Solar Boat Capstone Group

Transcription

1 Solar Boat Capstone Group Design Team Chris Maccia, Jeff Tyler, Matt Knight, Carla Pettit, Dan Sheridan Design Advisor Prof. M. Taslim Abstract Every year Solar Splash, the IEEE World Championship of intercollegiate Solar/Electric boating, holds a solar boat competition between various educational institutions. Groups from all over the country build solar powered boats to compete in sprint and endurance races. The solar boat capstone group is tasked with the goal of designing a sprint and endurance powertrain for the Northeastern Solar Splash team. At the start of this project the group began with in-depth patent and market research, mainly focusing on what other competitors in past years have done and what worked best. From this research it was determined that an outboard powertrain would be the optimal choice for both of the races given our restraints of time, material, and costs. The various components for the sprint and endurance powertrain were then each individually designed to create powerful and light-weight end results. It was also important that they would be easily mounted to the boat and capable of steering, pitch adjustment, and easily detachable for adjustments or repair. Our designs were further verified through boat measurements, hand calculations, solid modeling and FEA in order to make sure our powertrain would hold up in the expected environment. The models were then completed, drawings were rendered and each component was machined. These components will be assembled into our final sprint and endurance power train (Shown below), and raced in this year s Solar Splash Competition.

2 The Need for Project The powertrain is designed for the Solar boat team to use in competition to promote solar/renewable energy. The problem that has been presented is to design a powertrain to meet the sprint and endurance criteria for a 13ft solar powered boat, which will race in an international competition. The power train will be built for the Northeastern Solar Splash team and will compete in the Solar Splash competition on June 8 th through June 12 th 2011 in Iowa. Solar Splash is an international, intercollegiate solar/electric boat world championship. This competition s objective is to promote solar/renewable energy solutions to college students in a practical manor. The Design Project Objectives and Requirements An electric powertrain will be Design Objectives designed to allow Northeastern Two electric powertrain s must be designed to allow the boat to Solar Splash s boat to compete successfully compete in an endurance and sprint competition. The in an international competition. powertrain s must remain in compliance with the solar splash guidelines for the sprint and endurance competition (Rep. 2). For the sprint race the boat must run 300 meters in the fastest time possible and for the endurance race the boat must travel as far as possible in two hours. The typical boat powertrain is gas powered; however for this competition an electric powertrain is required. Design Requirements During the 300 meter sprint race the source voltage must not exceed 36 volts (Rep. 2). During the 2 hour endurance competition the source voltage must not exceed 24 volts (Rep. 2). The hull that the Northeastern Solar Splash Team built is 13 feet long and weighs approximately 237lbs, which is significantly heavier than some of the competitors hulls. Design Concepts considered Each component of the When designing the powertrain to a boat there are two main powertrain; motor, propeller, options: an inboard powertrain or an outboard powertrain (Rep ). gearbox, mounting bracket, and An inboard powertrain runs horizontally underneath the boat and is steering, have several design desirable for larger boat applications. Although efficient, they are very options. expensive, difficult to maintain and require a separate rudder system for steering. An outboard powertrain hangs vertically off the back of

3 the boat and is typically used in smaller applications. Outboards are easy to remove and maintain, easy to steer, and are more cost efficient because no modifications to the boat hull are needed. There are many options for electric motors, some including Perm Motor PMG 132, LMC 200-D126, AmpFlow C40-300, and Etek-R (Rep ). When considering these motors it was important to consider their performance at both 36 volts for the sprint competition and at 24 volts for the endurance competition. The important characteristics include weight, amperage, RPM, speed constant and torque. There are many options when selecting a propeller (Rep ). The first is a fully submerged propeller. This type of propeller is the most popular and can be found with 2, 3, 4, or 5 blades. The second is a surface piercing propeller (Rep ). These are usually used on high speed boats and are very complex to design. The last is a jet drive (Rep ). Jet drives are popular on small watercrafts such as jet skis. Some of the variables to consider when selecting a propeller include diameter, pitch, horsepower and boat characteristics. (Rep ). For the gearbox options the gearbox needed to be big enough to mount either 1 or 2 motors in any desired shape. The dimensions of the gearbox are determined by the size of the gears housed within, which is determined by the gear ratio. There is also the option to choose between a chain and sprocket drive or belt and pulley drive. Chain and sprocket is ideal for high initial torque however needs to be lubricated. Belt and pulley drive do not need lubrication, but can slip during high torque bursts. When designing the mounting system for the powertrain, it was desired to achieve steering rotation and pitch rotation. Also it was important that the system be easily detached from the boat for any repairs or modifications necessary. Two final designs were created each allowing for trim adjustment using a pin system. The Split Bearing design, would utilize an off the shelf split bearing to clamp around the down tube and allow for steering. The Hinge design, would use a custom hinge, which the group would machine and would be attached to the down tube to allow for steering. Both mounting options would be bolted to the transom of the boat for maximum power

4 transfer. Steering will be accomplished using a steering wheel and a pulley system to turn the entire powertrain about the mounting bracket. Recommended Design Concept A single outboard using two Design Description motors for the sprint and one The Solar Boat Capstone group chose to use a single outboard motor for the endurance will style powertrain for both sprint and endurance. For sprint, the provide power for the boat. powertrain will have two motors mounted on a large gearbox and for endurance a single motor will be mounted to a smaller gearbox The Etek-R electric motor was chosen as the best option for the powertrain. When running at 36 volts in the sprint competition the motor will run at 330 amps and 2592 RPM providing ft-lbf of torque (Rep ). When running at 24 volts in the endurance competition the motor will run at 30 amps and 1728 RPM providing 2.88 ft-lbf of torque (Rep ). The propeller will be fully submerged and the Bp-δ method was used to calculate the diameter and pitch needed to maximize efficiency and determine the RPM of the propeller (Rep ). A three-blade 9.25-inch diameter by 7-inch pitch propeller was chosen for sprint. This provides RPM and an efficiency of 50%. For endurance a three blade, 8-inch diameter by 6-inch pitch propeller will be chosen. This will provide 1228 RPM at the propeller and an efficiency of 47%. The sprint powertrain gearbox holds two Etek-R motors and the endurance power train gearbox holds one Etek-R motor. The gearbox for each setup will be a housing that will consist of two aluminum plates separated by threaded standoffs. This housing will contain gears and a chain and sprocket drive within. The chain and sprocket drive will supply an initial high torque and also prevent slip from occurring when the motors start up. Based on the propeller speed for sprint the gear ratio was made to be 3:1.The gear ratio for endurance has not been determined yet. The split bearing method was chosen as the mounting bracket for the powertrain. This design was chosen after performing a decision matrix and finite element analysis on both mounting options. The finite element analysis determined that the max stress on the hinge design occurred at the hinge making steering impossible. As discussed earlier steering will be accomplished using a steering wheel, pulleys, and cables to turn the entire powertrain about the mounting bracket.

5 Analytical Investigations After the final powertrain was designed and modeled in Solidworks, finite element analysis was performed on the entire powertrain using the modeling program Inventor. The analysis showed that the entire model met a safety factor of at least 5 except for in one spot. This failure was located on the mounting bracket at the pin of the pivot point, a spot which experiences the majority of the moment. After a redesign implementing a larger pin diameter at the pivot point, the FEA showed that the new pin could successfully withstand the resulting moment without causing deformation. See Financial Issues The cost of the project so far is $1300 with another $500 projected costs. Key Advantages of Recommended Concept The advantage of choosing a single outboard powertrain driven by two motors for the sprint competition is significant. Having only one outboard cuts back on a lot of weight. It also cuts down on the number of parts, making more feasible to have spare parts for the competition. The Solar Boat project has been more costly than the average capstone project. The costs can be split into motors, gearbox, mounting, and lower unit. The motors cost $970 and can be shared between the sprint and the endurance configurations. For sprint the gearbox cost $520, the mounting $200, the lower unit 0$ (donated), and the propeller $125. The remaining $500 comes from the endurance cost but the group still needs some more materials including a propeller, which should be around another $500. Recommended Improvements Potential improvements include One of the major setbacks with this project was the weight of the building a custom boat and boat that the powertrain s are being designed for. The weight governs propeller the top speed as well as propeller design and gearbox specifications. Overall, a lighter boat would lead to a better performing powertrain. Another potential improvement would be machining a custom propeller. This would help because finding a stock propeller that matches the calculated pitch and diameter as well as the shaft attachment hardware is a very difficult task. A custom propeller would allow us to maximize our efficiency while also being easy to install.

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