Marie's Engineering Blog: Day 1

This next task is to design a device that converts the rotational energy of a crank into a flapping motion. Our design is to be made primarily of delrin plastic and no one piece is to be bigger than 6" in any dimension.
This first day was dedicated to brainstorming ideas and sketching those ideas. My partner, Hande, and I spent most of this day thinking about the flapping motion and came up with a number of ideas.

"Weighted from Top"

How it works: You turn a rod which rotates an uneven cam. This cam lifts up a small ledge which causes the entire vertical rod to move up and down. When the rod moves down, the middle wing ends move down, the wings pivot on the structure, moving the outer wing tips to move up.

Why it was not used: This design is overly dependent on the elements on the vertical rod to stay firmly attached to the rod, not so feasible. This is also assuming that the small rod which you turn stays perfectly horizontal, a bad assumption. Due to these reasons, we did not decide to move forward with this design.

"Wobbling bird"

How it works: You turn a vertical rod which has an uneven cam at the bottom. This cam hit a disk attached to a rod. The horizontal rod moves back and forth, depending on a rebound from the edge of the structure to move in the opposite direction from the cam. The movement of the horizontal rod causes disks to hit the end of a wing, which tip the wing, causing a flapping-like movement. However, the disks alternate which wing is flapping at any given time.

Why it was not used: There is so many issues with this design. The wings are "floating." The rod moving back and forth relies on a rebound effect, which means that the force going the first direction will be greater than the force going the opposite, so the wings are not only flapping at opposite times, but in uneven amounts.

"Simple, Elegent"

How it works: You turn a rod which turns two uneven cams. These cams push up on the middle ends of the wings, which cause the wings to pivot on the edge of the structure, moving the outer wing tips to move down.
Why it was used: We picked this model to build a lego model on based on its simplicity. It is also important to note that the wings on this model rely on their fish-like shape stay in place and they also never meet in the middle.