Brake Setups

[FIAChamp]

Hello,
I'm working with the Stanford University team and would like to know of good resources regarding brake setups. I understand disk-brake operation and such but haven't dealt with it at the smaller scale of formula SAE cars. I'm looking to know about good disc materials that dissipate heat well as well as ways to attach them. I've heard of some being attached to the rim, this sounds interesting though it seems it would get the rims and eventually tires much hotter.

Thanks,
Rob

[FIAChamp]

Hello,
I'm working with the Stanford University team and would like to know of good resources regarding brake setups. I understand disk-brake operation and such but haven't dealt with it at the smaller scale of formula SAE cars. I'm looking to know about good disc materials that dissipate heat well as well as ways to attach them. I've heard of some being attached to the rim, this sounds interesting though it seems it would get the rims and eventually tires much hotter.

Thanks,
Rob

[JPS]

just to see different methods, you could start by looking at the galleries from this years comp.

ive heard of a korean team using carbon/carbon brakes but overall teams use steel rotors.
have rim-mounted rotors been used in FSAE? does it make sense(requires custom rims and calipers)?

[nathan s]

I think the rim mounted brakes you are talking about is along the same lines as what Buell does with the XB12. The only problem with it is that with the small wheel diameters that we use, you start cutting into your upright space. For this reason I think a lot of teams don't do that. As for heating, I don't think you would have much of a problem with everything being out in the open.

In my opinion, your best bet is to go with center mounted ventilated (drilled or slotted) rotors. Just make sure to test ventilated rotors to make sure you don't have cracking.

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by nathan s:
I think the rim mounted brakes you are talking about is along the same lines as what Buell does with the XB12. The only problem with it is that with the small wheel diameters that we use, you start cutting into your upright space. For this reason I think a lot of teams don't do that. As for heating, I don't think you would have much of a problem with everything being out in the open.

In my opinion, your best bet is to go with center mounted ventilated (drilled or slotted) rotors. Just make sure to test ventilated rotors to make sure you don't have cracking. </div></BLOCKQUOTE>

Take a look at WWU's site. They've done rim mounted rotors on what looks like 10" rims.

Other than that, materials to look into are steel, iron, and aluminum or aluminum MMC. A head's up on the MMC's, they are very difficult to machine and require PCD tooling. Waterjet and laser cutting can be used if you access. MMC's have excellent features, such as vibration dampening and heat dissipation, but you have to be careful on the selection of the MMC as there can be some with good properties at temperature and some with bad (basically take a look at the materials data sheet). Search around for other threads on brake rotors.

[Greg H]

To the guys who have run MMC discs, what type of pads did you use? Is anyone from Swinburne still out there?

[Colin]

hey greg, yea swinburne's still here. Getting Pad's for MMC material is a pain in the ass, much like sourcing it, parting it, machining it and cutting a profile in it. But it does have excellent heat dissipation properties and is very light. I think willwood has a compound that is suitable but I'll have to check that. After using it for 3 years we are going back to steel mostly due to availability but steel is a hell of a lot easier to manufacture.

[Agent4573]

When doing the brakes you really have to look into a bunch of different factors when looking at what setup you want to do. I would suggest staying away from really fancy systems if this is your first year doing the brakes(Its kinda important that the brakes work well). As for materials, I would suggest steel, we used 4130 this year without a problem, most motorcycles come with 1080 for brake rotors. Aluminum can be used and has been used effectively, but you need alot of it to keep it from getting too hot. I believe most aluminum(6061 anyways) only mantains its strenth upto something rediculously low, like 200 degrees C. Our steel rotors run right about 500 degrees C right now without a problem. There was a thread on here a few days ago about carbon rotors and pads. It was something like 400 per rotor and then more for pads. If you have money I say go for it, but we spent 400 or so on our entire brake system with steel.(including M/C's, rotors,calipers,pads, etc.)

[Psychosis]

Wilwood sell both al-mmc rotors and pads, we used to run them until i designed lighter discs from mild steel. the al-mmc rotors are recommended with the Poly-Q compound pads, however they arent the best and do have a limited operating temp. i tested ours on my dyno and had them up about 500C (the black anodize turned gold) but i wouldnt recommend running that hot. this year we used laser cut steel rotors with poly-A compound pads (a big thanks to lasered components, http://www.lasered.co.uk) they were 35% lighter than the al-mmc rotors and ran exceptionally well, they only required two brake applications before all 4 wheels locked. i spoke to toronto who run the B-compound because the A-compound can be a little violent. hope that helps

[Greg H]

With our current setup we have a very light system using extremely expensive ap calipers and steel rotors. I wanted to reduce rotating mass of the rotors, but in the end I will probably need heavier calipers since the aps don't have the appropriate pads, but we might save $1000 switching to Wilwoods. I would think that MMC rotors would not get as hot as the same sized steel setup that we run because of its superior thermal properties. Am I missing something here?

[Gareth]

As far as I know, most rotors are low carbon steel or cast iron. Higher carbon contents will heat treat during operation, become brittle and lose their strength as the carbon diffuses out. I believe motorbike brakes are stainless steel, but predominantly for aesthetic reasons. Some stainless steels have just slightly higher heat capacities, but I can't see that being a good enough reason to warrant the extra hassle/cost. If anyone can come up with a material with a better specific heat capacity that'd be appropriate for brake rotors, please let us all know.

It seems that thin motorcycle rotors, like what are typically used in fsae are mounted on bobbins or drive pins that allow the disks to float radially. This allows the hub and rotor to expand at different rates without introducing additional stresses. Larger, veined rotors can get away with this due to their greater inertia (thus stiffness). The last thing you want is a warped rotor as this creates "knock-back" where the rotor pushes the pad further than necessary. The effect is larger pedal travel and in the worst case, a double pump. You want your brake system to be as stiff as possible and designed to allow the least flex/compliance to minimize pedal travel. Drivers are better at modulating pedal force than displacement, not to mention the force application is far more linear when the movement is minimized.

Interestingly, a fellow team-mate that just returned from England mention that the F2003 has a "ridiculous" amount of rotor float, both radially and axially. Maybe something to do with how the carbon pads/rotors wear. I'm sure there's a good reason...there always is at Ferrai...

As for calipers the guys have good suggestions - look at what other teams are doing. You can get alarmingly small before things get bad. Unfortunately it would seem that there is a large compromise between weight, quality and cost. No surprises really. Has anyone looked into the 24mm bore Brembos? They're beautiful, but $$$.

[Colin]

Greg
Just because willwood makes the pad dosn't mean you have to use willwood calipers. For a lot of our setups we've cut the pad material off a pad and glued it to a backing plate to suit or just cut down a bigger pad to suit the caliper

[Dr Claw]

the hot tip with MMC rotors, is lotus elise brake pads http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Greg H]

I suppose they would have to keep some in stock even though the Elise switched away from MMC. Apparently their supplier company no longer exists. There's also the Plymouth Prowler...

[John Bucknell]

I wouldn't exactly pursue the Prowler part as a race pad. Don't ask how I know.

[James Waltman]

http://dot.etec.wwu.edu/fsae/HostedPics/Viking35/Thumbnail_Galleries/Main_V35_Gallery/images/DSC06235.jpg
http://dot.etec.wwu.edu/fsae/HostedPics/Viking35/Thumbnail_Galleries/Main_V35_Gallery/images/IMGP0214.jpg
http://dot.etec.wwu.edu/fsae/HostedPics/Viking35/Thumbnail_Galleries/Main_V35_Gallery/images/DSC00869.jpg

I think our "inside out"� brakes work well enough. Of course, there are some compromises to make them work. We don't really know how they influence tire temperatures. It doesn't really seem to matter for a single autocross run.

[Z]

James,

How did you attach the disc to the wheel? Do you have to separate the disc from the wheel to change the wheel? Or does the "floating" caliper slide of its two pegs as you remove the wheel?

Z

PS. Nice through-rod-shock-cum-pullrod-err-"coilunder"! I guess that's the twin-tube (or was it "rocket tube", or something??) chassis.

[James Waltman]

The disc bolts directly to the wheel. It is permanent. One of the compromises is that the rotor needs to be a little thicker for the bolts. It isn't that thick though. The whole package is still quite a bit lighter than a 13"� wheel. The floating caliper just slides on and off with the wheel. Not a big deal since we aren't doing pit stops.

We don't have a trademark on the name for the chassis or anything. Usually we call it a "twin tube (http://dot.etec.wwu.edu/fsae/HostedPics/Viking35/Thumbnail_Galleries/Brakes_and_Shocks/images/V35%20Chassis_jpg.jpg)".

I guess the shocks even meet your ideas for simple mounting. They didn't save us any time though since we made all of them.

A gallery with some more pictures is here. (http://dot.etec.wwu.edu/fsae/HostedPics/Viking35/Thumbnail_Galleries/Brakes_and_Shocks/index.htm)

[rjwoods77]

I love your ghetto ass nut retainer on the spindle. Its funny that we all spend lots of time engineering stuff to be perfect and nice and then we throw shit like that on our cars.

[nathan s]

Hmm... That looks like a nice job.

[James Waltman]

Yeah we just kept putting off that nut retainer until the very end. We actually went through tech inspection in 2004 without it. We knew that it was the only thing that we had left and while we sent some guys out to buy the bolts we figured we should go through tech just to make sure we weren't missing anything else. The tech inspectors were OK with everything else and when we added that they gave us our sticker. I was actually pretty proud of getting that sticker.

[kwancho]

So.... in doing my reasearch, here's about what I'm thinking:
3/16" rotors, dual outboard front and rear (don't want to debate that here)
9" diameter front, unknown rear (haven't done the calculations yet)
Wilwood dynalite singles (the f4i of calipers)
Wilwood E Pads
And I hear everybody talking about Wilwood master cylinders, but nobody saying which part they actually use. Anybody?

[GTmule]

Everytime you use Wilwood D-lite singles, god kills a kitten.

(edit: I'm amused by the fact that it said "thank you for contributing to the forum" when I posted, because...I wasn't)

[kwancho]

Hey man, hey man, you can say the same thing about F4i's, Keizers, and University Specials. And I still don't know what master cylinders people use.

[Kevin Hayward]

We made our own Master cylinders last year so that we could afford to have something resembling high-end masters. They work really well.

For '01 and '02 (OZ) we used Girling master cylinders. Nothing special I think they were trailer ones. Could get a really nice hard pedal. Have had them in push and pull configs. For our '03 car (Oz) we used nissin motorcycle master cylinders They were small and light. But by the time the car had reached the Us (in '04) we had Girlings on it. The pedal ended up much better than we could get it with the motorcycle ones. But that was more due to other pedal box improvements.

Not the lightest you will find but really cheap and work well.

By the way you can get some really well priced and good callipers if you are prepared to look around on the back end of motorcycles. We switched to a Brembo from the rear of a Ducati a couple of years ago. They are of equivalent size and weight to the Wilwoods as far as I know. Price was really good and they come in both left and right hand configs.

Cheers,

Kev

ex-UWA

[rjwoods77]

Hey Kevin,

I was looking into using an ap or brembo pull style master cylinder off a motorcyle rear brake setup. We dont require much because we have a light car with 6 inch rotors and either going to use single 1" pistons on each caliper or do a dual piston on each caliper with something with a larger area(if we make our own). Do you know how much line pressure is too much? I know what the lines will take but what is there any bad effects from running high line pressures?

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Rob Woods:
Hey Kevin,

I was looking into using an ap or brembo pull style master cylinder off a motorcyle rear brake setup. We dont require much because we have a light car with 6 inch rotors and either going to use single 1" pistons on each caliper or do a dual piston on each caliper with something with a larger area(if we make our own). Do you know how much line pressure is too much? I know what the lines will take but what is there any bad effects from running high line pressures? </div></BLOCKQUOTE>

It's only AP Racing that has the pull style. If you are interested, you'd be better off going with their car pull type master cylinders, instead of the motorcycle ones, because they are a little cheaper, but they are still pretty expensive.

[Cement Legs]

Do any teams use dual inboard brakes on the rear near the diff carrier to balance braking forces on the differential?

Where do I order the Rob Woods t-shirts? Will it help benefit FSAE? http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[rjwoods77]

The shirts will be for sale in about a month. They will cost prob 10 bucks. Not looking for profit. Just to break even would be good for me.

[Captain Redbeard]

Cement Legs, We had our brakes in near the diff this year, the two main reasons for doing it were to balance the braking forces on the diff and to keep the unsprung weight down (compared to outboard brakes.) They worked well and the rotors were very small. Check the comp pics if you want to see it.

-Redbeard

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Rob Woods:
Do you know how much line pressure is too much? I know what the lines will take but what is there any bad effects from running high line pressures? </div></BLOCKQUOTE>

The way I see it, higher line pressure = more "flex" in the brake system. More pressure means more compression of the fluid (it is not completely "incompressible") and more outward expansion of the brake lines, etc. It is a bit like bending a thin and a thick beam - the thin beam has higher stresses so it flexes more.

I reckon for a "rock hard" brake pedal (which IMO is a good thing) you want to keep the line pressures on the low side of normal. The cost is that low pressure =&gt; bigger than normal caliper piston area (for same force at pad) =&gt; bigger diameter master cylinder, or small diameter M/C with longer stroke but with smaller leverage ratio at the pedal. Small leverage on the pedal is also good for reducing pedal arm and joint stresses, and hence flex (eg. try leverage closer to 2/1 than 5/1). Also a smaller pedal leverage ratio lessens the amount of free travel while the little "refill" hole in the M/C gets bypassed.

Z

[Schumi_Jr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kevin Hayward:
We made our own Master cylinders last year so that we could afford to have something resembling high-end masters. They work really well. </div></BLOCKQUOTE>

Kevin,

What were your driver's opinions on the performance of your low-hysteresis master cylinder set-up? I'm curious because most high end Formula cars still use fixed mount MCs... do the UWA guys know something they don't http://fsae.com/groupee_common/emoticons/icon_wink.gif

[rjwoods77]

Z,
Thank you. Makes sense.

I have one other question. I dont like to follow "thats the way it is" kinda stuff so here it goes. Take a 2 piston floater vs. a 4 piston fixed caliper. The gurus out there say that those 2 calipers will have the same effective piston area for the equation you run them through. How is this. Wouldnt a floater half the force from the piston area halved because it is workin both sides of the rotor? Why do you ignore the one set of piston on a fixed caliper?

[Storbeck]

Rob, both calipers are working on both sides of the disk, one just has another set of pistons, and the other has a solid thing there. Imagine what would happen if you floated the four piston caliper and locked the pistons on one side.

Or to put it another way, figure out how much force is on each side of the disk with the two piston caliper, then figure out how much is on each side of the disk with the four pison caliper. It's the same either way.

[Denny Trimble]

Rob,
You can look at it from two perspectives, force and displacement.

The force from inside and outside pads must be balanced, otherwise you will bend your rotors and caliper mounts. So, on a "floater", the force on the piston side is equal to the force on the non-piston-side. On a "fixed" caliper with opposed pistons, the forces are equal on either side.

If you're thinking about displacements, then to compress the pads a certain amount (or take up clearance between pads and rotor), here's how it works out. The "floating" caliper has two clearances to displace, the inside and outside pad-to-rotor clearance. So, the pistons have to move twice the clearance to close the gap. (2 * clearance).

The fixed caliper will see each side's pistons move an amount equal to the clearance (2 sides * clearance).

Does that clear it up for you Rob?

Floating calipers would be great if only they would float well...

Perhaps a "floatation test" is in order http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Kevin Hayward]

Rob,

Any answer I would give you concerning high line pressures would be similar to Z's. The other thing to be concerned about with line flex is the fact that the lines running to your rear brakes will probably be considerably longer than those to your front brakes. However sensible choice of hydraulic lines will make line flex a non-issue for any reasonable line pressure.

Aaron,

I was one of the team's enduro drivers (for the last 4 years) so I can give comments on the master cylinders and how they compare to others. The simple answer is the braking performance of the car was notably improved over the last car. Brake balance was quite a bit more predictable. Not as big an improvement as going from the single rear brake to the twin outboards but definitely noticeable.

However the longer answer is that we cannot directly attribute the performance improvement to the changes in the master cylinder arrangement. The kinetics made things quite a bit different to start with and the car setup was also changed quite a bit.

Unfortunately we have not mounted brake pressure sensors to the vehicle yet. It would give us a much better idea of what is going on. So I cannot really confirm any 'gut' feelings that we had as drivers.

However making our own master cylinders was not done just for the hysteresis issue. They are also considerably lighter and smaller (read packaging) than any masters we had used previously. They also allow us a novel way of attaching the balance bar and pedal box arrangement that is better structurally.

We managed to get the pedal box length down far enough that we would almost never consider pull type master cylinders to reduce length further (although there are other good reasons for pull-style masters).

Making masters with a spherical each end also ends up being a really simple way to make them with a minimum number of parts. Its just like a mini shock only easier. No painful gland nut seals or valves etc.

As for high-end formula cars. We actually got our inspiration for the masters from the Ferrari Book, you know the one with a whole heap of pictures that us engineers drool over http://fsae.com/groupee_common/emoticons/icon_smile.gif Actually there are a lot of really good ideas in that book.

Cheers,

Kev

[Z]

Rob,

Re: "2 piston floater vs. 4 piston fixed caliper"

Or another way to think about it: The 2 piston floater actually has 4 pistons, but you can't see two of them because they are "invisible" and hidden inside the cylinders!

Looking at a front view section of the floater there are two (real) pistons pushing their pad leftwards, say, and there are another two "virtual" pistons, inside the cylinders, that are pushing the body of the floater, and the other pad, rightwards... Hence same forces on each side of disc, same amount of fluid used to take up clearance, etc... as noted by Storbeck and Denny.

Z

[Schumi_Jr]

Kevin - thanks for the reply. I was thinking about the Lola GP2 car when I meant high-end... I guess that's more of a mid-end formula car.

I agree with you on the Ferrari book. The judges often say to look at historics and Formula Fords rather than F1 for inspiration but there are some very elegant designs on the F1-2000.

Denny - I should admit that those 0.422 points are the most coveted ones of my FSAE career! Tell your accel driver not to be distracted by the cute blonde in the grandstands next time http://fsae.com/groupee_common/emoticons/icon_wink.gif

[kwancho]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Captain Redbeard:
Cement Legs, We had our brakes in near the diff this year, the two main reasons for doing it were to balance the braking forces on the diff and to keep the unsprung weight down (compared to outboard brakes.) They worked well and the rotors were very small. Check the comp pics if you want to see it.

-Redbeard </div></BLOCKQUOTE>

Anybody have these handy? Anybody else run dual inboard rear brakes?

[Homemade WRX]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Alex Kwan:
Anybody have these handy? Anybody else run dual inboard rear brakes? </div></BLOCKQUOTE>
we're looking to run them this year...working my way through the formulas right now actually

[Captain Redbeard]

Here ya go:
http://homepage.mac.com/matthodgson/FSAE/Diff-Brakes.jpg
Thats the best pic I could find

[kwancho]

Looks good. I'm looking at dual 5" discs with dynalite singles, 0.75" master cylinder and 47.6 pounds of force in the rear (50.5 front, means the bias bar will be set a little towards the front). WRX, what are you thinking?

[Homemade WRX]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Alex Kwan:
Looks good. I'm looking at dual 5" discs with dynalite singles, 0.75" master cylinder and 47.6 pounds of force in the rear (50.5 front, means the bias bar will be set a little towards the front). WRX, what are you thinking? </div></BLOCKQUOTE>
right now I'm at a hold up with wilwood waiting for Cf values on there pb-10 pad...looking at the ps1's at the moment...also been looking at dynalite singles...
I plan on running numbers for both calipers and seeing difference in weight between rotor size and caliper
for the Cf info checking to see if that is the pads Cf or Cf against say and alum or stell rotor...
for the MC I'll have to wait until I'm get the info so I can finish calculating brake torque