So you enjoy drone racing indoors and outside? With these 3D printed interactive air gates, you can take your racing skills to the next level. The gate has a light that turns from red to green when the ultrasonic sensor detects your drone getting closer.
You are going to need a HC-SR04 ultrasonic sensor, SparkFun Arduino Pro Mini 328, 9V battery, and a few other simple components to complete this. More info is available here.