Prepare the line follower PCB, the 4 M3x6mm screws, the 2 M3 25mm pillars, the ball caster
and the 6-pin female header
Screw the 25mm pillars into the main PCB using 2 of the 6mm M3 screws
Push the female header onto the male header on the line follower board, then push the
completed assembly into the female header on the underside of the main PCB. The holes in
the line-follower PCB should then line up with the pillars and the line follower board should
lie flush with the top of the pillars