Alien Egg Opening Mechanism

The biggest challenge with the Aliens kiosk is to find a way to open up 4 separate petals or lips on the 'hero' Alien egg, to expose the hidden holographic Facehugger, waiting to jump out and impregnate you with a baby Alien. I love these types of challenges as they're practically impossible to figure out and no matter how much you engineer it, you still have to get out some parts and just physically build and iterate. I love the process and am always kind of sad, yet relieved when it's completed.

I began by building a small woking model, using 4 continuous rotation servos controlled by an Arduino Uno. Normally servos are great, as the positional data you send them perfectly matches the servo angle. Although, with continuous rotation servos, we can only control the speed and still need a way to measure position, to find and set the home position on startup. Also, servos tend to be considerably weaker than stepper motors, so I ended up switching to steppers pretty quickly in the beginning prototyping stage.

Hoping to use 4 separate steppers controlled by one Arduino proved to be problematic, as there was not quite enough room in the kiosk and too many parts to control, which made the process more challenging. I settled for 2 steppers and built the basic control and programmed them with the Arduino. As a team, we determined the best placement for mounting them and essentially used the stepper motors as winches. By attaching a winch wheel to the end of the stepper shaft and tying high strength sail cord to a point on each of the petals, the steppers would spin and wind the cord tighter or loosen it to open/close the petals.

The opening mechanism was designed by Chris Tedin. He built it with high-tensile hacksaw blades as a way to support the very heavy silicone lips. The blades acted as strong springs to assist the motors when pulling the petals open and closed.

To determine the home and position of the stepper rotation and open/close position of the lips, we designed a way to attach a potentiometer to the shaft. This way, we could send 'open' or 'close' commands, which essentially rotated the stepper until it hit one of these potentiometer positions, then stop. This worked flawlessly. We attached the stepper motors to each side of the inner egg and the cord was sent over many small rollers to keep friction to a minimum.

Rev. 2: After delivery, we determined that the angle to view the hologram properly was angled a bit too high. Chris Tedin, gutted and rebuilt the hero egg. While he worked on that, I went about designing a much better system with regular, high torque servos. Since the new egg was considerably lighter and required less torque to open than the original, servos were a great way to go and a nice update. There is no need to find the 'home' of the petals and we could program the main sequencing much easier.

This post is dedicated to the Nespresso machine at Light Field Lab. Thank you Light Field Lab.

Author: Brian Dressel