Fig. 6. Example body kinematics for an (A) voluntary and (B) escape take-off. Lollipop diagrams show the 3D position of the fly during take-off. Lines represent the long axis of the fly, and the open circle represents the position of the fly's head. Positions are plotted every 2.5 ms. The center of mass (COM; Ai, Bi) was defined as the point along the long body axis of the fly 45% of the distance from the head to the tip of the abdomen. We defined the starting COM location of the animal to be the origin. Horizontal position of the COM is the Euclidian distance traveled in the horizontal (x-y) plane (parallel to the ground) from the starting position. Angular values (Aii, Bii) are expressed in a body-centered frame of reference. Roll, pitch and yaw position are the cumulative rotations around the x_b, y_b, and z_b body axes, respectively (see Fig. 1 for axes definitions). The fly's starting position was determined by solving for the roll, pitch and yaw angles associated with the rotation required to move the body-centered frame from alignment with the lab frame to alignment with the fly's starting position.