with five regions.
Mueller et al. [2013] generated multiple minimum jerk trajectories without con- sideration of the dynamic constraints of quadrotors. They demonstrated their tra- jectory generating scheme by letting a quadrotor hit a ball with a racquet. Their proposed scheme generates millions of trajectories and the trajectory that results in the best way to hit the ball is chosen. From all these trajectory generators, one can see the need for a trajectory generation scheme that can run in real-time on an embedded hardware.
2.10
Conclusion
In order to do high performance control and have an open-source quadrotor platform that can be used for hobby or research, the chapter has surveyed various open-source and commercial platforms that are in current use. The major advantages, hardware components and shortcomings of these platforms were outlined. The chapter also surveyed a selection of open-source avionics and electronic speed controller systems. From this survey and in order to overcome the limitations of current open-source and commercial quadrotor platforms and in support of many of the theories that will be developed in this thesis, the chosen avionics board is the PX4/Pixhawk and ESC32v2 electronic speed controller.
In terms of quadrotor modelling, the chapter has presented the shortcomings of the current static free air thrust model and the attempts made at improving it. These attempts do not fully account for changing aerodynamics such as gust and translational lift. The model for blade flapping which is considered as a drag force and induced drag along with current state and disturbance estimation schemes for quadrotors are also presented. From this, one can see the need for an improved quadrotor modelling scheme especially thrust force when the hover condition is vi- olated. Furthermore, the need for a new and efficient state estimation and control scheme for quadrotors was also outlined.
Chapter3
Experimental Quadrotor Platforms
3.1
Introduction
This chapter presents the different hardware and software components of the open- source software and hardware that make up the quadrotor platforms developed dur- ing the thesis. The quadrotors consist of heavy lifting and high performance low- cost vehicles that are based entirely on commercial off-the-shelf (COTS) hobby grade hardware. These hardware were chosen given that they most often come with open- source software that have active community support. The fact that the quadrotors are made out of COTS and open-source software and hardware implies that the de- veloped software are open-source and are made available to the hobby and academic community using the version control software, git. Furthermore, the framework pre- sented in the chapter ensures that any of the hardware components for any of the dynamic levels can be replaced.
The chapter is made up of 9 sections which can be grouped into: quadrotor hard- ware, the Robot Operating System (ROS) based ground station and the open-source software design. The first sections on the hardware components of the quadrotor describe the various hardware of the developed quadrotors and how they commu- nicate as shown in Figure 2.1 and Figure 3.2. The commercial off-the-shelf (COTS) open-source hardware make it possible for the different observers and controllers developed in subsequent chapters to be tuned to the performance limit of the hard- ware and thus make it possible for time-scale separation of the different dynamic levels employed in Section 6.3. The COTS and open-source software and hardware also make it possible to develop quadrotors for different applications as shown in Figure 3.1.
The quadrotor hardware is made up of the open-source hardware and software Pixhawk or PX4FMU/PX4IO avionics board, ESC32v2 electronic speed controllers (ESCs) and other hobby-grade components that are mainly from Hobbyking Hob- byKing [2015] and 3D Robotics (3DR) [Drone and UAV Technology, 2015]. The avion- ics board runs the attitude observers and controllers, the position and trajectory and velocity controllers at different frequencies. The open-source software and closed hardware ESC32v2 electronic speed controller (ESC) runs the thrust controllers at 1kHz. The ESCs receive desired thrust inputs at 50Hz from the avionics board via
(a) Black quadrotor. (b) Occular quadrotor. (c) HP quadrotor.
Figure 3.1: Three quadrotors developed during the thesis for different experiments.
Figure 3.2: Layout of the ground station and quadrotor hardware.
an inter-integrated circuit (I2C) bus. Using the same I2C bus, the ESCs send feed- back to the avionics board at 20Hz. This along with a proposed electrical dynamics model to bridge the gap between the current brushless direct current (BLDC) motor model and experimental results and a calibration procedure for the motor-rotor sys- tem parameters are covered in Section 3.4. The parameters identified will be key to the development of the proposed thrust controller in Chapter 5. Other components which include Hobbyking propellers, remote controller system, batteries and 3DR radio are also described. An overview of the major components of the Australian National University (ANU) quadrotor along with the ground station are shown in Figure 3.2.
A description of the software structure and publicly accessible repositories on the local ANU gitlab software and Github of the different software developed are described in Section 3.7. Finally, cost and weight analysis are carried out and a comparison to the current commercial products (3DR IRIS and Parrot AR. Drone) are also carried out to show superiority in terms of performance and cost of the developed open-source quadrotor framework.