Drone racing is nifty as heck, and a need all races share is a way to track lap times. One way to do it is to use transponders attached to each racer, and use a receiver unit of some kind to clock them as they pass by. People have rolled their own transponder designs with some success, but the next step is ditching add-on transponders entirely, and that’s exactly what the Delta 5 Race Timer project does.
A sample Delta 5 Race Timer build (Source: ET Heli)
The open-sourced design has a clever approach. In drone racing, each aircraft is remotely piloted over a wireless video link