Recent miniaturization of computer hardware, MEMs sensors, and high energy density
batteries have enabled highly capable mobile robots to become available at low cost.
This has driven the rapid expansion of interest in multi-rotor unmanned aerial vehicles.
Another area which has expanded simultaneously is small powerful computers, in the
form of smartphones, which nearly always have a camera attached, many of which now
contain a OpenCL compatible graphics processing units. By combining the results of
those two developments a low-cost multi-rotor UAV can be produced with a low-power
onboard computer capable of real-time computer vision. The system should also use
general purpose computer vision software to facilitate a variety of experiments.
To demonstrate this I have built a quadrotor UAV based on control hardware from
the Pixhawk project, and paired it with an ARM based single board computer, similar
those in high-end smartphones. The quadrotor weights 980 g and has a flight time of
10 minutes. The onboard computer capable of running a pose estimation algorithm
above the 10 Hz requirement for stable visual control of a quadrotor.
A feature tracking algorithm was developed for efficient pose estimation, which relaxed
the requirement for outlier rejection during matching. Compared with a RANSAC-
only algorithm the pose estimates were less variable with a Z-axis standard deviation
0.2 cm compared with 2.4 cm for RANSAC. Processing time per frame was also faster
with tracking, with 95 % confidence that tracking would process the frame within 50 ms,
while for RANSAC the 95 % confidence time was 73 ms. The onboard computer ran the
algorithm with a total system load of less than 25 %. All computer vision software uses
the OpenCV library for common computer vision algorithms, fulfilling the requirement
for running general purpose software.
The tracking algorithm was used to demonstrate the capability of the system by per-
forming visual servoing of the quadrotor (after manual takeoff). Response to external
perturbations was poor however, requiring manual intervention to avoid crashing. This
was due to poor visual controller tuning, and to variations in image acquisition and
attitude estimate timing due to using free running image acquisition.
The system, and the tracking algorithm, serve as proof of concept that visual control of
a quadrotor is possible using small low-power computers and general purpose computer
vision software.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/10051 |
| Date | January 2014 |
| Creators | Duncan, Stuart Johann Maxwell |
| Publisher | University of Canterbury. Electrical and Electronic Engineering |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Stuart Johann Maxwell Duncan, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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