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Leonardo Times DECEMBER 2013I
n order to show the developments and progresses of your research group and keeping up with other groups and get-ting in touch with them, visiget-ting a scien-tific conference can be very fruitful. In the world of MAVs, this is not different, but at the IMAV this goes a little further. In paral-lel with the conference, a competition is organized where teams can compare their capabilities by accomplishing several dif-ferent tasks.The definition of when an MAV is ‘micro’ is not well defined. For the IMAV, a maximum size of 1.00m is used as a hard constraint. As a result, there is still a large variation in the size of the vehicles that show up dur-ing the competition; flydur-ing wdur-ings that use the one meter allowance up to the last millimeter, as well as mini quadrotors that are downsized that far that people don’t notice them. The latter could qualify for the term ‘Nano Air Vehicle’. This variation in size (and configuration) is driven by the different applications MAVs can be used for. For this reason two separate compe-titions are organized: an outdoor and an indoor competition. Both competitions are built up from different mission ele-ments and teams can earn points by
suc-cessfully completing one or more of these elements. The number of points obtained when fulfilling an element depends on the amount of human interaction and the size of the MAV; the more autonomy a MAV has and the smaller it is, the more points are scored. The outdoor mission mainly focused on doing the elements with multiple vehicles in parallel. The mis-sion elements of the indoor competition mainly focused on collision avoidance. PREPARATION
An overview of the MAVs that our team used during the competition is shown in figure 1. To score points at the IMAV, it was important that every MAV could au-tonomously complete mission elements. Achieving this took a lot of preparation. For instance, the ARDrones had to be debugged, the Quadshot was in need of guidance routines and the DelFly was not yet able to avoid obstacles, or fly through a window. The MAVLab workspace was busier than ever during this period, be-cause quite some students were assigned to work on the competition. Some of them were already working on these ve-hicles for their own projects and in many
cases creating the additional features was something they had to do anyway. And since these students worked hard on achieving the goals set for the IMAV, they were welcome to join the competition in Toulouse for a unique experience. OUTDOOR COMPETITION
The second day of the conference was the day of the outdoor competition. The orga-nizing committee rented a small airfield for the occasion, so there was enough space for safe flights. There were differ-ent mission elemdiffer-ents located around the runway, such as a corridor that could be flown through, or a QR code that had to be detected and decoded. Since points were awarded per MAV, there was a large potential in using a lot of MAVs. However, the number of persons necessary to op-erate them divided the score obtained. Therefore, the MAVLab had only one oper-ator, for a total of twelve MAVs: seven AR-Drones, three Quadshots and two custom quadrotors. To achieve this every MAV was made fully autonomous to the extent that the only thing the operator had to do was put the MAV on the ground and plug in the battery.
Competing with Micro Air Vehicles (MAV)
The IMAV is an annual international conference and competition involving Micro Air
Vehicles (MAVs). In September, the 2013 edition was held in Toulouse, France. The
MAVLab from the faculty of Aerospace Engineering, TU Delft joined the competition
with a group of thirteen students (MSc/PhD) and staff members. The goal was not only
to win the competition, but also to highlight recent developments and demonstrate
capabilities of our group.
TEXT Ewoud Smeur and Sjoerd Tijmons, MSc and PhD students at the MAVLab, Control & Operations chair, Aerospace Engineering
MAVLAB
DECEMBER 2013 Leonardo Times
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The ARDrone is the commercially most successful quadrotor at this time. It is in-expensive and safe to use and is equipped with an HD camera. This makes it a nice platform for flight-testing of new algo-rithms, or for flying competitions such as the IMAV. It runs its own autopilot soft-ware, but to make it really hackable, the open source autopilot software system ‘Paparazzi’ was ported to work with the ARDrone hardware. Additionally, even though everything was autonomous, a data link with every MAV was still need-ed to monitor the status and being able to control each MAV in case of an emer-gency. This required a lot of connections, so for that purpose a router was utilized. The data coming from the router was then streamed to the Internet, and by down-loading an App; anyone could monitor the position and velocity of each ARDrone in real time.
The Quadshot is a flying wing MAV ca-pable of both hovering and forward flight. It is equipped with four rotors to achieve stable hover in the same way as a quadtor. The position control for hovering ro-torcraft and forward flying fixed-wing aircraft is totally different, so to make this vehicle fly autonomous the two separated controllers were interpolated in the tran-sition region. This worked nicely in test flights. However, the day of the competi-tion there was a really strong wind, which is why the Quadshot needed a lot of time to reach a destination whenever it was go-ing to hover mode. Nonetheless, it man-aged to perform most of the mission ele-ments and showed the benefit of having a fast forward flight mode with respect to
quadrotors.
Next to this, two custom quadrotors were performing mission elements, one of which was equipped with the small-est complete autopilot in the world: the ‘Lisa/S’. Its largest dimension is 2 cm and it weighs only 2 grams, but yet it has a full IMU, radio link and GPS on board. The IMAV was the first official flight for this au-topilot and it performed great.
It turned out to be a very windy day, which was also reflected in the performance of the participating teams. Few teams man-aged to show stable flights, let alone do mission elements. The MAVLab team had less trouble with the wind, and with the sheer number of MAVs and the single op-erator our team won with a final score that was an order of magnitude higher than the second placed team.
INDOOR COMPETITION
On the third day of the conference, the indoor competition took place. For the indoor missions our self-developed plat-form was used: the DelFly. Two different configurations of this MAV were used. The first one is what we call the standard con-figuration: it has a T-tail for stabilization and steering, it is operated manually via an RC link and it has an onboard camera with live video link. This equipment al-lowed a single operator to perform sev-eral mission elements remotely by only looking at a small display with the live video stream: flying through an open win-dow, flying through a field of obstacles, looking for a hidden marker and follow-ing a line on the ground. The advantage of this DelFly is its easy handling, allowing
the operator to do the mission elements smooth and quickly.
The second DelFly has a completely new configuration and is called the DelFly Ex-plorer. It can stand on its tail allowing au-tonomously vertical take-off, it has more precise roll control by aileron surfaces and, most importantly, it has a stereovi-sion camera with processing onboard. In contrast to the first configuration, this particular DelFly was functioning fully autonomous: it could take-off to a pre-defined height above ground, follow a fixed heading, detect and avoid obstacles by using the stereo system, and detect a window by using one of its cameras. Dur-ing the actual competition, flight the ob-stacle avoidance worked partly, the win-dow detection turned out to be not fully robust at that time. This is why our team won the first place in the Indoor Operation ranking, and the third place in the Indoor Autonomy ranking. A compilation video of our team at the competition days can be found at the MAVLab YouTube channel. The MAVLab in Delft will organise next year’s IMAV 2014. Additionally, we are also planning to participate with our own stu-dent team. Interested stustu-dents can con-tribute or even participate by doing their graduation work with the MAVLab. Con-tact us via microuav@gmail.com.
References
MAVLab website, www.mavlab.lr.tudelft.nl Official IMAV website, www.imavs.org MAVLab YouTube channel, www.youtube. com/user/microuav
Figure 1. The MAVLab team
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