Specifications for the project:
There were some mechanical obstacles to overcome when designing the robot. The specs for the project were:
The robot had to push down and lift up a sealed container to close and open. The weight of the lid on the container does not close the container on its own.
The project needed to be very robust and strong. It had to run hundreds of times every night.
The robot shouldn't be ridiculously expensive to create.
The sealed container did not have to be opened all the way. A couple inch gap would be sufficient.
The robot needed to hold the bottom of the container down while lifting the lid open. The friction in the seal is enough to lift the entire container.
Because of these goals, a Linear Actuator seemed like an appropriate solution. Although slow, they are very strong, and can exert force in either direction linearly. If you are not familiar with Linear Actuators, the animation below may help clarify (the .gif may not animate if you currently have the video above in the middle of playing, even when paused):
Learn more about Linear Actuators here: http://en.wikipedia.org/wiki/Linear_actuator
Unfortunately, they are fairly expensive to purchase on their own: roughly $130. Also this Instructable inspired me to build my own:
List of Mechanical Parts:
The design was simple enough so I broke out the pencils and paper; returning to my primitive experiences in drafting.
See the draft document for the design of the linear actuator. The pieces were professionally machined, welded and painted.
The shaft on a Linear Actuator (Shuttle, I'll call it) needed to remain in place and couldn't spin, otherwise the threading would never pass through the nut on the shuttle. So Guiding Rails were implemented in the design. The Guiding Rails hold the shuttle from spinning. They are covered in wheel bearing grease.
DC Motor Diagram provided by Servocity: http://www.servocity.com/html/90_rpm_precision_gear_motor.html