September 20, 2025
Description
This is a basic set of 3D printed sim racing pedals using hall sensors for accelerator and clutch, and a load cell for the brake. I've used all three pedals for ~1 month, daily, as of the original posting. This is designed as an all-round improvement over my V1 pedals, but uses different hardware (loadcell, m6 instead of m8, etc).
Assembly notes, pictures, STL+STEP files, code, KiCAD, and PCB gerbers are in the FreeSim-Pedals-V2.zip file.
I've only tested PETG, but I believe ABS and PLA should work.
Parts will print fine at 0.2mm or 0.3mm layer heights - the Brake-LoadcellAnchor part benefits from 0.2 as it has a significant number of overhangs compared to other parts.Â
Depending on your printer's bridging ability, the mounting slots on the Sideplate-BaseA/B may need support. Brake-LoadcellAnchor may also benefit from supports as the main slot for the loadcell is quite a long bridge.
6 perimeters (at least) and 95-99% rectilinear infill for the Sideplate-CarrierA-Brake, Sideplate-CarrierB-Brake, and Brake-LoadcellAnchor parts (these take the vast majority of the loads).
6 perimeters and 20% infill for other pieces.
The primary spring I used for the clutch and throttle and half of the brake are sourced from McMaster-Carr in a 5 pack, and all 5 are used - 9434K147, OD 0.72", Length 1.25", Wire diameter 0.072". Alternative springs are (heavier, 0.085" wire) 9657K341 or (lighter, 0.063" wire) 9434K141 . The brake additionally uses a yellow die spring (10mm ID, 18mm OD, 30mm length) from your choice of import vendor.
The springs on the brake are about as stiff as I think the PETG parts I use can handle, but the accelerator spring will probably be a bit light by the standards of sim racers - I based my spring selection to give a similar throttle and brake feel to my street car.
The main pedal pivot bearings work fine with the M5x70 bolts, but there is a slight wiggle since the major diameter of threads are slightly under nominal size. The M5x70 on each pedal can be swapped out for precision ground rod that you cut to length and thread on each end for a nut - this basically eliminates wiggle. The BOM calls for 6mm diameter shoulder bolts for the spring/pedalarm attachment, but you could also use an M6 bolt if you are willing to deal with the extra wiggle.
I used some o-rings I had around the house to put under the head of the M6x90 bolt that runs through the center of the spring arm to dampen the clack from letting off the pedals. This isn't spec'd in the BOM, but makes them a little friendlier to housemates. I also put a bit of plastic-safe lubricant on the spring arm bolt where it passes through the plastic to avoid squeaking.
The software is a quick and dirty hack for a SparkFun Pro Micro (and should work on other 32u4 based boards) that I intended to replace, but so far it works well enough that I haven't bothered. A short press of the button initiates a 10 second calibration sequence, where you should move the accelerator through it's full range of motion and push the brake to a comfortable 80% (BRAKE_CALIBRATION_POINT as float) feel. After calibration, the firmware lops off the bottom and top 3% (DEADZONE_PERCENTAGE as float) and adds the extra 20% brake to the range, and saves to eeprom. A long press of the button resets the eeprom in case there's something stored that's causing an issue, though I've never had to use that over just recalibrating. The brake has a specific DEADZONE_PERCENTAGE_BRK that sets the % of the lower deadzone on the brake, to allow for resting your foot on the brake without engaging. Note that this is very very similar to the V1 pedals and can run the V1 pedals, but has different pinouts.
There are debugMode and debugSpam constants for getting serial output of what's going on under the hood if needed.
Pin defines are in the code/data.h header file, and gerbers are included for an adapter PCB that has sockets for the Pro Micro, the HX711 loadcell amp, and either RJ11 connectors or JXT-XH 2.5mm pitch connectors to your preference. The JST-XH footprints are also close enough in pitch to use 0.1" headers as well.
Additional details can be found in the Assembly Notes folder, including pictures of sub-assemblies.
License:
Creative Commons — Attribution
Andrew B
