Performing rescuing and surveillance operations with autonomous ground and aerial vehicles become more and more apparent task. Involving unmanned robot systems allows making these operations more efficient, safe and reliable especially in hazardous areas. This work is devoted to the development of a cost-efficient micro aerial vehicle in a quadrocopter shape for developmental purposes within indoor scenarios. It has been constructed with off-the-shelf components available for mini helicopters. Additional sensors and electronics are incorporated into this aerial vehicle to stabilize its flight behavior and to provide a capability of an autonomous navigation in a partially unstructured indoor environment.
Collective robotics is a young research field, which is devoted to different ground, aerial and underwater systems [1]. Advantages of collective robotic are a high reliability, extended spatial properties, collective efficiency, which define application fields such as search and rescue operations, environmental monitoring or surveillance scenarios [2]. Especial attention is paid to micro aerial vehicles (MAV) due to their small size, low cost and a potential of creating a large-scale system [3].
The goal of this work is to develop an autonomous cost-efficient MAV, which is capable of indoor flight in a partially unstructured environment. MAVs have several advantages over ground vehicles due to their capability of passing objects in the third dimension rather than finding a suitable 2D route around an obstacle. This feature considerably improves the use of autonomous vehicles and also decreases computational complexity and difficulty for maneuvering to a point of interest.
Since a quadrocopter is like a Sikorsky helicopter 1 a very instable aerial vehicle, it needs several stabilization mechanisms, which always keep the vehicle in the upright position [4]. Without a kind of stabilization the MAV flights quickly towards one direction and can flip in the air. A very simple stabilization can be accomplished using two gyroscope sensors one for the nick and one for the roll axis with two independent PID 2 controllers to minimize the angular velocity [5]. 1 Named after Igor Sikorsky; developer of helicopter with single main and tail rotor 2 Proportional-integral-derivative controller (PID controller)
Although this kind of regulation provides relatively stable flight there are many complex enhancements possible.
Since this work originates from the swarm development [6] (see more in [7]), many technologies and ideas from Jasmine platform is used here [8]. For the MAV development we utilized two additional sensors such as gyroscope and ultrasonic sensors for the flight stabilization [9] and analyzing the surrounding environment. Therefore sensor reliability is imperative, because false readings could result in unavoidable crashes, leading to damages. In further developments the concept of collective embodiment will be used [10] as well as more complex sensors such as cameras [11], however they require powerful on-board hardware to react quickly.
Depending on the task, the computational requirements are important for an autonomous flight since reaction times are essentially shorter than for ground vehicles. Additionally, the micro controller has to perform various time-critical tasks in on-board and online manner [12], such as e.g. decision making [13] and a flight stabilization. Here, an application of a low-complex numerical approaches [14] for decision making and planning [15], [16] is required.
This work is organized in the following way. Firstly, in Sec. II we shortly describe the developed hardware and software system. Sec. III is devoted to encountered problems, which required a special attention in further development. Finally, several performed experiments are demonstrated in Sec. IV and we conclude this work in Sec. V.
The hardware design of the MAV [17] corresponds to the state of the art approaches for the quadrocoptertype of the aerial vehicles. There are four bars with four motors attached to the respective end of the bars. The other ends are held together in the middle, so that two bars are perpendicular to the others. All electronic components should be located in the center since a center imbalance will have only minimal side effects, see Fig. 1. Components in the outer regions will block parts of the propeller surface lowering energy efficiency. The bars attaching the motors also have an underestimated effect on the flight properties: depending on the material it might suppress or increase vibrations induced by the motors. The weight of the bars will also have a much greater effect on the torque inertia than masses located in the center.
This quadrocopter has been designed using the following components:
• four 17cm aluminum pipes Overall dimensions are 48 cm in diameter, maximum height in the center is about 10 cm. For the gyroscopes, the accelerometers and connections to the brushless regulators, ultrasonic modules, the RC receiver and two Jasmine mainboards holding the two micro controllers, a PCB was designed. The structure of the electronics is shown in Fig. 2. It was decided to use mainboards from the micro robots Jasmine [18] since they have proven to be a very stable platform in various experiments. Since we intend to study collective behavior of such MAVs [19], the already existing software for these mainboards can be re-used.
As a result only the inputs and outputs had to be connected to these boards. The constructed mainboard provides a reliable platform for the core components and makes it possible to connect different sensor mod- ules using TWI bus or switching to different rec
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