How do I implement my own local planner?

I want to implement my own local planner that adheres to base_local_planner for use with move_base. I need to make a planner that does not allow for rotation in place (car-like steering). I have tried going through all the documentation and reading the source on Github, but it's a bit overwhelming. Can anyone point to kind of a minimal example that would adhere to the interface, or maybe give some points on how I could modify either base_local_planner or dwa_local_planner to fit my needs? Thanks in advance.