https://www.instructables.com/GoBabyGo-Make-a-Joystick-controlled-Ride-on-Car/
The link above is currently out of date. Temporary link to updated/work in progress instructions: https://docs.google.com/document/d/1RHVrAkWGEfjWRzHnMl1gdjrIjJXBr14pojtLxGjQ4Rc/edit?usp=sharing
https://docs.google.com/drawings/d/1BKDrhKLFc0Y3o9NzUfYC5lIbI_fWCTx9kLZsG5Ts-0o/view
web programmer: https://gobabygocarswithjoysticks.github.io/programmer/
old code: https://github.com/gobabygocarswithjoysticks/classic
Onshape (make a copy of the model to make custom sizes!)
This webpage is on github here: https://github.com/gobabygocarswithjoysticks/index