Introduction/Background

The "Ready to Fly" karakuri model from Keisuke Saka's Karakuri: How to Make Mechanical Paper Models That Move is a model of a penguin intermittently moving up and down while flapping its wings. This is achieved by using a crank attached to a horizontal axle that houses two snail cams that move together (having the same orientation throughout). When the crank is turned, the cams push on a circular, flat base, which is connected to a follower rod that is fixed to the body of the penguin. Thus, the penguin moves up when the cams push upward on the base. The wings of the penguin are attached to a grounded vertical axle around the rod that holds the body and emerge from slots on the side of the body. The slots move up with the body, pushing on the wings. Since the connection point for the wings are grounded, they rotate rather than undergoing linear motion. The following pages aim to analyze the shape of the cam, and how it affects the kinematics of the body and wings given a constant input angular velocity for the crank. A video of the model is shown below.