The Cow Jumped Over the Moon

An upcycled, 3D printed automata

Between November, 2014 and April, 2015 I am co-facilitating a workshop for students ranging in age from elementary to high school. The students are building automata and a housing for submission to a Mini Maker Faire.

I am also building automata to learn the process, pitfalls, and practical advice to impart to these makers.

This is the third automata I have built this month. I call it "The Cow Jumped Over the Moon," after the nursery rhyme. 

I prototyped the automata in cardboard. I built a box the same size as the cigar box I wanted to house the mechanism.
I developed a narrative around the movement: a dog chasing a ball.
3D printing brought uniformity to the cams. Cams are 4.5mm thick, 40mm wide. Designed in Printed in 3mm ABS on a MakerBot Thing-O-Matic with an MK6+ extruder.
2mm thick Foamies held to the cam by pegs on the cam. Hot glue further secured the backing before final assembly. The Foamies provided more grip between the cams.
Automata breakthrough #1: square drive shaft keeps the cams aligned much more easily than a circular shaft. Additionally, squares are often easier than circles to accurately 3D print.
Cams, cam followers, and end stops. The pushpin acts as a pivot on one of the cam followers.
The original hand crank design was elegant. It proved too flexible once the load of the mechanics was introduced.
Automata breakthrough #2: a small collar on the cams and cam followers helps keep them aligned perpendicular to the drive shaft with little wobble.
Oval cam and cam with Foamies backing on drive shaft.
The cow needed to print with supports.
The model cleaned up well with a fresh hobby knife. The hind legs on the default model size were very thin and required patching with strips of left over support and model cement.
I was surprised by the level of detail my lowly Thing-O-Matic was able to produce on a small object.
An additional brace was designed and 3D printed. It supports a cam follower that interfaces perpendicularly with the cam.
Cam follower in position. The brass coupling reduces friction and provides additional guidance as the shaft passes through the housing.
A small hole was drilled into the cow model. A paperclip was bent to 90° at one end, about 3mm long. A small hole was drilled in the housing. 
The paperclip was loosely bent to provide enough grip to pull the cow model down but not so much as to put the mechanics under unnecessary load.
The housing was notched with a Dremel tool. The shaft that the moon is connected to the cam follower passes through the housing here.
The 3D printed pivot fits on the end of the cam follower shaft.
A pushpin inserted toward the edge of the cam follower provides the perfect pivot point.
Redesigned 3D printed hand crank. Housing open to display mechanics.
Ready for use.

Twitter: @joshburker


This work and images copyright 2014 Josh Burker