Quantity   Component name
2 × hard bases (can be a tupperware / lunchbox)
1 × threaded rod of 8mm with 2 washers and nut's
4 × bolts of 4mm with 3 washers and 2 nuts each
4 × Rubber bands (min 4)
1 × Wires and something to detect the movement (a metal piece, endstops or distance sensor, whatever you want)