by David Geer
Contact the author at geercom@windstream.net
Co-operative ASV Robots
Autonomously Investigate
Harmful Algal Blooms
Harmful Algal Blooms (HABs) are large and increasing masses of certain types
of algae that produce toxins capable of negatively impacting plant, animal,
and human life. Biology Professor David Caron and his team at USC are studying
HABs, and they are doing it with the help of some autonomous, aquatic,
robotic ‘friends.’ Researchers from USC use autonomous surface vehicles (ASVs)
to study HABs. The scientists have applied two ASVs to the task in
collaboration with special, sensor-enabled buoys as part of a
Networked Aquatic Microbial Observing System (NAMOS).
The Robotic Embedded Systems Lab at USC, lead by Professor Gaurav Sukhatme, regularly deploys two ASVs into the Redondo Beach Marina to monitor the
sea and take samples. NAMOS has already permanently
installed buoys in the area as nodes which monitor the
water. When these nodes find something significant, the
scientists send the ASVs on a mission to investigate areas
where the fixed buoys cannot go.
The ASVs divide
these areas of interest
between them
based on algorithms
programmed in by the
scientists. Each robot
must visit its own set
of points and not
those of the other
robot. Each robot
must visit each
assigned point only
once. The robots rely
on each other and
must stay in range to
communicate with one
another via Wi-Fi. They
must avoid obstacles
This angle showcases the
boat’s MS- 5 sensor, winch,
and other equipment
topside.
10 SERVO 08.2009
and avoid running into each other.
The robots use several algorithms to accomplish
these tasks. When the robots are well within range for
communications, they go to their own dynamically selected
/assigned destinations. When communications are at risk
because the robots, headings take them further apart,
some additional intelligence steps in.
With this intelligence, the robots determine which one
of them is closest to its next waypoint. That robot becomes
the leader, and progresses to that point. The other robot
becomes the follower, and stays within range of the leader
to ensure that they do not breach communications.
Whenever either robot is about to strike an object or
run into each other, they drop the current task to avoid
the obstacles. As such, the robots function based on which
priorities they must meet at any given time.
Hardware and Components
Each boat (ASV) uses the same hardware, including
a Mini ITX 2 GHz dual core and a 400 MHz Gumstix
controller board for auxiliary functions that require
additional I/Os (input/output buses). Researchers originally
applied the Gumstix to experiments, in which the boats
held their exact station (location) at each GPS waypoint
despite the waves and wind. The Gumstix controller board
managed devices like an anemometer which measures wind
speed and direction. The board then processes the resultant
data and forwards it to the primary computer (the Mini ITX)
for use in the boat’s maintaining position. The Gumstix also
monitors the boat’s batteries.
