I coded a mod that lets you ride an in-game bike by pedaling with my fitness bike using an Arduino + jSerialComm. It reads speed data from the serial port and applies it to the Minecraft bicycle. It’s a bit rough since I originally built it for personal use, but hey, here we are.
Right now, I can’t test the fitness bike integration because I accidentally fried the voltage regulator on my Arduino Uno (RIP), but the mod still works as a regular bicycle mod on its own.
It’s not super optimized, and the code is messy since it’s my first mod, but it works. I made the model in Blockbench and used Geckolib to animate it, though the implementation is a bit hacky.