UAS Sensor Placement: DJI Phantom 4 Pro and Walkera Runner 250R

Aerial Photography Services

For aerial photography and full motion video, I would choose a DJI Phantom 4 Pro electric quadcopter. The Phantom 4 has limited features compared to a larger aircraft like the DJI Inspire 2, however, I believe that the quieter flight and lower cost of the Phantom 4 Pro are large enough advantages to choose that aircraft.

Figure 1. DJI Phantom 4 Professional. (DJI, 2017a)

The Phantom 4 Pro weighs in at 3.06 pounds with propellers, battery, and camera (DJI, 2017a). The DJI Inspire 2 weights in at 7.58 pounds without a camera and gimbal (DJI, 2017b). The increased weight of an Inspire 2 results in a louder aircraft. More thrust is needed to life the heavy aircraft off of the ground. The decreased noise levels of a Phantom 4 Pro is greatly appreciated when shooting photos or videos near humans or wildlife.

The Phantom 4 Pro retails for $1,499 USD compared to $2,999 for a comparably equipped Inspire 2. Both come with a 1-inch CMOS sensor capable of 4K video at a resolution of 3840x2160 pixels and 20 megapixel images (DJI, 2017a; DJI, 2017b). With the same sensor size, both have the same characteristics in low light conditions. On the Phantom 4 Pro, the camera is mounted underneath the aircraft on a gimbal between the landing gear, giving a generally unobstructed view. The 50% cost savings by using a Phantom 4 would be better spent purchasing SD cards, extra batteries, and a case more suitable for travel to filming locations.

Although small, the DJI Phantom 4 Pro has a suite of exteroceptive sensors to assist in safe flight, obstacle avoidance, and accurate positioning. The aircraft has stereo vision sensors placed in the front, rear, and bottom of the aircraft (DJI, 2017a). These obstacle avoidance sensors are capable of measuring a 60° horizontal width and +/-27° vertically at a range between 2 and 98 feet when the aircraft is flying at speeds below 31 miles per hour  (DJI, 2017a). At higher speeds, the aircraft is banked too sharply resulting in obstacles positioned outside of the visible sensors area. The Phantom 4 Pro also comes with infrared sensing systems on the left and right sides of the aircraft. These sensors measure at a rate of 10 Hz at a horizontal range of 70°, vertical range of +/-10°, and a distance range of 0.6 to 23 feet (DJI, 2017a). These sensors provide an aerial photographer and cinematographer with invaluable tools to avoid collisions with obstacles, something other manufacturers and models are unlikely to provide.

First Person View (FPV) Racer UAS

Unmanned aircraft built for first person view racing possess far different qualities from a quadcopter for aerial photography. A racing UAS must be smaller, lighter, and more maneuverable than a photography UAS. These racing aircraft are built out of very strong and lightweight materials such as carbon fiber and usually lack the stable autonomous flight modes that are ideal for photography. A racing UAS lacks the collision avoidance safety systems to reduce weight. In addition, these aircraft are concerned with going forward at high rates of speeds and are unlikely to fly sideways or backwards into an obstacle. Thus, the most important exteroceptive sensors is the vision sensor mounted in the front of the aircraft. These cameras are chosen based on the best balance between frame rate and latency. A lightweight camera with a latency between 20 and 30 milliseconds is ideal.

For a FPV racer, I would choose the Walkera Runner 250(R). This aircraft weighs in at 0.98 pounds (Walkera, 2017), far lighter than the Phantom 4 Pro. This aircraft has a fixed camera mounted on the front of the aircraft with a 12 megapixel sensors that’s capable of 1920 by 1080 pixel video at a frame rate of 60 frames per second (Walkera, 2017). Compared to the aircraft built for photography, we’re less concerned about resolution and instead require the smallest possible video lag, high frame rate, and lightest weight. The Walkera 250(R) retails for about $330 USD at the time of writing.

Figure 2. Walkera 250(R). (Hobby King, 2017)

References

DJI (2017a). Phantom 4 Pro Specs [Webpage]. Retrieved on 12/4/2017 from https://www.dji.com/phantom-4-pro/info#specs

DJI (2017b). Inspire 2 Specs [Webpage]. Retrieved on 12/4/2017 from https://www.dji.com/inspire-2/info#specs

Walkera (2017). Runner 250(R) Product Page [Webpage]. Retrieved 12/4/2017 from http://www.walkera.com/index.php/Goods/canshu/id/26.html