My DIY Load Cell mod for T3PA Pro

Discussion in 'Sim Racing Hardware' started by Roots57, May 22, 2019.

  1. Roots57


    I designed and made this load cell mod for my T3PA Pro pedals and it is terrific, the throw distance and progression feels just like a real brake pedal and is fully adjustable. I basically borrowed the design from the Fanatec CSL LC brake pedal then took it a step further. It probably cost me about $150 including the load cell. I started off buying the Ricmotech load cell mod kit and it worked really well. The only thing that I wasn't quite happy with was the throw distance and progression feel. I really wanted the feeling and throw of a real brake pedal so I went to work designing my own. I ended up finding the exact same load cell that the Ricmotech kit comes with for $40 from Arrow Electronics, the rest of the materials I bought from McMaster Carr and Century Spring. The good thing about this particular load cell is that it is direct plug and play with the T3PA Pro pedals wiring without needing a special PCB, amplifier, or any other electronics. I am a mechanical design engineer with almost 20 years of design and CAD experience so this was fairly easy for me. I am happy to share the design with anyone who wants it. My description of a real brake pedal feel is that you have a bit of easy initial travel with little to no actual braking force, then it begins to rapidly stiffen up while the braking progression curve goes up exponentially. This allows for really precise modulation and allows way better control compared to POT based sim braking. I have recently been playing Dirt Rally 2.0 (love this game) and basically used this game to fine tune the pedal feel and it made all the difference in the world. I now have perfect control of the car and can throw it into corners and change direction on a dime with super precise braking. I don't know how I survived with a POT based brake pedal before this. Initially, I simply planned to more or less copy the design of the Fanatec CSL LC brake pedal by allowing for a number of different combinations of urethane springs to be placed over a central post. I bought urethane compression springs in 45, 65, 85, and 95 durometer and solid washers to separate each one in the stack, which is very similar to the Fanatec design. When I first finished my DIY version, I was happy with how adjustable it was, but in order to get the right feel, you need to use at least one really soft spring to simulate the very light initial throw/feel of a real brake pedal. I also added a ¼” thick urethane foam bushing to the stack that helps with the initial low force throw distance. The problem is that the 45 duro spring is too soft to then provide that sharp increase to a harder feel where the majority of the brake modulation lies. It just continues to squish down and expand outward with increased force. To correct this, I placed a small section of solid plastic tubing over ONLY the soft 45 duro spring. This section of tubing has an inside diameter a little larger than the outside diameter of the uncompressed spring. This allows the spring to be compressed, but only to the point that it fills up the inside of the tube, at that point it is essentially solid and the next spring (65 duro) in the stack is the one that is felt when pressing harder. For me the 65 duro was the perfect feel for that sweet spot of modulation control, anything over that is pretty much solid. I am still amazed at how good this thing feels. Take a look at the CAD model renderings and pics of the final outcome. If anyone wants to know more or see a video of it working, let me know.

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  2. Daz555


    Great info but perhaps you can do something with the wall of text.