UAS Sensor Placement
Sensor placement is a critical design decision that is
based on the objective that an unmanned system will be tasked to perform. Unmanned aircraft systems, in all shapes,
sizes and platform configurations can be equipped with a variety of sensory
platforms to accommodate any number of defined commercial operations or
hobbyist/modeler activities. This
research paper discusses camera sensor applications and placement
considerations for a system designed to provide full-motion video and still
aerial photography operations and for a first person view (FPV) racer.
DJI Mavic Pro
The DJI Mavic Pro
(Figure 1) is a compact portable quad-copter capable of providing professional
grade still and ultrahigh definition (UHD) video. Equipped with a 4K camera stabilized by a
3-axis mechanical gimbal the Mavic Pro is supported by a semi-autonomous flight
control system that allows the operator to focus on the photo op (DJI, 2018) .
Figure 1 DJI Mavic Pro adapted from http://www.directd.com.my/dji-mavic-pro
The sensory platform consists of 5 cameras, GPS & GLONASS, 2
ultrasonic range finders, redundant IMU sensors and 24 high-performance computing
cores supporting obstacle avoidance and precise hover capabilities (DJI, 2018) .
Camera
The camera, located on
the bottom front of the operating platform, provides unobstructed professional
grade stills and UHD video, with operating specs of 4K/30fps, 12 megapixels
photos (JPEG, DNG) and 1080p video [MP4, MOV (MPEG-4 AVC/H.264)] at 96fps (DJI, 2018) .
To obtain quality 4K
video, Mavic Pro is outfitted with a high precision 3-axis gimbal capable of
eliminating any vibrations incurred during airborne operations. Similar to professional sports cameras, the
Mavic Pro comes with a 1/2.3 inch CMOS image sensor and an aerial enhanced lens
with a 28mm focal length (DJI, 2018) .
FPV Racer
First
Person View or FPV racing refers to a hobbyist/modelers form of
sport/recreation where the pilot in command tests their piloting skills against
other drone pilots. Using a platform mounted
forward looking sensor (camera) capable of transmitting real-time data to the
pilot via a video monitor or specialized goggles, the view realized by the
pilot is as if they were sitting in the cockpit (DRL, n.d.) ,
hence the term FPV. The racing platforms
are typically small quadcopters (Figure 2) equipped with platform mounted
forward looking sensors (camera) (DRL, n.d.) .
Figure 2 FPV Quadcopter
adapted from https://www.rcgeeks.co.uk/image/cache/catalog/category-images/newmenu/drones_hobby-drones_fpv-racers-750x430.jpg
In addition to the camera, operational control is realized using onboard
flight stabilizing sensors to account for the aggressive manual command and
control (C2) inputs necessary to navigate through the obstacle course at speeds
up to 120 mph (DRL, n.d.) .
Camera
Critical to all
FPV operations the camera (Figure 3) must be capable of collecting and transmitting
real time high definition video to the operator without any latency issues.
Figure 3 Typical FPV Camera adapted fromhttps://www.arrishobby.com/runcam-swift-mini-fpv-camera-for-fpv-racing-drones-p-3597
The camera must also be mounted in a frame that allows
it to be tilted at an angle capable of providing the pilot with the best field
of vision when the drone is operating at racing speed (Figure 4).
Figure 4 FPV Camera Tilt adapted from https://learnassets.getfpv.com/learn/wp-content/uploads/2018/04/30013237/CameraTilt123.jpg
As depicted in Figure 4 (3rd image), when the drone reaches
full throttle / forward pitch and the camera tilt has not been adjusted, the
operator will only see the ground and not the drones relation to the horizon (Escalante, 2018) .
Camera tilt and
operating angles of attack accounted for, another significant concern is that
of video transmission latency. In his
article, What Is FPV Camera Technology In
Drones And Best Uses (2018), F. Corrigan noted:
When flying at 50 mph
(a typical speed for an experienced FPV racer), a 100 ms delay can mean your
drone will travel about 6 feet before you receive the video, which could mean
the difference in you missing an obstacle or hitting it. By using a
dedicated FPV camera, your FPV system will have a much lower latency. A
latency of less than 40 ms is what you can expect.
The camera must also be capable of providing high quality resolution at 60
fps with a wide field of view (FOV) to allow the pilot to see around turns (Smith, 2015) . Since most FPV cameras are mounted on the
front of the racing platform it must also be durable enough to withstand any impact
(Corrigan, 2018) .
Summary
Concept of
operations is an essential part of any UAS design process. A reiterative process, it is incumbent on
design engineers to have a complete understanding of the intended
application. Where cameras are
identified as a primary sensor in realizing/supporting a specific operation
(i.e. photography, FPV racing), engineers must identify the most cost effective
sensor on the market, the most probable location/placement on the given
platform and the cameras ability to withstand risks associated with the
platforms operating environment (i.e. vibrations, weather, latency, durability,
etc.). But one thing remains constant,
camera placement on any operating platform supports an unobstructed view for
the operator, enhancing situational awareness and optimum operational results.
References
Corrigan, F. (2018, April 21). What Is FPV Camera
Technology In Drones And Best Uses. Retrieved from DroneZon:
https://www.dronezon.com/learn-about-drones-quadcopters/what-is-fpv-camera-fov-tvl-cmos-ccd-technology-in-drones/
DJI. (2018). Mavic Pro Whereve You Go.
Retrieved from DJI: https://www.dji.com/mavic
DRL. (n.d.). What is FPV Drone Racing?
Retrieved from DRL: https://thedroneracingleague.com/learn-more/
Escalante, J. (2018, May 2). FPV Camera Angle:
Solving the Mystery of Fast Flight. Retrieved from GetFPV:
https://www.getfpv.com/learn/fpv-flight-academy/fpv-camera-angle-full-throttle-flight/
Smith, K. (2015, July 7). Drone Racing: What is it?
Retrieved from MyFirstDRone:
https://myfirstdrone.com/blog/drone-racing-what-is-it
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