Step 19 Build x2
Note: This step uses thinner 2mm bolts and nuts to attach the servo to the head, the same as you used in Step 12 for the Arm servos. Also, the Left Eye is attached to the head through a Servo using a Servo Horn Screw – the one which has a pointy end.
First take two thin (M2x10mm) bolts and poke them through the holes to either side of Marty’s left eye hole. Grab an Arm/Eye Servo and screw it into place using the small nuts and the bolts you just inserted.
The initial angle of Marty’s eyebrows is important, this step should be followed carefully to give Marty the maximum range of expression (view video above or diagram below for more detail).
With the servo secured, take an Arm/Eye Servo Horn like the one in the picture and attach it to the face in the orientation shown in the pic. It’ll fit snugly on the servo spline. Take the Left Eye and put it over the servo horn, making sure the two eyes line up so both eyebrows are flat. Use a Servo Horn Screw (pointy) screw to secure the Left Eye to the servo.