Gearing up For the Circus: Mechanisms Final Project

Or how I learned to stop worrying and love the Laser Cutter.

Note: I will soon include Illustrator files as well as the Arduino code / wiring diagrams for recreating all of these mechanisms, so keep an eye open for that.

For Mechanisms and Things that Move, my final project was a long work in progress. Around the time of midterms, I knew that I wanted to create a narrative automaton. I quickly realized that this goal would not be finished in time for a midterm project so I set my sights on making this a final project.

Gabriela Gutierrez and I realized that we had similar interests in building mechanisms / automatons and decided to work together on this final project. We discussed a variety of potential stories at the beginning of the project to explore including those taken from children’s books, mythology, and the bible. In the end, inspired by both Alexander Calder, we elected to create a circus. One benefit of using the circus motif over one of the other narratives is that the story of the circus is independent of a timeline, so it makes sense that the automaton is continuous rather than having a set beginning middle and end which would have to be somehow reset.

Originally we planned to have one timing belt drive the entire circus, including all of the independent circus acts. We realized that in the event one of our circus acts failed, it would bring the whole mechanism to a halt. We opted instead to run the mechanisms independently, mitigating any failure from one of them.

One of the first things that Gaby and I did was to figure out how best to create a supply of gears. In experimenting with the laser cutter and making gears, Gaby and I created a bunch of gears using Inkscape’s gear rendering function, which we then copied to Illustrator in order to cut them on the laser cutter. Inkscape has a goofy quirk in that it lets you select the gear size in pixels as opposed to real measurements, but since we were not planning on using any off-the-shelf gears, we did not worry about this. All of the gears we used in the project had a diametral pitch of 20 pixels, which meant that any time we produced a new gear we knew it would interface perfectly with all of our older gears as well. Unless otherwise noted, all material used in this project was this material, chosen to set up a juxtaposition by using wood as precision pieces. Embarassingly enough (though successful) the adhesive of choice was hot glue, with the occasional use of super glue (mostly to keep nuts in place on spinning threaded rods). All circus performers were created in illustrator, mostly by tracing and altering existing images online.

Our first challenge was to tackle building a path for our audience members to view the circus. We purchased this belt, but elected to not by the timing belt pulleys that went along with it. This however led to our first great success with the laser cutter. Gaby and I were able to find an illustrator file online matching the belt type (L-series which means a pitch of .375″). We tweaked the file and cut test pieces out of mdf before coming upon the exact size matching the belt. We were then able to print multiple copies of 1/4″ mdf timing belt pulley cross sections, which we then glued together to form the actual pulleys (5 high with one slightly larger on either end to form a guide). We chose 6 pulleys with the belt forming a hexagon. 5 of the pulleys are floating, with the 6th one attached to this motor, which drives the entire belt.

In the end, we finished with 5 circus acts and two sets of flags. I will tackle each of the circus acts separately because they all created vastly different problems.

The Man Shot Out of A Cannon

The Man shot out of a Cannon was the first circus act completed, but before that it went through several iterations. I knew right away that in order to make it successful, I would have to use a mechanism similar to those used in Planetary Gears, with the inside of the loop being geared and the outside of the loop being where the man would remain. I started by borrowing a few of the gears we had lying around (16 teeth) and created a large wheel-shaped gear with the teeth in the interior. I originally toyed with drilling holes into a block of wood to space smaller gears equidistant on the opposite sides of the large gear, but this was a fools endeavor as I could never perfect the alignment on the drill press. I elected instead to use the laser cutter again to build cross bar pieces that would maintain the correct distance. This allowed me to set the gears on cut 5/16″ threaded rod pieces, and then to let the large gear rest on the smaller gears. I then cut more supporting cross bars so that the wheel could be suspended above the table. I turned one threaded rod into a motor shaft by using the metal lathe to cut a small hole in one end before super gluing the rod directly to the motor. Initially the motor would spin freely instead of spinning the large gear because it required less effort / had less friction. I remedied this problem by creating a motor collar around the front and back of the (geared dc) motor , secured with smaller pieces of threaded rod (3 #8-32 and one 1/4″ piece all about 2 inches long). The actual man was also laser cut and attached to the outside of the wheel.

I had a lot of problems with the violence of the spinning undoing nuts placed onto the threaded rods, so I used superglue to clamp them down in place. Also worth noting is that there is a weight attached to the bottom of the motor collar to keep the entire thing balanced.

Tiger Jumping Through A Hoop

The tiger jumping through the hoop was the second mechanism/circus act created. We knew that we wanted a rhythmic motion that would convert the motor spinning in a circle into something that moved back and forth, so we settled on this mechanism. Once that was decided, it was just a matter of making sure the parts were scaled to the correct length and that the tiger would fit through his own hoop (this took three separate iterations). As in the Man Shot from a Cannon, all of the gears and other pieces are attached together using threaded rods.

Dancers

The dancers were the third mechanism created. Gaby and I decided we wanted something beautiful, but also simple. By attaching the dancers both to gears, they spin in opposite directions and also only require one motor. Gaby had endless issue getting the stepper motor to work with the Darrington Array (frying at least one Arduino in the process) but in the end by switching to H-bridges and using the code / arrangement available on Tom Igoe’s post on stepper motors we were able to work through the problems and get the dancers to twirl together. There were also a few issues with the axle of the second dancer causing too much friction and consequently the motor to stutter, but this was fixed by making sure both gears were aligned above the platform to reduce friction.

Tightrope Walker

This circus act uses a rack and pinion set to push the tightrope walker forward and backwards along his walking path. Originally I had planned on attaching the tightrope walker directly to the toothed rack, but Luis Violante suggested (and provided) piano wire as well as the idea to attache a counterweight and keep the walker himself upright. There is a stepper motor on the base of the circus attached to a threaded rod which goes up to the rear platform of the tightrope. There is a pinion attached to the rod, which pushes the rack forward and backwards. The rack has the wire attached to the front of it, run across the length of the circus to a second platform at the front which acts as a guide. Guides above the rack prevent it from jumping out of place (though these guides are not tightened down). There were also a few issues with friction and the stepper motor slipping but these were solved by repositioning the pinion gear higher on the rod.

Elephant pushing a ball

The elephant pushing a ball was the last circus act constructed. While this circus act was originally conceived as “An Elephant Riding a Ball,” the balance required for this did not work out quite as well as I had hoped. Luis Violante also had several helpful suggestions for this circus act, including forcing a hole through the ball with a hollow rod and pushing wire through the rod to allow rotation with minimal friction. Jen Shannon was also nice enough to lend us a high-powered stepper motor to push both the elephant and ball around in a circle. The elephant was designed to be an assembly of three parts: two leg cross sections with bodies and tails that matched up, and a set of ears to be placed perpendicularly over the elephant. I then drilled a hole through one elephant and attached another piece of wire through its body. I attached the elephant and the ball with the somewhat less than pretty solution to the motor by using large globs of hot glue directly to the motor shaft. When the motor is activated, the ball rolls and the elephant appears to gallop after it.

Flags

The Flags were constructed by Gaby and are each a set of three. They are directly attached to a servo motor (with two sets of flags in total). The servo motors are attached back to back, and when the flags are activated the flags rotate in opposite direction, first away from each other and then towards each other, stopping in a place somewhere in-between.

Electrical
The nest of wires we have hidden underneath the circus stage is slightly less than pretty, but worked as long as nothing got too jostled. The audience members (wooden people attached to the timing belt) trigger roller switches as they travel their path around the circus. These roller switches are hooked up to Arduinos (three in all) which then tell the motors to activate. For DC motors requiring a trigger (the cannon and the tiger) the Arduino sends a signal to a transistor which allows current to flow through to the motor of one of those circus acts. A timer allows this current to flow for a set period of time (1.5 seconds) before the signal from the Arduino stops and the transistor stops allowing the motor current. For circus acts attached to the stepper motors (elephant, dancers and tightrope walker) the Arduino uses the stepper library to run through a set number of steps. The dancers and the tightrope walker move forward and then backwards, while the elephant completes enough steps to finish a rotation and a quarter. The belt itself is run by a dc motor on continuously. Most of the circus acts required only the five volts provided by the Arduino, but the tiger and the audience members are run off a laptop power supply which provides twelve volts and up to 3 amps of current. We had one minor issue with this amount of power just before the second day of the show, when I observed a smoking transistor connected to the Tiger which burned out the motor as well as burning myself when I went to remove it. Note to all: Electricity is powerful, be careful.

Reception

The circus was well received at the ITP Spring Show (2011). The vast majority of the acts did not work during the first day with only the dancers, the flags, and tightrope walker being the only ones full functional and the cat and cannon available with a request. People still seemed to love the look and feel of the circus, even though it was not interactive at this stage.

Day Two we had everything up and running (except for the Tiger burning out just as the day started). One thing that was really amazing about the crowd is that they would form a half circle about four to five feet away from the circus table and stare for minutes at a time. It was nice to see the same motions that mesmerized me over and over again were able to do the same thing for other people.

Future Goals
One of the things we had originally wanted to include but failed to create for this iteration was a way for the observers to interact with the automaton. With the future version, I would like to include a crank which lets an observer control the audience members at his or her own pace, but still only allowing the wooden audience members to trigger the various circus acts. On the first day of the show someone suggested to build this type of mechanism into arcade machines and have it be coin operated which is a path I plan on exploring this summer. For the time being the Circus is on display at the Summer Gallery at ITP, but I plan on polishing it a bit more before beginning to submit it to other galleries or art competitions. I also plan on writing instructables for the individual circus acts to provide a more step by step plan for those interested in recreating or tweaking what we created.

Overall I learned a lot about constructing mechanisms, using the laser cutter, group work, and the simple pleasure of both creating something and watching it move. I plan on using the skills I gained from working on this project heavily in my future work.

Special Thanks to those who helped document the project: Alex Kozovski & Spike McCue.