IMPORTANT: Since this one servo can only swing on one axis, you might want to choose an axis that will let the eye appear to swivel slightly up and down as well as side to side, to add crazy. Use bluetack or doublesided tape to hold the eyeball on the servo temporarily to get an idea of how it will look.

If you have it right, the servo will swivel about your chosen centerline of the base nicely from 0º to around 90º or more without hitting the sides. The splines on the shaft only give you so many choices, but it should be possible to get close. Twist the servo to see where 0º is and if its not quite right facing at the right direction, unscrew the shaft screw and put it back on the arm at a new angle. That way when it swings from 0º to 90º the eye will appear to go fully from left to right. You will need to set it up so the servo body is sitting nice and flat relative to the base when it is internally at around 45º. You might need to get a longer screw for the shaft. Then drill two holes in the base, one dead center that will take a screw that goes right down the shaft of the servo, and another a few millimetres to the side for the screw that goes in the shortened servo arm. To mount it, take one of the normal servo arms and shorten it a bit, but leave enough so that you can still screw one screw into it. The resulting mutant servo works the same, but is now small enough to mount in the center line of the plastic base and still be able to swivel free. They screws will have to cut their way deeper into the top of the case, and eventually might come right out the top. I removed the bottom part of the case then re-screwed the 4 mounting screws back into the two remaining parts of the case. This servo is in a three part plastic case held together with 4 thin screws. The Servo barely fits, in fact I had to modify mine.

I mean, it will anyway, but we don't want it jab TOO much. IMPORTANT: The minimum height on the smallest side when the two are stacked together needs to be about 23-25mm, there needs to be enough depth for the servo and most of the eyeball to go inside, so any less and the servo is gonna jab into your eye as it swivels. Don't glue anything yet, just make the two parts and check they sit well together. To get the fit right, stick it in your eye socket, then cut a bit off, rinse, repeat until it seems right. You need this piece to conform to your eye socket fairly well and not end up sticking out at a weird angle, so it needs to be about 10-12mm taller on one side. The plastic lid is easy to drill and file and cut with the Xacto knife or even sturdy scissors, but it's also surprisingly easy to crack. You want about a 5-6mm ring left at the end. If your jar lid has a nice existing indentation like mine did, it makes sense to extend the hole out to that, as the indentation adds strength. This took a while for me, my files were too small and I quickly learnt the thin metal wants to buckle, so use even strokes in the same direction, and remove the burr as you go. The jar lid is likely to be a) not really brass, so the finish scratches easily b) really thin so it's hard to drill and file, but with a bit of diligent work you should be able to drill successively bigger holes in it then finish the job with the half round files. I found a nice brass lid on a jar at a craft shop which was 42mm wide, and a deodorant bottle lid turned out to be very similar, though slightly tapered. The lids need to be pretty much the same diameter as each other, and they can't really be much smaller than 42mm or the servo won't fit inside. Blue Tack for temporary holding of things.Paint - Acrylic Model paint works well - Brassy Gold, Dark Brown, Pale Grey.Epoxy (‘Fast Cure’ or ‘5-Minute’ is preferred).1-2 meters thin brown hookup wire or thin twin core bell wire.Assorted crusty old-school slotted screws.

A watch strap or similar sized buckle for the strap, or some velco if the back will be hidden.

Some flexible leather for the strap, but not too soft if you plan to use a buckle.

3 x AAA Batteries (better get more, they only last about 1-2 hours).

1 x Micro servo 9g TowerPro MG90 Servo or similar (smaller is better).

1 x flat plastic lid like the top of an ice cream or yoghurt container.

1 x tall plastic lid about 40mm wide by 30mm tall (e.g deodorant bottle top).

1 x large bright blue semi circular dolls eye - 26 - 30mm.

1 x nice shiney brass bottle/jar lid about 40-45mm wide.

Cutting plastic eyeballs