Tennis and badminton racquets look pretty simple; just string woven around a hoop like a basket, right? But those strings are under massive tension, which is necessary to get good rebound on the ball or shuttlecock. Maintaining string tension while weaving the string usually requires a big and expensive machine. But the DIY KhordUino is both compact and affordable, making it realistic for hobbyists and even small businesses to string badminton racquets on a budget.
The KhordUino is a designed specifically for stringing badminton racquets, though the process seems fairly similar for tennis racquets. Antoine Colin took care to make the machine as flat as possible for easy storage and it uses mostly 3D-printed parts, keeping the cost down. That is possible because Colin put the tensioning mechanism inline with the clamps that hold the hoop in place. This directs all the stress along the long axis of the machine, which is a compression force that the 3D-printed frame and clamps can handle.
An Arduino Nano board tensions the string using a stepper motor that drives a lead screw. That provides a lot of torque to get very tight strings. To keep it from breaking strings or the machine itself, the Arduino monitors a load cell from a luggage scale through an HX711 amplifier. The user can set the tension to apply, then press a button to start the mechanism. It will pull the string taught, then the user can clamp it in place, loop it around, and repeat.
If you want to string your own badminton racquets, then the KhordUino would be very helpful.