Trying to encourage your child’s tennis skills, but can’t serve to save your life? Daniel Bauen uses a pedal-powered ball launcher. From his site:

Both cleanly powered and built from 2 recycled bicycles, scrap steel and wood, leaking 5 gallon water jug and a lacross stick, our pedal powered tennis ball launcher is a unique innovate or die entry. It allows players varying in skill levels to practice to be better at both tennis and cycling. The launcher is towed to the court on its built-in bicycle trailer. A bike is secured to it and functions to drive the device. Pedaling the cycle as one would on a trainer drives the two launcher wheels. The cyclist then aims and pulls the lever to launch balls to the hitter.

Via HacknMod.