MIT ROV TEAM Michelle Aquing, Heather Brundage, Lauren Cooney, Bridget Downey, Eddie Huo, Albert Kwon, Harry Lichter, M. Jordan Stanway, Kurt Stiehl, ThaddeusStefanov- Wagner, Daniel Walker Hello, we are the MIT ROV team. This is the third year we’ve competed in Marine Advanced Technology’s Remotely Operated Vehicle national competition.

Goals Build a highly maneuverable vehicle capable of operating in confined spaces at depth. Small size (~ 1 foot cube) Small tether Able to complete mission tasks: Re-establish the communications link to the science package Retrieve data probes located within a drawer on the science package. Collect a sample of red fluid from the crevice. Measure the temperature of the venting fluid. At the beginning of the year, our team came up with goals for this year’s competition. From experience, we knew that large ROV’s with bulky tethers were hard to maneuver. With the space and time restraints placed on us in this competition, we knew that maneuverability would be a major factor. Because of this, our main goal was to build a highly maneuverable vehicle capable of operating in confined spaces at depth. We also wanted to complete all of the mission tasks presented in the competition. These are: Re-establish the communications link to the science package Retrieve data probes located within a drawer on the science package. Collect a sample of red fluid from the crevice. Measure the temperature of the venting fluid.

Power Supply Limited to 12v 25A onboard supply. Use 10 1.2v, 20Ah size “M” NiMH cells. In order to meet these goals we decided to take a new approach this year and operate our vehicle off of on-board batteries. Though this meant we could not use as much power, due to competition guidelines about on-board power, it allowed us to significantly reduce our tether size and not worry about power loss over the tether. Though on board batteries take up space and added significant weight to our vehicle, these were trade offs we were willing to make in order to improve maneuverability. After researching small, efficient, 12-volt (a competition requirement) batteries, we decided to use 10, 1.2 volt, 20Amp-hour NiMH battery cells.

Battery Packs Split into two waterproof Otter boxes Each box has a 30A slow blow fuse These we split into two waterproof Otter boxes, each with a 30 A slow blow fuse in order to protect the batteries. A 25 amp fuse on the entire power system is located in the control box in order to meet competition requirements. Two sets of two battery packs were built in order to allow for charging, and each can easily be discounted from the main system using waterproof impulse connectors. The Otter boxes are rated to 100 feet.

Task #1 & #2 – Communication Link Reconnection and Probe Retrieval The decision to keep the ROV small and to use on board power affected the rest of the design of the vehicle. When deciding on how to complete the mission tasks of retrieving the probes, we hoped to use a method that would be passive and not take much time. We hoped to find a way to descend on the probes, grabbing all three at once, and then ascending again. The mission specifications were not specific enough for us to design for this, however, and so we ended up choosing a relatively simple cork-screw design. We decided that in order to keep the system simple and compact, we would use the same method to carry the communications link to the connector. This Prevented us from needing to deal with more appendage on our vehicle that would stick out and get caught, and also decreased the complexity of trying to add a manipulator to the vehicle. In order to retrieve the probes, we first need to open the drawer. Though we considered many ideas for the drawer opener, we decided to keep it completely passive and just use a hook and the thrust from the ROV to open the drawer. This meant we didn’t need to add more motors to allow the hook to swing out when it was needed, then tuck away when it was done – which would take space, power, and add complexity.

Task #3 – Fluid Collection Bag collection system no change in buoyancy little pumping resistance passive dummy/sample separation Windshield washer pump Small internal volume Little initial dilution Again, simplicity, size and power constraints guided our design for Task # 3 – collecting a sample of fluid from the crevice. Last year we used a two-bag system with a bilge pump to collect a fluid sample. This year, we improved that system. We liked the bag collection system, as there is no change in buoyancy from the empty to the full state. The two bags allow for an undiluted sample, as the fluid primed in the pump will first flow into the dummy bag, letting the undiluted fluid fill the sample bag after the dummy bag is full. The main improvement this year was the switch to a windshield washer pump instead of the bilge pump used last year. This allowed us to reduce the size of the system, since the windshield washer pump is smaller, but more importantly, the pre-flooded volume of the new pump is about 10% of what it was last year, allowing for a smaller dummy bag. The new system is also faster, as it can fill 500 ml in 20 seconds. Another improvement over last year’s design is that it is placed in the front of the vehicle, and is unobstructed by any lower appendages.

Task #4 – Temperature Measurement RTD - resistance temperature detector Wheatstone bridge and amplifier circuit The range of our sensor is -7˚ to 61˚ C In order to complete the 4th task – measuring the temperature of a venting fluid, we use a resistance temperature detector (RTD) to make temperature measurements. The RTD is connected to a Wheatstone bridge that shifts the base level of our measurements. This bridge is balanced for a zero output near the freezing point of water. The measurement is then amplified to compress the sensor’s range. We do this because the measurement is read into an analog-to-digital converter in our controls, and our accuracy increases with a smaller range. ****** Our AtoD chips are XX-bit; this gives us a final temperature measurement accurate to XX. ****** We have 3-second response to XX. ****** We also record and plot a time trace of our measurements, so we can pick out the highest or lowest temperature we have seen over the course of the mission.

Switching Video System 4 color cameras with LED lights 2 channels of video up fiber tether 2 computer playback cards for portability 1 switching board underwater

Schematic

Video System Advantages Choose any two cameras Small in size Not need additional expensive displays

Tether Single strand, single-mode fiber optic cable 500 meter passive spooler on ROV 2 video lines and RS-232

Pressure (depth) Sensor Membrane/strain-gauge type sensor Measures differential pressure Allows operation at higher absolute pressures (greater depths) with a more affordable sensor Ours measures 0-206 kPa (0-30 PSI) Provides useful readings to 20 m (66 ft) This sensor is part of a family of sensors that has a wide range of operating pressures. If we want closed-loop depth control on deeper missions, we can easily swap for a higher pressure sensor, but sensors with a smaller range are more accurate within that range. Not required by any mission task, but useful to ROV control and mission performance

Control 2 Computer system Topside slave laptop handles user input commands and displays data Bottomside master microcontroller activates motors, reads sensors The ROV has two computers that make up its control system. The topside computer is a standard Windows laptop. The bottomside computer is a Microchip embedded microcontroller. The two talk to each other through a standard serial port language and speed, 8N9600. A laptop was chosen for the topside controller because it is easy to create a graphical user interface (GUI) with a laptop. This GUI lets the pilot display systems data and create custom flight routines. An embedded controller was chosen for the bottomside computer because of its low cost, small size, and selection of onboard analog, digital, and timed pins. Every 1/10th of a second, the bottomside controller tells the topside controller that it is functioning, and gives some useful data like depth, speed, and temperature. The topside control responds by telling the bottomside controller any new instructions from the pilot. This is called a master-slave arrangement; the bottomside controller is the master, and the topside controller is the slave. The bottomside controller was chosen to be the master because it is more important than the topside control: it needs to create motor signals, read sensors, and implement feedback. It does this much faster than the pilot and topside controller is able to give it instructions. As a result, it is more efficient to make the topside controller wait for the bottomside controller, rather than vice versa.

Thrusters 4 fixed thrusters 2 150W thrusters: 1 Heave, 1 Surge, 2 10W Thrusters: for both Sway and Yaw How many thrusters does your vehicle have? Why? The ROV is actuated in four degrees of freedom, all 3 translation directions, and rotation about the Z axis. This can be accomplished by a minimum of 4 actuators. For simplicity we used 4 fixed thrusters. There are two large thrusters used for moving forward and vertically. Two smaller thrusters are used to move laterally and rotate How much thrust does each produce? Not measured, but expected in range of 5 lbs bollard How many watts does one thruster use at full rpm? Max RPM and no load = 30W How many amps does one thruster draw under full load? 150 W at 12V = 12A Explain how you measured thrust. Put thruster in water, measured pull on a spring scale How is power (watts) used by one thruster related to the thrust it produces? They are proportional. Power is the rate of energy transfer, to overcome system drag at a steady velocity or to change kinetic energy through acceleration. Do you know the forward speed of your ROV? How did you measure this? No but would do so in the testing tank with a stringpot, video, or timing a taped off distance

Thruster Design Bearings Motor Seal Gearbox The main thruster uses a deWalt drill motor in a custom housing. The front spindle uses paired angular contact bearings to provide high stiffness in a short space. The main shaft is sealed with a teflon seal. The main housing is sealed with two pairs of two o-rings. One on the front cap and one on the back. Seal Gearbox

Frame and Floatation 80-20 frame for modularity Donated structural polyurethane foam Integration: Impulse connectors Frame – 80/20 for modularity Safty features: Fues in batteries, 25 amp auto reset circuit breaker.

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