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PRELIMINARY DESIGN REVIEW

PRELIMINARY DESIGN REVIEW. Outline. Background Information Team and Motivation Project Focus Mission Statement Design/Performance Criterion Goals Inspiration Design Overview - Primary Overall Concept and Generation Mechanism Design. Primary Analysis Kinematics Cam Profiles

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PRELIMINARY DESIGN REVIEW

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  1. PRELIMINARY DESIGN REVIEW

  2. Outline • Background Information • Team and Motivation • Project Focus • Mission Statement • Design/Performance Criterion • Goals • Inspiration • Design Overview - Primary • Overall Concept and Generation • Mechanism Design • Primary Analysis • Kinematics • Cam Profiles • Gear Ratio • Torque • Packaging • BOM • Controls • Hardware and Packaging • Software • Design Overview - Secondary • Overall Concept and Generation • Mechanism Design • Logistics • Cost • Schedule Speaker: Nick Schwartzers

  3. BACKGROUND INFORMATION Team and Motivation Speaker: Nick Schwartzers

  4. Team Composition Speaker: Nick Schwartzers

  5. Objective To design and create an automatic Continuously Variable Transmission (CVT) for a bicycle, eliminating discrete steps in gear ratio in order to maintain the ideal human cadence, with no user input. Speaker: Nick Schwartzers

  6. Motivation • For years bicycles have relied on the same basic transmission design. • While this is an efficient and light weight design, there could be massive improvements for the average recreational rider • The inexperienced casual rider is often bewildered by derailleur shifting • Increase human efficiency by continuously maintaining the ideal cadence • Make bicycling more user friendly in order to elevate bicycling as viable transportation and reduce emissions Speaker: Nick Schwartzers

  7. Human Efficiency vs. Cadence • Cadence: The pedaling speed in RPM’s • The optimum cadence for human efficiency is shown to be near 100 rpm • This will lead to lower fatigue and a more enjoyable experience Speaker: Nick Schwartzers Taken from : Cycling Science

  8. Comparison to Current Designs Gear Inches: the diameter of the drive wheel times the gear ratio You’ll have an infinite number of ratios within its range to seamlessly transition to exactly the right ratio for you and your personal riding style. Speaker: Nick Schwartzers

  9. Project Focus Mission Statement, Goal, and Design Criteria Speaker: Nick Schwartzers

  10. Mission Statement “ TO PROMOTE THE ACTIVITY OF BICYCLING BY ENHANCING THE EXPERIENCE FOR THE CASUAL RIDER, BY DESIGNING, DEVELOPING, AND PROTOTYPING A DEVICE THAT WILL OPTIMIZE THE PEDALING SPEED OF THE USER THROUGH A CONTINUOUSLY VARIABLE TRANSMISSION WHILE REMAINING AESTHETICALLY PLEASING. BICYCLING WILL BECOME A MORE ENJOYABLE MEANS OF EXERCISE OR MODE OF TRANSPORTATION. WE AIM TO PROMOTE CLEANER TRANSPORTATION AND A HEALTHIER POPULATION. ” Speaker: Nick Schwartzers

  11. Goals • Requires minimal user input and easy to use. • Contains a gear range suitable for average rider. • Automated and maintains user-selected, constant cadence. • Automatically adjusts gears for riders preference, position, and conditions. Compact, unobtrusive and light-weight. • Uses a standard interface to easily mount to any bike frame. • System is safe and low maintenance. • Quiet and efficient Speaker: Nick Schwartzers

  12. Design Criteria • Maximum of 10 net pounds of additional weight • Q-factor < 12 inches • Efficiency of 85% • Gear ratio range of at least 1:1 to 3 ½: 1 • Controls cadence to within 5 rpm while bike is in gear range • Retail Price Below $300 • Maintenance of 1 year or 2,000 miles • No more than 20% increase in noise (decibels) Speaker: Nick Schwartzers

  13. Concept Generation Inspiration and Ideas Speaker: Nick Schwartzers

  14. House of Quality Results: Emphasis on Packaging,contact stress, torque capability Speaker: Nick Schwartzers

  15. Previous CVT Work Four Different Types of CVTs have been developed: • Variable diameter pulley systems • Toroidal or roller-based CVT • Hydrostatic CVTs • Ratcheting CVTs Speaker: Nick Schwartzers

  16. Decision Matrix = Optimal = Acceptable = Unacceptable

  17. Ratcheting CVT • Uses static friction ratchets as opposed to dynamic friction • Uses variable kinematics to change ratios. • Capacity to handle larger torques without slipping Speaker: Nick Schwartzers

  18. Ratcheting CVT Example Speaker: Nick Schwartzers

  19. DESIGN OVERVIEW Primary Design: Non Variable Cam

  20. Assembly Models Speaker: Nick Schwartzers

  21. Assembly Models Speaker: Nick Schwartzers

  22. Assembly Models Speaker: Nick Schwartzers

  23. Sub Systems • Cam and input shaft • Follower assembly • Moving output shaft • Motion Control Speaker: Nick Schwartzers

  24. Assembly Models Speaker: Nick Schwartzers

  25. Assembly Models Speaker: Nick Schwartzers

  26. Design Analysis Primary Design: Non Variable Cam

  27. Desired Characteristics • Constant output torque • Constant follower velocity vs cam angle • At least 1 follower in this segment at all positions • Continuous displacement and velocity • Requirements for cam: • Constant Velocity segment • Smooth return • Low pressure angle • No undercutting Speaker: Tom Gentry

  28. Lift Curve Cycloidal Half Rise Cycloidal Half Rise Cycloidal Fall Constant Velocity Rise Speaker: Tom Gentry

  29. Lift Curve Speaker: Tom Gentry

  30. Kinematic Analysis of the Cam/Follower System Speaker: Tom Gentry

  31. Kinematic Analysis of the Cam/Follower System Speaker: Tom Gentry

  32. Design Inputs Speaker: Tom Gentry

  33. Kinematics Speaker: Tom Gentry

  34. Kinematics Speaker: Tom Gentry

  35. Kinematics Speaker: Tom Gentry

  36. Cam Profile Speaker: Tom Gentry

  37. Output Analysis Speaker: Tom Gentry

  38. Output Analysis Speaker: Tom Gentry

  39. Output Analysis Speaker: Tom Gentry

  40. Design Outputs Speaker: Tom Gentry

  41. Efficiency • Major Contributions: • Kinematics ~94% (High), ~99.8% (low) • 2 Chains ~98% each • Follower Sliding Friction ~7.5% (High), ~1.8% (Low) • Roller Follower Rolling Resistance ~3.2% • Spring Energy ~3.2% • High Gear Efficiency – 80% • Low Gear Efficiency – 86% Speaker: Tom Gentry

  42. Losses Due To: - Friction and Rolling - Chain - Spring - Cam Pressure Angle - Follower Pressure Angle Speaker: Tom Gentry

  43. Efficiency Speaker: Tom Gentry

  44. Design Optimization • Parametric Model • Optimization method • Gradient based • Non gradient based • Inputs • Ranges/types • Outputs • Maximize/Minimize/Target Speaker: Tom Gentry

  45. Excel Parametric System Model Speaker: Tom Gentry

  46. Isight Capabilities Speaker: Tom Gentry

  47. Isight Capabilities http://www.simulia.com/download/products/Fiper_Isight35_web.pdf Speaker: Tom Gentry

  48. Gear Ratio Low Gear (1:1) High Gear (3.5:1) Speaker: Andrew Shaw

  49. Output Analysis – Gear Ratios and Torques Speaker: Andrew Shaw

  50. Follower Type Translating Roller Follower Oscillating Flat Faced Follower • Pros: • Flexibility with cam profile (positive radius of curvature) • Multiple rises • Less wear • Cons: • More Parts • Slightly more contact stress • Pros: • Lower number of parts • Pressure angle is always 0 • Cons: • Wear • Friction Losses • Spring Packaging Speaker: Andrew Shaw

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