My first idea was using lasers, one LDR sensor and mirrors. But the mirrors were absorbing the light from ther lasers too much. So at the end of the beam, the LDR wasn't receiving any more light. So I had to change my idea. We need a series of around 7 LDRs connected to a comparator module. THis will give a HIGH oir LOW output to the Arduino. We need the lasers, the 3D printed files, a battery and a charger and wires. We also need a 7 segment display to show the speed. Check the list below.