All right vets, lets hear it. What kind of crazy design questions have you gotten owned by in the past?

Last year our suspension guy got pwned by Claude asking something simple like distribution of roll stiffness front to rear and also which tires are more heavily loaded when steering with caster......ya, I don't think he even got to any crazy questions. That's what happens when someone practically rebuilds a previous design and doesn't attempt to understand the theory.

i too have been pwned by claude in design. He asked me what the roll stiffness distribution was, and i grabed my comp. to see what the exact number was, and he got offended and said "if you can't remember these things about your car, you must not love it. What is your girl friends phone number." and i had to reached for my phone.

The one i was not able to answer at the time was:
"What is the elastic modulus of your brake pads?"

We didnt get owned but one question that we got last year at West was how would you adjust the brakes if you were running in the rain.

With the brake pedal?

quote:

Originally posted by Kyle Walther:
i too have been pwned by claude in design. He asked me what the roll stiffness distribution was, and i grabed my comp. to see what the exact number was, and he got offended and said "if you can't remember these things about your car, you must not love it. What is your girl friends phone number." and i had to reached for my phone.

Wow! He straight up dissed you and proceeded to tear you a new one! I think he was a little out of line in saying that, though.

Judges at FSAE West did not do much 'owning'. At any rate, our judges pretty much waited for us to talk to them rather than ask us detailed questions as they do at Detroit.

The pad modulus question is one I got in Michigan 2004.

quote:

Originally posted by pablo180:
We didnt get owned but one question that we got last year at West was how would you adjust the brakes if you were running in the rain.

yeah, yeah, i know. replying to old posts. how sad.

but....

by chance i found the brake bias one in Olley Chassis Design because I am finishing to read one chapter i long left due to falling asleep in the middle of it. yeah. how sad too that I dont read Playboy un sundays.

so, Olley says you can use for example 60:40 in the dry and 55/45 in the rain. his exact words are:
----------------------------------------------
On a dry road, with 60/40 brake distribution the rear brake force meets the brake capacity line at point A (this is just relative to the car params of some kind of 50s saloon car. Chris). From then on the rear wheels are locked, but extra deceleration can be obtained from the front brakes.

With 55/45 brake distributionthe rear wheels lock sooner. Extra deceleration is obtained from the front brakes.

On the wet road with 60/40 distribution the front wheels will lock first.
With 55/45 distribution the rear wheels will still lock first (but with a higher value of deceleration. Chris)
Probably there are some reasons for keeping the 55/45 distribution even though it sacrifices some stopping power on dry roads.
-------------------------------------------

I am somewhat confused as to why the good ol god of vehicle dynamics accepted the fact that the rear tyres will lock first. possibly at low speed this is ok but from my experience at high speed this may cause fishtailing and general mad twirling of the steering wheel while pumping the pedal to avoid skidding!

oh well. is that what Claude would like to hear?

LOL for the phone no. of the gf tho! To be honest who needs to know the number by heart unless they carry a US army Vietnam wireless phone in their backpack??

I wouldnt get too upset about this stuff, even if it ruins ones chances in the final. fact is, sometimes shit happens.

I was just curious if anyone could explain why it is important to know the modulus of your brake pads.

I think before you start measuring the elastic modulus of your brake pads you should try measuring the distortion in your brake calipers when you mash the pedal.

At any rate, as long as the pedal is stiff who cares if the thing distorts 1 or 2 thou?

By the by Chris, you are still one crazy Catto

Chris, I would guess that the judge was looking for a response along the lines that in the rain you use less front bias because you have less weight transfer due to lower overall grip.

About the brake pad modulus question. That is, in my opinion, a silly question.

I would be much more concerned with the stiffness of the caliper itself (from both its design and the elastic modulus of the material it's made from), the stiffness of the lines leading to the calipers (diameter, wall thickness, material, and length all matter) the bulk modulus of the brake fluid (and if it is well bled) the stiffness of the master cylinder mounting, pedal assembly and it's mounting, master cylinder quality, and correct sizing of master cylinders and brake calipers.

Also the friction properties of the pad and rotor material, and how they are affected by temperature.

In fact the elastic modulus of the caliper pistons and the sole of the driver's shoe probably matter more than the pad material.

Perhaps the question is fishing for something like the answer above, otherwise I would have gotten it wrong. Even if I know what the modulus of my pad material was.

Luckily for me I was never asked that question.

I don't understand the logic behind letting the rear wheels lock up more quickly in the wet. Once the rears are locked the car spins. Have you ever seen a single-seater lock a rear wheel? It doesn't happen because that would cause the car to spin if it has even the tiniest amount of lateral force. If the fronts lock than the car goes straight and at worst you miss the apex by a few meters, but at least the car is still facing approximately the right direction. I've only ever seen drivers add brake bias to the front in the rain.

DJ:

by adjusting the brake bias rearward your not attempting to make the rears lock up first your just trying to increase the brake efficiency of the system. since in the rain the surface CoF goes down the potential weight transfer goes down. therefore require less bias towards the front. the best way to visualize this is to plot a performance diagram. Gillespe(sp)talks about this is one of his online lectures. all this is is a plot of the weight transfer and how close your brake bias is to the actual weight transfer of the vehicle. what you'll see is that if a system is tuned to brake at 1.6 to 1.8 g's the efficiency of the system is very low in the region of a wet surface or a low road CoF. when adjusted this higher efficiency will then allow you to squeeze out just alittle more accel from your brakes. But i could be wrong, and knowing this forum someone will let me know.

Hey Kyle, do you mind pointing me in the direction of Gillespie's online lectures?

Kyle, this Gillespe(sp) talks, is it free and is it still online?

i wish i could remember what the website was called. a member on these forums called "fade" told me about it sometime ago. you have to login and then put in some special password. i don't even know if it is still there.

there is a section in brake design and safety by Rudolph Limpert called Comparison of Optimum and Actual braking forces (chapter 7.5) that goes over the same thing he just calls it something else.

That is what I thought just wanted to see if i missed something. Stoptech has some pretty good free papers on brakes basics:

http://www.stoptech.com/tech_info/tech_white_papers.shtml

"Brake Bias and Performance: Why Brake Balance Matters" has some diagrams covering what Kyle was saying (I think).

The only other thought I had on the modulus was if brake it is somehow generally related to COF, but that would be a backwards way to ask pad COF in design.

I went to the FSAE Claude seminar in '02 or '03. If I remember correctly the brake pad modulus thing had something to do with a particular driver he worked with not liking the feel of the brakes and it ended up being a change in brake pad that had a different modulus. For some reason this particular incident must have stuck in his head so he must feel its important. I feel if this is the limiting factor in your FSAE brake system, good on you.

I remember getting "owned" for not knowing the MOI of the car and the castor thing (which I feel really stupid about now).

LOL DJ Hache in the mix. Yeah I am still one crazy cat.

Just got back from Brno after free practice day one. Some nice DTMs out there for those who are into superlow front V8 engines and interiors that look out of a spaceship

Personal stuff aside, what Kyle is saying is perfectly correct (?!) since the driver just shifts the balance a bit to account for a lower min deceleration so less wt transfer. I would guess this is also linked to the springs you are running and the ride heights. Oh dear, I ve already found more ways to make the problem complex.

As for the pad modulus, I would say in something like sportscars, F1, Indy etc it would be quite noticeable. I would say even changing to a harder compound on your day car might have some effect (provided there are no air leaks in the system making your pedal already very soft.)

How noticeable is this gonna be? Ummm, I think the deformation in the hoses and the brake fluid will make up a large percentage of brake squidginess (new term for your Pi Toolbox channel). I know our FSAE car had a very stiff pedal but then we had a short travel AP master cyl and the leverage ratio was small so the pedal did not move much at all. Kind of weird. Dunno if good idea or not for the driver to brake relying on foot pressure and little/no foot travel.

Say hi to Jeff at Cranfield and enjoy your beer at the CSA.