Brake System Help Needed!!!

[drivetrainUW-Platt]

Hey,
since our brake system kicked us at comp this year (we were no wheres near passing braking), i would love to hear what teams have had success with as far as master cylinders/ calipers goes. what we attempted to run was wilwood cart calipers (2 front 1 rear) and some motorcycle masters, somewheres the math was wrong and we werent gettin anywheres near enough pressure into those cart calipers. any help will be great.
Mike Duwe
UW-P Drivetrain Leader 2004-05

[Denny Trimble]

Magic Numbers to get you started are:
brake pad coefficient of friction = .35
pedal input force for 1g braking = 80lbf

You need to work out the load transfer (normal loads on tires due to a certain braking deceleration, wheelbase, CG height, static normal loads), brake torques, pad tangent forces, pad normal forces, hydraulic pressure, MC forces, then pedal forces. It's pretty straightforward. The numbers above should get you in the ballpark.

[Didier Beaudoin]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by drivetrainUW-Platt:
Hey,
since our brake system kicked us at comp this year (we were no wheres near passing braking), i would love to hear what teams have had success with as far as master cylinders/ calipers goes. what we attempted to run was wilwood cart calipers (2 front 1 rear) and some motorcycle masters, somewheres the math was wrong and we werent gettin anywheres near enough pressure into those cart calipers. any help will be great.
Mike Duwe
UW-P Drivetrain Leader 2004-05 <HR></BLOCKQUOTE>

Your equipment seems fine to me... Maybe the system wasn't well bled? Or the mechanical advantage of the pedal was too low? We did run Wilwood calipers and morotycle calipers and all went well (except for Columbia crashing right before us and the weather alert, but that's another story http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif).

[Dr Claw]

I'm doing an entire overhual on our brake system too.DoE here we come http://fsae.com/groupee_common/emoticons/icon_smile.gif

and like i said erlier, keep an eye out for our brakes next year. they are gonna be wicked (provided my prototypes work of course, which i'll either have to confirm or otherwise deny failurehttp://fsae.com/groupee_common/emoticons/icon_razz.gif)

[RaID]

to get you in the ball park
just follow what Denny said

if youre still having trouble
pick up a copy of the Brake Handbook
by Fred Puhn
that spells it out step by step
you really cant go wrong


your equipment is more then adequate, by the sounds of things you either havent
got the lines bled properly or most likely your pedal ratio is too small to provide enough pressure or your running too big master cylinders


watch out for a few nifty things in our brake setup this year http://fsae.com/groupee_common/emoticons/icon_wink.gif

[jack]

bleeding brakes correctly is very important, i found that out the hard way. at first we had many problems with our system which used student designed/built calipers. the easiest thing to do was to blame the calipers for brake malfunction, but after several frusterating nights, we found it all came down to bleeding the system correctly. In detriot, our system failed brake tech forst try. i totally freaked out, because last time we tested, nothing had changed. i re-bled the brakes again, still didnt work, really started to freak, turned out to just be the vent on resiviors not functioning. past brake tech easily after that was fixed

Dr Claw and Raid, do you mind hinting about you new setups? i would love to see more student designed/built calipers in the future.

[Marc Jaxa-Rozen]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>or your running too big master cylinders <HR></BLOCKQUOTE>

The opposite can be true as well- after completely neglecting to check hydraulic displacement values we started off with 1/2" bore MCs, which bottomed out much too soon and didn't provide any decent stopping power. Like Didier says the system worked fine once we switched to 5/8" bore, though.

Marc Jaxa-Rozen
École Nationale d'Aérotechnique

[RaID]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by jack:
Dr Claw and Raid, do you mind hinting about you new setups? i would love to see more student designed/built calipers in the future. <HR></BLOCKQUOTE>

unfortunately no custom callipers http://fsae.com/groupee_common/emoticons/icon_frown.gif, in hindsight that would have the best way to go for, its more from the actuation side http://fsae.com/groupee_common/emoticons/icon_wink.gif

[alfordda]

Go to Race Tech's website, and download their free braking software. It is a farily simple excel program, with a few assumptions, but it will at least get you started.


http://www.racetechmag.com/practicalracer/ontrack.asp?menu=4


Daniel

[Chris Clarke]

Hope your not planning on using electronically activated brakes, which are not allowed in the rules.

[Dr Claw]

Well, i'll tell you i found some 10 mm cup seals, and i am very happy http://fsae.com/groupee_common/emoticons/icon_smile.gif

Also, i'll say it's twin opposed and under half a lb.

I'll get a chance to test the hell out of it all at TRW's test lab too, so im going to have a book's worth of "it's not going to break, sir".

[drivetrainUW-Platt]

Hey,
so what is the correct way to bleed brakes, what we were doing was opening and closing the bleeder valves as someone pumped the pedal, what we later found out was that it works best to place the caliper lowest run the fluid out of the bleeders, close them then tap the lines to get out air....didnt get to try that method, i know everyone talks numbers and such for brakes but what have heard is that what it comes down to it, run the biggest disks that fit in the rims up front and the back is always up in the air as far as single/duel disks go. I havent had any hydraulic/fluids classes yet so numbers wont get me very far. would love to learn thou, the help is always appreciated
Mike Duwe
UW-P Drivetrain 2004-05

[Dr Claw]

well, the "biggest rotor that fits" works, but there isnt any engineering finesse involved in that. you can (and should) optimize for best stoping power with weight in mind, but then again that is easiest said rather than done.

As far as bleeding brakes, (havnt tried this on a formula brake "system" yet, but we do this for testing at work), but if you can rig up a way to put the brake system under vaccum, and then allow brake fluid to subsequently fill the lines, you eliminate all possibilites of there being air in your lines. good old Vac-and-fill. i would say that if your able to apply vacume through the bleeder, and rig up a bleeding-purpose-only master cylander cap that has a resevoir ABOVE it, and a valve to keep the brake fluid out whilst applying vacume, you'd be in good shape. when vaccume has been reached, throw the valve (slowly perhaps..) and watch the brake fluid completely fill your entire system. remove that cap, and apply your 'race' one.

hell, you could even feed from the bleed, have it lower than the master like you said, and apply vaccum from the master cylander resevroir. This might be the better way now that i think about it. The pistons just won the championship, and im to tired to erase everything.

anyways, vac-and-fill is pretty reliable if done properly (*disclaimer* air can still be in your lines if you dont have good vaccume. be carefull)

[Colin]

a vacuum system can help out if your having trouble bleeding your system we've had a lot of luck with a syringe "sucking"� fluid from the bleed valve on the brake master cylinder. Here's the method we use
1. start with front system, remove piston actuator of rear master cylinder
2. remove front callipers and raise as high as possible
3. open brake calliper bleed valve on one side attaché syringe and "suck"� new fluid through, when fluid stats to fill the syringe lock of bleed valve do the same for the other side.
4. once this is done get someone to press the brake down while the bleed valve is open then lock it up and let the pedal come back. Once your confident there is no air lock up the bleed valve during a brake depression, repeat for other side
5. with the fronts done attaché rear master cylinder actuator and remove the front one and repeat the process for the rear.

I often find that you need to re-bleed the system the next day after the air bubbles that where broken up during the initial process have had time to regroup, everyone's got a different method I'm sure but this one works for us.

[Marc Jaxa-Rozen]

After going through a distressing amount of DOT4 bottles, syringes and general crap to bleed the SOBs using conventional methods, one of our guys came up with a pressurized system using shop air to drive the air out...I don't quite recall the details (it's 3:20) but it worked fine.

If all else fails, there's always good old-fashioned human vacuum...

http://www.enaf1.com/PDR_0026.jpg

Marc Jaxa-Rozen
École Nationale d'Aérotechnique

[Vector006]

yeah, never use bike masters...we ran out of travel and blamed it on air in the lines. We spent about 3-4 days trying to fix it...and we found that the caliper (wilwood dynalite single) had just enough flex in it under load that it was causing the master to bottom out just before it would have enough force to lock up the brakes. We were using wilwood PS-1 in the front, and for some reason we had no problem using the bike masters for them. I seriously think there is evil forces at work in the braking realm. it is definately a system worth spending the time designing and testing off vehicle just like any other system.

[Charlie]

I wouldn't say stay away from motorcycle masters, just know what you are doing, and getting into if you get any master cylinder. Brake system calculations involve a few parameters that are hard to accurately define (Denny approximated a couple) but the math itself is easy. But lots of teams get it wrong-usually, I suspect, from not even trying to design the brake system, just throwing it together. (I know we've had guys do it like that in the past).

[Dr. Bob Woods]

My textbook "Modeling and Simulation of Dynamic Systems" from Prentice Hall presents a complete math model of the FSAE brake system (including weight transfer) and shows how to size each component.

Dr. Bob Woods
Faculty Advisor, UTA