We’ve seen all sorts of Pi-powered robots in our time, but the Discoverer is the first with a built-in metal detector. Mounted on a PVC pipe arm in front of the four-wheeled robot, the detector emits a beep whenever it passes over a metallic object. Prolific robot maker Ingmar Stapel, from Munich, came up with the idea after watching a TV show about people trying to find gold with a sophisticated metal detector. “I was immediately inspired to build my own affordable robot-car with a metal detector in order to discover some treasure in my garden,” he tells us.
The full article can be found in The MagPi 48 and was written by Phil King
The basis for the new robot was his previous cardboard car, which required some major adaptations. “First, I had to look for a different chassis that is also suitable for outdoor usage. Second, I needed a metal detector that fits to the robot-car and the Raspberry Pi to ensure remote-controlled treasure hunting.”
For the chassis, he used a plastic storage box to contain all the electronics, adding PVC piping around the exterior to hold a pan-and-tilt camera and the metal detector. At first, Ingmar tried using a cheap electric-cable detector from a DIY store, but its coil was too small to detect metal in the ground. He then came across the Gary’s Pulse-AV metal detector. “With support from Gary, I was able connect the metal detector to the Raspberry Pi and to get everything working.” This involved using a step-down converter to change the detector’s 12V output to 3.3V for a GPIO pin on the Pi.
As Ingmar wanted the Discoverer to stream live video to a laptop, it would need a camera. After mounting a Pi Camera Module on the front of the chassis, he found the angle of view was too limited. “I bought the pan-and-tilt kit and mounted it in the middle of the robot and I got a much better overview.” Some trial and error was involved in getting the live video streaming to work with very low latency, since even the tiniest delay would make remote control difficult. In the end, he used MJPG-streamer with some patches to get it to run on the Pi 3: “The video is very fast with a very low latency… it is even possible to make some robot-car races in our apartment.”
While originally just remote-controlled, the Discoverer is now able to move autonomously using a GPS receiver, Sense HAT (for the compass), and a Python program Ingmar had already developed. “It is still in a beta version, but it is already able to import a KML file with GPS waypoints generated via Google Earth. Imported into my Python program, the robot-car is able to drive from one GPS waypoint to the next.” When it’s finalised, he plans to include a manual in his first book, due to be published (in German) this autumn. While the Discoverer is mainly for fun treasure hunting, Ingmar thinks it could also have some serious applications, such as detecting mines in war zones.
