Proposal for a Design of a Autonomous Bridge-Mapping Hydroplane Proposed for: 2.017 Design of Electromechanical Robotic Systems Professor Franz Hover Lab Instructor Harrison Chin September 29, 2009 1. Objective This project aims to create an autonomous surface vessel which will be able to investigate under and around the supports of a bridge, specifically the Harvard Bridge located in the Charles River of Boston, MA. The design will encompass various settings for the speed and level of control used for different portions of the mission and will also optimize the energy use and speed of the mission. 2. Project Description and Approach 2.1 Background The use of autonomous surface vehicles allows the surveying of large areas of water without the need for directed operation. The researcher may use an unmanned vehicle in situations where it is impractical or dangerous for a human operator to be present. High-speed unmanned vehicles also allow a larger area to be surveyed in a shorter amount of test time, a valuable resource in both research and industry. 2.2 Specific Goals In this project, the vehicle is being designed to survey the footings of the Harvard Bridge which spans the Charles River. The mission sees the vehicle steering itself to the bridge and photographing a bridge piling at multiple perspectives. The team is modifying a commercially available, high-speed electric hydroplane to run smoothly at differing optimal speeds. The vehicle, a Pro Boat Miss Elam, will be outfitted with a range of sensors. The energy consumption during the mission is also of concern. Although the vehicle will most likely meet its power requirements with additional batteries, the will also be a proof-of-concept for meeting these needs with an attached solar collector. Further, the motors and main power drawing elements of the system will be optimized to conserve energy where possible. This complex autonomous system will require both a rigorous control system and a rugged, waterproof design. 2.3 Functional Requirements Much more than just a camera and a means to trigger will be necessary for the successful completion of this mission. One major challenge will be ensuring the proper positioning of the boat with respect to the bridge pilings. To this end, the boat will be outfitted with a range of sensors such as gyroscopes, accelerometers, and a GPS system to assist in the navigation of the river to the bridge. A laser range sensor will be used in positioning the vehicle while it surveys near the bridge, as GPS data will be unreliable beneath the bridge. Another key ability is the power use-optimizing “modes” mission plan the team has identified as critical to the completion of the mission. The boat is quite small and can only carry so much on-board power. Far from the bridge, high speed will enable the boat to get to the bridge as quickly as possible. However, near the bridge speed is much less necessary and more power will need to be routed to the sensors. The team plans to use “modes” as a scheme for the speed of the mission and the power allocation within the vehicle. The robustness of the boat and the component attachments is perhaps the most crucial aspects of the mission, despite its mundane nature. The wave environment in the Charles River is roughly 1ft 1 Group 2waves at around 1hz, which is probably the worst-case environment for the Pro Boat Miss Elam. Sensors, such as the gyroscope and the compass, will help to gauge and compensate for these forced motions of the boats. 2.4 Preliminary Design Figure 1: Block Diagram of Planned Tasks The mission requires the boat to act as a stable platform, capable of carrying a large array of sensors, batteries and power collectors even at high speeds. To that end, several vehicle modifications have been planned to make room for the equipment and ensure that it is optimally positioned. Sensors such as the gyroscope, accelerometer, compass, and the Arduino microcontroller will need to be housed in a waterproof housing, so the geometry of the boat must be altered. The removable cowling currently encloses a mostly empty space, but this space will not be large enough to accommodate these sensors plus the additional batteries required to power them so it will need to be enlarged. The gyroscope and accelerometer will be mounted as close as possible to the center of mass of the vehicle, to try to minimize the lateral motion the gyro will experience and the rotational motion the accelerometer will experience. The laser rangefinder and camera will be mounted as high on the vehicle as possible, to minimize the impact of waves on the readings. If possible, the existing spoiler will be used as the mounting point. However, if the spoiler proves to be too far back, or structurally incapable of sustaining the required load, the camera and laser can be attached to the extended cowling. To allow the vehicle to both follow the walls of the supports by “looking” at the wall from the side of the boat and to avoid obstacles by seeing them from the front, the laser rangefinder will be mounted to a small servo which will rotate the components as needed. It is currently unknown whether the steering ability of the boat will be sufficient for this mission. Experiments are planned to test this aspect of the boat control and if it is deemed insufficient, the first step will be to add bow planes to increase the ship stability in pitch and roll. Finally, the ability of the hull to cut through waves may also need to be improved. As currently designed, the boat seeks to ride over waves instead of cutting through them. This is a good design for a 900 Watt boat with no purpose or ballast other than speed, but it will not work for this mission. The heavy components will weigh down the ship and the position sensors would be quite confused by the wave motion of the ship. The front of each pontoon will be made sharper and less sloped to allow the boat to cut through the waves. 3. Project Plan 3.1 LTI Modeling To successfully complete the mission, a robust control system must be developed that takes into account both the dynamics of the boat and the wave characteristics of the