Hickory Dickory Dock

A Mechanics Demonstration Automata

In order to best understand the mechanics of the automata that Joseph Schott and I are helping student build, we constructed a demonstration automata over the course of a week. The automata includes wood, aluminum, and 3D printed parts. Much of the wood was left over from other projects in Joseph's workshop and was repurposed with little modification in its shape or patching of old drill holes. The demonstration automata serves as a visual guide for the students in our automata workshop to understand the machinery that they will incorporate into their own, larger automata.

Gear and adapter

Custom 3D Printed Hardware

We started the project by developing a collection of 3D printed hardware to use in the automata. By starting with a common vocabulary, we hoped to both simplify the engineering process as well as visually unify the six automata the students are building.

Joseph designed the hardware using Sketchup. The hardware was designed to adapt both 3D printed gears and wood cams to 1/2 inch aluminum tubing, which is used for the drive shaft. Additionally, a now obsolete piece of hardware adapted gears and cams to 1/4 inch square wooden dowels. We decided for the larger automata we would use smaller diameter aluminum tubing, with a 3D printed adapted identical to the 1/2 inch adapter.

1/4 inch adapters stacked along a 1/4 inch wood dowel. Dowel is secured to stock using screws.
The 1/4 inch adapter could be attached to other material using screws or rivets. Additionally, there was a small slot to secure the dowel using a pin left over from the rivets.
The adapter can be attached with a screw or left detached to serve as a stop for the dowel in the frame.
Redesigned 19 mm adapter with screw/rivet holes. The shape was redesigned to reduce the amount of plastic needed as well as to shorten print time.

One of the most important pieces in the catalog of 3D printed automata parts is a 19 millimeter adapter with screw/rivet holes. The interior diameter of the adapter is the proper size for the aluminum tubing, while the exterior diameter is the proper size for the 1 inch cutter drill bit we used to drill holes in the frame. This adapter could be attached with a screw or a rivet to a 3D printed gear or to a wood cam. Additionally, there are two rivet holes in the vertical part of the adapter for attaching the adapter to an aluminum tube.

Preparing to rivet 19 mm adapters to gears.
19 mm adapter attached to aluminum tube with rivet.
Small 25 mm tall adapters with interior diameters of 19 mm were 3D printed to hold the aluminum tubing in the wood frame.
This 25 mm tall adapter holds the tubing in place.

Josh designed the gears in Tinkercad. He used the Pro Gear Community Shape to generate a 2 mm tall gear, then resized the gear slighty, raised it 2 mm and placed it atop the slightly smaller gear. This created a crown gear shape.

Tinkercad crown gear.
Stacking two 2 mm gears, the top one slightly larger, created a good crown gear-type shape.
The first gears were printed on a MakerBot Thing-O-Matic in ABS.
Subsequent batches of gears were printed two at a time on a MakerBot Replicator 2 in PLA.

The Frame

The frame for this automata and the students' larger versions are made from primed stock three and 3/4 inches wide. The demonstration automata frame measures 23 inches by 13 inches. The stock is joined with wood screws that are concealed by using a Kreg jig.

Demonstration automata with drive shaft installed. A student's larger automata is behind it.

Hand Crank Design and Construction

The hand crank that powers the automata is built from 6 inch wood discs left over from a previous project, aluminum tubing, and 3D printed hardware. Additionally, it used wood screws and rivets in its construction.

Josh's sketch of the hand crank concept.
A crown gear was riveted to a 19 mm adapter. The gear and adapter were placed on the drive shaft, positioned to the height of where the hand crank would be located, and riveted to the drive shaft.
A piece of plywood with a hole drilled in the center was attached to the wood frame. The gear on the drive shaft has not yet been riveted.
A 19 mm adapter was riveted to a five inch piece of aluminum tubing to use as the handle. This tube was later shortened to four inches.
The handle fit into a 1 inch hole drilled towards the edge of a six inch wood disc. It would be attached to the disc with wood screws.
A two and a half inch piece of aluminum tubing was attached to a 19 mm adapter with a rivet. The adapter was attached to the center hole of the 6 inch wood disc. The aluminum tubing was inserted through the plywood, which had a modified 25 mm adapter (pictured on the table) inserted in the hole in the plywood.
Two 4 mm gears serve as spacers. Subsequently, a new 8 mm spacer was printed. The gear and 19 mm adapter are attached to the two and a half inch piece of aluminum tubing with a rivet.
The drive shaft gear and the hand crank gear mesh perfectly.
Hand crank debugged and working. It moves incredibly smoothly.

Cams and Gears Working Together

One student needed to transfer the direction of motion from the vertical drive shaft to a horizontal plane and rotate it, like you are looking at the propellor from a submersible cruising away from you.

He worked on a series of sketches illustrating how to use cams to transfer the direction of motion.

I used a large wood cam mounted on the drive shaft to begin with, but ended up needing to replace it with a smaller cam. Both construction techniques were the same.

The larger cam, on the bottom, was covered with a piece of Foamies craft foam. The foam was cut to size. The smaller cam follower was set in the center of the larger disc and traced with the snap blade to remove the foam from the center of the large cam.
Contact cement was applied to both the foam and wood. The cement sat for fifteen minutes, then the foam was attached to the wood cam. The foam increased the friction on the cam for the cam follower to better grip.
The cam follower was mounted off-center of the size board. It was attached to the 1/4 inch dowel with the 3D printed adapter. 
Another 1/4 inch plywood plate was attached to the wood frame, this time on the rear side of the frame.
A 3D printed gear was attached to the small drive shaft behind the wood cam follower.
The wood cam and cam follower worked beautifully. There was a little wandering in the cam follower because the drive shaft is attached to the frame on only one side.
 A hole was drilled in the rear plywood panel and a gear with a third drive shaft was meshed with the gear on the secondary drive shaft. The secondary drive shaft has been extended across the frame for stability.
Limitations imposed by the frame's size meant changing the wood cam on the drive shaft to a smaller sized disc. It, too, was covered in foam for additional friction.
A small plywood support left from a previous project was attached to the frame to hold the third drive shaft stable. The support's shape adds a bit of whimsy to the design.
Larger holes were drilled part way through the frame so the mounting hardware could be recessed.
An oblong cam, cut from a circular wood disc, was added to the drive shaft. It was attached with a 19 mm adapter with screw/rivet holes to both the drive shaft, with a rivet, and the oblong cam, with wood screws.
A small circular cam follower rests on the oblong cam. It feeds through a piece of aluminum tubing that is riveted to a 19 mm adapter and attached to the frame with wood screws. The aluminum tubing extends below and above the frame to guide the cam follower and its wood dowel shaft and to keep it positioned on the oblong cam.
Front view.
Back view.
Hand crank.
Back of hand crank, gear meshing with drive shaft gear.
Wood cam on drive shaft. Cam follower on secondary drive shaft. 3D printed gear meshing with 3D printed gear on third drive shaft.
Cam, cam follower, gears, third drive shaft. Oblong cam on drive shaft and cam follower at right.
Cam follower on oblong cam. Aluminum guide tube.


After completing the automata and demonstrating it to the workshop students, they were impressed but a bit underwhelmed. The mechanics were interesting, but ultimately the piece lacked a narrative. In order to be complete, the automata's movement needed to tell a story.

One of the best pieces of advice I learned about building automata is to watch the movement the machine creates and build your characters and narratives around these movements. Resist the temptation to shoehorn a movement you desire into the automata machinery that might not move the same way you desire.

I observed the movements this automata made. There was a spinning drive shaft on the top of the automata and on its face, near the hand crank. There was also an irregularly shaped cam that moved up and down and had the tendency to spin. After consideration, I decided to keep with the nursery rhyme theme I previously explored and use "Hickory Dickory Dock" as the automata's narrative.

3D printed mouse. http://www.thingiverse.com/thing:61909
The mouse sits on the drive shaft on top of the automata.
Clock face and hands. http://www.thingiverse.com/thing:42092 They are mounted on the drive shaft that is on the face of the automata near the hand crank.
This project needed more cowbell! An additional bracket was added to hold the cowbell over the cam follower that is on the irregularly shaped cam.
A bracket and striker was added to the shaft attached to the cam follower that comes out the top of the automata. As the cam follower travels up and down and around it rings the cowbell.
The narrative completes the automata by bringing whimsy and a recognizable story to the machinery.

Many thanks for Joseph Schott's designs, workshop, materials, tools, and guidance.

3D models were built in Sketchup and Tinkercad.

3D models were printed on a MakerBot Thing-O-Matic with an MK6+ extruder in MakerBot red and tan ABS 3 mm filament and on a Replicator 2 in MakerBot red and natural PLA 1.8 mm filament.

This work and images copyright 2015 Josh Burker