I designed and programmed my first robot for solving a 3 × 3 Rubik's Cube in the summer of 2007. It used just two light sensors to scan the cube's colours, then calculated a solution of 50 moves or fewer directly on the NXT brick. The complete process took almost ten minutes for a thoroughly scrambled cube.
The main challenge was achieving reliable colour detection, as changes in lighting strongly affected the sensor readings.
My robot was one of the first LEGO robots capable of solving a 3 × 3 Rubik's Cube.
In 2010, I redesigned the robot, retaining the same basic mechanism: one motor flipped the cube in quarter-turns, while another positioned and gripped it.
I used an Android phone's camera to photograph each face of the cube, then applied image filtering algorithms to identify the colours. With the phone's greater processing power, the two-phase algorithm found a 20-move solution in less than five seconds on a Google Nexus phone.