Ideas on Brake Rotors for 10" Wheels and Steering

[dsoule15]

Hello all,

My name is Drake and I'm on the University of Colorado Denver's FSAE team. I'm in charge of the brake and steering systems and I could use a little help, please.
I have a good idea of the entire braking system: we're gong to (try to) use the calipers left over from the team two years ago, I've got the brake pedal (with adjustment bar) picked out, master cylinders are very close to taken care of as well.
My only trouble is finding brake rotors that will work with the 10" rims we want to do. It seems like most teams are going to the 10" wheels in competition and for good reasons (less overall weight, reduction in unsprung mass, etc...). Our team would like to use 10" rims as well. The rims/hubs have been chosen and a spindle has been created in Solid Works that we plan on machining. I'm having trouble finding brake rotors though. The rims have a 9.5" inner diameter and when allowing for clearance of the calipers, we'd like to go with brake rotors of about 7.85" diameter. I just can't find any this size anywhere. We're considering machining our own if we can't find any to buy. Is that what everyone else is doing? Or is anyone buying them from anywhere? I've considered ATV brake rotors but I'm not sure that the ones I've found would tolerate the conditions FSAE will expose the rotors to (and I don't know much about ATVs at all).
What does everyone recommend? I know that machining and treating rotors will be kind of difficult and time consuming but if that's the route I have to go, what kind of material and treatment? I saw another thread on here that recommended a strong steel, 1040 perhaps. If people are buying rotors this small, where are they buying them from?
Also, I'm not too sure about the steering system. If I could get some of you guys to point me in the right direction for things to research so I can come back and discuss it more I would appreciate that as well.
Thanks in advance for everyone's input.

[Jon MW]

We manufacture custom made brake discs for a lot of FS/FSAE teams. The only restriction we have is that the mounting diameter of the disc can only be in steps of 5 mm, so 150, 155, 160 mm and so on and the thickness is 5mm. We can make discs with other mounting diameters as well but that means making a new special fixture which will take some extra time and might cost a bit more. If you PM me your e-mail I can send a mounting instruction pdf and a generic cad of a disc and the mounting button when I get to work tomorrow. I'm pretty sure we should be able to something that would work for you.

Jon
ISR-Brakes (http://www.isrbrakes.se)

[Jay Lawrence]

dsoule15,

I would say that the majority of teams get their rotors manufactured (or manufacture their own). It is probably the simplest major part to make/get made as it is only a 2D profile. There are a number or suitable materials, and a good way to find out which you want to use it to research what bikes use. Some people have been asking about cast iron, but I've not seen any near modern bike with cast iron rotors so I'm not sure where that's coming from.

As for steering, there's heaps of info on here that should get you going. Jonny Rochester's UTAS build thread has some good practical sort of information, and there's lot's of stuff elsewhere on trail and self-aligning torque as well.

[MCoach]

dsoule15,

http://www.mcmaster.com/#6544k69/=tsqero

[EPMPaul]

There are multiple advantages to the cast iron ( I believe they use grey cast iron disk. The following list comes from p76 http://www.sae.org/events/bce/tutorial-ihm.pdf

• High strength and durability to sustain torque loads from braking
• Stable mechanical and frictional properties through range of expected service temperatures
• High wear resistance through range of expected service temperatures
• High heat absorption capability to absorb braking energy
• High thermal conductivity to transport frictional heat away from braking surfaces
• High vibration damping capacity to minimize NVH issues
• Minimal thermal expansion to minimize performance variability
• High degree of corrosion resistance
• Excellent machinability
• Inexpensive material and processing costs

So basically it's the be all and end all of brake materials in conventional car brakes.

In formula most teams I've seen use steel mainly for manufacturing ease and because a lot of the factor above aren't really an issue. (Wear, Noise). The fact that you can get a set of steel rotors laser cut and on the car for cheap and in no time pretty much makes it a no brainer. Most times don't have them ground( to my knowledge) but it may prove to be a good move to eliminate any runout issues on the disk which could cause vibrations.

Otherwise you can buy a set of blanchard ground (http://tciprecision.com/literature/Blanchard.pdf)cast iron blanks from Kaz tech and machine them to size. It's more expensive but technically " better" from a purely mechanical standpoint.

Hope this sheds some light on your problem

[tromoly]

I agree with Paul on the Blanchard grinding. A couple years ago we received donated cast iron for brake rotors, a local company did initial Blanchard grinding to remove warping in the material, then the pieces were put on our waterjet and the rotors were cut out, then they went back to the company for a final Blanchard grind to the desired thickness. Worked very well and took one or two weeks from start to finish.

[MCoach]

I used to get our rotors blanchard ground. Now, we just leave the tolerance up to whatever we buy the sheet at and there is no noticeable difference in performance after you bed the pads and break through the steel surface coating. Smooth sailing for a total investment of less than $15 per rotor real world cost (including all the spare rotors).

On that note, people used to give the 'wink and nod' of "You're braver than us to stoop that low at undercosting your car". Then I tell them that we actually cost things very accurately, and I'll show them some of the parts, like the rotor, and they're shocked at how few operations we put into everything. Most of our guys come from a very OEM world where such is the norm. There's a reason why Kettering is so good at cost. Most parts aren't popped off a multi-axis CNC mill.

Can it be a carbon fiber thing that was designed by some student such that it must be made of composite materials that are only available deep in the jungles of Bolivia, which are then blessed by the Pope himself, pre-pregged by the world's best composite technicians in Seattle, and frozen naturally in the Antarctic winter until needed? Sure, it's high performance that way. However, this part must then be laid up on a perfect steel, 5-axis milled mold, and heated naturally at the surface of the sun. After a 4 month process, the part is delivered to the team, bolted on to the car in a clean room, approved by NASA. Some parts I've seen in the series don't seem too far off from that...

Our world: Can it be made of out steel? Awesome. Mild? Even better, no heat treat required. Can it be 2D manufactured in house? Sweet, I'll take 10 in varying thicknesses.

[Simactive]

We have be machining and creating our own rotors from the start. It has been the easiest way if you have access to a machine shop and CNC cutter by mill, water or laser.

We have tried a bunch of materials for rotors including testing Aluminum which we didn't really have much luck so we've shelved them for awhile now. Maybe we'll go back to it one day.

[EPMPaul]

Our world: Can it be made of out steel? Awesome. Mild? Even better, no heat treat required. Can it be 2D manufactured in house? Sweet, I'll take 10 in varying thicknesses.

Damn have ypu been attending some of our meetings?

[MCoach]

Paul, maybe someone from our team gave out all the secrets already?

I've been preaching this for years. :P

Wait until you see our uprights. I'm going for "shock and awe" of what can be made out of little bits of sheet metal. 0.020" sheet steel all the things!

[EPMPaul]

Concerning the upright we re trying some sheetmetal this year too. A little nervous as to how its gonna turn out. Some of the thinner brackets on our car have been buckling during welding and it s happenend a little on the uprights ( although it s .080 steel) because there s a bunch of pockets(apparently not the best idea on sheetmetal). But yeah been pushing for more 2d cut based parts just coz it s darn cheap and laser/water cutting shops are a dime a dozen. What s tricky is actually the tooling. Has a few nasty surprises with that this year.

Trick with sheetmetal uprights is to get the bore and various stubs down to an acceptable weight. Because we had a design team of 3(1 for the chassis, 1 for the driver controls,1 for the rest) it got overlooked and screwed us(1.2 kg for a rear upright is pretty hefty). Also post machining weldments is somewhat coz everything gets crooked during welding even with a jig.


Anywyas back to the original subject. Yeah haven t run the simple laser cut disks yet but not really expexting any problems per say. Difficulty is in getting a floating setup to work properly on laser cut tolerances(+-.002). We side stepped the issue by using bolt holes on the disks and radial slots on the hub to make the arrangement floating.( photos available on demand). The thing with the cold rolled sheet is the fact that the area of the disks is so low that total run out isn t so bad and most floating setups have so much slop that it probably doesn t matter anyways.

Bottom line is laser cut disks are a viable option for fsae. Maybe thicker disks make it more necessary to have cast iron but at our thicknesses <.25 laser cut steel seems to work fine.

[anjello91]

We have tried a bunch of materials for rotors including testing Aluminum which we didn't really have much luck so we've shelved them for awhile now. Maybe we'll go back to it one day.

So what material did you end up sticking with? Cast Iron or Steel? And why?

[Ahmad Rezq]

what are the calipers you will use ?
why didn't you involve in the decision of choosing 10 tyres as a braking member?
you must set with the suspension man to check your space room to put your brakes components?
i suggest you chose a small calipers and for sure your calculations will give you the complete pictures and do manufacture your rotors but you must do the heat calculations very well because your rotor will become lighter.