Control of a Folding Quadrotor with a Slung Load Using Input Shaping
Johnson, Nicholas Andrew
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Quadrotors are being used in an increasing number of applications. One such application is in carrying suspended payloads. However, as the payload swings --- due to quadrotor motion or due to a disturbance --- it also pulls on the quadrotor. The resulting force and torque from the payload can be significant and destabilize the quadrotor. Additionally, the swinging may be undesirable for fragile payloads, or the payload may collide with an obstacle. A typical approach is to allow the swinging to damp out, but this takes away from the limited battery life of the quadrotor. Instead, input shaping techniques can be implemented in the software to reduce the payload oscillations. Input shaping has been shown in similar systems (cranes, double pendula, and helicopters) to significantly reduce the amount of residual oscillation after a maneuver. Because it is a passive technique, the position of the payload does not need to be obtained in a motion capture facility or by using computationally expensive observer algorithms. This allows the quadrotor to be used in a variety of applications, including in disaster relief and cargo transport where cost is a factor. In this thesis, the dynamics of the quadrotor and payload are derived and explained in depth, including physicalparameters not usually considered. Then PID feedback is explored in controlling the system. In addition to the simulation results, hardware limitations must also be considered. Input shaping is then integrated into the system. The simulations show that input shaping greatly reduces unwanted residual oscillations. Finally, a folding quadrotor design is presented. Quadrotors must have large frames in order to carry large payloads, and a folding design saves space when transporting the quadrotor between flights. The quadrotor can then be placed in the trunk of a car or deployed from a rocket to reach an inaccessible area to provide aid.