In Sunriver, Oregon, residents dislike how the Aspen Lake is infested with rotting, unattractive, and smelly duckweed. This problem can also lead to eutrophication (when there is an excessive amount of nutrients and demand for biological oxygen so the lake runs out of resources and cannot support life). We are developing a fleet of autonomous robots to address this problem. The first conveyer belt will collect the duckweed, and the other will hold and drain the material before dumping into shore. This dumping can be either in a centrally located container for removal and composting
INVENTION STATEMENT: Catlin Gabel High School’s Global and Community Engineering Club’s invention is a low maintenance autonomous robot designed to skim and remove aquatic surface vegetation such as duckweed and algae from small lakes and ponds. This robot would offer a substantial reduction in the cost of removing the vegetation in comparison with the other methods of removal that currently exist. With this invention, we are able to serve a niche in the market for both small bodies of water and for bodies of water whose ecosystems are fragile or protected. Not only will our invention be useful where other technologies are not, it will also be substantially less expensive. For example, one of the current methods of removal would cost our target customer an estimated $100,000 to $200,000 for a single treatment lasting only a month. Contrarily, our target cost for our invention would be $30,000 (the cost of a team of three robots). Our invention would be the first in a new category of inexpensive environmentally friendly yet effective methods for removal of surface vegetation.
DETAILED DESCRIPTION: The robot’s design would be based upon a single person pontoon boat. The pontoons would allow space for a set of conveyer belts on either end of the robot. As mentioned previously, the robot would use a series of two conveyor belts: the first conveyer belt to remove the aquatic vegetation from the water’s surface, and the second to move the vegetative material from the robot to the shore to be dumped in a manner which facilitates either proper decomposition or easy dumping in a portable container. The conveyer belts would be built for durability out of stainless steel woven wire. For propulsion, the robot would use two paddle wheels, one on either side of the robot. These wheels will have the ability to run in both reverse and forward directions to give the robot the ability to rotate around its own axis. Another trait of the paddle wheels is that they would be built in a way that would prevent them from becoming tangled in the many subsurface weeds in the lake. As a solution to the robot’s need for long range, it would be necessary for the robot to have a large 12 volt battery. Placed in the bottom of the craft, this would also serve as ballast for our top-heavy design. However, it will most likely be depleted in a single day’s use, so in order to charge the battery we will need a large constant source of power, one that solar panels will not be able to deliver. Because of this, we will need to build an AC powered docking station to charge the robot when it is not in use. In total we can estimate the robot would be approximately 5-6 feet long, 4 feet wide, and 250 pounds. Our robot will use a Raspberry Pi or Beaglebone as the controller, with software written in Java. To locate each robot, we will use the Piksi, an RTK (real-time kinematic) GPS made by Swift Navigation that is accurate within two inches. One GPS unit mounted on a base station will calculate ionospheric interference and transmit the data to the GPS on each robot. The communication between robots and the base station will use XBee pro radios, which have limited bandwidth but a range of 1.5 miles. The range should allow all units working in a single body of water to use a central base station. If a longer range is necessary, relay stations will be required. Additional input devices will include a compass, two ultrasonic sensors, a capacitive proximity sensor, and a camera.
We will develop the software in phases, allowing our hardware to be tested early while more advanced navigation code can be tested on a functional robot. Our first software phase will be basic joystick control. The drive code will be similar to our FIRST robots, except that we will have to detect motion using a compass and compensate for drift. The next phase will consist of basic navigation around shorelines and the location of disposal sites. The layout of islands and other obstacles in a body of water will be recorded by manually driving the robot around each hazard and storing their locations into a grid. Each grid square will be one square foot and be occupied by either land or water. Two ultrasonic sensors, one facing downwards under the robot and one facing forward will alert it of additional hazards such as dogs or boats. At this phase, the robot will drive straight until it approaches a hazard, turn, and continue. While this will not perform intelligent or systematic sweeps, it will allow us to develop and test GPS and radio input. We will also record the positions of possible disposal locations, and utilize a capacitive proximity sensor to detect when disposal is necessary. It will approach these locations and orient itself using a compass. Once we are capable of building accurate map files and finding accurate GPS coordinates, we can begin development of a more advanced autonomous mode. This will involve grouping the grid squares into sections, and keeping track of the time since each section was last visited. The robot would then navigate to the desired section using a node graph and a simple path finding algorithm. Once there, the robot would perform a systematic sweep of the section before repeating the cycle. This would be effective assuming that all areas of the lake require an equal amount of attention. This, however, is not the case. Wind and water flow, as well as sunlight levels, affect the amount of vegetation buildup in each area of a body of water. Therefore, we will also develop a desktop application that will communicate with the robots, allowing users to select areas of lake for the robots to prioritize. The final phase of development will involve collaboration between multiple robots operating in one area. The robots will communicate directly with each other, sharing a map of the area. Upon completing a task, a robot will find the area with the most urgent priority and proceed to clean that area, updating the shared map so that other units do not go to work on that area.
BACKGROUND RESEARCH SUMMARY
PROBLEM: Duckweed (Lemnaceae) has posed an aesthetic concern to Sunriver homeowners for years and exacerbates eutrophication in Lake Aspen. Eutrophication is when excess nutrients encourage population growth of aquatic organisms and therefore raises the biological oxygen demand (BOD) to a level the lake cannot support. It covers the surface of the water in what appears to be green sludge. On closer inspection, duckweed leaves resemble lily pads and are about half a centimeter across. With no roots connected to the lake floor, duckweed floats only on the surface. It begins to bloom in April and populates the lake until it freezes over in fall (1). In warm weather, populations of this aquatic vegetation can double in as little as three days (1). In Lake Aspen, masses of duckweed can reach ten tons during the peak of the season, July and August (1). The Sunriver Nature Center and the Sunriver Owners Association (SROA) have received complaints about duckweed covering the lake and smelling for years (2). When the lake freezes over, almost all of the duckweed dies and rots. Decomposing duckweed emits a terrible odor that the residents must face. This decomposition also increases the biological oxygen demand.
ALTERNATIVE SOLUTIONS: Other possibilities for removing duckweed include hydrologic manipulation, aeration, chemical treatment, and physical removal. In the case of Lake Aspen, hydrologic manipulation is not ideal. The source of extra water, flooding, and the nutrients flushing into the Deschutes River are all concerns (3). Aeration would not be the most efficient solution because the air diffusers would stir up sediment, release nutrients, and promote duckweed and other aquatic vegetation growth (3). Chemical treatment is not effective either because once the duckweed and other aquatic growth dies, it will sink to the bottom, contribute nutrients, and therefore continue to exacerbate eutrophication (3). Our invention would avoid each of these problems.
COMPETITIVE MECHANICAL SOLUTIONS: The existing aquatic weed harvesters for lakes and ponds share some concepts with our invention. Established competitors with algae-cleaning boats are ProSkim and Weedoo. ProSkimmers are in-water flotation devices that collect the weeds and send them back through a hose to a filtration system on the shore that separates the water and weeds (5). The ProSkimmers have a limited range of efficiency because they are stationary and suck in both water and weeds. Weedoo creates ten-foot boats that use a conveyor belt to collect the weeds and hold them onboard (6). Due to its size and demand of time from an operator, Weedoo boats are impractical to clean small bodies of water.
PATENTS: Patents and similar machines on the market show that our design is a workable strategy. One of these patents was published as number US 20040079003 A1 (7). The patent expired February 12, 2013 due to unpaid maintenance fees (7). The device serves a different market since it is about thirty feet long and is dependent on a human to be present on the boat and steer. This invention can only operate in large bodies of water and customers must be willing to provide human labor. However, it presents paddle wheels as a capable propulsion system and conveyor belts as viable weed collectors. One gathers the weeds, another holds them, and a third dumps onto shore (7). Our idea combines the last two belts to contain, drain, and dump the duckweed.
SOLUTION: Throughout the process of ideation we have considered many solutions to the problem at hand, however, we regard a robot as the best solution. This project is suited to our team’s strengths and therefore feasible due to the background and knowledge of building robots of many of our members provided by Catlin’s FIRST robotics program. The invention will collect, hold, drain, and dump the duckweed with two conveyor belts. A charging station will supply energy to the conveyor belts and the paddle wheels. Durability, long range, compact size, light weight, water resistance, and the ability to resist becoming tangled in weeds growing below the surface are all traits we have considered to make our robot a viable solution to the aforementioned problem.
CONTEXT: Our invention will navigate the surface of Lake Aspen, which is about .5 square miles and contains two islands (3). A slow moving body of water called the Sun River runs through Lake Aspen and along the Sunriver development and golf course. Weeds such as coontail and elodea, three species of fish, the Oregon spotted frog, and the western toad inhabit this lake (3). Our robot is designed to avoid inflicting any harm to the wildlife of the lake. FEASIBILITY: The technologies we have selected for our robot have been shown as workable in the past. We therefore know our robot can feasibly be compiled and operate in Lake Aspen. Our goal is to collect one ton of duckweed over the growing season (April to October). This will be feasible due to duckweed’s inability to survive winter and our robot’s capacity to remove the duckweed before it can multiply. Our robot will be able to carry ten pounds of duckweed at a time and perform twenty dumping cycles in a day. This would remove about 200 pounds of duckweed per robot every day.
SCHEDULE: The first phase of this project will extend through June 2014 and will culminate with a proof of concept prototype to be tested and refined over the summer of 2014. Depending on the results of those tests, additional funds will need to be raised to continue to the next round of production prototypes.
1) Bowerman, Jay. “Interveiw With Jay Bowerman at the Sunriver Nature Center.” Group
Interveiw. 15 August 2013.
2) Jendro, David. “Q&A with the Sunriver Owner’s Association.” Group Presentation. 16 August 2013.
3) GeoEngineers, Inc. (2011). Field Study of the Sun River Aquatic Management Plan. Sunriver, OR: Ambrose, J., Wright, W.
4) Blank, B. (June 19, 2012). Robosnail One Step Closer to Being Released. Retrieved from http://reefbuilders.com/2012/06/19/robosnail-2/
5) How the Proskimmer System Works. (2013). Retrieved from http://www.proskim.com/how_it_works.html
6) Products. (2011). Retrieved from http://www.weedooboats.com/boats.php
7) Aquatic weeding device US 20040079003 A1. (2012). Retrieved from http://www.google.com/patents/US20040079003