How much is needed for a brake system to work?

[Futterama]

Hi forum,

I'm new here and have a bit of a special question.

I'm in the process of building a brake dyno for small 2-stroke engines. For this purpose, I have purchased a brake disc, rear brake caliper, caliper holder and brake pads, just the cheapest I could find which happened to be for a VW Polo IV Hatchback (9N) 1.4 FSI. These are mounted to my rig and I can apply braking force using the handbrake system that is present on the rear type brake caliper.

Now, I would like to progress this setup to be using the hydraulic portion of the brake calipers. But I don't know how this is accomplished. How much do I need for a simple setup?

I need a brake line to attach to the brake caliper. This needs to be flexible.
Then I need a master cylinder. These comes with 2 outputs and 2 inputs and sometimes even with a brake fluid container attached.
I don't have a vacuum available so I will not be considering a brake booster.

How do I go about only connecting a single brake caliper to a master cylinder that is made for 2 brake circuits? Can I just leave 1 circuit unconnected?

Would I need to be careful to find a master cylinder that is for cars without ABS or does this not matter for my purpose?

Will the flexible brake lines used at the wheels connect directly to the master cylinder?

My main source of knowledge comes from this animated video: https://www.youtube.com/watch?v=Xk2zGvKfrhc

Thanks.

[AW111]

The simplest solution for the master cylinder is a Hydraulic handbrake.

[Futterama]

AW111 said:

The simplest solution for the master cylinder is a Hydraulic handbrake.

Thanks, that could be an option. Searching for that lead me to a clutch cylinder, could that be used or is the pressure and flow too different between clutch and brakes?

[tapkaJohnD]

Futterama,

Master cylinders with two outputs are dual piston and are for vehicles with a split brake system. You don't need that.
Look for a M/c from an older model of car that didn't have that (scrapyard?, or classic supplier?) or buy one from eBay or Demon Tweeks (in ascending order of cost!)

A bike M/c might do!

[AW111]

tapkaJohnD said:

Futterama,

Master cylinders with two outputs are dual piston and are for vehicles with a split brake system. You don't need that.
Look for a M/c from an older model of car that didn't have that (scrapyard?, or classic supplier?) or buy one from eBay or Demon Tweeks (in ascending order of cost!)

A bike M/c might do!

A bike master cylinder sounds like the go. Easy to get one second-hand and try.

OP: A clutch cylinder may work also.

The hydraulic handbrakes I'm familiar with, the master cylinder is approx the same size as the normal rear brake cylinder.
Note that disk rears use a different size m/cyl than drums.

[Futterama]

tapkaJohnD said:

Futterama,

Master cylinders with two outputs are dual piston and are for vehicles with a split brake system. You don't need that.
Look for a M/c from an older model of car that didn't have that (scrapyard?, or classic supplier?) or buy one from eBay or Demon Tweeks (in ascending order of cost!)

A bike M/c might do!

That's correct, I don't need the dual piston type but can it be used with only a single circuit as in when the one circuit in a car fails? They are the easiest to come by and also cheaper than e.g. MC brakes.

Thinking about the clutch cylinder idea, the pressure will surely be lower since the clutch does not have a booster like the brakes do. But maybe a clutch cylinder can easily supply the brake force I need, I don't have to stop a car in the smallest amount of time, I just need to brake down a 15-20 hp engine.

I've got some pointers now, I need to see the components in real life to be 100% sure, but I'm shopping online so it's not that easy. Bu I do see that the flexible brake lines are made with internal threads in each end and the cylinders also come with internal threads, so I'll have to find or make an adapter to fit in between.

[Peanut Gallery]

Two minor points - if you get a dual circuit brake master cylinder - what do you do with the secondary circuit? - you could try blocking it off, but then you would not be able to depress the pedal, or you could just pipe the fluid back into the reservoir - easiest option!

You say the clutch system is going to be of a lower pressure - that said you will not have the servo assist that is on the normal car brake system, so this would be a good idea!

There are a few hand pumps out there for testing fluid pressure systems, spending £60 on one of these might be cheaper in the end by the time you have added a clutch master cylinder, reservoir, pedal arrangement, etc.

The note about a bike brake is a good one! - and in other questions - are bike rear brakes ever servo assisted? -I assume front (hand lever) are not.
(I am not allowed a bike, I would do myself in at the end of the first straight.)

[stevieturbo]

what is the purpose of the dyno ?

Does it need some form of control ? Will the braking system need heat management ? What will actually provide the load ? your hand ? your foot ? other ?

Obviously this will also vary with heat etc.

[Futterama]

Peanut Gallery said:

Two minor points - if you get a dual circuit brake master cylinder - what do you do with the secondary circuit? - you could try blocking it off, but then you would not be able to depress the pedal, or you could just pipe the fluid back into the reservoir - easiest option!

According to the video I mentioned in my first post, you should be able to block the first brake circuit off and all the pressure on the piston would transfer to the second part of the piston. Or I could pipe the fluid back to the reservoir as you mention.
Coming to think about it, the 2 brake circuits should be able to work independently - e.g. front brake pads are worn and need a longer travel than rear brakes, the rear brakes would apply pressure to the one circuit first - just like a blocked off circuit will. I don't know.

Peanut Gallery said:

You say the clutch system is going to be of a lower pressure - that said you will not have the servo assist that is on the normal car brake system, so this would be a good idea!

What I mean is that the difference in the construction of a clutch and brake master cylinder could be an issue. The clutch cylinder might be a bigger diameter and stroke length for lower pressures but higher fluid volume movement. Also I have to consider that I need the brake lines to fit the threading, though this is a nice-to-have so I don't have to make too many adapters on the lathe.

Peanut Gallery said:

There are a few hand pumps out there for testing fluid pressure systems, spending £60 on one of these might be cheaper in the end by the time you have added a clutch master cylinder, reservoir, pedal arrangement, etc.

That's a great idea, thanks, I'll take that into consideration, small car jacks are pretty cheap and might do the trick.

[Futterama]

stevieturbo said:

what is the purpose of the dyno ?

Does it need some form of control ? Will the braking system need heat management ? What will actually provide the load ? your hand ? your foot ? other ?

Obviously this will also vary with heat etc.

Purpose: Graph torque and HP of the engine to be tested. The engines are for RC model airplanes.

Control: Yes, I plan to control the brake pressure manually to begin with but I have plans to add some automatic system to do this. This could be a windshield wiper motor with a winch that pulls on the brake pedal/handle.
I will also like to control the engine throttle with a RC servo to prevent the engine from over-revving. The engine is normally kept at a certain max RPM simply by the load of the propeller, I won't have than on the dyno.

Heat: At the moment I only have a single solid brake disc. I have calculated the mass of the disc part that the pads come into contact with (heat generation) and using cast iron as reference, I can get the amount of required energy to heat up the disc 1°C. Currently the most powerful engine I have produces 12hp, this can be added to the calculation, so I'll get a 7°C temperature rise in the disc every second at full brake power. I have found from the internet that a disc temperature of 200°C is not uncommon in road cars, so that gives me around 25 seconds to do the testing.
I will be monitoring the disc temperature with an infrared temperature sensor.
If all goes well with the dyno build, I have plans to make a version 2 for bigger engines or just better heat management with bigger disc diameter, internally ventilated discs and 2 discs in the setup. Alone the bigger diameter and using a ventilated disc (overlooking the fact that it has ventilation) gives the disc a much higher mass and will then be able to consume more heat energy with less temperature rise which enables me to test stronger engines or test the smaller engines faster in a row without having to wait for the disc to cool between runs.

Regarding what will provide the load, I'm not sure whether you mean the load on the engine or the load on to the brake cylinder. But I think both are answered above, otherwise ask again

[Peanut Gallery]

Go for it!

Just to say that in a twin system, one brakes the front right and back left, the other the front left and back right. - When I lost one system on an old car of mine, the pedal was just a little softer, but hitting the brakes could easily lock up front right and back left. - If you were to block of one system, this would stop the pedal from moving.

Yes, a clutch is designed at a different pressure, but bear in mind a clutch works without a servo - without a servo what fluid pressure are you getting from a brake master cylinder?

I do not think you need to worry about fittings, from my limited experience with brakes, they are all generic fittings, you might need to get a pipe flaring tool though. The pressure needed on the pedal I believe would need to exceed that of what could be achieved with a wiper motor or such, for repeatability a small hydraulic pump with a variable pressure regulator might serve you best.