Building a PC from all new components can be a serious headache if one of those components happens to be malfunctioning. Because none of the components have been proven, you don't know which component is causing the problem. Similar conundrums can occur when you develop new prototypes. Is the problem with a particular piece of hardware? Is the problem your circuit design? Is the problem your software? It is difficult to narrow down the problem and find the culprit. To at least ensure that his servo motors are good, DJ Harrigan used an Arduino to build this four-channel servo tester.
Harrigan likes to work on animatronics and those require a lot of servo motors. This device is useful for two reasons: it lets him test his servo motors to make sure they're functioning properly and it lets him control his animatronics before designing a dedicated controller. With this device, Harrigan can build the mechanical structure of an animatronic, mount the servo motors, and move up to four of them at a time. If everything works as intended, he can then start designing a dedicated controller for the animatronic’s servos. The device can handle up to four servo motors simultaneously and has dials for adjusting each servo's position.
There are thorough instructions on how you can build your own servo tester. The bill of materials (BoM) includes an Arduino Mega board, a 2.2" ILI9340C-based LCD screen, a 5V 10A power supply, four potentiometers, and two rotary encoders. Harrigan constructed the enclosure from laser-cut plywood panels and 3D-printed frames. The two rotary encoders let the user configure the range of each servo channel, the four potentiometers control each servo's current position, and the four push buttons activate or deactivate the corresponding servos. The code that Harrigan supplied handles all of the hard work of generating the pulses that servo motors understand.
If you work with servo motors often, this servo tester is well worth your time to build.