This is a list of the parts that you will need to complete this project. Most of them will be available at either a local electronic components store or an online retailer:
The Raspberry Pi
A 3 mm MDF (600 x 600 mm)
M3 and M4 screws, washers, and nuts
The M3 threaded bar
4x micro servos (www.amazon.co.uk/Vktech-MG90S-Geared-Helicopter-Airplane/dp/B00FF26480)
Servo extension cables (www.amazon.co.uk/300mm-Servo-Extension-Cable-Futaba/dp/B009REWWGU)
A relay board (www.ebay.co.uk/itm/New-8-Channel-5V-Relay-Module-Board-for-Arduino-PIC-AVR-MCU-DSP-ARM-UK-/151105724470)
Geared motors (www.rapidonline.com/Electrical-Power/950d5001-Gearbox-and-Motor-500-1-6mm-Shaft-6-15v-37-1114)
0.1 inch pin headers
0.1 inch female-to-female pin jumper wires
0.1 inch male-to-female pin jumper wires
A 18 AWG wire
Thick copper wire (www.clasohlson.com/uk/Copper-Wire-1.2-mm/30-5028)
A small section of a prototyping board (www.maplin.co.uk/p/veroboard-copper-stripboard-100x160mm-a62rl)
A 9 V battery
A 9 V battery...