Controllability with unilateral control inputs

Many control systems contain control inputs which are constrained to be nonnegative. Unfortunately, the unilateral nature of such inputs makes them similar to a drift term, and correspondingly complicates any attempt to determine controllability. We present a controllability test in which Lie brackets are characterized as "good" or "bad," from which controllability follows from the relationship, between these "good" and "bad" brackets, This test is relatively straightforward to apply and its application is illustrated with an example.