Brake master cylinder choose!!!

[alijoon8]

im working on the brake system of iut fromula car.we have one mutual brembo/p34 on front tires and a single mutual brembo/p34-30 on rear axle acted on the diffrential.I choose 19mm tilton master cylinder for this system for both circuit.now i have three question:
1)whats the relative between the caliper piston size and master cylinder bore size?is there a defined equation between them?
2)is it necessery that the both master cylinder of two circuit must have equal bore size?
3)in your mind my choose is true or fulse?

thanks friends
Ali Dehghani
Isfahan University of Technology
www.iutracingteam.com (http://www.iutracingteam.com)

[alijoon8]

im working on the brake system of iut fromula car.we have one mutual brembo/p34 on front tires and a single mutual brembo/p34-30 on rear axle acted on the diffrential.I choose 19mm tilton master cylinder for this system for both circuit.now i have three question:
1)whats the relative between the caliper piston size and master cylinder bore size?is there a defined equation between them?
2)is it necessery that the both master cylinder of two circuit must have equal bore size?
3)in your mind my choose is true or fulse?

thanks friends
Ali Dehghani
Isfahan University of Technology
www.iutracingteam.com (http://www.iutracingteam.com)

[PatClarke]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">and a single mutual brembo/p34-30 on rear axle acted on the diffrential. </div></BLOCKQUOTE>

Ali, make sure you use an LSD or other locking differential with this design.

Pat

[exFSAE]

Don't they teach fluids anymore?

[Mikey Antonakakis]

I'm working off the top of my head here so take everything I say with a grain of salt.

1)You need to know friction coefficient between pads and rotors to "truly" calculate this. I don't know a number to give you to start with, although I would tend to think it's less than 1. You apply a force to the brake pedal. This pushes on fluid in the master cylinder. The pressure in the brake lines is force/area, or force/(pi*(bore/2)^2). Same deal in the calipers, except now you know the pressure, so you can calculate the force. Hopefully I don't have to explain the algebra in that calculation. I think you will find that a larger master cylinder bore results in a smaller force on the brake pads. The relationship should be Fpedal/Fpads=Bcaliper/Bmc where Bcaliper and Bmc are master cylinder and caliper bores. Knowing your coefficient of friction, rotor major and minor diameter, and brake pad shape, you should be able to calculate the force as acting through a single point on the brake pad by finding its centroid. Then you can calculate the reaction torque, then wheel force.

2)That is entirely up to you, although it's probably best to try to distribute braking force based on weight distribution under full braking. i.e. if you have 50/50 weight distribution and a mass center height above the ground, you're going to want more braking force on the front brakes than the rear. Use what you learned in mechanics class to calculate that. I'll give you a hint though, free body diagrams, and sums of moments and forces are all you need. A calculator might help too. Make sure you account for different rotor sizes, if you are running different rotors in the front and rear. And to be nice, you want your brake distribution to equal your weight distribution under full braking. Freebie! Oh and build in some adjustability with a bias bar or something.

3)Don't think I can help you there, I don't really understand the question.

[Mikey Antonakakis]

Oh and if you're using a single rotor in the rear, don't forget to account for that in your calculations. And I second Pat's comment. You'll have a hard time passing the brake test without one.

[kapps]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by exFSAE:
Don't they teach fluids anymore? </div></BLOCKQUOTE>

You mean they actually taught you something useful in fluids at your school http://fsae.com/groupee_common/emoticons/icon_confused.gif

Ali, do some searching. I was put in charge of the braking system of our car a couple years ago and was able to find some good info on this site. There are some spreadsheets around that include calculations for force, stroke, system pressure, etc. After finding a nice one and adding some other calculations, I was able to come up with a braking system that has performed just as expected.

[exFSAE]

Kapps.. my fluids teacher was a maniac. Worst / toughest prof in department. Didn't learn an awful lot.

But hydrostatics and shit like this for determining pressures and forces... pretty straight forward.

[Adambomb]

F=P*A

or

P=F/A

or

A=F/P

If I remember right they taught that in like 8th grade science class???

[Adambomb]

Ooh, almost forgot I did have something USEFUL to add...

As a "starting point" for brake pad friction, 0.35-0.4 should be a good ballpark range for standard off the shelf pads and steel or iron rotors. Outside of that, look at each component, brake pedal, master cylinder, caliper, rotor, tire, make some free body diagrams, set some constraints, make some assumptions, and that's it!

[Wesley]

Hell, even physics I should cover Pascal's law. It's a trivial calculation, even for a high school student.

Also, Mikey, you do mean you want your brake distribution equal to your dynamic weight distribution accounting weight transfer due to braking decel, correct?