DIY G29 Hydraulic Load Cell brake

Actually I give up on this setup.
I have tried different ratios on the pedal arm, different return spring strength, different length of push rod and although each of them gives a different feel and I can get it to feel exactly like a real brake it has one fatal flaw.
I cannot get the feeling of just touching the brake and having it register. If I make it sensitive enough to do this then full braking comes in too easy and it locks up. If I set it so I get full braking without locking too easy then I have to press too hard to get that initial braking and then I can't judge how far to ease off the brake for trail braking.
And when I look at my telemetry it is this transition from full braking to trail braking and trailing the brake all the way into the corner where I am losing all my time. And I mean ALL my time - I can brake at exactly the same point with exactly the same brake force as the Professional driver telemetry from VRS, turn in at exactly the same point, hold exactly the same line and accelerate out at exactly the same time, but between turn in and accelerating out I lose about 10kmh because I can't ease off the brakes without losing all braking so I have to hold them a bit harder and then come off them too soon because I have lost too much speed
Thrudtmaster TLCM pedals are now on my shopping list - unless anyone has nay better ideas or (affordable) options ?

I have found the issue - the current setup doesn't start registering until there is 2v output. I read that this is standard for the G29 pedals - any idea how I can rectify this ? Is it something in the pedals that doesn't send a signal to the game until 2v or is it something in the software, PC or game ??
Maybe thats why people use an arduino board instead of just the INA122 amplifier ??

D'OH - the issue was very simple to fix.
I have a Leo Bodnar Logitech to USB converter and there is software to calibrate the converter - once I did that it was registering just a slight pressure on the pedal so now I can trail brake like a pro (well almost.....)
I still think the wii fit loadcell is not the right option and will try a disc type loadcell. The cheapest one I can find is on back order so I won't get it for 6 weeks or so. Will report back if that makes any difference.

Update time

I redid my wii fit loadcells by taking 2 of the bare loadcells (without the pressed steel bolt on bits), placed them back-to-back in a X and then dropped them in my caliper. This got rid of any flex that the pressed steel bits had (and they ended up bending out of shape anyway) and made the pedal a lot harder.
Then I tried different pedal arm leverage ratios and found it is very dependent on getting that just right. Too much leverage and the pedal is too soft and spongy and not enough and the pedal is like standing on a brick.
I have it just about right but would like it a tiny bit harder - unfortunately can't do that unless I build new pedals with infinitely adjustable leverage ratio.

Just did a quick race at Spa in a M3 and got straight down to 2:20's where I was usually in 2:21 bracket. Did one lap at 2:19.8. Braking was just so natural and trail braking all the way into the apex felt the most realistic yet.
In fact I would say it absolutely felt exactly like real brakes

I think I might fork out $80AUD and get a 200kg button type loadcell. When I went from one wii loadcell (50kg) to 2 (100kg) it made a huge improvement. So I am thinking a 200kg one might be even better. Also it will fit in the caliper better

Stay Tuned ........

Good idea. I also use the wii fit load cell.
I think it 500kg to 1000kg.
You should check with scale before using the $ 80 AUD.

there are 4 in the fit board and the board is only rated to 150kg and allowing for some safety factor I assume each loadcell is 40-50kg - no way is it 500-1000.
I have also tried the cheap 50kg eBay loadcell and the wii ones have about the same sensitivity.
I am pretty sure a 200kg button style loadcell will be the best option. They don't bend and are a true pressure style measurement. i think the tiny bit of flex in the current setup is detrimental and will be my last area of improvement (apart from continually fiddling with the pedal leverage ratio)

Another quick update.

I put the pedal back to the lowest lever ratio (from 3:1 to 2:1 roughly) so it is hard to push - even on the middle setting it was too soft and had too much travel and I was struggling to trail brake properly.

I was also trying to use the variable resistor on the Derek Speares loadcell amplifier board to adjust the sensitivity. If you set it so it is really really hard to get full braking (F1 car) and then adjust it lower for Gt or road cars it then increases the bottom of the range. Sometimes so much that the brakes are on when you don't even touch the pedal. And you have to adjust it between cars or the F1 cars lock too easy if you have it set for GT cars.
So now I have figured out that you adjust the resistor so it only read max when you are at max pressure you can physcially apply and leave it alone.
I have a Leo Bodnar adapter for the Logitech pedals to Thrustmaster wheel and in the software you can adjust the pedal range (same as the brake range in AC etc). I set the minimum slider so that when you take up the master cylinder slack the signal sent to the game is around 100 (or 10%). This will stay the same for any car now.
Then I adjust the maximum value to suit the car - 1024 for F1, 910 for GT and 800 for road cars (lower number means less pressure to reach 100% in game)

Just took another 3/10th of my M3 Imola best

More updates - just in case anyone is still following my ramblings.......

Turns out my X shaped loadcells wasn't the best execution - as they were only glued together and the glue I used wasn't very good so they would move in the caliper. This then meant that the loadcell sensor and wires would sometimes get caught by the caliper piston and one of the sensors failed.

So I machined (well used a grinder actually) a 1mm notch in the back of one the loadcells so the other one would slot into and stay at exactly 90deg and used a better glue. Then put that into the caliper with one of them upright (like a Cross) rather diagonally (like an X).

Now it is just about perfect and my settings had to change because the readings were more stable and they didn't change as I used them since they were no longer moving etc.

So I now have the minimum brake range set so that at rest it is on zero in game. That way the master cylinder free play takes up the slack (where you would normally set minimum brake in game above zero to avoid lockups) so when you first feel the brake pedal resistance in game reading will be around 10-15% (I have it at 15%). Then set the maximum brake range to where you apply your own max brake pedal force. And adjust from there to your liking and/or car.
Obviously the actual in game settings should then be 0-100 brake range and 1.00 brake gamma

I replaced the wii fit loadcells with a mini button 200kg loadcell.
Now it is a very stable setup and finally works 100% - braking is now very easy, realistic and awesome.
Also with this proper loadcell there was no need to do anything with the setup - just put everything on 0-100% and 1.00 brake gamma and then just adjust how hard to push to get full braking with the adjustable pot.
I can now say it is a success

Here are pics of the (almost) complete setup

Ignore the cable ties - they are just temporary as I haven't finalised the rest of the rig yet.

And a run down of what it is :
$30 eBay caliper and master cylinder for a scooter (mounted to my G29 pedal)
$70 eBay 200kg button loadcell in the caliper (replicating the disc)
$40 Derek Speares loadcell amp (can DIY for less but savings aren't significant)
$30 Leo Bodnar G29-USB adapter (not required if you have G29 wheel or if you have different pedals/wheel)
So $170 total. (all prices in AUD)

That is one HELL OF A GOOD IDEA!!!

Thank you
Have been using it for a while now and it really is awesome.
Just adjusted the settings so that it is set where you have to press really really hard to get 100% braking and now it doesn't lock up (or only just) when you panic brake. Still getting used to having to press a bit firmer but seems to be the way to go.
My times tumbled from 2:20 to high 2:17 in an M3 GT2 at Spa

Just in case anyone is still following this saga :

So I rigidly mounted the caliper (not that I think that makes any difference but it looks a lot better).
And I put the brake pads back in after removing all the pad material (so just the backing plates really). I di dthis because one of the pistons would retract all the way and one was fully extended and the loadcell would hit against the caliper body. Now the pistons can't do that and the loadcell stays central. Not really sure if this ahd any effect on the actual performance but I think it did, just not sure how.

But the biggest change was the settings. I have finally settled on the right way to have it.

I turned the Potentiometer in my load cell amp all the way hard (1000ohm resistance) and set the minimum slider in the Leo Bodnar software to just 1 above the resting output (51)
Then I set the maximum slider to the value of when I pressed as hard as I could (605) Then I went for a drive in a M3 GT2 (so no ABS) and braked as hard as I comfortably could after getting used to it for a few laps. When I checked on the telemetry I was only getting 93% braking. So I worked out what 93% of 554 (605-51) was (515) and added that to 51 (566) and set my max to 560. Now I was getting 97% braking. So I set to 567 and got 99% braking and finally set it 566 and now get 100% braking, with no (or very little lockups) and great trail braking (once I got used to having more trail braking available).

Pretty sure that I have finally nailed it - only took me2 years. In fact I just looked at my first post and it was posted exactly 2 years ago today !!

And I mounted all the electronics in a box and tidied up the wiring and fluid reservoir and remounted the Master Cylinder to make it more rigid - so pretty much done

Yeah I worked it out as you can see

updated pics

2 weeks later and I am now very, very happy with the result

I have 2 more tweaks that I would like to try - changing the pedal/rod ratio and adding stainless steel braided line - but enjoying it too much so they will have to wait ...........

Slightly off-topic but I finally got around to stiffening my rig so now the seat, pedals and wheel don't move at all. I also downloaded Content Manager for Assetto Corsa and spent time setting up the FFB for the wheel.
And wow what a difference - everything is so much smoother and more accurate with no unwanted movement from the rig. Doing PBs with nearly every car and track - including a 1:42 in Ferrari F2004 at Spa and before doing the brakes and the above mods I could hardly even drive an F1 car and would be 10secs off the pace instead of just 1 or 2 now

Don't know if it is because I have got used to the brakes or because everything is no longer flexing but I had to move my brake settings out because I was hitting full braking too easily. I have gone from 560 to 800 and can press past 800 if I really try (1023 is max).

And more off-topic I read up that F1 brakes need 100-120kg of force so I put a bathroom scale between my foot and my brake pedal and could only muster 60-70kg using all my might

I am very interested in your project so first of all good job. How will you then solve the lack of weight for the F1 brakes?

I don't understand your question - I can brake with all my force and not register 100%. So unless you have a huge amount of leg strength and can push more more than 80kg then there is no issue. If you can puchmore than 80kg then you just need a different resistor in the loadcell amp to adjust thevoltage being sent to the game. If you max out the loadcell (mine is 200kg) then you can either adjust the pedal ratio or get a bigger loadcell and possibly a bigger caliper to fit that loadcell.
But seriously you won't need any of that as I can't see anyone maxing out the setup as I have it. If you build one you may need to make it with an adjustable pedal ratio and you can also calculate what pedal ratio will give you what kg force on the loadcell using the master cylinder bore size etc.
And even if F1 drivers do use 100+kg of force doesn't mean we mortals have to - would you like to have press that hard for lap after lap or would you prefer just to have press somewhat hard relative to your strength or compared to your real car ?

With mine being more rigid and when watching the calibration sliders it felt like it was more spongy than before and I was wondering why and how I could fix it. But I put my H shifter back on and drove a manual for the first time in ages (since before doing this mod) and when i went from the clutch to the brake with my left foot the brake was like rock solid. So I guess it was just being used to the feeling before and once that was eliminated with the soft clutch pedal it was back to being really hard in comparison. Also when you physically look at the brake when pressing it it doesn't move more than a few mm once you press down and take the pad slack out of the caliper.