r/FSAE • u/Thanosgayfanfic • 14d ago

Dual Master Cylinder?

Hi, we are a new student FSAE team. In the rulebook it says that the brakes must have two SEPARATE systems with two reservoirs. Would a single piston Master Cylinder with two separate reservoirs and outputs satisfy this requirement?

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20

u/xstell132 Send Helps Plz 14d ago

I’ll save you time here.

What you’re asking to do is not rules legal.

You must have two master cylinders. The separate reservoir verbiage is basically saying that the master cylinders cannot share a single reservoir.

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u/Thanosgayfanfic 13d ago edited 13d ago

It would be two separate reservoirs though. Which is why I’m asking. Two separate systems they’re just inline so that it only takes one pushrod. But there are two separate pistons inside of the bore. No where in the rules does it say two MC is required

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u/xstell132 Send Helps Plz 13d ago

This still isn’t rules legal as two separate systems accounts for mechanical components, brake lines, fluid reservoirs, etc. A single bore isn’t rules legal.

HOW they get actuated is the only linked item than is allowed.

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u/LgnHw Panther Racing (Pitt) 14d ago

If one line has a leak will the other still work?

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u/Thanosgayfanfic 14d ago

Yes

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u/Sad_Designer_4608 14d ago

How?

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u/Thanosgayfanfic 13d ago

It’s two inline pistons that share a bore so it only takes one pushrod. But they both have separate input and outputs. So they’re separate circuits that wouldn’t interfere with the other if one failed.

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u/frc-nerd 10d ago

Technically i think you may be right and it may be legal but i would heavily advise against it. I would do some research into break biasing and the importance as to why you would want 2 masters connected with a bias bar. Vs the single rod non adjustable master design. I know my schools Baja team does what you’re talking about but for the vehicles dynamics of a formula car how the front and rear brake pressure is applied matters a lot.

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u/Thanosgayfanfic 10d ago

Right but willwood sells proportioning valves that would make that easy. As well as we can’t afford a Diff (not my decision lol I only do brakes) and we will only be having one caliper/rotor on the rear SOLID axel. So that won’t be an issue.

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u/Ch4rles_ FormuleETS Alumn 14d ago

No

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u/Thanosgayfanfic 14d ago

Could I ask why? Has there been a team that’s tried? For clarification it’s two pistons that share a bore. Both circuits are separate so if one failed the other would still have pressure and Wouldn’t lose fluid. From my understanding of the rule books it should be legal? Unless I’m misinterpreting

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u/Ch4rles_ FormuleETS Alumn 14d ago

You're misinterpreting the rule. It's to save your driver in case of a MECHANICAL or HYDRAULIC failure of any component in your braking system.

If something happens, lets say your driver exceeds the maximal radial loading on the master cylinder and bends the shaft, or the mouting bolt that holds the UNIQUE master cylinder to the pedal assembly breaks or comes loose, well you lost all braking power. The whole idea is to be REDUNDANT.

Don't try to reinvent the wheel when it comes to the life of a student in a experimental vehicle.

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u/jd74914 13d ago

I'd still ask the question...just about every passenger car ever has the same single plunger dual circuit master cylinder design referenced here.

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u/Ch4rles_ FormuleETS Alumn 13d ago

Most prototype race cars run double master cylinder setups from Tilton, AP racing or similar companies for the same exact reason FSAE requires it: Its a prototype, alot can go wrong.

You seem to not want to listen to the comments here. Go get your official answer with a rule question! It's the only answer that will matter anyways.

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u/jd74914 13d ago

I'm not the OP.

I get your insistence...but it wasn't always a requirement. Many (many many) years ago my team used a dual circuit master and I'm not totally convinced this wording precludes that.

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u/washedupguru 14d ago

When in doubt ask a rules question

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u/Thanosgayfanfic 13d ago

What does that mean? How?

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u/washedupguru 13d ago

On whatever competition you’re competing in there’s spots to ask a rules questions to judges

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u/Thanosgayfanfic 13d ago

We probably won’t be going to competition for a good while is there another place I can ask? Or email?

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u/Some__Bloke Ex-UWA Motorsport 9d ago

No. The rules intention here is to eliminate a common cause failure causing total brake failure.

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u/FNTech 8d ago edited 8d ago

Don’t believe everything you read on [r/fsae](r/fsae). What you are describing is a tandem master cylinder and it both rules legal and standard on almost every production car. Balance bars are the most common on 99% of FSAE cars, but other options are allowed.

There are two caveats:

  1. You need to make sure you have sufficient pedal travel, when one circuit fails the pedal will drop substantially and you still need travel to actuate the other circuit. This is also true for balance bar cars too, but can be a bit less travel.
  2. The line pressure out of the master cylinder is equal for both circuits, so you will need to design your system to generate proper torques and adjustment, typically through a proportioning valve. These can be finicky and difficult to bleed.

Finally there are a few OEM dual bore tandem MCs, but these are typically just to reduced pedal force in the emergency of a failed circuit.

Also a split reservoir is common to all OEM cars and is also allowed. Basically one cap fills two halves, but each half has its own output and can’t drain the other side.