of this type. Racing motocross (did that before shifter carts-not with a slipper though) you are constantly slipping the clutch to control traction, dive into corners, drift out of corners, etc. Therefore, your stock clutch plates shouldn't have a problem with the auto/slipper clutch, in fact, most manufacturers state LONGER clutch life providing you aren't slipping more than 1 gear too low for the conditions; which under restrictor racing you would be an idiot to do anyway (this time I mean idiot in a bad way). Top of the line for these motors is around $650-$700; these will offer full adjustability and full function of stock clutch disenguagement.

Overall its an expensive feature either way but could make a positive difference. If you want it but don't want the car to cost more, spend less on something else. If you don't want it, don't buy it. I also may suggest throwing a temper tantrum and shouting out, that you don't want it, REALLY loud

Sorry for the long post but it seems like the more recent posts were inquiring more on experience with what the motors can handle and how it feels to drive a 4 wheeled vehicle with a slipper in it so I figured I would share.

Steve

PS. since the shifter cart has no susp. it does show that there are other purposes besides suspension control; however, I do agree that in a racing motorcycle that is its primary function.

[Chris Allbee]

I'm fairly certain the purpose of rev-matching isn't to reduce engine braking, but to reduce the shock on the drivetrain during a downshift. In fact, while the motor may be off-throttle it is still pumping air and without producing power of its own (assuming fuel cut on decel) the faster it is spinning the more power it will absorb. Hence, rev-matching to a lower gear and therefor a higher RPM would actually increase the amount of energy the motor is trying to dissipate (more engine braking).

There has been a lot of good discussion on techniques to work-around some of the problems people are having and these would be the preferred method in my opinion. They are cheap (only cost gas and seat time) and get you valuable experience in the car. However, I've said this once and I'll say it again, if you can afford it and don't have the time to train properly a slipper clutch is a nice band-aid to cover for some of these deficiencies.

[BryanH]

Originally posted by KU_Racing:
I would like to point out again that there is no major racing series on planet earth (someone correct me here if I am wrong) where a slipper clutch is used. Most series whos rules I understand have not outlawed a 'back-torque limiting' style of clutch, and still no one uses them.
A couple of V8 Supercar teams were using slipper clutches mounted in the wheel hubs in a rule bending exercise to get around the mandated spool diff. they were banned from the start of 2007.
If you are wondering if a F-sae car would be smoother/quicker with a slipper clutch, find a video of Mark in RMIT at Detroit 05. Don't know if the boys used it in 06. Upkeep is not as bad as Pro stocker but it did need to be checked/ adjusted often. Just to be precise RMIT used a Drag race style centrifugal primary drive clutch initially without a hand clutch lever, added later for more rpm's on launch. The car was much easier to drive and quicker on the test track.
The race bikes use a one way clutch with ECU controlled overrun drag, so it only freewheels when the Race Engineer wants it to.