Current bicycles and recumbent tricycles are good forms of human powered transportation for most regions. However, for those that live in hilly or mountainous terrain, conventional human powered vehicles (HPV’s) are not well designed to traverse up and down the often severe grades in these regions. Unless the rider is in top physical shape, climbing hills will slow the vehicle to 3-4 MPH and require an extreme amount of physical exertion. In addition, some vehicles are not well designed to handle the descents, which can reach upwards of 35 MPH.
Several companies market motor assist kits to add electric power to existing bikes. Most kits include motors rated below 1 hp and have limited battery capacity which severely limits the range between charges. While these kits are good for level terrain they do not have the power or capacity required to climb steep hills at a reasonable speed. Another option, offered by some manufacturers, are power assisted recumbent tricycles. RunAbout Cycles (www.runaboutcycles.com) markets an electrically assisted recumbent trike that has a 40 mile range.
The recumbent design allows for a comfortable riding position and eliminates any balancing issues for those who may not be able to ride a conventional bike.
The objective of this project is to design, build, and test a lightweight human electric hybrid recumbent trike that will improve upon the capabilities offered by current vehicles. Analytical modeling, FEA, and CFD will be used to optimize the vehicle to meet the following preliminary requirements:
Maximum Assist Speed – 30 MPH on 0% grade, 20MPH up 10% grade
Range – 50 miles on 0% grade, 20 miles up 10% grade
Weight – less than 150#
Prototype Cost – less than $3000
Suspension – three wheel independent with damping
The preliminary requirements will be finalized after doing market research, and after evaluating analytical performance models. Before the design work is started, a Design Specification document outlining the requirements of the design will be written. In addition to the functional specifications, the vehicle will be designed with attention to manufacturability and industrial design.
The following steps will be used to accomplish the goals of this project:
- Research existing human powered and power assisted vehicles – A comprehensive search for existing powered and un-powered HPV’s will be conducted to evaluate how other vehicles compare to the proposed specifications of this project. Vehicles will be evaluated by cost, range, weight, and power to see what is the current state of the art.
- Create Excel performance model –
Build an analytical model to predict performance of the vehicle. Model will include calculations for rolling resistance, aerodynamic drag, and motor and transmission losses. Model will allow for range and top speed predictions using different components to aid in selection of the correct motor and batteries to meet the specifications.
- Develop design specifications – Create a Design Specifications document outlining the vehicle’s design requirements. Document will define performance, weight, and cost requirements for the project. This document will also describe the analyses and tests required to meet the specifications.
- Design and create solid model of power assisted vehicle – A Sun EZ Tadpole donor tricycle (see attachments) will be used for many of the vehicle’s components such the as seat, wheels, controls, and drive train components. Solid models of the Sun trike’s existing components will be built in SolidWorks, and a new frame, suspension, and power train using will be designed.
- Perform weight study – Calculate weights for all components using the solid model and determine the mass distribution of vehicle using riders of different weights. Weight should be evenly distributed between the three wheels and within the weight target.
- Analyze vehicle components and structure using FEA – Analyze and optimize key structural components using CosmosWorks finite element software to determine part stresses. Design and analyze suspension movement using CosmosMotion motion analysis package. Build CFD model of trike and rider using Cosmos FloWorks software to determine drag and investigate drag reduction options.
- Produce drawings for fabricated components – Produce detailed drawings for all fabricated components. Create assembly drawing and parts list for all required components.
- Fabricate and procure components – Submit drawings for quotes, select vendors, and order all necessary components. Track all outsourced work to ensure schedule is maintained.
- Assemble prototype vehicle – Assemble all components and bench test sub-assemblies. Test motor – controller module before installing on vehicle, road test vehicle and adjust as required.
- Test vehicle – Instrument and test vehicle per tests specified in design requirements document. Make modifications if necessary and retest as needed, analyze, and document results.
This project will be evaluated by testing the final product against the goals set forth in the design specifications developed in the beginning of the project. A successful vehicle will be one that meets the performance and cost requirements and is a significant improvement over vehicles currently available in the marketplace.
Upon completion of the project, a report will be written summarizing all activities and accomplishments of the project. An oral presentation of the project will be presented before the School of Engineering and any questions or concerns will be addressed.
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