Rotorama Laptimer measures drone race laps based on sound level and frequency.
Put your phone close to the place where you have start/finish of the track.
Set the trigger volume to appropriate level. Default value should work for most cases. If the device doesnt record laps, set the trigger volume lower. If the device triggers new laps even when not flying through the finish gate, set the trigger volume higher. Current volume and maximum recorded volume infobox can also help while finding a good trigger volume.
You are ready. Every lap is recorded and current laptime is spoken to you. Use bluetooth speaker placed close to you to hear the time well. Dont forget to raise the volume.
Suitable for one pilot flying at a time.