How a simple stick figure became a Monkey in Motion
When designing an automaton, we decide what kind of character will fit with the movement; a frenzied motion suits an intense-looking character, while a slow and graceful motion is appropriate for an elegant figure. This particular hand-crank mechanism creates a happy and playful movement – a monkey seemed the perfect choice.
A basic stick figure armature was made with springs in the neck and torso. The arms were loosely jointed with the hands attached to the legs so they followed the up-and-down motion of the legs. The balance and movement of the springs seemed relatively natural as it eased in and eased out of the motion on its own.
This prototype Automaton originally seemed very simple but became more complicated with the added weight of solid resin head, hands and feet. Although the parts seemed relatively light, they made the armature droop and hard to move. Extra counterbalancing springs were needed to bring it back into balance. Since this is a working prototype, the parts are made of scraps of wood and other materials on hand; everything is light duty and not meant to last but only to see if the design will work.
The controller designed for this Automaton prototype is a stacked crankshaft, chosen for mechanical flexibility (varying speed and direction). To test the mechanism integrity, all the holes are roughly eyeballed and glued together. This showed promise, so the next step was to machine the parts with precise measurements and use more robust materials. My desktop machine shop enables me to make parts, which are accurate within tolerances of a thousandth of an inch. This includes a miniature Unimat lathe, Sherline CNC-Ready milling machine; cut off saw, scrollsaw, jewelers drill press, and all the cutting tools that complete the set up.
To make the crankshaft strong and accurate, the discs are center drilled using a miniature lathe — this hole becomes the reference point for the other disc measurements. I originally thought the crankshaft would not require this degree of accuracy, but the holes that link the parts required techniques used in gear cutting. The machine tools have digital readouts so accuracy is assured if the piece is set up and clamped carefully. A keypad is used to advance the discs to the keyed in position. The parts can be drilled safely using tools like this because all setups are done without the cutting bits in motion.
The next stage is silver soldering the discs to create a concentric crankshaft that will not wobble and wear out the bearings. Another disc is used as a handle and the finished controller is polished. This type of controller will enable the mechanism to be cranked in either forward or reverse, and at varying speed.