This paper proposes a Negative-buoyancy Quad Tilt-rotor Autonomous Underwater Vehicle (NQTAUV). for which an attitude-tracking controller is designed for the hover and transition modes based on a disturbance-rejection control scheme. First. the structure of NQTAUV is illustrated. https://countryscenesaddleryandpetsuppliers.shop/product-category/barrel-saddle/