In this paper, we present a coupled inertial and body-fixed frame non-linear complementary velocity aided attitude filter and a linear velocity controller for quadrotors. The coupled observers provide estimates of attitude and the different velocities associated with quadrotor motion. With the estimated body-fixed frame velocity, we propose a velocity controller and show that the resulting error dynamics are asymptotically stabilised by the controller. The observer-controller scheme is exploited using an external interface to an android based phone that enables human interaction with the quadrotor. Results of the velocity aided attitude observer compared to ground truth Vicon measurements are presented to illustrate the effectiveness of the estimation scheme. Results of using the an-droid based phone application in setting the desired velocities to illustrate the tracking performance of the controller are also presented.