DIY G29 Hydraulic Load Cell brake

I just finished my DIY hydraulic load cell brake module on my G29 pedal.

Took an ebay rear motorbike master cylinder, reservoir and 2 piston caliper and put a Wii fit board loadcell in the caliper to replicate an actual disc.
Built a loadcell amp with a INA122 and variable resistor.

Cost about $50AUD - 30 for the ebay caliper, 20 for the load cell amp and nothing for the Wii fit board load cell. I didn't even have to modify the G29 brake

Works really well but I only have the standard G29 to compare it too. I am still getting used to it so struggling to go any faster but at least now I can trail brake

It certainly feels a lot more like a real brake, especially on the proper race cars.

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So I have been tweaking it and got it set up pretty good - it really does feel like a real brake. A stronger return spring will improve that I think.(it is just the standard G29 spring at the moment - amazingly it was exactly the right size to cover the actuator rod)
It is very dependent on the leverage ratio of the pedal. I can adjust this by moving the actuator rod up and down the back of the pedal - by sheer fluke the G29 metal rod that normally fits there is exactly the right OD for the actuator rod in the master cylinder and I just used the existing slot in the pedal arm itself.
It is also dependent on the sensitivity of the loadcell amp - adjustable via the variable resistor. When I had it just right for the Formula cars it was a bit too hard for GT cars and WAY too hard for road cars. I need to get a decent rotary knob to be able to adjust this easily between cars.
But for now it is working well.
The biggest differences I can tell from the standard G29 pedal is the smoothness (or sensitivity) as you get off the brake for trail braking - there isn't a sudden big drop in brake pressure (in the game) and you trail brake much more effectively and for longer.
And you can just touch the brake to modulate speed when you overcook it (which unfortunately I do a lot) in a corner and it won't lock up or throw you off the track.

And does the load cell not break when pressed by the brake caliper?

Considering it takes all my leg strength to get the load cell to register its max capacity I don't think it is being over stressed.

And it is only doing what it is designed to do. The wii fit loadcell has 2 plates bolted to either side that are compressed from each side in the fit, exactly as they are in the caliper.

And have you seen a load cell - its a 12mm thick piece of steel !!

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Cost about $50AUD - 30 for the ebay caliper, 20 for the load cell amp and nothing for the Wii fit board load cell. I didn't even have to modify the G29 brake

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Hi there.

Cool build. Looking to do this myself in the near future.

Would you say this cylinder has the same dimensions as the one in your pictures?
Link:
https://www.aliexpress.com/item/ Brake cylinder + calipers

That is exactly the same caliper.
But I would not recommend using the G29 pedals as I have done. The pdeal arm ratio and positioning of the brake rod mount is all wrong.
I haven't done it yet but I plan to make a new pedal arm to have a longer throw / less rod movement.

It still works ok as I have done it and is still better then the standard G29 but a new arm setup will (hopefully) make it so much better.

Ah cheers mate. I'll hold back for now then. Curious how you to see it when it's done

Have you tried connecting a pressure sensor to the pro micro instead of a loadcell, like this:
https://lebois-racing.fr/srt-brake-pedal-p1#shopping-list

No - I had a wii fit board lying around so the loadcell cost me nothing. I also figured that measuring the pressure actually applied to the "disc" (Loadcell) by the caliper would be a better realworld approximation. Plus I also thought it would be a lot easier and cheaper than a hydraulic pressure sensor, especially since all the HPS seemed to be very expensive when I first started looking into it.
I think once I have the correct pedal arm and geometry (I need one just like in the link you posted but I don't have a 3d printer or access to a cheap 3d printing shop) it will be a lot better.
Don't get me wrong - my current setup is miles better than the G29 even with all the mods. I can brake really well and lockup is easier to control. My main complaint is lack of feel as to how hard I am pressing and lack of consistency when I ease off - both of which I believe is to do with the geometry, especially since the arm is not pushing the rod straight into the cylinder but at an angle which differs as you press the arm.
Once I have a longer arm which sits at a 90deg angle to the cylinder and has the rod attached very close to the pivot it will be much better. I really should pull my finger out and do it but I can never find the motivation......

A wii board! that's awesome.
I like the idea of keeping the Logitech pedals and modifying them to use with all these different braking systems. Nice to see everyone's solutions.

I'm trying the loadcell thing before the hydraulic route. Was going through Lebois's shopping list and will cost around a $100 + printed parts. Also, not sure how to code the Arduino to use the data from the pressure sensor to work as a brake.

I'm also keen to try out a 50kg scale loadcell to put in a printed piston for the G29. Unfortunately, not getting any data from the 3-wire cell into the HX711. Not sure what i'm doing wrong yet. I did bridge one of the wires as suggested by GP race SIM. For now, waiting on parts to make a DIY amp with an INA122p. If that fails, then a Bodnar amp is the next step to save another headache.
If I can get these small loadcells to work, I'd be keen to try them with your system as well.

Also waiting for another loadcell to try with this design.

I am just using a INA122P - easy peasy to make - just make sure you use a nice big pot to change the sensitivity as you drive.

Cheers. I'm new to the electronics thing, but gonna give it a go when the components land in the postbox

Also, Lebois made his design compatible with the G27/29
FB Link

If you can get someone to print the cylinder housing, perhaps the new alignment could sort out the feel?

That is pretty much how I had mine setup. The problem is the leverage ratio is not high enough and the angle of the pivots means the pedal is trying to push the master cylinder rod down instead of back towards the cylinder.
I have just modified my pedals to replicate the typical real world pedals - so the pivot for the rod is now directly above the pivot for the pedal and is a lot closer to it as well. this gives a direct push of the rod back towards the cylinder and more leverage.
I also machined up some inserts to go inside the brake caliper pistons. I discovered that it was pushing awkwardly on the loadcell rather than flat against it. Now the piston is solid rather than a cylinder and that made a big difference.
Still a got a bit of fine tuning but I can say it is a huge improvement so far. Stay tuned for more updates. Just don't hold your breath as I work real slow

So did some more testing and turns out the leverage ratio is super important. With the cylinder rod pivot being just above the pedal arm pivot I had lots of travel but the pedal was squishy all the way through the travel. So I moved it up higher (further away from the pedal arm pivot) and it was way too hard with almost no movement.
I moved it back down half way between the 2 and still too hard with little movement, so I moved it down to about 1/4 and still a bit hard. Moved it down an 1/8 and now too soft again - so it is very susceptible to small changes. I guess the fact the pedal arm istelf isn't very long means small changes to the distance between the pivots has a fairly large change to the ratio - the longer the pedal the less effect this would have. So ideally I need a screw adjustment on the location of the rod pivot so I can finely adjust it by 1/10ths of mm. But for now I will just try and get it as close as I can with my sliding bolt adjustment.
Pretty sure if I can get this right I will have the most realistic sim brakes ever*






*well the most realistic I have used anyway

Don't know how much of an effect it had but I used another wii fit loadcell and this time trimmed it down to slide down into the caliper perfectly so there is no movement. This means the pistons are definitely pushing flat against the whole side of the load cell - the old loadcell was being pushed diagonally (so just on the 'moving' ends of the plates and these plates actually got bent !!)

Looking good

I have a similar setup - but use hydraulic pressure to measure the force. The pressure sensor simply outputs a voltage so a load cell is not needed. I use a pull type slave cylinder and can adjust the feel of the brakes using plastic / rubber disks

It is very important that the rod of the master cylinder shaft penetrates the master cylinder as straight as possible. I have had problems bleeding the brake fluid because the rod did not enter the cylinder straight.

Yes but the loadcell came free with an old wii fit board
Not sure if using it as a "disc" makes it better, worse or no difference since a real disk has no give in it but the loadcell has a few mm - bit like your "discs" having give in them. Do you find harder or softer ones better ?

Yeah my setup allows me to tilt the master cylinder to keep the rod straight when I change the pedal pivots.

I tweaked it a little more and got it where it was firm enough to feel and modulate but not so firm as to feel like standing on a brick. Could still be improved but my first decent lap at Laguna Seca with it and here is my brake traces (in red) compared to VRS Pro Driving Instructor (blue obviously) - not perfect but pretty damn good IMO.
Look how much smoother my line is compared to the pro - I assume this may be because of the resolution of the loadcell / hydraulic system compared to whatever the pro was using - or is he just modulating the brakes more/better than me ?
Turn 2 (Hairpin)


Corkscrew

Turn 5

DO NOT USE THE WII FIT LOADCELL

It is not strong enough to withstand the pressure from the caliper

I will report back when (if) I have a solution.......

The 2 metal plates that are screwed to the loadcell are too weak and are bending with the force of the caliper.
I took them to an engineer to see if they could make something stronger but they said they are as strong as you are going to get. The only option to make this really work is with a disc or button type load cell. So that is what I am going to do. Anybody know where to buy a cheap disc loadcell ?