The past decade has seen an increased interest in Autonomous Micro Aerial Vehicles (MAVs). Rotary wing MAVs such as quadrotors, can operate in confined spaces, hover at a given point in space and perch or land on a flat surface. This makes the quadrotor a very attractive aerial platform with tremendous potential. The main goal and key contribution of this paper is to design and prototype an MAV that weighs less than 30g and is capable of autonomous flight. We have also shown how to scale the quadrotor design down to a little over 4 inches in diameter. An added benefit of scaling down, is that it not only increases the agility of the robots but also increases the ability of the robots to operate in tight formations for flying in confined spaces. We envision the final goal of this project as a large swarm of pico-quadrotors to be deployed outdoors for surveillance / mapping applications. We illustrate the agility of our newest design in indoor autonomous aerial navigation experiments at top speeds of 6m/s.