This article is about machine manufacturing for Maritime RobotX Challenge 2018.
In a word, we lacked everything: number of developers, period for developing, experience, money, place, and so on. We began designing machines in April 2018 (last only 7 months for shipping) with only four students including three seniors who had to do graduation studies and prepare for entrance exams of graduate schools. Furthermore, we had no experience for developing machines which work on the sea, so what we could do was limited.
Since explaining what we have manufactured in words is difficult, let me show a figure of CAD model of the boat and a picture on site at first.
I put numbers from 1 to 4 for characteristical parts in the figure. Descriptions of each part are following, which are based on Technical Design Paper we submitted during competition.
- Improvement of stability by additional floats
We mounted floats which make additional buoyant at the stern of the hull (1 in figure) so that the boat would not turn over. We used Styrofoam as floats, and structure materials of aluminum support the buoyant which occurs when the Styrofoam sinks in the sea. We also used GFRP (Glass Fiber-Reinforced-Plastics) not to damage the Styrofoam even if it contacts the obstacles. It made sailing steady because it produced large buoyant in spite of its lightness.
- Review of the sensors arrangement and type
The upper part of the hull is used for detecting the location information of the objects around it. In order to secure an adequate visual field, we arranged the sensor at height. We placed a stand to arrange Ai pilot upon the MD/Sensor Box and the Jetson Box (2. in figure) so that the hull won’t be detected by the LIDAR. In addition, we selected the dual LIDAR structure, which has another LIDAR at the stem of the hull. As a result, we could get information about view of both wide field and detailed forward.
- Stabilized navigation by lowering the center of gravity
At the last competition, our machine had a big problem with stability due to the high center of gravity caused by arranging batteries on the deck.
To deal with the problem, we introduced the mounter for batteries and Power Management Box under the deck (3. in figure), and made center of gravity lower. This improvement enabled the boat to sail stably.
- Realization of lateral movement by sophisticated driving mechanism
In order to increase the flexibility of movement of the hull, two azimuth thrusters were adopted. Two outboard electric motors (LACOMETA), which have 86 pounds of thrust each, rotate around the yaw axis by using servo motors (XM540-W270, Dynamixel) and mechanism of timing belt pulleys. With this improvement, the hull could move omnidirectionally.
Although we actually tried to create many other machines to challenge other tasks: one for ball-launching, another for take-off and landing of AUVs for example, these were not completed because we had limited resources as I mentioned. We are disappointed with this incompleteness, but we had made a gradual progress from past competition, that is to sail stably, to get clear information around the hull, and to enable omnidirectional move. This may seem to be simple, but is essential for autonomous navigation. We could form the basis of hull this time, and would like to apply these experiences to the next competition in 2020.
We greatly appreciate all people supported our activities. Thank you so much for their kindness.