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WP1



WP1.1: Conceptual Design 
    In WP1.1 the challenges required by the project objectives have to be addressed. The quadrotor (or multi-rotor) can be built as 4-, 6- or 8- rotor aircraft. The appropriate mechanical concept, batteries, motors, propellers with flight time calculations and the payload have to be defined. The low-level electronics requires an investigation on available hardware chips (microcontrollers, sensors, peripherals) and an overall concept review based on already built low-level stabilization electronics. 
    A big challenge is the vision hardware. Before the division between onboard and off-board processing can be made, a concept of a possible onboard solution has to be made. Getting enough processing power onboard to do at least part of the vision processing requires a very lightweight and energy efficient hardware design with high performance and complex processor or FPGA hardware systems. 
    A part of a possible vision hardware could be an optimized digital video link with preprocessed images. Several approaches of how to transmit onboard data to the ground and between vehicles have to be evaluated in cooperation with WP3.


WP1.2: Modeling 
    The mechanical design requires modeling the helicopter mechanics for analysis and production. This is done with a CAD/CAM system. The development and production steps can be optimized, as well as the flight time and mechanical robustness can be simulated.


WP1.3: Control and Stabilization 
    Micro helicopters are challenging to control for three reasons; they are under actuated, non-linear and subject to large disturbances. In order to be autonomous, a micro helicopter has to be able to take off vertically, hover and fly in reasonable air disturbances and this comes at the expense of greatly increased modeling and control complexity. In the particular case of a quadrotor helicopter, it is under-actuated and non-holonomic. It can be flown directly to any position x, y, z in space and its yaw angle can be independently controlled. Its roll and pitch directly determine its lateral acceleration and hence these parameters cannot be independently controlled. The complete list of control variables is as follows: 
  • Yaw control: The yaw of the helicopter is the least critical of the controls required since it has no further effect on the helicopter’s motion. In a typical flight, the demand for yaw will be largely constant and hence, since disturbances tend to have a relatively small effect on yaw, only low bandwidth yaw control is required. Further, small steady state errors are normally acceptable since (unlike roll and pitch) any errors will have no further effect on the helicopter’s motion.
  • Roll and pitch: Given the symmetry of a four-rotor MAV, control of its roll and pitch is independent and that their responses are the same. Unlike yaw however much higher bandwidth control is required for pitch and roll, since their value has a direct relationship to lateral acceleration. 
  • Position control: The lateral (x, y) position of the helicopter is controlled by adjusting its roll and pitch. The combined effect of the helicopter’s rotors will always be to produce a lift acceleration approximately equal to g, in a direction normal to the plane of the helicopter. A small angle of roll or pitch will therefore result in a lateral acceleration. 
  • Height control: Controlling the height of the helicopter provides the greatest challenge for three reasons. Firstly, it is hard to measure the system response, particularly at low frequencies, since the safe working volume is limited. Secondly, the ground effect means that the system response changes with height. Lastly, the response varies noticeably with the battery charge level. 
Already existing methods for all levels of onboard stabilization (attitude including height, position and waypoint navigation) have to be revised and adapted for integration with the vision systems. Video and data compression and preprocessing have to be implemented and tested in accordance to the concept design.


WP1.4: Integration and Testing 
    During the development of several prototypes, all multi-rotor helicopters have to go through intensive flight and robustness testing. During the different phases of the project all payload has to be integrated and tested in flight. Several prototypes will be delivered to other partners for their tests and integration. All hardware has to be planned for medium quantity production (10-20 units) during the project time.
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