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Our long term goal is to build the first autonomous vessel to circumnavigate the Earth. In order to reduce this ambitious goal to manageable size, we're building progressively more capable boats. The first one is our current solar-electric boat, TSV Disputed Right of Way.
TSV Disputed Right of Way (TDRoW, for short)
TDRoW is a heavily modified 18' two-person kayak. It was the cheapest one on Craigslist in the Seattle area when we decided to take that approach. We built up the hatches with foam and fiberglass to take flat hatches, and we added substantial internal reinforcement to support solar panels, batteries, and an electric motor.
Propulsion & Power
Propulsion is provided by a refurbished and modified Minn-Kota trolling motor that draws 30A @ 12V. Power is provided by a pair of 31-950 lead-acid truck batteries. The Minn-Kota has a rather odd speed and direction control system that consists of making and breaking connections between the power source and the four wires (red, black, yellow, and white). Instead of figuring out how the wiring is supposed to work and using a brush motor driver, we use a box full of automotive relays to mimic the behavior of the stock equipment.
Battery power is provided by a pair of big lead-acid truck batteries. They have the advantage of being simple and durable -- no special charging equipment or protection circuitry is required.
Three 12V solar panels and a simple charge controller round out the power system for long range cruising.
The control system is a two-tiered system, with a Beaglebone for high level processing and an Arduino Mega for real time processing. Navigation data comes from a GPS and a 9-DoF IMU for compass heading. Currently, the Arduino attempts to steer a given course provided by either the Beaglebone or the shore operator. There is also a manual steering mode for fine maneuvering and troubleshooting.
Prior to the current version, our control system was based around MAVLink and QGroundControl... which are not so good. Now, we're working on a REST interface. It's going a bit better, and it gives us the flexibility to operate with a partial system, which we lacked before.
Steering is provided by a waterproof servo and reduction gear from Servo City.
Currently, it has a 7:1 reduction gear on it. This is more appropriate for off-shore operations, so we're going to cut it back to 2:1 for greater control authority during in-shore operations.
The core sensors are a 9-axis IMU for compass heading and a GPS for position. We are currently in the process of adding stereoscopic depth cameras and an AIS receiver for obstacle and ship avoidance.
Communication is provided by a 900 MHz ethernet bridge for ship to shore
communications and a 2.4 GHz wifi router for onboard networking. This
is because waterproof network cabling is generally kind of a pain in the
ass and using wifi onboard makes it trivial to add sensors and so on in the future.
There's also a horn (to warn operators when it's ready to start) and status lights to indicate the state of the Beaglebone and the Arduino. At Toorcamp, we added grab ropes along the side ease shore handling and launching. They were immensely effective; we should have added them years ago. A ballast bulb (really a length of 2" PVC stuffed with rebar) is strapped to the bottom of the boat to keep things upright.
Building on an existing hull really was not the best way to go. The next hull, assuming we can get funding, will be a version of the advanced sharpie hull frequently used by the late Phil Bolger. An advanced sharpie hull is nice because it's reasonably efficient when thin and very easy to build.
Since the only way to make an autonomous circumnavigation is via the Southern Ocean, I don't think that solar-electric is going to work for the high-latitude travel, or will result in progress so slow that the entropy of simply being at...Read more »