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xBot III: Exploring Treacherous Spaces
Battery-Powered, Pressure-Tolerant Design With Fiber Optic Tether Allows Micro-ROV to Access Constricted Spaces

By Daniel Pol
Engineering Program Manager
John Tomasi
Mechanical Engineer and Naval Architect
Phoenix International Holdings Inc.
Largo, Maryland

Typical remotely operated vehicle (ROV) designs rely on the use of pressure-resistant housings to maintain vehicle electronics at one atmosphere. For a system designed to operate in 20,000 feet of seawater, these bottles are usually made of stainless steel or titanium and have very thick walls. The size and weight of these bottles impact the size and shape of the ROV, making the vehicle larger and more cumbersome as its depth capabilities increase. Additionally, as the ROV becomes larger, its power requirements also increase, leading to a larger umbilical.

In recent years, Phoenix International Holdings Inc. has developed ROVs for operation in extreme depths, hazardous environments and highly restricted spaces. These vehicles were made possible through the investigation and design of pressure-tolerant electronic systems and components, pressure-tolerant batteries and battery management systems, and light-emitting diode (LED) lighting.

The xBot, a micro-ROV developed by Phoenix, is one result of these research activities. This ROV, now in its third generation, has been successfully deployed in multiple high-profile missions, including an extensive survey of the RMS Titanic and, more recently, a survey of the Deepwater Horizon.

In 1999, Phoenix was involved in the successful search for the INS Dakar, an Israeli submarine lost in the Mediterranean Sea on its maiden voyage in 1969. The subsequent survey of Dakar in 10,000 feet of seawater revealed that the forward section of its hull appeared to be intact and accessible for an internal search. Traditional ROV designs, with their bulky, pressure-resistant housings, cannot operate in tight quarters such as those found on Dakar. While the Dakar project schedule did not allow for the production of an ROV to explore the interior of the wreck, the mission led Phoenix to consider the merit of offering such a vehicle to customers, and so initiated development of xBot.

The xBot III.

Design Philosophy
The concept for the first xBot was to produce an inexpensive, small deep-diving video-inspection ROV suitable for the high-risk mission of wreck penetration. The system cost should allow for expendability, given that the ROV would be operating in an extremely hostile environment where any entanglement portends a vehicle loss. Furthermore, the desire was to optimize the area that could be explored within the wreck. These requirements led to a battery-operated ROV design concept that incorporated an onboard supply of fiber optic cable for command, control and data transfer. The decision to eliminate the powered cable avoided the drag created by a long length of large-diameter umbilical.

By designing a battery-powered ROV with an onboard supply of fiber optic cable, the vehicle could enter the wreck and explore the interior with little concern for cable entanglement—the tether could free-spool as the vehicle proceeds through the wreckage. The ROV has no need to retrace its exploration steps, and it can exit the site wherever feasible. Once it returns to its host platform or cage, the fiber optic tether can be cut if it is entangled. This feature also effectively doubles the penetration range of the vehicle. The xBot has the flexibility to operate as an independent system as well as from a manned or unmanned host platform. The use of a host allows the xBot to be transported to great depth while minimizing expenditure of tether and preserving battery power.

xBot Design Evolution
The original xBot, released in 2002, was a basic video inspection system whose primary sensor was a video camera on a tilt mechanism. The vehicle used Phoenix-developed pressure-tolerant lithium batteries, thrusters and an incremental ballast-drop system. Lighting was provided through multiple Phoenix-designed pressure-tolerant LED arrays. The operator's control box was a small desktop unit that provided video outputs for any standard monitor.

The original xBot's maneuverability, stability and low cost caught the eye of filmmaker James Cameron. His filming requirements for the 'Last Mysteries of the Titanic' influenced the development of the xBot II, significantly advancing the number, arrangement and technology of the LEDs on the vehicle. The second-generation xBot also had upgrades to the thrusters, batteries and ballast drop. For filming, multiple xBot II units were installed on two Russian Mir submersibles, and the vehicles were piloted by Cameron himself. The xBot vehicles demonstrated their capabilities by penetrating deeper into the hull of RMS Titanic than has ever been done before or since, collecting imagery of the Turkish baths, the Straus stateroom and the ship's scullery. Extensive use of the xBot on this project identified areas in vehicle maintainability and operability—notably the need to have a shortened turnaround time—and led to the third generation of xBot.

xBot III
The xBot III, which was released in 2009, was reengineered using lessons learned from operational experiences with the previous two generations, as well as other small-vehicle developments by Phoenix. The earlier xBot generations proved that a very small, battery-powered, full-ocean-depth ROV could be successfully developed and deployed. The third-generation xBot focused on refining the vehicle design for simplicity of manufacture and ease in maintenance and repair. xBot III is a flexible platform that allows for future growth to adapt to varying customer requirements. Future payloads could include sonar heads, laser measurement devices, oceanographic sensors, hydrophones, data-connection docking mechanisms or a two-function manipulator.

The xBot III upgrade began with a review of all subcomponents. Every Phoenix-designed component—the LEDs, thrusters, circuitry and batteries—was upgraded based on operational experience and the latest technological developments. Phoenix reengineered the thrusters, selecting a commercial off-the-shelf (COTS) Maxon Precision Motors Inc. (Fall River, Massachusetts) servomotor and developing custom electronics and a propeller, packaged into a small, pressure-tolerant, easily replaceable unit. A similar approach was taken for the xBot III's lights, packaging Lighting Science Group Corp. (Satellite Beach, Florida) Titan-series LEDs into small, pressure-tolerant units. The battery upgrades were based on extensive work with the U.S. Navy on lithium safety issues. A three-tier design provides control at the cell, module and battery levels with embedded electronics to protect each cell during charge, discharge and handling.

xBot III installed on the NOAA science ROV.
All other system components are COTS items, which improves the maintainability of the system and reduces manufacturing costs. All components use Teledyne Impulse (San Diego, California) IE55 connectors, mated to a single junction box and physically attached to a central chassis. This architecture allows each component to be quickly and easily isolated from the system for rapid maintenance. Future growth capabilities are assured by including a payload weight in the vehicle's weight budget and by providing power, bandwidth and penetrator reserves. To further provide flexibility to the user, Phoenix has developed optional lead-acid batteries and shallower-rated foam.

Other improvements to xBot III include updated software code and a newly designed topside operator control console. The new user-interface device is smaller and easier to manipulate. The topside computer also has the capability of interfacing with a USB game controller.

Phoenix's experience with xBot III has shown that, due to its high stability and intuitive controls, just about anyone can successfully pilot the vehicle after a few minutes of instruction.

Field Applications
One of the xBot III systems was provided with the NOAA full-ocean-depth science ROV, Discoverer, that was designed and built by Phoenix. xBot III resides in its own garage located between the larger ROV's manipulators. The garage is outfitted with a hydraulically activated door and a fiber take-up spool that prevents the spent umbilical from posing an entanglement hazard. xBot III affords the host ROV the ability to explore small spaces or potentially hazardous situations and objects from a safe distance. It also provides the operator an additional viewing perspective beyond that provided by the host vehicle as well as the ability to perform an inspection of the host.

Another xBot III that was concurrently built with the NOAA xBot is used by Phoenix's ROV operations group. This field-proven vehicle has successfully performed a pollution assessment survey of the William H. McAllister in Lake Champlain. The 1.4-millimeter diameter, Kevlar-jacketed, self-dispensing fiber optic umbilical from Burnham Polymeric Inc. (Fort Edward, New York) was one of the primary reasons that the customer selected xBot III for this project. The near-neutrally buoyant umbilical requires almost no force to pull it from its supply spool. Therefore, its size and weight posed minimal risk for damaging the wreck during inspection operations as compared to a potentially more hazardous traditional ROV umbilical.

Phoenix more recently integrated its xBot III on the Navy's Deep Drone ROV for participation on this past summer's U.S. Coast Guard forensic investigation of the Deepwater Horizon drilling rig. xBot's primary mission was to penetrate any suitable entry point to hazardous, highly constricted areas of interest and to comprehensively explore their condition. xBot's maneuverability and small size facilitated its passage through the tightest of spaces, allowing it to safely move through the structure and its jumbled wreckage while collecting extensive high-quality color video. These data would not have been obtainable using more traditional underwater vehicles.

After each dive, xBot returned to Deep Drone, where its umbilical was cut free using the Deep Drone's manipulators. xBot's modular design permitted very short turnaround times between excursions and contributed to the project being completed ahead of schedule, exploring all areas identified by the investigators.

Phoenix's advancements in pressure-tolerant electronics for ROV designs have provided an ability to tailor a vehicle to meet specific and unique mission needs. Their use avoids the constraints imparted by large, heavy and expensive pressure-resistant electronics bottles while offering additional advantages of lower cost, the possibility of expendability and increased safety.

Daniel Pol has been with Phoenix International Holdings Inc. for five years, where he is an engineering program manager. He has been involved with multifaceted engineering projects for the marine industry and other related industries for more than 20 years, including numerous underwater vehicle developments.

John Tomasi has been with Phoenix International Holdings Inc. since 2007 as a mechanical engineer and naval architect. He has worked on a variety of marine projects, including manned diving and rescue systems, underwater tool development and remotely operated vehicle design for vehicles ranging from micro to work-class. He is also an experienced xBot pilot.

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