Latis II Underwater Remotely Operated Vehicle Technical Report

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12 Figure 13: Arms Collecting a Crustacean TASK #3 –SAMPLE NEW VENT SITE This task requires Latis II to measure the temperature of the venting fluid in three different locations along the chimney height and collect a sample of vent spire to return it to the surface. A waterproof thermistor was installed on the right gripper to record the venting fluid temperature. This task provided another reason for the increased dexterity of the arms for the gripper needs to clamp on the tip of the vent which is at a 45deg angle and hold on until the temperature value is displayed on the computer screen. By having the thermistor situated at the end of the gripper and allowing the gripper to hold on to the vent, the ROV will be stabilized as the thermistor reads the fluid temperature. Furthermore, the net attached to the front of the ROV will allow room to store the vent sample that needs to be returned to the surface. TASK #4 – AGAR SAMPLE This mission task requires Latis II to collect a sample of a bacterial mat and return it to the surface. A special AGAR sampling tool was designed using PVC pipe and fittings to collect the proper amount of bacterial mat. The tool relies on suction power and the ability of the arms to break the surface tension of the AGAR. The depth of the AGAR sample tray was taken into account such that the diameter of the PVC LATIS II TECHNICAL REPORT device was the only adjustable factor in collecting the proper volume of AGAR. The design allows for the tool to simply be pushed straight into the AGAR and then pulled out with the AGAR held by suction inside the tool. The device and AGAR fit in the net on Latis II to prevent the extra trip to the surface. Through testing, AGAR was found to hold its shape and not disintegrate when collected so the holding net could be made of simple window screening and no special alterations were required. ROV DESIGN The ROV was designed with buoyancy, strength, size, dexterity, maneuverability and stability in mind. The overall idea incorporates six simply mounted thrusters, two identical 4 DOF arms with open-close grippers, three cameras for vision, a hydrophone and a thermistor for measuring sound and temperature respectively. FRAME The ROV frame was one of the most highly discussed components for the second semester. While the simple design of the prototype with its cylindrical water proof enclosure surrounded by a metal frame was effective, it wasted valuable space for electronics and was difficult to mount components to. It was finally agreed upon to make the upper structure both waterproof and structural so that there was no need for both, square for ease of fabrication and mounting, and made out of light plastic for buoyancy and strength. The bottom plate and lower skids were made of stainless steel for weight and resistance to corrosion in water. Constructing the lower portion of the ROV out of heavy stainless steel and the top section out of buoyant plastic creates a pendulum effect in the water causing the ROV to always tend toward an upright attitude and increases its
stability. Since the ROV is bottom heavy, the primary thrusters for forward, backward, turning, and strafing motion were mounted on the underside, allowing Latis II to maneuver easier since the thrusters’ force is applied close to the center of mass. The skids also protect the thrusters from being damaged and provide a solid stand for the ROV to sit on the pool floor. The ROV was tested in a tow tank and coefficient of 13 Figure 14: Main Frame Parts ARMS Many different arm design ideas were considered during this part of the design process. The team eventually decided on using Hitec 7775MG digital hobby servos for the majority of the arm linkages, and Hitec 805BB analog high toque servos for the heaviest joint- the shoulder rotation. Most joints utilized a chain and sprocket power transmission design not only for its simplicity and effectiveness, but also for the ability to use sprocket ratios to increase the power at any given connection. The range of motion for each link was decided and the corresponding sprocket ratio calculated to reach that desired range from the 180deg range of the servos. Since the range was always less than 180deg the torque available at the link would always increase proportional to the range decrease. The servos were sized for their power, size, and weight. To waterproof the servos they were dipped in Plastic Dip. A LATIS II TECHNICAL REPORT greased O-ring was installed between the servo case and the servo sprocket to protect the opening where the spline enters the case. Figure 15: Servo Waterproof Testing Lightweight plastics were utilized wherever possible for easier manufacturability and their high strength-to-weight ratios. HMWPE was used for the larger pieces of the arm and the connecting pins; a quarter inch thick PVC plate was used for the main structure of the links, and Teflon (PTFE) was used for bushings between the connecting pins and links as a soft slippery interface to reduce friction. All connections were made using press fit sizing to reduce the need for heavy metal fasteners. The grippers were designed using a rotation-tolinear linkage system and the grippers themselves were dipped in Plastic Dip to add extra grip. Figure 16: Latis II Arms
Page 1 and 2: 2010 Latis II Underwater Remotely O
Page 3 and 4: BUDGET/ EXPENSE 3 LATIS II TECHNICA
Page 6 and 7: SURFACE CONTROLS MAIN CONTROLS Lati
Page 8 and 9: 8 Figure 8: Onboard ROV Electronics
Page 10 and 11: 10 Read 3D Navigator Convert 3D nav
Page 14 and 15: TETHER The tether supplies Latis II
Page 16 and 17: attling leaks. Hours of research wa
Page 18 and 19: LOIHI SEAMOUNT The Loihi seamount i
Page 20: REFERENCES School of Ocean and Eart

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