Control of a Quadrotor

Abstract: The objective of this thesis is to investigate the use of commercial devices as user interfaces on a quadrotor and to investigate solutions to the problem of slung load control. A slung load is a uniform mass attached with a wire which is allowed to swing freely to the bottom of the quadrotor. The purpose of substituting the radio control (RC) controller with a commercial smartphone is that they are more easy to grasp and might therefore be easier to use for a novice than an RC controller. The existing radio control link does not exist on a smartphone so it was complemented by a wireless network connection via transmission control protocol (TCP) or user datagram protocol(UDP). The smartphone does not have the same interface as the RC controller either so the same functionalities were implemented by using the touch screen and the inertial measurement unit (IMU) of the smartphone. However, this requires altitude control since the lack of multitouch in Android does not allow several inputs at the same time, thus making it impossible to adjust the thrust as the pitch and roll is adjusted. Another commercial device that was investigated was a PlayStation 3R gamepad (PS3 gamepad), whose joysticks were very similar to the RC controller’s but its shape was smaller and more ergonomic. It also communicated via TCP or UDP over a wireless network connection. The purpose of slung load control is to reduce the oscillations of the slung load and its effect on the quadrotors flight performance, thus enabling it to handle heavier loads. The slung load control consisted of several subproblems; model of a slung load, altitude control, filtering of noisy sensors and the slung load control itself. These were all solved but the last one where the slung load control was not implemented on the quadrotor due to lack of time. The model of the slung load was done by letting the dynamics of two traversed simple pendulums approximate the slung load’s angular movement. The altitude control consists of a PID controller extended with anti-windup and bumpless transfer which is combined with a feedforward control of the tilt angle. The controller acts upon a low-pass filtered pressure sensor as a measurement signal and receives its setpoint from one of the commercial devices mentioned above. The low-pass filter of the pressure sensor is a second order Butterworth filter, whose purpose is to reduce noise and the impact of spikes induced by events in the surroundings.