The Graffiti Drone is a truly unique project by Tsuru Robotics, implemented in association with Interactive Lab. It was the world's first painter drone, with complete automatic control. Misha Most, the artist, drew on a computer - that prefigured drone's trajectory. After that, the drone painted the surfaces with spray paint.
In the last publication, we explained certain technical aspects of graffiti drone. This time we’ll talk about electronics.
The unique real-time location system was specifically designed for this project, with the help of which, the drone moved with incredible precision - up to 0,19 inches.
Cameras monitored machine's movement through LED markers that were fastened to it and transmitted the data on drone's location to our server.
The special software was written - a path planner, based on the Unity3D engine - software that programs, simulates, and then tells the drone where it is supposed to be at the given moment.
The server combined two types of data and transmitted it to drone. Then the drone would calculate the specific actions it would have to take to move to the designated spot. To transmit the data on the drone, we used a specific radio channel. A special circuit board was developed, that combined two radio modules: a standard WiFi and the other - that operated on the same frequency and ensured that the data for the real-time locating went uninterrupted.
Why not transmit the data via the regular WIFI? It doesn’t work that way – regular WIFI would cause arbitrary delays, which are unacceptable. We use regular WIFI to transmit the telemetry, where delays are not crucial.
So, the drone had received the data from the server. The word received, however, does not accurately reflect what happens. The data are sent to the drone 60 times per second – that’s why the delays are unacceptable. There’s a microcomputer on the drone, it’s called an autopilot, and it has a software, which, among other things, controls the drone automatically.
How does the control system operate? We should say up front, that even receiving external data 60 times per second - isn’t quite enough for it! To operate efficiently it needs more data, and it needs it more often. Luckily the system collects the data on its own, using the onboard sensors like –a gyroscope, a compass, an accelerometer (measures acceleration), and a pressure sensor (measures altitude). It collects the data 1000 times per second.
Having received the information from the sensors, the microcomputer combines it with the data from the server and determines its own location. It does that 1000 times per second!
But why isn’t it enough to have just one external real-time location system? The explanation comes from the American movies. Let’s imagine the police officer pulls you over, assuming that you are drunk. He then asks you to walk a straight line. You can see the line (the real-time location system works), but you keep staggering (the alcohol impairs your vestibular system) The outcome – you’ve been busted. Well, the onboard sensors are the vestibular system of the drone. You can imagine, by analogy, what would happen if these sensors were absent.
But let us come back to our “sober” drone. The software reconciles the current and the target position and then issues the command to the engines to move to the designated spot. Of course, it’s not that easy. Because in order to move from point A to point B, the drone has to perform a massive number of coordinated actions – to lean, to hit the gas, to move (while keeping the altitude), to hit the brakes without reaching the point, and to stop precisely at the point B. With all that, the software issues the commands 400 times per second.
And so, moving from point A to point B, the graffiti drone paints picture by picture. It paints completely on its own.