Figure 2
The central red circular hub is connected to four black circular nodes by straight black arms forming an “X” shape. The four outer nodes are labeled “1”, “2”, “3”, and “4”, each placed at the end of an arm. The node labeled “1” is positioned toward the lower-right, “2” toward the lower-left, “3” toward the upper-left, and “4” toward the upper-right. A label “Body Frame” appears near the central region. From the central hub, a red arrow extends diagonally upper left side, showing one axis of the body frame. Near this arrow, a counterclockwise curved arrow is drawn and labeled “psi”. Another red arrow extends diagonally toward the lower-right from the center, aligned with the arm pointing to node “1”, and is labeled “Front”. Near this arrow, a counterclockwise curved arrow is labeled “phi”. A third red arrow extends diagonally toward the lower-left, aligned near the arm pointing to node “2”, with a clockwise curved arrow labeled “theta”. At the lower-left of the diagram, a separate coordinate system labeled “Inertial Frame” is shown. Three arrows originate from a common point: one blue arrow pointing upward, one green arrow pointing diagonally upward to the right, and one red arrow pointing horizontally to the right. A dashed line extends from this inertial frame origin toward the central hub of the quadrotor. Each rotor node is surrounded by a faint circular shaded region. The black arms connect symmetrically from the central hub to each of the four labeled nodes, forming a cross-like pattern rotated diagonally.Quadrotor frames and variables