With Lynn Burke and Barbra Mack.

Here is the tail of our trials and tribulations trying to build our Rube Goldberg Egg-Cracking Machine for Mechanisms.

Original Plan

1. Turn on fan. Fan will naturally start to swing around.
2. Swing movement unplugs water container.
3. Water moves egg in boat down a ramp into canal.
4. Fan blows egg in boat.
5. Water overflows in canal and pushes open “floodgate” or breaks a “dam”
6. Water rushing out deposits egg safely onto a grate (eventually a baking rack).
7. Water rushing out fills basin below the grate.
8. Basin filling up with water tips see-saw to release rope holding up a weight.
9. Weight falls smashing egg through grate.

Additional Self-inflicted Requirements
We want to keep the set-up simple and aesthetically clean. We settled on an all white and clear plastic look and feel which we managed to pull off except for the see-saw and basin.

Challenges

Generating Wind

Right off the bat, the fan we had was too weak, or rather, the power to weight ratio was too low for it to swing itself out. It really needed energy input in the beginning to build on, otherwise it just hung in place.

Our solution: Have the fan commit suicide to generate more force by balancing it on a skinny 1×2 leg and then turning it on to destabilize the leg. In other words, we set up the fan with a lot of potential energy and then use a little bit of the fan’s power to release that potential energy.

Unplugging the Hole

Plugging hole in the water container with suction cup doesn’t work because apparently suction cups really do need 100% seal to work.

Solution: Create a plug using a wad of adhesive putty. Adhesive putty as it turns out a) creates a pretty reliable water seal and b) is re-usable.

The adhesive putty plug on a hook + a large 5″ diameter pulley meant that the drop of the fan was enough force to slowly unplug the water container.

The Egg Boat

The next challenge was figuring out a way to transport the egg in a boat that wouldn’t also get in the way and protect the egg when it was time to crack the egg.

First, Barbra created a beautiful egg-shaped styrofoam boat. However, it wanted to roll and capsize in the water.

Then Lynn made a styrofoam speedboat with the egg sitting in the middle. the speedboat was awesomely stable. However, we couldn’t figure out how we’d get the egg out of the boat when it came time to smash it. Then I made a foam donut that fit just around the egg, but leaving the top and bottom of the egg exposed. However, the foam made the dismount onto the baking rack unpredictable as it would get stuck between the grilles. Furthermore, even though the donut left most of the egg exposed, it still managed to act as a “brace,” keeping the egg shell together even if it was cracked.

Opening The Floodgates

Apparently it’s kind of hard to create a dam or floodgate that is both water-tight and will break cleanly, all-at-once just from water pressure.

As it turned out, 100% water-tight and the ability to break all-at-once were both crucial characteristics, otherwise there wouldn’t be enough water pressure to flush the egg out of the canal. If the canal leaked or if the damn broke on one side but the not the other, the egg would get trapped behind the partially broken damn while all the water rushed out around it.

Things tried:

• Sugar cube wall glued together with Elmers. The wall didn’t disintegrate evenly, as a result the water would leak out slowly. Even when all the sugar (and water) was gone, there remained a grid of Elmers blocking the exit of the egg. The effect was kind of cool though.
• A Press and Seal dam. Press and Seal it turns out really does seal water, especially if you double it
  I lined the 2nd half of the canal with a sheet of press and seal and folded the end up into a drawbridge-style gate
  (except with sides, like the spouts on cardboard salt containers).

I tried using the Press and Seal’s inherent stickiness to keep the gate closed, but alas, the Press and Seal adhesive was too strong! Also, it was incredibly difficult to keep the two sides equally secured. Inevitably, one side would break before the other and all the water would rush out.

What we needed was a floodgate with a single point of failure.

After many hours of trial and error, the final design consisted of a Y-shaped rig that held up the Press and Seal drawbridge-style floodgate by tacking it to the back of the canal, the gate’s single point of failure.

Change in Thematic Direction: Chucking the egg boat + floodgate design, which precluded the use of a ramp meant that our original “Venetian Canal” theme turned into “Birth Canal.”

Dismount and Smash

Controlling where the egg landed on the baking rack was a challenge too. We tried erecting walls on the baking rack, but they got in the way of the falling weight, which never quite fell in exactly the same place every time.

For the weight, we strapped together the bases of two decapitated “helping hands” in a plastic box. However, we knew we couldn’t completely smash the egg because then the shell would get pulverized and drop through the grille into the basin along with the egg.

So first we tried sticking a wood-boring drill bit out of the bottom of our box. But we couldn’t control the dismount of the egg accurate enough to ensure that the drill bit would strike through the egg. Instead, it would bounce off the baking rack and prevent the full-force of the weight from landing on the egg.

Right before class on Monday, I rigged up a foam collar on the baking rack that was exactly the dimensions of our weight. The collar was about 1/2 the height of the egg. The collar had 2 main benefits: 1) It prevented the egg from rolling away on the dismount and kept it within the footprint of our square weight; and 2) The weight would land on the egg, but would not completely pulverize it.

Just to keep us guessing, after many repeated trial runs our see-saw gave out and we had to scramble to pull together a new one.

Our Final Configuration

1. Turn on fan, destabilizes kickstand, fan falls.
2. Fan falling unplugs water container.
3. Water fills up canal with naked egg in it.
4. Water overflows and breaks open canal floodgate.
5. Egg dismounts onto baking rack clamped to table, hemmed in by a 1-inch foam collar.
6. Water fills up basin, which tilts a see-saw, releasing a string holding up a weight.
7. Weight falls and smashes egg.

The Real Trial…

In our final run, a few things went right and a few things went wrong.

1. The fan, kickstand and water container plug went perfectly.
2. After performing without fail well over a dozen times on Sunday, the floodgate started to fail. The plastic was overstretched and water started to pour out of the top of the floodgate spout *before* the single point of failure failed.
3. Because of the new collar design I put in place right before class, the canal was *not* placed hanging over the edge of the table as it had been the whole previous day. As a result, the water pouring out of the canal bounced off a lower shelf attached to our table. This is when I “cheated” and nudged the canal forward so that all of the water wouldn’t go all over the floor.
4. Because we lost some of our water, the see-saw didn’t tilt decisively and as a result, the weight didn’t drop decisively.
5. Still, the egg cracked and slowly but surely, the contents of the egg slithered out. Perhaps it was all for the better as it was a more appropriate metaphor for birth.

What I Learned:

1. Trial and Error does work. But maybe next time I’ll try Googling for ideas on how to solve simple mechanical design problems too.
2. Pay attention to yield strength. Materials get tired and testing your set-up includes figuring out how many times you can run through it before you have to “change the tires” so-to-speak.
3. If you make one change, it will always have unintended and unforeseeable consequences on the rest of your system. The only way to find out what they are and fix them is to text your system end-to-end.

Here are just a few snippets of video from our many, many, many runs of the egg machine. (Michell I believe captured the “official” run in class.)