quote:

Probably not a bad idea to adapt an existing commercial brake rotor off something or other, rather than trying to fabricate something totally from scratch.
After all, we don't attempt design our own calipers, wheels, or a whole host of other things.

I disagree. Solid Disk Rotors are one of the cheapest and easiest parts on the car to design/make yourself.

can't say the same for calipers (still not hard to do, but harder to do better than premium off-the-shelf options).

quote:

Originally posted by Buckingham:

quote:

Probably not a bad idea to adapt an existing commercial brake rotor off something or other, rather than trying to fabricate something totally from scratch.
After all, we don't attempt design our own calipers, wheels, or a whole host of other things.

I disagree. Solid Disk Rotors are one of the cheapest and easiest parts on the car to design/make yourself.

can't say the same for calipers (still not hard to do, but harder to do better than premium off-the-shelf options).

+1, rotors are a piece of cake if you don't overthink them too terribly (although this is FSAE...). On the other hand, I could spend hours massaging the rest of the parameters in the system to make it workable by adding the constraint of a rotor designed for another application that can't really be modified.

The reality is, that specialist manufacturers can mass produce a great many parts a lot cheaper, and almost certainly with much better quality control than you can do it yourself.

Engineering is just as much about practicality and cost saving, as it is about brilliance of design.

Nobody makes their own nuts and bolts, bearings, seals, rod ends, tires, or a great many other things.
It simply is not practical or cost effective to do so if "a bought one" is perfect for the job.

There are more than enough really challenging and vexing problems to tackle as it is.

quote:

Originally posted by Z:

quote:

Originally posted by typeh:
front braking torque=279 N.m

Typeh,

If you design your discs/calipers/etc. for "ultimate failure load" of 279Nm, then they WILL fail.

That load corresponds to a horizontal braking force at one front wheelprint of about 120kg, which is easily exceeded.

Take front outer wheel vertical load during very hard braking and corner entry as, say, 200kg (because of load transfers). Now multiply by Cf ~1.5 (high grip tyre on high grip road), giving horizontal load of 300kg (could be Cf~2?). Finally, add a bump/pothole/kerb that increases vertical load, and thus also horizontal load, by, say, ... 3G? Could be more for a big pothole, but the organisers wouldn't do that, would they? Of course, you might be testing on that old parking lot out back...

Bottom line is that I wouldn't want the front brake structure failing at anything under wheel torque = 2kNm.

Or, to be on the safe side, 10x your 279Nm figure.

Would anyone who has done these calcs properly like to comment? My figures are plucked out of the air, and this is a fairly important safety issue.

Better yet, has anyone suffered catastrophic brake failure, and can they provide estimated failure loads?

Z

i didn't design accoording to this method my way start by assuming pedal force getting master cylinder pressure then force on peda from it get braking torque and decelration.
the way u r describing in brake handbook but i didn't feel it prefered this method.
i will try to compare results form both methods although seem great difference and will take in mind high factor of safety.
again u confirm to me heat load will be neglected compared to mechanical load

thanks,

Alexandria University Motorsports
FSG 2012

quote:

Originally posted by Buckingham:

quote:

Probably not a bad idea to adapt an existing commercial brake rotor off something or other, rather than trying to fabricate something totally from scratch.
After all, we don't attempt design our own calipers, wheels, or a whole host of other things.

I disagree. Solid Disk Rotors are one of the cheapest and easiest parts on the car to design/make yourself.

can't say the same for calipers (still not hard to do, but harder to do better than premium off-the-shelf options).

Accept with u and our team will try design our own calipers. FSAE is chance to learn so let's do it well and apply target from competition but still decisions need more wisdom and overall view.

Alexandria University Motorsports
FSG 2012

quote:

Originally posted by typeh:

quote:

Originally posted by Buckingham:

quote:

Probably not a bad idea to adapt an existing commercial brake rotor off something or other, rather than trying to fabricate something totally from scratch.
After all, we don't attempt design our own calipers, wheels, or a whole host of other things.

I disagree. Solid Disk Rotors are one of the cheapest and easiest parts on the car to design/make yourself.

can't say the same for calipers (still not hard to do, but harder to do better than premium off-the-shelf options).

Accept with u and our team will try design our own calipers. FSAE is chance to learn so let's do it well and apply target from competition but still decisions need more wisdom and overall view.

Alexandria University Motorsports
FSG 2012

Facepalm!

Really guys just focus on getting the car running well. Leave innovation for the coming years. At least if you bought most of the components and the car works then you will have a benchmark to equal or beat for the next car.

Design the calipers....good luck with that. Although it would be a good project for senior year teammates as team R&D, until proven to be working well.

Don't do the same mistake again...

Just a comment from my side:
If you are designing your calipers on your own expect the scrutineers at FSG to put special emphasize on that and if they have any doubt in the presented solution, you will not pass.
I am not saying, that it is impossible, we had teams with self-designed calipers before, but they had a hard time in scrutineering and it became, more or less, the first part of the design report for them.

quote:

Originally posted by TMichaels:
Just a comment from my side:
If you are designing your calipers on your own expect the scrutineers at FSG to put special emphasize on that and if they have any doubt in the presented solution, you will not pass.
I am not saying, that it is impossible, we had teams with self-designed calipers before, but they had a hard time in scrutineering and it became, more or less, the first part of the design report for them.

Thanks for appreciated advice
maybe will be better to keep design on papers and discuss with judges about it and apply it next year.

AUMotorsports
FSG 2012

quote:

Originally posted by Z:

quote:

Originally posted by typeh:
front braking torque=279 N.m

Typeh,

If you design your discs/calipers/etc. for "ultimate failure load" of 279Nm, then they WILL fail.

That load corresponds to a horizontal braking force at one front wheelprint of about 120kg, which is easily exceeded.

Take front outer wheel vertical load during very hard braking and corner entry as, say, 200kg (because of load transfers). Now multiply by Cf ~1.5 (high grip tyre on high grip road), giving horizontal load of 300kg (could be Cf~2?). Finally, add a bump/pothole/kerb that increases vertical load, and thus also horizontal load, by, say, ... 3G? Could be more for a big pothole, but the organisers wouldn't do that, would they? Of course, you might be testing on that old parking lot out back...

Bottom line is that I wouldn't want the front brake structure failing at anything under wheel torque = 2kNm.

Or, to be on the safe side, 10x your 279Nm figure.

Would anyone who has done these calcs properly like to comment? My figures are plucked out of the air, and this is a fairly important safety issue.

Better yet, has anyone suffered catastrophic brake failure, and can they provide estimated failure loads?

Z

According to method you state yes braking torque is near 2 KN.m .
vertical load on wheel due to max.braking + max.lateral acceleration + bump load.

I considered before there is no bump load ,also didn't take in consideration lateral load.

This torque is resulted from tire forces; so i calculate caliper pressure from it ,or just from pedal force? i think from pedal force because pressure generates due to force applied on pedal.

AUMotorsports
FSG 2012

quote:

Originally posted by TMichaels:
I am not saying, that it is impossible, we had teams with self-designed calipers before, but they had a hard time in scrutineering and it became, more or less, the first part of the design report for them.

If you follow a real design process and validate your parts, you should not have any issues. For example, Michigan has had self-designed and -produced calipers for more than 10 years and never had a problem with tech inspection at any competition.

On the other hand, frantically rebuilding a caliper in 10 minutes on the autox course at Silverstone because of a machining issue is not something you're likely to do if you buy a caliper off the shelf...

quote:

If you follow a real design process and validate your parts, you should not have any issues. For example, Michigan has had self-designed and -produced calipers for more than 10 years and never had a problem with tech inspection at any competition.

My comment was more directly related to their situation. Being a second year team with no remarkable experience and the obvious lack of resources, I would deem it to be more or less impossible and additionally unnecessary. Gains lay elsewhere in their situation.

quote:

Originally posted by TMichaels:
My comment was more directly related to their situation. Being a second year team with no remarkable experience and the obvious lack of resources, I would deem it to be more or less impossible and additionally unnecessary. Gains lay elsewhere in their situation.

Absolutely. This competition is about resource allocation and execution. Engineering is really the easy stuff!

PS I'm American and put my Walter Roehrl quote in German...funny that you put yours in English...

quote:

Originally posted by typeh:
yes braking torque is near 2 KN.m .
vertical load on wheel due to max.braking + max.lateral acceleration + bump load.
...
This torque is resulted from tire forces; so i calculate caliper pressure from it ,or just from pedal force? i think from pedal force because pressure generates due to force applied on pedal.

Typeh,

Yes, the caliper pressure is generated by the pedal force. But you also have to consider the various leverages involved (mechanical at pedal, and hydraulic between MC and calipers).

An important decision you have to make is this:
How much force must the driver apply to the pedal to lock-up the brakes?

If you use the "maximum pedal force" of 2kN (200kg), then the driver will need legs like an Olympic weightlifter. I suggest a brake lock-up force of about 0.5-1kN (50-100kg) for easier driving. (Anyone like to post their numbers?)

If lock-up occurs at 50kg pedal force, then from my previous calcs (on smooth track) this corresponds to front wheel torque of (roughly) ~300kgxGx0.25m = 0.75kNm. Now, if pedal force increases x4 to the maximum of 200kg, then potentially the wheel torque can also increase x4 to ~ 3kNm! It just depends how big that bump is...
~~~~~~o0o~~~~~~

I should also point out that if a structure fails after "a few hundred hours", which might be a few thousand cycles (Buckingham's example earlier), then it is not too far from failure by a single overload.

Putting it another way, "a few hundred hours" of moderate braking might be the same as ten hours of aggressive braking on a bumpy track. In this case the components should be "lifed" and exchanged after, say, 5 hours. But that's sounding like F1, not the "amateur weekend autocrosser".

For brakes, I suggest a generous "safety factor".

Z

quote:

Putting it another way, "a few hundred hours" of moderate braking might be the same as ten hours of aggressive braking on a bumpy track. In this case the components should be "lifed" and exchanged after, say, 5 hours. But that's sounding like F1, not the "amateur weekend autocrosser".

And since they intend to take part in FSG2012 and our head of dynamics really likes to put hard braking zones directly in bumps...

quote:

Originally posted by Z:
I suggest a brake lock-up force of about 0.5-1kN (50-100kg) for easier driving. (Anyone like to post their numbers?)

Z

We have used just under 0.6 kN pedal force for full braking with good driver feedback.

quote:

Originally posted by Adambomb:



+1, rotors are a piece of cake if you don't overthink them too terribly (although this is FSAE...). On the other hand, I could spend hours massaging the rest of the parameters in the system to make it workable by adding the constraint of a rotor designed for another application that can't really be modified.

+2
We send out the DXF file for our rotors and get them cut out of 1020 for free.

Rotors are probably one of the easiest things to manufacture on an FSAE car if you have the right connections.

In my opinion the only reason for holes and slots are for slightly better rotor bite, slightly better cooling, and cosmetics.

In other words, rotors are not something to spend an excess amount of time on, compared to...everything else.

You won't find mild steel brake rotors on any production car, or any serious race car. Try ordering mild steel brake rotors from Girling or Brembo, they are just not made. Cast iron is a far superior material because it very rapidly work hardens, just like the bores of a very soft cast iron engine block become extremely hard.

Brake rotors are drilled or slotted, and sometimes the pads are slotted to release any trapped gas that may contribute to brake fade.
It helps in the same way that a tire tread helps grip in the wet.

quote:

Originally posted by Warpspeed:
sometimes the pads are slotted to release any trapped gas that may contribute to brake fade.
It helps in the same way that a tire tread helps grip in the wet.

Absolutely not. This was true when asbestos was used in friction materials. This is no longer the case, modern pads really only off-gas during the burnish and first fade.

Pads are slotted for many reasons including:

1) to change the natural frequency of the friction couple to eliminate/attenuate noise (squeal)

2) to reduce pad stiffness in order to improve the pressure distribution for better wear characteristics

Golly, I never knew race cars used drilled and slotted discs and pads to reduce brake squeal.

Usually the pad backing plate is made as stiff as practical to promote even all over pad pressure.
And slotting the pad material is going to have a negligible effect on total overall pad stiffness.

It is those ubiquitous thin metal stampings interposed between pad and piston that are used to damp resonances.

Even pad wear in very severe operation is usually achieved two ways, either by tapering the pads over their length, or piston stagger in multi piston calipers.

Cutting a giant slot through the middle is certainly not going to improve pad wear in any beneficial way, but it just might allow an escape path for trapped gas and debris.

quote:

Originally posted by Warpspeed:
Golly, I never knew race cars used drilled and slotted discs and pads to reduce brake squeal.

Usually the pad backing plate is made as stiff as practical to promote even all over pad pressure.
And slotting the pad material is going to have a negligible effect on total overall pad stiffness.

It is those ubiquitous thin metal stampings interposed between pad and piston that are used to damp resonances.

Even pad wear in very severe operation is usually achieved two ways, either by tapering the pads over their length, or piston stagger in multi piston calipers.

Cutting a giant slot through the middle is certainly not going to improve pad wear in any beneficial way, but it just might allow an escape path for trapped gas and debris.

Hi Tony, it seems that you're explaining the racing version of brakes, where I'm trying to explain the OEM version of brakes. To me it's better to get students thinking about the entire system and all the dynamics involved. Focusing on the racing stuff only does students a disservice.

Please note I didn't say anything about rotors.

I work on brake NVH daily, I've got my data. The shims you refer to only work in the 5.5+kHz range, so often it's required to pursue structural changes to solve noise issues below this threshold. These often originate at the friction couple. Adding slots changes the couple which changes the frequency. Both CEA and brake ODS plots can show this.

If you feel otherwise, then we can just agree to disagree. It wouldn't be the first time people disagreed about brake engineering. But I would be remiss if I did not attempt to correct an inaccuracy.

I will give you one thing, pad slots can definitely be used to clear debris and let heat out. In racing, where people don't care about noise, it seems like a decent idea.