The brains of the project is the raspberry pi zero, £5 from official supplies like pihut or pimeroni and from eBay for £20+
Also required is a power supply £6, hdmi cable and adapter £7, usb snes controller £6 and a micro sd memory card £8.
Step 1: R2D2 Preparation
First thing to do is strip poor old R2 down! A twist of head and a few screws and R2 is in pieces.
Step 2: Confirm Polarity of the Switch
Before connecting the micro usb connector for the pi I need to find the polarity of the cables. With the power connected and the pish button on, I use my multimeter on the lowest volt setting and attach the motor wires. It shows approx 5 volts, as expected as it's usb powered. The way to determine which cable is the 5v and which is the ground is easy, if the multimeter shows a negative value then the probes are reversed so switch 'em round and it will show +5v. When it shows a positive value then the ground probe is on the ground wire and the live probe is on the live wire, simple! Take a look at the photos too.
Attach the micro usb connector to the correct wire - the live wire on the usb is red and the black one is the ground, the other cables you can cut back and ignore them.
R2 has a push switch and led indicator and this way I managed to use them with the pi. Push to turn on and the led lights up to say it's on.
Step 3: Add Your Pi Filling
I used a suitable width drill to drill a series of holes and then filed them through to make the 3 port holes. I decided against using my rotary cutter as the required holes were a little too small and too close together.
With the holes made and the pi in position I put a small screw through one corner hole of the pi through the centre leg to hold it in position and to give it some rigidity when plugging the cables in. The pi was further secured by some good old hot glue!
The power cable is fed from the inside through a small pot on R2s head and then plugged into the lower usb connector on the Pi.
A quick test to make sure it's all ok then I rebuild the case around the pi. Some parts on the case needed to be trimmed so the pi sits where I wanted it too.
With the pi in this position I can easily pop the lid off and replace the sd as and when I need to, one day a retro games machine and the next day a media player!
Pop the lid back on and it's done!!
I used a little Sugru around the drilled holes to tidy them up and make them look pretty - see photos!
Step 4: Software
Download the image here - https://github.com/RetroPie/RetroPie-Setup/wiki
Step 5: Playtime!
At the moment it's a single player machine bit with the addition of a USB hub and an extra controller you'll be playing Mario karts with a mate in no time! I would use a powered hub to be sure there is enough juice to power everything.
Have fun and I hope to see your Instructibles soon :-)