Flying a kite can be fun, but what’s not fun is trying to wrap hundreds of feed of string onto a spool when you’re done. In order to avoid this annoyance, Matt Bilsky designed his own “Automatic Kite String Reeler-Inner” to do it for him. The design is something of a remake of a device he made when he was 8 years old. While that one never really worked as he’d hoped, with new engineering and design techniques learned in the next 20 or so years, he’s revisited the project, making something that appears to works quite well.
His new build consists of mostly 3D-printed parts, and uses a motor from a standard portable power drill to reel in the string. This gives it enough torque and speed for the job, and allows him to use off-the-shelf rechargeable batteries for power. He even embedded a pair of USB ports, as well as a 12VDC socket in the rig, enabling it to also charge phones or even as a power source to blow up inflatable beach toys as needed.
Mechanically, the project is quite clever, and features a rotary cam system to pull the string back and forth in order to balance how its winding. He even made the device in such a way that the spool can be used independently and placed in the winder when needed — potentially useful when flying multiple kites. The device is demonstrated in the first video below, and more info on the design and build process is seen in the second.