Development of a Small Electric Robot Boat for Mowing Aquatic Weeds

Highlights A small, automatically guided electric robot boat was developed to control the growth of aquatic plants in lakes. The robot boat was able to mow without becoming entangled with aquatic plants due to the paddle propulsion mechanism. The average speed was 0.41 m s -1 , and the lateral deviation from the set path was 9.4 cm. The growth restraint effect was confirmed using aerial images collected by a drone. Abstract . At present, aquatic plants are becoming a problem in various lakes. Aquatic weeds that grow to high densities cause decreases in the oxygen concentration in the water, accumulation of sludge, and adverse effects on water use facilities and fisheries. Although there are large machines for cutting and harvesting aquatic plants, their use is limited due to their high cost, large size, and heavy weight. On the other hand, manual cutting is very labor intensive and inefficient. Therefore, in this research, we developed a labor-saving and low-cost robot boat to mow aquatic plants. This robot boat is automatically controlled by a real-time kinematic global navigational satellite system (RTK-GNSS) and is characterized by its small size, light weight, excellent portability, and low energy consumption. In addition, a paddle mechanism that replaces a conventional propeller was introduced as a propulsion mechanism to prevent entanglement of water plants and enable long-term automatic navigation. Mowing lotus (Nelumbo nucifera) in Lake Izunuma, Miyagi prefecture, Japan, confirmed that mowing could be properly conducted with a lateral deviation of 9.4 cm, average speed of 0.41 m s-1, and average power consumption of 518 W even when lotus was at its densest growth. If the cutting width of the robot boat was 1.2 m and the sidelap width was 0.3 m, the theoretical field work rate would be 0.133 ha h-1. Images captured by a drone confirmed that cutting with the robot boat was effective in suppressing the growth of lotus. It was found that the effect of suppressing growth was maximized by mowing at the time when the stopping leaves appeared in the late growth stage of lotus. Keywords: Autonomous navigation, Lotus, Moving baseline, Robot operation system, RTK-GNSS, Virtual private network.