One type of these devices with a rotating base and underactuated arm that was developed by Katsuhisa Furuta is a common test case in nonlinear control theory. One of these systems is suspended from a V-shaped pair of strings that draw Lissajous (“lee-sa-ZHOO”) curves in a harmonograph. A simple feedback control system can be used to keep an upside-down one of these devices (10[1])stable atop a cart. (10[1])If 3 cosine theta-one plus (10[1])cosine theta-two is greater than 2, a flip cannot occur in coupled “double” examples of these systems (10[1])that exhibit chaotic motion. Under the small angle approximation, these systems exhibit motion with a period proportional to the square root of L over g, acting as a simple harmonic oscillator. For 10 points, name these systems consisting of a mass suspended at the end of a rod. ■END■