Introduction: Slithering Snake Automaton
I thought it would be fun to make a simple mechanical automaton imitating the slithering movement of a snake.
So I started with a Fusion 360 model in order to design the automaton, visualize the snake movement, and figure out dimensions. The model is shown above, including three animations. With one model parameter I can change the camshaft design to simulate variations from a slow sinuous movement to a much faster one. The three animations above are for a camshaft twist angle of 15°, 30°, and 60°. My build uses a 20° angle.
You don’t need the Fusion 360 model for the build.
The automaton is basically a box with camshaft and crank, and a steel rod to serve as a pivot axis for 16 levers that rest against the camshaft. The levers swivel back and forth when the camshaft turns. The 16 levers are decorated at the top to look like a stylized snake. The movement is wavelike (sinuous) and looks quite elegant.
Supplies
Hardwood, 1/2 inch and 3/8 inch thick for the box and the camshaft
1/4 inch diameter oak dowel, about 15 inches long
1/8 inch diameter steel rod, about 12 inches long
Wood screws, washers, and glue
Table saw, drill press, band saw or scroll saw
Step 1: Build the Frame
For the frame of the automaton you build a U-shaped 'box' like shown in the pictures and drawings. The two ends will have a 1/8” and 1/4” hole in the locations shown. Do not glue the frame at this time, just use wood screws. You will need to disassemble at least one side later on to install the camshaft pieces.
Next you build the crank and glue it onto the 1/4” dowel.* I used a 3/8” wide oak spacer to give some clearance between the crank and the box side. Insert the dowel/crank into the box and try it out. The crank should clear the bottom of the box while you turn it.
*If I did it again I would build the camshaft on the 1/4" dowel first and attach the crank later after assembling the box.
Attachments
Step 2: Camshaft
For the camshaft you need 16 wooden disks with an off-center hole. I made the disks with a 1-1/2” hole saw bit in my drill press and a 1/2” thick board. Be sure to remove the centering drill bit, you don’t want that hole! Clean the disks by sanding and removing any rough edges.
To drill the off-center holes (1/4” dia) I clamped a right angle stop to the drill press table. Also, I made a pencil mark on the table so I could make a reference mark on each disk before drilling the hole. This mark will be important later on when you assemble the disks onto a camshaft dowel.
Next you need to make a second mark on each disk to set the angle by which the camshaft should twist. An angle of 20 degrees from disk to disk gives a smooth looking movement. You could go with higher angles to produce a faster or more ‘energetic’ movement along the snake as shown in the animations in the introduction. Use the angle template to mark each of the 16 disks. Center a disk on the template, line up the original reference at 0 degrees, and make the second mark at your chosen angle. The template has lines at 5 degree increments, starting at 15 degrees. You don’t have to be super accurate with your marks!
I had to slightly enlarge the 1/4" holes in the disks by sanding so that they would fit onto the dowel. You want a snug fit, but you need to be able to slip them into position and turn them to the right angle before glueing.
Glue all 16 disks to the dowel and to each other to complete building the camshaft. Pay attention to the angle markings and twist each disk before gluing it to the prior disk.
Step 3: Levers
The 16 levers are cut from a 1/2” wide board that is 1/4” thick. Each lever is 5 inches long. I used a right angle stop on the drill press to cut a 1/8” hole 2” from the top. You may have to enlarge these holes slightly so that the lever will easily swivel on the steel rod. Put a few of the levers on the steel rod and try them out on the box and camshaft. I used six #6 washers between the levers. Each lever should rest on the center of one of the camshaft disks. Run a test of the full assembly like I did to see if you need to make any adjustments. I needed to round off the bottom of the levers by a little bit.
Step 4: The Snake
To make the automaton interesting I added a stylized snake body to the top of the levers. The snake segments were cut from a 1-1/4" poplar dowel and are 0.4" thick. Before I cut the segments I cut 1/8" off the dowel to create a flat side along the dowel. I then cut a shallow groove into each segment and glued it to the levers. This was probably more complicated than it needed to be. If I were to do this again I would cut the lever/snake segments with a scroll saw or laser cutter as one piece (looking like a lollipop).
So now when you put the lever/snake segment onto the steel rod you have a problem: it is top heavy. We need to add some weight to the bottom. Two 1/4" washers fixed with CA glue to the lower end of the lever will do the trick! Remember that the mechanism relies on gravity!
Now is a good time to run another test of the mechanism. Looks good so far, see the last animation above.
Step 5: Snake Head
I found a drawing of a snake head that would give a nice finish to the automaton. I cut this out from a 3/8" thick piece of maple and smoothed and rounded the edges. A dado was cut along the neck to strengthen the glue joint. I also cut the lever at an angle to tilt the snake head, it looks better that way. The snake head was glued to the lever and the joint was further strengthened with a small piece of wood. Finally I had to add some extra weights to the lever/snake head; it took five washers.
Step 6: Assembly
To complete the automaton box and make it stronger I put in a side wall and a partial top/side cover as shown in the pictures. Feel free to design your own. I think it interesting to see the mechanism inside, so I did not attempt to enclose the entire box.
Now it's time to put everything together. Unscrew the side wall and remove it from the camshaft dowel. Insert the steel rod and start putting on the levers and washers. I used six #6 washers to space the levers apart. Put a few washers between the side walls and the levers on each end. Slip the side wall/levers/steel rod back onto the dowel and fasten the screws from the bottom. Test the assembly to make sure everything moves/turns ok. Then tighten all screws and attach the top/side cover. If everything works well trim the dowel and steel rod.
As a final touch I made a forked tongue for the snake. That's it! Enjoy!
