UAS Sensor Placement: A Comparison


Unmanned Aerial Systems (UAS) rely on onboard sensors for navigation and to provide an operator or ground observer with imagery captured by the aircraft.  The selection and placement of these sensors is dependent on the design of the aircraft and the intended purpose.  Today’s blog will examine sensors utilized for DJI’s Phantom 4 Pro, a UAS designed for aerial photography, and ImmersionRC’s Vortex 250 Pro, a UAS designed for first person view (FPV) drone racing.

DJI Phantom 4 Pro


DJI’s Phantom 4 Pro is an excellent UAS for obtaining high definition aerial video and still images at altitudes below 400 feet.  The quadrotor UAS is capable of flying for up to 30 minutes at speeds up to 31 mph while shooting 4K/60 fps video or still imagery, all while avoiding obstacles (Phantom 4, 2017).  The quadrotor design of the aircraft, as opposed to the use of a traditional fixed wing, enables the aircraft to operate in all directions (forward, backward, left, right, up, down) as well as hover, enabling the operator to capture slow or dynamically moving objects, or operate the aircraft in confined areas, such as indoors. 



DJI. (2017). Phantom 4 Pro Sensors [digital image]. Retrieved from https://www.dji.com/phantom-4-pro

Single operator control of the UAS and onboard camera is facilitated through the Phantom 4 Pro’s onboard positioning and obstacle detection sensors.  Obstacle detection and avoidance is accomplished through the use of stereo vision sensors, located on the front, rear, and bottom of the aircraft, as well as the primary video camera.  By comparing the images acquired from each camera, the aircraft is able to determine relative speed and distance from an object (Phantom, 2017).  Detection of objects on either side of the aircraft is accomplished utilizing infrared sensors.  These sensors have a 20-degree vertical and 70-degree horizontal field of view, allowing them to detect objects out to 23 feet (Phantom 4, 2017).  Altitude control is accomplished through the use of ultrasonic rangefinders located beneath the aircraft (Phantom 4, 2017). 

Additional positioning data is obtained through the use of dual global positioning system (GPS) receivers and redundant inertial measurement units (IMU) and compasses (Phantom 4, 2017).  The IMUs determine angular velocity and linear acceleration through the use of gyroscopes and accelerometers (Woodman, 2007).  Data collected utilizing these position and obstacle sensors is used to create a 3D map of the aircraft’s surroundings, enabling the aircraft to detect and avoid objects along the intended flight path, while under operator control or when operating autonomously about a given point or along a given flight path.  Placement of sensors on the front, rear, and sides is particularly critical as the main imaging camera (viewed by the operator) may not be orientated in the direction of flight.  The use of these sensors is critical as they relieve navigational workload for the operator, enabling them to focus on obtaining the imagery desired.  It is important to note, however, that the vehicle does not have upward facing sensors, and thus care must be exercised when flying near overhanging obstacles (tree limbs, roof overhang) or close to ceilings while indoors. 

 Vortex 250 Pro


ImmersionRC. (2016). Vortex 250 Pro [digital image]. Retrieved from https://docs.google.com/document/d/1psnkyrIOMzA81SEG3yxdGLjIXhTMVJpHdpMnwNlMR8Q/edit#
ImmersionRC’s Vortex 250 Pro is an excellent off the shelf FPV UAS racer.  Like the Phantom 4 Pro, the Vortex 250 is a quadrotor UAS with a video camera, and is capable of speeds in excess of 62 mph (ImmersionRC, 2016).  In addition to the built in forward-facing video camera, the Vortex 250 Pro has a provision for a high definition GoPro video camera for recording race imagery.  The user must also add their own battery, and as a result video quality and endurance vary (Vortex 250 Pro, 2017).  Although it is not equipped with a GPS, the Vortex 250 Pro does come equipped with a digital altimeter and IMU.  Both sensors are utilized to aid in vehicle stabilization.  In addition to providing the operator with pertinent flight data, the altimeter is utilized to award racers points for remaining within a given altitude (remaining lower to the ground results in more points during a race) (ImmersionRC, 2016). 

As the Vortex 250 Pro is designed for first person racing, the operator must rely on the video imagery transmitted from the forward-facing camera for obstacle avoidance.  Obstacle detection sensors are not utilized as they add weight (which would slow the aircraft) and are not required as the operator is always looking in the direction of flight (the UAS is not intended to race sideways or backwards).  As a result, the operator trades a decrease in vehicle weight (and the increase in top speed and maneuvering) against an increase in the possibility of an impact with an obstacle. 

The Phantom 4 Pro and Vortex 250 Pro are both highly advanced and capable UAS.  Although their onboard sensor systems differ, the sensors utilized on each are best suited to maximize the aircraft’s capability while meeting the user’s requirements.


References:


ImmersionRC. (2016). Vortex 250 Pro Instruction Manual. Retrieved from https://docs.google.com/ document/d/1psnkyrIOMzA81SEG3yxdGLjIXhTMVJpHdpMnwNlMR8Q/edit#heading=h.ai0z0mjy4p9x.
Phantom 4 Pro. (2017). Retrieved from https://www.dji.com/phantom-4-pro?site=brandsite&from=nav.
Vortex 250 Pro. (2017). Retrieved from https://www.immersionrc.com/fpv-products/vortex-250-pro/#specifications.
Woodman, O. (2007). An introduction to inertial navigation. (Technical report). Retrieved from https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-696.pdf.

Comments

  1. UnknownDecember 6, 2017 at 3:41 PM

    John,

    Great post! I chose the Phantom 4 Pro for similar reasons as you for this assignment. It's extremely cost-effective for the operations it performs. You also make a great point that I didn't think to make with obstacle avoidance on the racing UAS. Initially, it shocked me when you said there aren't any additional collision avoidance sensors, but on further reflection it does make sense. It would save weight to not include these sensors since they aren't entirely necessary for the racing purposes of the system and that saved weight probably helps with handling and speed requirements.

    -Kristin

    ReplyDelete

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