Designing a UAS takes a lot of
carful consideration of the mission it will be asked to accomplish. UAS can carry a multitude of payloads and
sensors and can have a very wide performance envelope. Because of these vast capabilities, one must
be carful to not overdesign a UAS by adding features and components that are
not required and that do not contribute to the mission. For the crash lab mission that I selected I
went through several design iterations to get the right combination of components
which highlighted some of these challenges for me.
UAS Design
For my original design I started
with the Gadfly Quadrotor base chassis, however I quickly realized that I was
not able to fit the required components onto the design. The chassis was not able to support a
gimbaled camera or a camera with both Electro-Optical (EO) and Infrared (IR)
spectrums. Due to these limitations I
was quickly forces to switch to the larger Condor Octorotor Professional base vehicle. This chassis allowed for a gimbaled camera
with both EO and IR capabilities to be fitted, as well as a Synthetic Aperture Radar
(SAR). For the ground control station,
the Handheld controller was selected to allow for easy operation, minimal
operator training and maximum portability.
While the ARVL controls were rather cumbersome to use, the real-world handheld
controller would have been the perfect match for this system because it would
allow for precise control of the UAS and the cameras fitted to the UAS (ERAU
Hub, n.d.).
Performance
Performance
was an important aspect of this UAS design.
The initial design utilizing the Gadfly Quadcopter had the highest performance
from both the speed and agility aspect and the battery performance aspect. Infact, this high performance turned out to
be somewhat of a challenge to control.
At maximum speed the Gadfly would reach an airspeed of about 40 (no
units in ARVL). This performance was
just not necessary for the mission the UAS was being designed for and it
increased the skill level required for the operator to ensure safe
operation. The first design change to
the Condor Octorotor solved this problem by cutting the max speed in half and
making the UAS much easier to control.
Unfortunately do to the increased power requirement from eight electric
motors and increased sensor payloads, the battery life was cut from 18 minutes
to 14 minutes. However, due to the small
size of the batteries this was not an issue because the operator could easily
carry multiple batteries and change them out as required. The final performance aspect was communication
signal range. The dipole antenna was
selected on both systems, however range still seemed to be more limited on the
Gadfly chassis. This limitation was not
an issue for the crash lab mission due to the short-range requirements. The switch to the larger Condor chassis
increased the range, but the change was almost un-noticeable (ERAU Hub, n.d.).
Mission
The mission
accomplishment forced one change to the UAS design. The original design control scheme was
automatic. However, this present planning
challenges due to the rudimentary planning software included in ARVL. It was difficult to get the UAS into the
right position and impossible to keep it there once it began the mission. While the automatic flight planning did
reduce the operator’s workload, making camera control easier, it made getting
the right shot for the mission almost impossible. For this reason, the second major design change
was from automatic control to manual control.
This allowed the operator to fly the UAS into the proper position, allow
it to automatically hover in position and then adjust the camera as required
for the images they needed to capture.
This did increase operator workload, but it was essential to ensure
mission accomplishment. The only other
change that as made during the mission testing phase was that the operator view
had to be changed from the pilot perspective to the onboard perspective. This was due to the UAS being to small to see
clearly at the distances it was flying from the operator. It was impossible to determine orientation
and camera angles without the onboard view (ERAU Hub, n.d.).
In the end the UAS I designed was able to accomplish the
mission with no limiting factors or problems.
While it took multiple iterations to the design, this was expected and
had it not occurred it would have been due to pure luck, as modifications are
always expected when designing a new system.
References:
ERAU Hub [Computer software]. (n.d.). Retrieved September
28, 2018, from https://erau.instructure.com/courses/84078/pages/resources-virtual-hub?module_item_id=4529679
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