Bucky's jaw is held in place by a pair of springs. We need to install a permanent pivot for the jaw and also eliminate the springs because they are too much mechanical resistance for the servo. We'll use the cable ties as our pivot.
Using a drill bit the same size as the cable tie, drill a hole through the jaw and into the skull as shown right. Drill a second hole into just the skull, to the rear of the jaw bone as shown far right.
Insert the cable tie from the inside of the skull down into the jaw bone, loop it back inside the skull through the second hole (right) and fasten it inside the skull. In fastening the cable tie, tighten it just enough so the jaw won't flap around but still has freedom to move.
Repeat the same for the other side of the jaw then remove the springs and all associated hardware.
|The next step is to drill a hole in the skull that will allow us to connect the servo to the jaw using a piece of the music wire. The wire will run from the front of the servo horn (left) to the hole in the left side of the jaw where the spring was originally mounted (right).
|While holding the servo in place, make a mark on the skull in line with the two points described above (left). Drill a 1/4" hole in the skull at this mark. If you were really good (lucky?), the hole will line up perfectly between the two points, if not, you'll have to "modify" the hole slightly to be in line.
|Next, using a pair of long nose pliers, create an offset bend, as shown left, in one end of a 6" piece of the music wire. Attach it to the outer hole in the servo horn as shown right.
Feed the wire through the hole and install the servo in the bracket using the #4/40 screws and nuts. I find that using just two screws will hold it securely in place.
In preparation for the next step, position the servo horn as shown right.
|With the servo horn in the position shown above and the jaw fully closed, bend the music wire at the point adjacent to the hole in the jaw (left). Complete the installation by inserting the wire in the jaw hole, bending it upward and trimming it off as shown right.
|At some point, you're probably going to need to adjust the position of the servo horn on the servo. I recommend drilling a small hole in the side of the skull, as shown left, to accommodate a small phillips screwdriver. Be careful when drilling the hole so as not to slip and drill out the center core of the servo (please don't ask me how I know about this).
There are several ways to drive the servo. I've developed a circuit to drive it with a audio source. Click here for details.
|last update 11/2019