Low budget load cell mod for Logitech G25/G27/G29

Gerzson

100RPM
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Jun 24, 2017
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Hi,
This mod is something I designed and built based on many things I found on the net.
None was easy enough to make at home with simple tools and common scrap materials.
I went for the cheapest of everything on eBay, but it doesn't mean it's worth less.

I made a few more of these sets for sale if anyone is interested in pre-assembled and tested pieces of handcrafted products. :)
 
Dec 17, 2017
2
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Hiya, I'm interested in how the ones you've put out so far are performing - they still holding up well? If so I'm certainly interested
 

Gerzson

100RPM
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Jun 24, 2017
161
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Hiya, I'm interested in how the ones you've put out so far are performing - they still holding up well? If so I'm certainly interested
Hi,
It's holding up quite well.
I'm racing in the same league as the ones having these kits and there have been no complaints so far.
 
Jan 27, 2019
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Hey @Gerzson,

I think this is what I'm looking for months to extend my G29.
Tried other brake mods (rubber change, 3Drap, etc.) but none of them gived back the real pressure output and feel.

I'm also from Hungary...
Is there one piece in stock for me?
Anyway, How can I contact you?

Thanks in advance.
 

Gerzson

100RPM
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Jun 24, 2017
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Hey @Gerzson,

I think this is what I'm looking for months to extend my G29.
Tried other brake mods (rubber change, 3Drap, etc.) but none of them gived back the real pressure output and feel.

I'm also from Hungary...
Is there one piece in stock for me?
Anyway, How can I contact you?

Thanks in advance.
I saw you writing to my inbox. I'll reply you there.
 
Nov 5, 2019
3
2
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Hi, how do you invert the signal? At the end of the video, you see that full red is no input, with input decreasing it rather than increasing it. For games that don't let you invert the signal, how do you do it electronically?
 

Gerzson

100RPM
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Jun 24, 2017
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Hi, how do you invert the signal? At the end of the video, you see that full red is no input, with input decreasing it rather than increasing it. For games that don't let you invert the signal, how do you do it electronically?
Good question. I don't do that. What games don't support inverting the signal?
The ones I play allow it.
 

AccAkut

2000RPM
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Mar 21, 2015
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Hi, how do you invert the signal? At the end of the video, you see that full red is no input, with input decreasing it rather than increasing it. For games that don't let you invert the signal, how do you do it electronically?
You could also just switch GND and +5V input where you splice the loadcell into the normal pedal loom
 
Nov 5, 2019
3
2
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Good question. I don't do that. What games don't support inverting the signal?
The ones I play allow it.
While Assetto Corsa allows it, and I think BeamNG.drive does, the ones that do not support it include Project Cars 2, F1 2019 and the Forza games, as well as most older, arcade titles (eg. Need For Speed games). I also want to use my pedals on Xbox, and no Xbox games support inverting the pedal. I basically want it to act as it did from Logitech, no messing about so in case I ever sell them or give them away, they will act as expected.

You could also just switch GND and +5V input where you splice the loadcell into the normal pedal loom
It isn't as simple as that, the load cell gives out a certain voltage that is then amplified. It should go from about 3.3V at zero pressure to 0.8V or so at full load, you can't just swap wires to fix that.

But after mucking about with some stuff for a while, I did work out a way to do what I wanted. I found this reddit post:
https://www.reddit.com/r/simracing/comments/92exmk which used the same amplifier but then used a different chip to invert it.

What I ended up doing was slightly different, I used one of these to do the inversion:

It took a while with messing about with resistors and trim pots to get to the right compromise of deadzone and pressure/sensitivity, but I got it to something I'm happy with. Once I build my simulator I'll make a full post on r/simracing to explain everything I did, including the pedal bracket I fabricated.


TLDR: If you do this load cell method, you really do need to invert it for it to work in a lot of games.
 

Panicpete

10RPM
Nov 18, 2017
16
22
Assuming the Circuit uses an INA122 or similar amplifier, you just need to switch around the wires from the load cell and connect the VRef pin of the amplifier to +5V instead of GND.
The circuit then subtracts the amplified load cell signal from 5V instead of adding it to 0V. No additional chip required.
 
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AccAkut

2000RPM
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Mar 21, 2015
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Assuming the Circuit uses an INA122 or similar amplifier, you just need to switch around the wires from the load cell and connect the VRef pin of the amplifier to +5V instead of GND.
The circuit then subtracts the amplified load cell signal from 5V instead of adding it to 0V. No additional chip required.
yeah, I do have this circuit here, and I can just switch it around, the amplifier works in either direction
 

GeekyDeaks

250RPM
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Dec 26, 2019
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I am working on something similar, but using some bathroom scale load cells (the little square ones) and keeping the output inverted as original as I want to use it on the PS4. Fortunately, as mentioned above the INA122P allows inverted gain

I have a little git hub project with the PCB design and the current 3D models for printing. Still working on the models over the holiday :)

 

Gerzson

100RPM
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Jun 24, 2017
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I am working on something similar, but using some bathroom scale load cells (the little square ones) and keeping the output inverted as original as I want to use it on the PS4. Fortunately, as mentioned above the INA122P allows inverted gain

I have a little git hub project with the PCB design and the current 3D models for printing. Still working on the models over the holiday :)

I used these bathroom scale cells too, I used them in pairs, that way it works like a 4-wire load cell.
I drilled out the rivets on the cells and used M2.5 bolts to fasten them together back to back.
 

GeekyDeaks

250RPM
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Dec 26, 2019
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Yeah, doing something similar for the same reason. Also mistakenly thought it would double the load range, but a brighter friend kindly pointed out that they don't work like that when in series! :) Should still increase the resolution though.

The brighter friend has also kindly printed off my design and I have had a chance to test it.

IMG_20191230_080316.jpg


Needs a bit of tweaking. My measurements near the base were off by about 1mm and I forgot about the protrusion of the ground screw hole.

We made a spacer instead of joining the two cells and created a cavity to allow the whole assembly to compress. Drilling out the rivets would save a little space and make the assembly more stable so I'll check that out, but this seems to be working ok for now.

I am also going to test with one cell and create the other half of the bridge on the circuit. This way I can unbalance the bridge at rest and have the load bring the bridge back into balance instead of inverting the difference.

It's way too stiff at the moment. I used an M10 bolt with 3 rubber washers resting on top to transfer pressure from the top piston to the cells, but the rubber has hardly any give. This is what it looks like:

IMG_20191230_080620.jpg


Might take another 5mm off the guide cylinder and put a low profile nut on the end of the rod to hold a washer in place so I can try experimenting with springs.