The vertical position of the body of the penguin is measured as the distance between the bottom of the penguin and the base. Thus, it is the instantaneous radius of the cam (the vertical distance from the center of rotation to the top of the cam, see previous page) minus the minimum radius of the cam. This plot is shown below. A constant input angular velocity of -1 rad/s (clockwise) is assumed.
Theta=0 was defined as when the penguin was at its highest point and about to drop down. We can see that at this point, the position of the penguin is at 2.3 cm, or 3.9-1.6 cm, matching the maximum radius of the cam (radius of the larger semicircle) minus the minimum radius of the cam (radius of the smaller semicircle). During the drop, the point of the cam which is in contact with the base of the follower is the sharp corner of the snail cam. Thus, the vertical distance is the maximum radius of the cam, multiplied by the cosine of theta. A rest period of no motion follows, as the radius is at a constant minimum when the small semicircle of the cam points upwards. At theta=180, the cam radius begins to increase, following the simple harmonic motion mentioned in the previous section.
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