Logitech G25, G27, G29, G920 load cell DIY project

[cteters]

Seeing that I haven’t completed the work, allow me to showcase the work of others in my place, as this is starting to become more of a repository of ideas on the topic.

RD member GeekyDeaks showcases a bathroom scale based load-cell project on his github
- More details about bathroom scale based loadcells

RD member Grezson built one by using a 20kg straight Bar load-cell (which are very cheap btw)
- More details about straight bar based loadcells not specific to logitech

- More general information about load-cells
- Some older research completed that is still relevant

- RD member Panicpete has also shared a lot of detail about his own project that can be found on this thread

Provided in the spoiler below is all the most pertinent information I’ve dug up on building a button load-cell for the Logitech brake pedal. Very similar in design to that of Richmotech’s model. The total cost for this project would come around $60 to $70 on the low end roughly. Be advised, I’ve not actually completed this project and ended up installing the AXC Sim brake mod in it’s place, which comes at the same cost it would take to build a button load-cell mod.

Spoiler: button based load-cell project

Parts list:

Steel Spring:
30mm Outer Diameter (This is wrong, I will updated the O.D. and I.D. later)
2.0mm Wire Diameter
50mm length
A length of 50mm is overshooting it, so the spring would need to be shorten to length with a dremel. A dual rated spring such as what is used with the nixim and gteye mod might also work, but I presume that having a combination of the spring, rubber and the load cell should provide for enough change in pressure. I've also read of some success by using a product called Real Pedal that can be found on ebay, which comes with a spring and sponge, but a bit over priced again at $30. So best to DIY this imo.

Load Cell
The load cell should have an Outer Diameter or 25mm and not likely much larger, but definitely not greater than 28mm. The Logitech housing that holds the spring assembly has an inside diameter of 30mm, so it needs to be a bit less than that. The actual rating of the load cell should be around 45kb (100lbf) and a 3 wire system that can be supplied with up to 5V.

Example load cell:
Button Load Cell (50kg) - CZL204E
FC22 Compression Load Cell (45kg)
note: This particular model would need to have the mounting brackets edged off with something like a dremel.


Amplifier:
An amplifier might not actually be needed if the supplied voltage is maintained, but they are pretty cheap and might be a good fail safe to have. An affordable standalone load cell amplifier by Leo Bodnar or maybe something like a SparkFun Load Cell Amplifier - HX711. Can't really say for sure what the best option is just yet.

OR build your own:

Spoiler

Parts:
Amplifier:
INA122PA
or
Op-Amp (Through-Hole) - LM358
Ceramic Disc Capacitor
Ceramic Disc Capacitor 10nF
Resistor
10K Ohm Trimmer Trim Pot Variable Resistor

Rubber fuel line:
This should have an outsider diameter that doesn't exceed the insider diameter of the steel spring (possibly a hair shorter to be on the safe side) and then just trim it up to fit inside the spring.

Felt or Foam:
To wrap around the load cell so as to make a more snug fit.

For assembly, simply refer to any Ricmotech style information, such as,
Sim Racing Garage review
Ricmotech assembly manual

 

[GeekyDeaks]

Hey @dirko13 - I am running on PS4 (cannot justify a PC rig at the moment) - the trick is to fully emulate the potentiometer in the stock G29 pedal. Happy to offer hints on this if your friend is up for a challenge . I even have some spare PCBs for my DIY load cell amp that I am happy to send out to fellow tinkerer's looking to play

 

[Panicpete]

Ok, to explain how my setup works: The bottom spring housing is not attached to the original mounting rail, instead it is mounted to the flat aluminum profiles that run on both sides inside the original rail and pivot around the larger diameter of the pedal bushings at the front of the rail. The brass tube inside the mounting hole of the bottom spring housing then presses onto the load cell sandwich, which is attached to the original mounting rail. The load cell sandwich consists of a spacer at the very bottom with holes to make room for the two bolts fixing the pedal to the housing and the M6 bolt for mounting the pedal set to the rig. Above that are the aluminum parts and load cells in the order you can see them laid out in the picture in my second post. The two thin pieces are what is actually in contact with the brass tube in the lower spring housing. I had to remove some plastic from the spring housing to expose the bottom of the brass tube.

I have to say your idea looks very promising. The biggest challenge when using the original spring housing is to find something that is compact enough to fit in there and also has the right amount of stiffness. By getting rid of the housing you gain a lot of room where you can experiment with different materials and just use a longer piece of something that would be too stiff in a length that fits inside the housing. I would suggest to put a spacer inside the soft spring to transfer the force to the fibroelast pieces after the low-force travel of the pedal. I'm not sure how the soft spring would react when it is fully compressed and has to transfer even more force, it might not like it

As GeekyDeaks wrote, the DIY-amplifiers fully emulate the potentiometer and use the stock electronics of the wheel, so it should be no problem to use it with a PS4.

 

[Panicpete]

One thing to keep in mind when using "softer" elastomer buffers/springs is that they will probably take some time to fully return to their original shape, so the feeling might change depending on how long ago you last used the pedal. This is why i got rid of my garden hose spring and now use a stack of disc springs instead. However, i think with these "proper" elastomer springs this should not be a big problem, as some (if not most) commercial load cell pedals also use these elastomer elements.

 

[dirko13]

Thanks for your replys guys.

My friend told me yesterday that his wheel and pedals pased by over the rainbow and he sended it back to get a full refund and than change to some Fanatec ones, so no more amplifier is needed for him, but very kind of you GeekyDeaks to offer some of your spares. I really appreciate that.

@Panicpete: Yes to get rid of the original springhousing gives you much more possebilitys to modify
the system.
The elastomere springs are designed for that kind of use and should act like a real spring.
They are used in skateboard axes for example and in some real (sport) cars in the suspension as well.
You are abselutly right about the spacer in the soft spring, you can't let the complete pressed spring transfer all the presure without any, don't guess that'll work for long. So I will make some out of I think teflon.

When I had a closer look to the bathroom scale I'm going to use for that mod I had the idea to use the display as well and make some kind of brake presure indicator out of it but I dont know if it will also work with just 2 of the cells connected.

I wanted to order the missing parts today (Bodnar Board and hall sensors, magnets and fibro springs)
but unfortunally I recieved a nice picture of me in my real car with 30km/h over limit wich will cost me more than e.g. a new Fanatec Pedal Set
So have to wait for fresh money income next month.

 

[GeekyDeaks]

@Panicpete: Yes to get rid of the original springhousing gives you much more possebilitys to modify
the system.

The other thing I really like about that approach is that you can tweak the feel much easier too as the axis of travel under compression is separate to that on the load cell. It's the one real niggle that I have with my approach as I'm finding myself cutting different lengths of threaded rod to alter the travel before the pedal firms up

I wanted to order the missing parts today (Bodnar Board and hall sensors, magnets and fibro springs)
but unfortunally I recieved a nice picture of me in my real car with 30km/h over limit wich will cost me more than e.g. a new Fanatec Pedal Set

Ouch... not great... but, one thing I'd like to point out.... If you are undertaking this project purely to save money, then I'd suggest taking a close look at the AXC TrueBrake. Doing it this way is a great project for learning and whilst I don't regret my decision for a minute, it has already cost me more money, not to mention time, and I'm still not quite done

 

[dirko13]

@GeekyDeaks

yeah thats a good point and the AXC looks great as well but I like doing stuff by my self very much and lets say the mecanical part is not a problem.

The ticket over 300 euros just crossed my plans.

But thanks for your advice

 

[J_P]

.... but unfortunally I recieved a nice picture of me in my real car with 30km/h over limit wich will cost me more than e.g. a new Fanatec Pedal Set

Are you sure is you driving your car? Couldn't be your grandma?

I'm been looking for this kind of solution, and my initial though was to keep "original setup". The spring is just to preload (5-10mm) and original rubber to give some travel as pressure is applied to scale load cell.
What's wrong with this rational?

 

[GeekyDeaks]

I'm been looking for this kind of solution, and my initial though was to keep "original setup". The spring is just to preload (5-10mm) and original rubber to give some travel as pressure is applied to scale load cell.
What's wrong with this rational?

That is exactly what I did. I was waiting for my friend to return and print out the updated model, but it's now finally finished.

I have updated my GitHub page with the latest model and some pictures https://github.com/GeekyDeaks/g29-load-cell

I'm happy with the end result and have noticed I'm trail braking far more consistently. The pedal feels more like a road car than a racing car though, so might not be everyones cup of tea

EDIT: I re-read your comment and now I am not 100% sure I got the gist of what you were saying. Do you mean you think the original setup sufficiently emulates a load cell, so there is no need to do this kind of mod? If so, then my advice would be, if you are happy with it, don't worry about it!

 

[J_P]

EDIT: I re-read your comment and now I am not 100% sure I got the gist of what you were saying. Do you mean you think the original setup sufficiently emulates a load cell, so there is no need to do this kind of mod? If so, then my advice would be, if you are happy with it, don't worry about it!

No, you got it right.
Already saw your new pictures, that's exactly what I want to do.
Since I have my 3D printer ~85cm from my "personal computer" (now, simulation station ) I can easilly fine tuning the solution (the preload will be stronger, more compressed, and cutting the rubber piece is also an option).

I'm not trying to simulate a real pedal (spoiler: is not a real car either), just want to have a method with more control.
For comparision, my IRL car has automatic transmission (yes, we also have those in Europe ) and I accelerate and brake with my right foot. In simracing, I always used left foot to brake (not even thought about it), even when I had manual transmission cars (left=clutch, period!), by that I mean, my previous IRL 28 years driving experience.
After 4 years driving a double-clutch automatic transmission, I get in a manual transmission car and everything just flows. We adapt to the environment, and that stays hardwired in our 'brain'.

If our simracing rig is consistent, that's enough an even better than keep changing (always in adaptation period...).

 

[J_P]

@GeekyDeaks BTW, can you still use original cover with your design?

 

[deaduotja]

Would this of the shelve components work directly replacing poti? also inside the pedal!

Standalone Load Cell Amplifier : Leo Bodnar Electronics

Leo Bodnar Electronics Standalone Load Cell Amplifier - Standalone amplifier to connect load cells to any standard analogue input - Connect load cell to screw terminals - Connect the amplifier pins to a potentiometer (analogue) input of your controller - Works with any controller standard...

www.leobodnar.com

+

35.82€ 10% OFF|Micro Load Cell miniatuur load cell Gewicht Sensor Robotic Robot 5 KG 10 KG 20 kg 30 kg 50 kg 100 kg 200 kg 300 kg 500 kg 1 T 2 T 3 T 5 T|load cell weight|weight sensormicro load cell - AliExpress

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[cteters]

Would this of the shelve components work directly replacing poti? also inside the pedal!

Standalone Load Cell Amplifier : Leo Bodnar Electronics

Leo Bodnar Electronics Standalone Load Cell Amplifier - Standalone amplifier to connect load cells to any standard analogue input - Connect load cell to screw terminals - Connect the amplifier pins to a potentiometer (analogue) input of your controller - Works with any controller standard...

www.leobodnar.com

+

35.82€ 10% OFF|Micro Load Cell miniatuur load cell Gewicht Sensor Robotic Robot 5 KG 10 KG 20 kg 30 kg 50 kg 100 kg 200 kg 300 kg 500 kg 1 T 2 T 3 T 5 T|load cell weight|weight sensormicro load cell - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

nl.aliexpress.com

Yeah, that is essentially what the Ricmotech brake mod is, with the addition of a couple other components. I think people have done it, but it is not documented very well. Check the spoiler at the start of this thread for the details I've put together in regard to a mod like that.

It looks like you've found a reasonable load cell, but from what I'm reading, only models that are 300kg or higher have the desired diameter of a 26mm. Definitely overkill, possibly an issue. In my own experience, I came to a personal conclusion that the TrueBrake mod is a better investment of the time and trouble. If you do give it a shot however, be sure to share your work!

 

[Locoblade]

@GeekyDeaks BTW, can you still use original cover with your design?

Yep you can, at least I have on my G25 setup which I think uses the same mouldings etc.

 

[AccAkut]

It looks like you've found a reasonable load cell, but from what I'm reading, only models that are 300kg or higher have the desired diameter of a 26mm. Definitely overkill, possibly an issue.

probably an issue as with that high max weight I doubt it has the wanted accuracy down low. I use a ~50kg max loadcell in my converted G25 pedals

 

[Locoblade]

You could always sleeve the 50kg rated load cell to make it fit if it's a smaller diameter, find a bit of suitable tubing with ~20mm ID and 26mm OD or 3d print an adapter, or just go with GeekyDeak's design that uses a $2 load cell

 

[Locoblade]

Yeah, that is essentially what the Ricmotech brake mod is, with the addition of a couple other components. I think people have done it, but it is not documented very well.

I also documented my take on the GeekyDeaks mod using a LeoBodnar USB module on his Github page here https://github.com/GeekyDeaks/g29-load-cell/issues/1

 

[RustyNaki]

Hey guys, I'm currently working on this for my g920 pedals. I actually want to run them stand alone from the arduino With a load cell brake and existing pots for the throttle and clutch. @GeekyDeaks I have printed your double holder and set it up to fit my load cells and have it all wired up working and the arduino is reading it however I cant seem to get any sketch I can find to run it at all. I don't know arduino at all and have no idea what's not right. https://github.com/MauriceRowe/USB-Sim-Racing-Pedals-with-Load-Cell I have followed this but still can not pick up the load cell on my PC, the arduino appears as a controller but I don't get anything from the load cell. Any help would be awesome.

 

[GeekyDeaks]

Hi @RustyNaki - I had a quick look at the github project and it looks like it has all the right parts, so first I'd like to check how far you got.

have it all wired up working and the arduino is reading it however I cant seem to get any sketch I can find to run it at all

Does this mean you have verified that the HX711 is working and sending values to Arduino with your own sketch, but that you cannot get this part to work with a sketch that also exposes the pots for the accelerator and clutch?

 

[RustyNaki]

Hi @GeekyDeaks, Firstly thanks for the prompt reply.

Does this mean you have verified that the HX711 is working and sending values to Arduino with your own sketch, but that you cannot get this part to work with a sketch that also exposes the pots for the accelerator and clutch?

Yes I have confirmed that everything is working and I can get values from the load cells in serial monitor with an HX711 Example sketch. I must admit I haven't spent anytime researching writing my own sketch yet. I have tried a few other load cell as joystick sketches too and I'm not having much luck there either. I have confirmed button operation with the first sketch, will be connecting my pots today to see if that works too. Not really worried about the buttons and I do have the components on the way for the skidude88 mod and your mod for my son on PS4 but would prefer to go standalone Arduino to PC for my pedals if I can. Plan is to use the Logitech mechanics to get started while I build something or mod them for better feel, have 4 sets to play with lol.

I am about to start researching this more myself and any help would be appreciated. I'm fairly confident what I want to achieve is possible just got to work out how to code it. Looking forward to putting your mod together when everything arrives.

 

[GeekyDeaks]

Yes I have confirmed that everything is working and I can get values from the load cells in serial monitor with an HX711 Example sketch

Perfect! It sounds like you have everything you need and it's just a bit of tweaking of the code is required. I noticed that the github sketch you shared doesn't seem to define the pins the HX711 is going to use the same way skidude88 did is his project e.g:

brake_pedal.begin(LOADCELL_DOUT_PIN, LOADCELL_SCK_PIN);
brake_pedal.tare(BRAKE_PEDAL_LOAD_CELL_TARE_REPS);

I suspect the library may have changed the way it is initialised. Could you share the code you used to verify the HX711 was working so we can confirm?

I think you need to just change the line:

HX711 scale(0, 1);

To

HX711 scale();

and then add the .begin() somewhere in the setup() e.g.

scale.begin(0, 1);
scale.set_scale(-10000);

Just replace the 0 and 1 for the pins you are using for the DATA and CLOCK of the serial on the HX711

I'd personally also change the variable name `scale` to something like `brake` for clarity. Also note that skidude88 was using a 1:1 scale to get the raw value from the HX711, then manually calculating the value to send, whereas the sketch you provided is going to take the raw value and divide it by -10000. I'm not sure why you would want to make the value negative, so I can only assume the original author accidentally wired up the loadcell in reverse and decided to correct this by negating the value in the software.