Carmack wrote the lens distortion shaders and found a software hack in the gyros/accelerometers to get it running at a higher hz and did his own filtering of the raw data from the sensors based on his experience building autostabilizing rocket ships.

The devkit ended up using better sensors etc. , but both Luckey and Carmack were important in making the initial unit that was in the E3 demo that helped build confidence for the kickstarter.