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. (10[2])A simple feedback control system can be used to keep an upside-down one of these (10[1])devices (10[1])stable atop a cart. If 3 cosine theta-one plus cosine theta-two is greater than 2, a flip cannot occur in coupled (10[1])“double” examples (10[2])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■