P08454Pugh’s Matrix JustificationVersion 3

Mechanical Energy to Thrust

  • Adequate Thrust
  • This criterion was selected because it will satisfy the first physical requirement listed in the Project Specification of “Continual Thrust.”
  • Ranked at 14% because this is the main feature of the thruster. Without equal or better thrust there is no market for our product.
  • Price
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 10% because the thruster needs to be in a comparable market for its performance. Thruster prices vary greatly, however, a price lower than the Tecnadyne thruster is desired because the Tecnadyne unit is what Hydroacoustics uses on their top-scale ROV.
  • Efficiency
  • This criterion was listed because it received one of the highest relative weight ratings in the QFD.
  • Ranked at 13% becauseefficient energy consumption is directly related to providing the ROV withthe longest possible dive time. Inefficient use of energy will shorten the ROV drive time.
  • Inertia
  • This criterion contributes to better efficiency and consumes less power which is what the customer requested.
  • Ranked at 7% because the inertia of a thruster will consume more energy, may cause sudden jerks at sudden direction changes, and cause more wear if the inertia was high. However, the truster for this project is relatively small. Ifthis were a larger thruster or pump, then inertia would of greater concern.
  • Size
  • This criterion is listed because our propeller needs to be of a comparable size to our competitors as listed in the Project Specification.
  • Ranked at 7% because size is important in that it needs to fit into a general envelope on the ROV butthere are many motor selections available that will meet this requirement.
  • Modularity
  • This is another important criterion as shown in the Project Specifications under compatibility.
  • Rankedat 14% because the underlying scope of the project track is to make all parts modular for future design changes and implementations for future applications.
  • Number of Parts
  • This criterion represents the quality control which leads to a robust design necessary as shown in the Project Specifications.
  • Ranked at 8% because as this is not a major road block in design of the thruster. For ease of manufacturingfewer parts are better but no set requirement is needed.
  • Reversibility
  • This criterion represents the 6th Design Specification in the Project Specifications.
  • Ranked at 11% because the ability to move the ROV in reverse is very important but the pace at which the ROV moves is not as big of a concern. The reverse motion should be slower because there is no way to see to behind the ROV with the current camera set-ups.
  • Hydrodynamic
  • This criterion was listed because it received a high relative weight rating in the QFD.
  • Ranked at 5% because the importance of hydrodynamics of the thruster itself is not very crucial when looking at the large design of the ROV.
  • Safety
  • This criterion was listed because it received a high relative weight rating in the QFD.
  • Ranked at 6% because the propeller will be shrouded to protect it from anything near the ROV thus leaving no major concerns.
  • Reliability
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 6% because the only major durability factor of the thruster will be the motor life since the propeller will be protected by a shroud and be connected using a magnetic coupling causing damage will be minimal is anything enters the shroud. The housing will be made of aluminum or high strength plastic able to handle the specified pressure. The thruster protected by the ROV frame.

Electrical Energy to Mechanical Energy

  • Efficiency
  • This criterion was listed because it received the highest relative weight ratings in the QFD.
  • Ranked at 18%, the electrical mechanical efficiency is a major factor that must be considered in order to provide the ROV with the longest possible dive time.
  • Price
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 14%because the thruster needs to be in a comparable market for its performance. Thruster prices vary greatly, however a price lower than the Tecnadyne thruster is desired because the Tecnadyne thruster is what Hydroacoustics uses.
  • Safety
  • This criterion was listed because it received a high relative weight rating in the QFD.
  • Ranked at 12% because the motor will be sealed and oil filled for heat dissipation. The seal must not leak to prevent any kind of contamination.
  • Service Life
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 16% because the only major durability factor of the thruster will be the motor life. The motor needs to have a similar or better service life compared to the motor currently used.
  • System Complexity
  • This criterion was listed because it represents the customer requirement shown in the QFD and leads to a robust design necessary as shown in the Project Specifications.
  • Ranked at 12% because the ROV must have a simple design so that the end user can easily manufacture or repair a module.
  • Reliability
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 18% because the motor will have to function properly in any conditions that the ROV encounters underwater. A sealed motor will be more reliable because it will be protected from the oil inside the enclosure. A brushed motor will not be as reliable as the brushless motor because the brushes will suffer wear while it is being used.
  • Size
  • This criterion is listed because our motor needs to be of a comparable size to our competitors as listed in the Project Specification.
  • Ranked at 10% because the motor must fit inside a housing that fits into the given amount of space available on the ROV.

Shaft Sealing

  • Withstands 200psi
  • This criterion is listed because our sealing needs to be able to withstand pressure comparable to our competitors listed in the Project Specification.
  • Ranked at 21% because the seal mustnot allow water into the housing department while allowing the mechanical energy of the motor travel through to the propeller. This has the highest rating because if the seal fails due to pressure, water will get into the housing and the thruster will likely fail.
  • Price
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 11% because a reliable and durable seal will prevent water from flooding the motor and rendering the ROV inoperable. Replacing a flooded motor will cost more than a well-made shaft seal.
  • Friction
  • This criterion represents the quality control which leads to a robust design necessary as shown in the Project Specifications.
  • Ranked at 14% because friction will reduce energy transfer. A high friction seal will make the motor less efficient and perform poorly.
  • Reliability
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 21% because the seal will have to be able to withstand the constant rotation of the shaft without any wear leading to leakage that may cause the motor to stop functioning and essentially cripple the ROV during a dive.
  • Safety
  • This criterion was listed because it received a high relative weight rating in the QFD.
  • Ranked at 9% because the failure of the seal would only have significantly negative effects on the motor of the ROV and not its surroundings.
  • Size
  • This criterion is listed because our seal should to be of a comparable size to our competitors as listed in the Project Specification.
  • Ranked at 9% because the size of the seal is not significantly important as long as it seals the enclosure properly.
  • Number of Parts
  • This criterion represents the quality control which leads to a robust design necessary as shown in the Project Specifications.
  • Ranked at 15% because the fewer number of parts used to seal the shaft the smaller the probability of the seal failing and vice versa.

Signal Processing and Control

Mechanical Speed Controller definition: This controller uses a servo that essentially drives the arm of what is effectively a potentiometer. When the servo pushes the link to the mechanical speed control forward, the resistance is reduced, and so the current running to the electric motor is increased and the motor output is higher.

Driver definition: Motor drivers are little current amplifiers. Their function is to take a low current control signal and turn it into a proportionally higher current signal that can drive a motor.

Voltage Control definition: This is simply a coarse control of a motor by switching relays on or off to provide full voltage to either terminal of the motor.

  • Feedback
  • This criterion represents the quality control which leads to a robust design necessary as shown in the Project Specifications.
  • Ranked at 16% because information pertaining to how the motor is operating at any moment is important and necessary for creating an efficient thruster design.
  • Accurate Control
  • This criterion represents the quality control which leads to a robust design necessary as shown in the Project Specifications.
  • Ranked at 15% because the controller needs to be very accurateso that the ROV does not come into contact with any object that could damage it.
  • Ease of Use
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 16% because the control software needs to mesh with the current joystick control used by the ROV.
  • Modularity
  • This criterion represents the customer requirement of having a robust design as shown in the QFD and in the Project Specifications.
  • Ranked at 12% because the controller need to operate all of the motors and all of the LED lights on the ROV.
  • Reliable
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 18% because the electronics needs to be sturdy enough to function through small bumps so that the ROV does not die in the middle of a dive.
  • Price
  • This criterion was listed because it represents the customer requirement shown in the QFD.
  • Ranked at 9% becausecontrollers are relatively inexpensive compared to the other components that the thrusters require. An efficient controller will result in an efficient thruster which will result in better performance.
  • Safety
  • This criterion was listed because it received a high relative weight rating in the QFD.
  • Ranked at 7% because the motor may require a large amount of current to function properly. A controller design that can handle the required amount of current will be selected.
  • Size
  • This criterion is listed because our controller needs to be of a comparable size to our competitors as listed in the Project Specification.
  • Ranked at 7% because the controllers need to be able to fit inside the housing provided for the motor of the ROV.