Robot control architecture provides structure and principles for designing a variety of specific robot controllers. In general, while there are an infinite number of possible controllers, to date they have been classified into the following basic types of architectures: reactive, deliberative, hybrid, and behavior-based. Interestingly, these architecture types are inspired by biological systems, ranging from insect locomotion to human cognition. We introduce and describe each in turn, then focus on behavior-based control and its biomimetic properties. An appropriate slogan for reactive control is "Don't think, react!" Reactive control is directly inspired by the tight coupling between sensory inputs and motor outputs in biological systems, which enable animals to respond to a variety of changing conditions, threats, and opportunities. Similar capabilities are crucial for robots, even for mundane tasks such as navigating around corridors in a populated building. In general, the ability to respond effectively to quickly changing and unstructured environments is termed reactivity, and it typically implies an underlying reactive controller. Reactive responses are inspired by reflexive reactions in animals: consider the ability to pull the hand away quickly from a hot stove or jerk a limb in response to impact. In order to react so quickly, however, a robot cannot take the time to do complex processing. Consequently, reactive systems are defined by a lack of internal models and representations, and, subsequently, a lack of ability to learn or change over time. They are capable of maintaining a short-term state that can allow them to avoid repetitive actions and cycles (e.g., getting stuck in corners), but such an ephemeral state is purposefully lightweight in terms of processing, so as to not slow down the response time of the system.

We surveyed existing human data and developed some basic size specifications for the robot M2. A minimum degree of complexity was chosen to accomplish the task of three dimensional walking. The robot has twelve actuated degrees of freedom and is sized after a 50th percentile human male(but lighter). There are three degrees of freedom at each hip, one at each knee, and two at each ankle. The robot weighs 62lbs without batteries, and 72lbs with roughly an hour and a half worth of NiMH batteries. This weight makes the robot manageable in a research environment, as opposed to a full weight adult human.