UAS Sensor Placement

In the world of small unmanned aerial systems (sUAS) sensor placement is a critical design element and decision that is based on the desired mission or use of the platform.  In this paper the author, who is an avid quadcopter hobbyist, will look at two different design of sUAS platforms that have a similar set of sensors but are used in different ways thus resulting in different sensor placement.  This paper will examine the DJI Phantom 2 Vision Plus and the Walkera Runner 250 Advance.  Both of these systems are quadcopters that are GPS enabled, but the Phantom is designed for aerial photography, while the Runner is designed for what is known as first person view (FPV) racing.

The Phantom 2 Vision Plus is a 350mm quadcopter, which means it measures 350mm from the furthest two propellers (i.e. port forward to starboard rear).  It is equipped with a camera on a gimbal that can tilt and roll, this not only acts to point the camera in a direction other than where the craft is facing, but allows for stabilization of the image independent of the aircrafts attitude.  This image is sent back to the user via 2.4 gHz so that the operator at the control of the ground control station (GCS) can see in real-time what the aircraft sees (Phantom2 Vision+ User Manual V1.8, 2015).  Furthermore, this camera is mounted underneath of the aircraft for two reasons typically, one is due to the size of the gimbal and arms, and the second allows the camera to keep the aircraft out of the image (Phantom2 Vision+ User Manual V1.8, 2015). Additionally the Phantom is equipped with GPS to allow for precise positioning while flying and knowing where it started from, this antenna is built in to the housing of the quadcopter (Phantom2 Vision+ User Manual V1.8, 2015).  Lastly newer versions of the Phantom such as the Phantom 4 is equipped with ultrasonic sensors and vision sensors to allow it to hold a much more precise position and allow it to avoid obstacles if the camera is not facing the forward direction (Phantom 4 User Manual V1.2, 2016).

The Walkera Runner 250 Advanced is a 250mm quadcopter.  It is one of the few FPV Racing quadcopter equipped with GPS from the factory (Walkera Runner 250(R) Quick Start Guide, 2015).  This is a fairly unusual option since weight is the enemy in most any form of racing.  In a class where most racers are under 500 grams, the additional weight of a few grams from a GPS antenna can cost a race, but this platform was chosen to try and make a closer comparison of the two types of platforms.  The camera on the Runner is not attached to a gimbal and mounted directly to the quadcopter on the forward point on the body, this gives the controller the feel of being inside the cockpit of an aircraft (Walkera Runner 250(R) Quick Start Guide, 2015).  The image is stabilized with two rubber bulbs that act as shocks so that vibrations from the propeller does not create what is known as the “Jello” effect.  This is where the image moves as if the user is looking through moving JELLO or water.  Just like the Phantom this image is sent back to the operator at the GCS and displayed on a screen or what is known as FPV Goggles.  Additionally the image is not stabilized independent of the aircraft because this allows the users to infer the attitude of the aircraft as if they were actually in it.  Lastly the GPS is not integrated into the body shell, as it does not have one in the same way the Phantom does.  The Runner is a racer, so again, weight is the enemy and the frame is the main support and made of carbon fiber, so the antenna is placed on the top of the carbon fiber with a plastic post to set it up a little higher for a less obstructed view to the sky.  While the GPS obtains the same information, it is mainly used as a way for the user to see their position and relative to the aircraft and allows for a return home function, both similar features found in the Phantom, but unlike the Phantom the positioning is not meant to be as precise and is susceptible to drift from the wind and altitude is only accurate up to about +/- 3 meters (Walkera Runner 250(R) Quick Start Guide, 2015).

While these platforms offer a similar sensors, they are arranged differently and operate differently due to the intended use or mission of the system.

References

Phantom2 Vision+ User Manual V1.8. (2015 Jan) DJI. Retrieved from http://dl.djicdn.com/downloads/phantom_2_vision_plus/en/Phantom_2_Vision_Plus_User_Manual_v1.8_en.pdf

Phantom 4 User Manual V1.2. (2016 Mar). DJI.com. Retrieved from https://dl.djicdn.com/downloads/phantom_4/en/Phantom_4_User_Manual_en_v1.2_160328.pdf

Walkera Runner 250(R) Quick Start Guide. (2015 Oct 20). Walkera