Hydraulic Brake Build [V2] (G27 Based)

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pilmat

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In an overflow from a thread on brake thoughts (LINK) I decided to try building a hydraulic brake to test it's merits.

The theories are borrowed from MANY places and I take no credit for inovation here, I'm just sharing the experience so we can all learn something together :)

Theory being tested: pressure based braking system provides the best feel for simulation braking.

I make no claim to knowing this to be right or wrong, but I want to see for myself.

Goal: build a hydraulic braking system based on simplicity, and to the best extent of reasonable cost.

I'm privelidged here as I work in a speed shop, I have easy access to everything necessary on the hydraulics side. The rest of the technology is bought from help within the sim world.

Here is what I've started with:
  • G27 pedals, completely stock apart from the lobotomy.
  • CNC 340SBU clutch kit (10.25" pedal @ 5.2:1 ratio, 3/4" bore master cylinder and 7/8" bore pull type slave cylinder).
  • mV pressure transducer.
  • DSD 12 bit controller w/ integrated load cell amp.


The initial work will be fitting the brake pedal within the G27 environment. Then modifying it to achieve a compatible height. Basically cutting off the end of the pedal and welding a pad back on (I use DSD pedal pads on my current G27 pedals).

Why G27 pedals? I have a Human Racing GT Chassis which mates perfectly with the pedals, so I would like to keep with what looks good :lol:



More info to follow, with pictures :)
 
Last edited:
Just trying to size up some ideas here (sorry about the dark photos, I'm a race engineer, not a photographer :D):


There will be a steel plate to go under the pedal, one in the shape of the G27 to screw to the base. The pedal will then be bolted to the plate.

The pedal needs to be leaned back substantially. I will drill a new hole in it and cut the master cylinder push rod down (re-threading if I need to go deeper).

The fittings are all in stock, as is the braided hose. It will only take a few minutes to get that part done.

Next will be off to the skate shop for elastomers. If I can't find anything stiff enough, I'll source some sway bar bushings. But with the cut down pedal, the motion ratio will also be substantially reduce, so I don't think I need anything too stiff (could be wrong though :nervous:).

This looks like it will be a Saturday project now!
 
Looks like a good start. Hope you are keeping tack of part numbers and a list of modifications so tinkerers like me can duplicate your efforts (if it works):drool:
 
pilmat
Just trying to size up some ideas here (sorry about the dark photos, I'm a race engineer, not a photographer :D):


There will be a steel plate to go under the pedal, one in the shape of the G27 to screw to the base. The pedal will then be bolted to the plate.

The pedal needs to be leaned back substantially. I will drill a new hole in it and cut the master cylinder push rod down (re-threading if I need to go deeper).

The fittings are all in stock, as is the braided hose. It will only take a few minutes to get that part done.

Next will be off to the skate shop for elastomers. If I can't find anything stiff enough, I'll source some sway bar bushings. But with the cut down pedal, the motion ratio will also be substantially reduce, so I don't think I need anything too stiff (could be wrong though :nervous:).

This looks like it will be a Saturday project now!
Click to expand...
Whaaaat, Saturday? Noooo, I can't wait. You have to start today! :D :P


No seriously, keep us posted. Describe every little detail how you go about constructing everything (with part numbers included).
I don't ask for much. :sly:
 
Last edited:
I took some time away from paperwork (that's all I seem to do recently...) to muck with the pedal some :D

I reversed the pedal instead of drilling a new hole as the hole was offset to the rear. Now it needs scalloped for clevis clearance (the Sharpie line). I also cut down the push rod to see if it is enough, alas it is not. The threading will commence! The base plate is also being cut. Pictures will follow once it stops looking like a piece of flat bar stock!

 
Thank you Mr. Basher :)

This will be it for today:


Here you can now see the base plate that will bolt into the G27 base as per the brake (it is 1/8"/3mm thick steel). I will use the 4 normal mounting screws, and I think I will also screw the 2 pedal mount screws through the base too. This will mean I don't have to countersink the base plate allowing for a stronger installation.

Next will be to cut the base plate ribs and trim the cover minimally to allow the pedal to sit in. The cover will be required as it provides a lot of rigidity of the pedal box. And in the Human Racing GT Chassis, the pedals are only mounted with the gas and clutch mounting screws (the 4 corners).

The push rod on the master cylinder has been cut down again after re-threading part of the rod. Basically all the original thread has been cut off.

The slave cylinder is shown with a stack of washers for mounting the elastomers. The bleed nipple and mounting for the sensor are shown on the body too.
 
My only recommendation would be, and I suppose it's somewhat late, is to remove the G27 pedals from their housing and mount them and the brake on something more secure. It probably won't matter, but you can generate and amazing amount of force with your foot, especially when pressing the brake.

Let us know how it goes, I'm curious as to the strength of the G27 base plate. The standard CSR pedal base plate surprised me in this respect.

Not knocking what you are doing AT ALL, just an observation. I'd have tried what you are doing first as well, no sense in over-engineering it.
 
mrbasher
My only recommendation would be, and I suppose it's somewhat late, is to remove the G27 pedals from their housing and mount them and the brake on something more secure. It probably won't matter, but you can generate and amazing amount of force with your foot, especially when pressing the brake.

Let us know how it goes, I'm curious as to the strength of the G27 base plate. The standard CSR pedal base plate surprised me in this respect.

Not knocking what you are doing AT ALL, just an observation. I'd have tried what you are doing first as well, no sense in over-engineering it.
Click to expand...

Constructive criticism is appreciated! I have certainly not thought of everything :)

But that I have thought about. I can of course make a custom base plate that all the pedals mount to, but as you said I will start simple and build up from there.

And about foot force, I hear you. I was part of the mechanical team developing a fly-by-wire rudder system for a commercial jet. Some of the loads that we have to test are a bit scary! :scared: It's amazing what force a foot can generate in a panic situation (like braking too deep into a corner in a sim :lol:)
 
Agreed!

In reading some studies ion braking force vs foot force, etc. I came across one from the 60's I believe it was. Thus the braking technology was somewhat different and less efficient. The normal forces exerted on the pedal were well above 100 pounds, some exceedingly high to achieve lockup once the brakes started to fade. Pretty interesting stuff, but as usual there is A LOT of information to wade through...
 
pilmat
I took some time away from paperwork (that's all I seem to do recently...) to muck with the pedal some :D

I reversed the pedal instead of drilling a new hole as the hole was offset to the rear. Now it needs scalloped for clevis clearance (the Sharpie line). I also cut down the push rod to see if it is enough, alas it is not. The threading will commence! The base plate is also being cut. Pictures will follow once it stops looking like a piece of flat bar stock!

Click to expand...


Hi Pilmat.
is it me or you have a bit of a mechanical problem that you might have missed in this photo.
in this configuration you will need to go to the trouble of cutting off the pedal pad section and reversing it to weld it back on.

maybe i missed something or you already planned to do as i stated
 
novadave
Hi Pilmat.
is it me or you have a bit of a mechanical problem that you might have missed in this photo.
in this configuration you will need to go to the trouble of cutting off the pedal pad section and reversing it to weld it back on.

maybe i missed something or you already planned to do as i stated
Click to expand...

I said it in the first post, but maybe it wasn't clear :) The pedal is too tall for the G27 environment at 10.25". The G27 pedals are a little over 7" tall from the bottom of the plastic base. Plus they are leaned back quite a bit. SO I always knew that I would have to cut the pedal down. Add to that I don't like the rubber pedal :ill:

There will be a small plate welded at the right height on the cut down pedal so I can mount DSD pedal pads. It should look a bit like this when done (my current pedal configuration), but with a master cylinder stick out back:
 
Watching with interest.

Just a thought, you could add extensions to the other pedals to bring them into line with the brake as others have done to give better feel. Not sure it would work in your Human GT tho.

REgards
BAD
 
Hi pilmat, also watching this with interest after all the "discussion" in the other thread. Just wondering if you could use the existing G27 brake pedal arm to actuate the pushrod on the master cylinder? This would mean that you're pedal positions would be unchanged, the question would be whether the G27 pedal arm would have enough throw to compress the master cylinder...
 
BAD808
Watching with interest.

Just a thought, you could add extensions to the other pedals to bring them into line with the brake as others have done to give better feel. Not sure it would work in your Human GT tho.

REgards
BAD
Click to expand...

Hi BAD. First, welcome to GTPlanet :)

In my opinion, the deal at full height will allow too much travel at a good pedal stiffness. Remember that shortening it will reduce leverage too, providing a stiffer feel and at a shorter throw for the same pressure output. I'll have to confirm a balanced feel when I start testing it, but I'm pretty sure the shorter pedal will work quite well.

As for extending the stock G27 pedals, you made me realize I wrote it somewhere else. Yes, this is one of my intentions. With the DSD pedal pads in should be a straightforward mod. While I'm welding a pad mount to the cut down brake pedal, I might as well weld pad mounts onto the gas and clutch too :)

Thanks for your interest. I should be back at grinding up the G27 base and cover today :D
 
ravey1981
Hi pilmat, also watching this with interest after all the "discussion" in the other thread. Just wondering if you could use the existing G27 brake pedal arm to actuate the pushrod on the master cylinder? This would mean that you're pedal positions would be unchanged, the question would be whether the G27 pedal arm would have enough throw to compress the master cylinder...
Click to expand...

Hmmm, didn't think of doing that... See what I mean when I said I didn't think of everything! :lol:

I'll look at this and post some ideas/pictures with my ideas of whether I think it could work easily enough to make it practical. More to follow :)

And thanks for your interest, there will be lots more discussing when I get this done!
 
To get the most realistic brake pedal "feeling", you should install a vacuum brake booster (and probably in my case a caliper with a load cell) and a electric vacuum pump. Or you could connect the master brake cylinder to a drum brake. This way you don't need the booster and the vacuum pump.
It's not a pretty sight but it is the best way to have a true and realistic brake pedal.

For me personal, looking at the videos of DIY hydraulic brake pedals, the perfect pedal and the clubsport pedals, the throw of the pedal is going to be too short.
 
kikie
To get the most realistic brake pedal "feeling", you should install a vacuum brake booster (and probably in my case a caliper with a load cell) and a electric vacuum pump. Or you could connect the master brake cylinder to a drum brake. This way you don't need the booster and the vacuum pump.
It's not a pretty sight but it is the best way to have a true and realistic brake pedal.

For me personal, looking at the videos of DIY hydraulic brake pedals, the perfect pedal and the clubsport pedals, the throw of the pedal is going to be too short.
Click to expand...

ravey1981
Do race cars have servo assisted brakes though? I know high end race cars (f1 etc) don't...
Click to expand...

Thanks for your input!

When converting road cars to race cars, one of the first things you do is remove the vacuum assist brakes. The system is only used to reduce the effort required at the pedal (Wiki link), and with the single master cylinder (as most road cars have), this is not needed for racing. The brake system is much improved by installing two separate, properly sized master cylinders. And as ravey says, I haven't seen a race car above a "street stock" type that has the vacuum still attached.

And as for pedal throw, remember that I will control this with the springing on the slave cylinder. I can make it initially soft and very stiff at a point I want :)
 
For me personal it's not about replicating a race car brake system. I just want the same feeling as I have in my car. I don't see the point in replicating a race car brake system because you're stationary in you cockpit. :D

It's all about the feel of the brake pedal. A vacuum booster makes the pedal easier to operate/push. The DIY brake pedal system I mentioned in my previous post take too much effort to push.

Control this with the spring on the slave cylincer? :confused:. What do you mean?
 
kikie, your question is a good one that might not be apparent to everybody, let me explain it:

eefabpedals2.jpg


Please allow me to borrow this image from this post.

The master cylinder here controls the slave cylinder (gold). The slave is a pull-type clutch cylinder (same as my blue one). The red, black and white things that are trapped between the large diameter washers are elastomers (rubbers). When applying brakes, the pedal is really just compressing the rubbers by pulling them towards the gold body of the slave cylinder with hydraulic pressure. We then measure that pressure and send the digitized information to the computer.

What I meant by this is that I can select elastomers and spacers to allow the type of travel that I feel is required. In this picture for example, the white one might be very soft allowing for the initial travel that is felt in a real brake, then it goes into the harder black one, allowing the brake to "work" around a certain feel that you want. The red elastomer is basically a spacer that have a very high compliance to allow some give if you slam the brake. This is just an example as I don't really know that that pedal. But it gives you an idea of what I think can be achieved.

You'll note in my Cut Back Pedal with Base picture that I show a stack of washers that will be used for this purpose
 
Here is a look at ravey's question about using the G27 pedal:

The mod is of course possible, but not a great practicality. The existing pivot location is quite high on the G27 pedal and there is no easy master cylinder mounting. I think it would be more trouble than it is worth. If I'm going to have to cut, grind and weld, the CNC pedal is an easier starting point.

Good question though, I'm glad you asked and we looked at this!
 
So basically, if I understand correctly, you are going to replace the elastomers on the slave cylinder with springs? Can you make to brake pedal as stiff as you want and make the throw of the pedal as long as you want by choosing certain rubbers or springs?
 
kikie
So basically, if I understand correctly, you are going to replace the elastomers on the slave cylinder with springs? Can you make to brake pedal as stiff as you want and make the throw of the pedal as long as you want by choosing certain rubbers or springs?
Click to expand...

To a spring as anything that stores energy through elastic deformation and returns to its original shape from the energy is released. So a coil spring, torsion spring, cantilever spring, elastomer, etc. are all springs to me :) My intended spring in this build is different stiffnesses of elastomer.

Here is the pedal fit to the G27 base. Man that hacked cover is starting to get uglier to my eyes...


That will be it for today. I'll work away at it this week. It still needs the bolts for the pedal and a mount for the slave cylinder. The pedal can now be trimmed for the mounting pad, and I'll decide before if I'm going to increase the pedal heights...
 
About ravey's question on using the stock pedal to actuate the cylinder. I found this pic from another website and thought it was pretty interesting.

21c5mbd.jpg


I actually prefer the look of the pedal you are using Pilmat. Excellent job on this project so far.
 
An advantage of using a stock potmeter or hall sensor, - that replaces the stock potmeter -, is that you can still connect thet pedals to the wheel, when creating a force based brake pedal instead of the standard travel based brake pedal.

If you are going to use a load cell or a(n) hydraulic brake pedal, you need a joystick controller/load cell amplifier and thus making the pedals a stand alone (unless you use the Bodin Load cell mod for the T500) device which you can't use in games that only recognize one controller. The throttle and clutch must also be connected to the joystick controller, I think.
 
A little progress today:

All I got done was the two holes through the plastic base for the pedal frame bolts (1/4" x 1"). The forward hole goes right through a rib in the base, on the bottom side. It was a simple little grind to get rid of it. The 4mm mounting bolts are not yet installed. They are only a little insurance in spreading the load over a wider area. They are probably not even needed, but they are easy to put back in :)

The bushings were ordered and shipped today. I got the full range of Shorty'e Doh-Dohs (88, 92, 95, 98 and 100). They should be here on Wednesday.

For plumbing, I will use:
1x -3 to 1/8" NPT Straight (eg. Earl's 981603)
1x -3 to 1/8" NPT 90 deg (eg. Earl's 982203)
1x 6" -3 braided hose with 1 straight and 1 90 deg fitting (eg. Allstar 46302-6)
1x Aluminum line clamp 1" for the slave attachment (eg. Allstar 18307)

The pedal will be cut to size and the pad welded tomorrow. I decided to start with the pedals at G27 heights. Mods will be made if needed!

I might even stick on a pressure gauge as I have one sitting on my desk... Maybe a plumbing change then :)
 
Great seeing this project. Some thing I also really like to do. I'm content for now with the CSP v1 ( with a Dave Struve set on it's way for more realism I hope).
But in the future I guess I will give this a go at the old G25 which is lying around here.

Keep up the updates

Bryan
 
The project is ongoing!

The brake pedal is cut down and the pad fabricated. Welding and painting will happen tomorrow.

The slave cylinder is attached to the base:
​

And I have a selection of elastomers (88, 92, 95, 98, 100):
​

The controller should be here by next week :) All the other bits are on hand and the wiring will be straight forward.
 
do ya reckon that plastic will be strong enough? there will be a bit of force on the slave (or am i back to front lol)
 

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