Deep sea design: high school & college students compete to reach Titanic depths.

The mission was straight forward--go to the stateroom and retrieve a package.

Yet, few things in life are truly straightforward. The stateroom was in the wreckage of the Titanic, more than two miles into the inky, cold depths of the North Atlantic. The package was an underwater remotely operated vehicle (ROV), marooned during a previous mission, whose electronics container lost integrity and was now flooded, lending the machine a negative 10 lbs of buoyancy. To handle the mission would require a second ROV to be sent into the seabed graveyard, enter the ship through the same small opening as the first ROV, maneuver through the hallways to the stateroom, drag the ROV out the door and bring it to the surface.

Moreover, the entire scenario was a backdrop for a design competition. No one was going to be riding North Sea waves to rescue any hardware--at least, not this time around.

The competition

The Marine Advanced Technology Education (MATE) Center is national in scope, but works through regional partnerships to create new curricula, collect information from employers, and share 'best practices' related to Marine Technology Education. One of the Center's main goals is to collect information from employers as to what skills, knowledge and abilities are needed for select marine related occupations. The MATE Center and its partners have developed several curriculum modules and programs including an introduction to aquaculture, career scenarios (problems) for the classroom, technology-rich lab exercises, an A.S. degree program, high school pathways, and a careers course. The MATE Center has also implemented a successful national and regional internship program that places students in technical positions.

Additionally, the MATE Center coordinates and helps to facilitate ROV competitions that range from regional to national. The contests vary depending on the sophistication of the ROVs and the mission requirements In addition to being fun and educational, these competitions connect students and educators with employers from marine industries, highlight marine-related career opportunities, and promote the development of technical, problem solving, critical thinking and teamwork skills.

The First Annual ROV Design & Building Competition for High School & College Students was held in conjunction with the NOAA/NASA Link Project 2002 Symposium at the Kennedy Space Center at Cape Canaveral in Florida. A tale of sunken pirate treasure was created as the mission objective against which the competing vehicles were to work. The second competition, held the following year at MIT and co-sponsored by the Marine Technology Society and Walden Media, drew upon a lengthy Titanic scenario merely touched upon at the start of this article.

Winner '03

There were two competition classes for the 2003 challenge--the 12 to 25 group (named for its 12V/25A vehicle limit) that would have 20 minutes to recover as many objects (representing science probes) as possible, and an Open group that would be permitted to use up to 48V/40A to grasp and maneuver a two-cubic-foot package with 10 lbs negative buoyancy.

The ROV built by Lake Superior State University engineering students was designed for several applications. LSSU would use the system as a research platform for educational purposes upon which electrical systems, control algorithms, and various mechanical systems can be developed. The final vehicle was also used at the ROY competition. Based on work from previous designs, LSSU was able to narrow its final design down to what is referred to as a workhorse style ROV-a tethered vehicle generally used for heavy load applications and exploration. This type of frame allows for the most design flexibility in future design modifications.

Design challenges

LSSU requirements included the vehicle be capable of operating at a depth of 300 feet, use 300 VDC at less than 4A, be maneuverable using a joystick, and be neutrally buoyant for maximum stability. Financial constraints dictated that the vehicle's housing and electronics had to be designed and built in-house. The MATE mission for the competition required that the vehicle operate using 48 VDC at less than 40A, be capable of retrieving an object weighing ten pounds, and have the ability to maneuver in the Titanic Mock-up in which the object being retrieved was located.

The final design used six motor housings (two forward/reverse and four up/ down), a camera housing, a main housing for most of the electronics, and floatation for neutral buoyancy. All these components were contained within a stainless steel crash frame. Two separate power distribution systems were used to meet the LSSU and MATE power requirements. It was also decided that a single hook would be sufficient as a retrieval device.

The most challenging portion of the design was the motor and propeller combination. Propulsion had been a definite concern as it was necessary to design a workhorse style ROV. The team studied and designed motors and motor control systems to assure the ROV had the required maneuverability. Further complications included the need for an embedded system for communicating between the user and all of the ROV systems, which had to be accomplished using as few wires and underwater connectors as possible.

Development

The finished unit weighed 280 lbs, moved at speeds up to 2 ft/sec, and turned within its footprint. The thruster design went through several iterations and testing of many motor and propeller combinations. In the end, 48 VDC, ultra-low inductance brushed gear RE-40 Maxon motors with GP-42C planetary gearheads and 8-in. propellers were selected, producing a thrust level of 12 lbs per motor. The motor-gearhead combination provided a maximum torque of 346 oz-in, at a speed of 443 rpm, assuming an efficiency of 81%. In generating this thrust, the motors only drew 1.7A each, indicating that the motors had plenty of power left for future enhancements to the propeller design. The design also included a variable speed control, modified propellers, and a custom-designed waterproof housing. The gearmotors are dual shafted, with the reduced end attached to the through-hull shaft via a flexible shall coupler. The other end is attached to an incremental encoder. The pulses from the encoder are used to determine motor speed for feedback control functions.

The most demanding housing to design was for the motor. Although similar to the camera and electronics housings, the motor's housing also incorporates the greater design task of sealing a protruding motor shaft. The final motor housing was comprised of a tubular aluminum hull, a connector endcap with a pressure fitting, a motor endcap, and O-rings. Each motor housing provided a mounting location for the motor, as well as the supporting electronics and sensors.

All the housings were required to operate at all depths from the surface down to the 300-ft limit, and had to be able to withstand temperature changes that occurred from friction and the cold temperatures of the water: Standard and thrust bearings were used to align the propeller shaft, absorb the radial load (associated with shaft rotation) and the axial load (associated with the pushing and pulling of the shaft). The ROV was also designed for operation in a chlorinated pool and in fresh or salt-water environments. The housings, seals, and other materials exposed to the water were designed to be non-corrosive and durable under these various conditions.

Because Maxon motors easily adapt to a variety of controllers, the design team was able to select two different microcontroller platforms to facilitate the needs of both the LSSU and MATE specification for the final ROV design. The LSSU functionality incorporates a 16-bit Motorola HS 12 family micro-controller. The MATE functionality is controlled by a PICmicro controller.

Final design

The fully assembled ROV has four vertical thrusters for up and down movement. It also has three horizontal housings. Two small horizontal housings are motor housings, which allow the ROV to turn, as well as to move in a forward or reverse direction. The large diameter housing is the main electronics housing. It carries the micro-controller and sensors not associated with the motors. A clear acrylic housing mounted to the front of the main electronics housing is the main camera housing. A large octagonal foam floatation device is mounted on top of the ROV to allow it to remain neutrally buoyant in the water. Finally, a stainless steel crash flame encapsulates the entire system. This flame is meant to withstand any possible collisions in the water.

Important to the overall design was the ability to control the ROV from the surface using a joystick. The joystick commands had to be recorded, put into a transmittable package and sent to the vehicle through up to 400 feet of tether. This data had to be received, read, unpackaged, and distributed to the proper components. To provide this function and to allow for further expansion, Delphi (a PASCAL based software development tool) was used to create the user interface. This interface shows the status of ROV sensor data as well as error messages that may occur in the system, such as the presence of leaks. The user interface sends the data to the ROV, which is comprised of several separate housings. The data must be managed in the main housing, then distributed to the individual motor housings, controller housing, and camera housing. All the circuits that allowed for control of the vehicle were designed and developed by the LSSU student design team.

The final ROV design also incorporates two hooks mounted to the front of the vehicle. Since there was only one item the ROV had to bring up, a storage device, such as a basket, was not necessary. A vision system was used because of the depths at which the vehicle had to operate. High intensity, low current LED rings were designed into the system as a light source, allowing two compact, low-cost cameras to collect video information.

Rewards

While a competition helps introduce new design ideas into a theme, the team at LSSU definitely received lessons in task management in a real-world project environment. Documentation became a critical issue as the complexity of the project grew, and finalizing system design prior to purchasing components was shown to be a necessity.

Insofar as the ROV is concerned, future work would involve altering the machine so that it could monitor and maintain its own depth. Additionally, a "wish list" includes adding a second, rear-facing camera to observe the tether, and modifications to the joystick interface so that the control is non-linear for better control at low speeds and less sensitive control at high speeds.

Circle 130--MATE, or connect directly at www.rsleads.com/411df-130 Circle 131--Maxon, or connect directly at www.rsleads.com/411df-131 Circle 132--Motorola, or connect directly at www.rsleads.com/411df-132