Aircraft sensor placement is as much an important design consideration as what sensors to install. Incorrectly placing sensors can lead to erroneous or misleading data inputs to avionics or cockpit displays. Valid data streams are of critical importance on Unmanned Aerial Systems (UAS), since they provide the sole source of information for remote pilot or autopilot decision making. A vehicle will be selected and sensor placement analyzed in two UAS mission examples.
Aerial Photography UAS
The first step in selecting a platform for a particular mission should be defining the requirements. The following characteristics, in descending order of importance, were used to select a UAS for aerial photography flying less than 400 feet Above Ground Level (AGL).
- Camera stabilization and control
- Resolution
- Vehicle station-keeping
The FreeFly ALTA was selected since it offers the best capability in those areas. Camera stabilization is maintained by the MoVI 3-axis gimbal system. With the optional MIMIC controller, a second operator can independently control the pan, tilt, and yaw of the main sensor (FreeFly, 2015). FreeFly has taken advantage of adaptive autopilot controllers now available in high-end sUAS by allowing the 3-axis gimbal to be positioned below or above the vehicle. This adds an entirely new perspective, which allows filmmakers to be more creative, and provides a new angle for structural inspections. High resolution stills or video can be captured by a wide range of professional digital cameras thanks to the ALTA’s 15 pound payload capacity and modular mounting system. Sensors such as the Red Epic Dragon can generate 19 megapixel images at 100 frames per second (fps)(Red Inc., 2015). High frequency vibration isolators are installed at the sensor gimbal/airframe interface to eliminate interference from the six rotors (FreeFly, 2015). This is crucial to maintaining smooth video when the sensor’s frame rate approaches a harmonic frequency of the propulsion system. The autopilot draws from avionics-grade rate sensors which combine with the hexacopter configuration to provide extremely precise control. Adding the MIMIC controller would increase station keeping ability by dividing piloting and sensor slewing workload between two people (Lavars, 2015).
Racing UAS
Assuming all aircraft were similar in racing capability, the following sensor-related characteristics were used to select a UAS capable of competing on a First Person View (FPV) racing circuit.
- Field of view
- Refresh rate/link latency
- Picture and telemetry presentation
The STORM Racing Drone had a good compromise of the items above in an affordable package (HeliPal, n.d.). The main charge-coupled device (CCD) sensor has a 110o field of view, which will provide the pilot with sufficient obstacle awareness. The main sensor was also positioned relatively close to the center of gravity. Other models of racing UAS had the camera slung beneath the body (similar to those for aerial photography), which would likely exaggerate pitch and roll rates to the pilot due to the long moment arm. The STORM’s 3.2GHz, 250mW transmitter advertised consistent video feed at a range of 1 mile, which user reviews appeared to agree with. This vehicle also includes a visor-type display for the pilot. These are preferable to screens, since they are not subject to sun glare. Depending on the model of visor, battery time remaining and signal strength can also be displayed.
References
FreeFly Systems. (2015). Redefining Movement. Retrieved from http://freeflysystems.com/products/2015/alta/
HeliPal.com. (n.d.). STORM Racing Drone (RTF / Type-A). Retrieved from http://www.helipal.com/storm-racing-drone-rtf-type-a.html
Lavars, N. (2015, April 15). High-end Freefly Alta drone flips aerial photography on its head. Gizmag. Retrieved from http://www.gizmag.com/freefly-alta-drone-photography-nab/37026/
Red Inc. (2015). Epic Dragon Tech Specs. Retrieved from http://www.red.com/products/epic-dragon#tech-specs
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