We built 2 small cars which used Bluetooth Received Signal Strength Indicator (RSSI) measurements to navigate towards a stationary base station. The cars and base station used a Bluetooth Low Energy (BLE) 4.0 module to take the measurements and a PIC32MX250 microcontroller. The cars also used a 3 axis magnetometer as as compass in order to reliably turn, as well as 2 micro 9 g servos to drive. Each unit was powered with 3 AA batteries. Finally, the chassis and wheels of each car were 3D printed.
The robots are made from 4 3D printed pieces: 2 wheels, the frame, and the caster in the back. The servos, a 3 AA battery holder, and a perfboard containing all the circuitry are mounted directly to the frame.
The robots where designed in OpenSCAD, and their source code is available in our git repository and below. There are three files,
wheel.scad, for each of the three parts. The main modules are defined in
main.scad, and the other files just instantiate them. The following renderings show each part:
The parts were printed in ABS using Maker Select 3D Printer v2 printers. All parts were printed with a layer height of 0.3 mm, as there was no need for a smooth finish or high tolerances. The parts where sliced with Cura.
Full system (base station and 2 robots):
Multiple views of the robots: