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CRITICAL DESIGN REVIEW

CRITICAL DESIGN REVIEW. Outline. Background Information Team and Motivation Mission Statement Project Focus Design/Performance Criterion Goals Design Overview Cam Ratcheting Follower Control System Frame. Analysis Kinematics Cam Profiles Gear Ratio Torque Controls Hardware

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CRITICAL DESIGN REVIEW

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  1. CRITICAL DESIGN REVIEW

  2. Outline • Background Information • Team and Motivation • Mission Statement • Project Focus • Design/Performance Criterion • Goals • Design Overview • Cam • Ratcheting Follower • Control System • Frame • Analysis • Kinematics • Cam Profiles • Gear Ratio • Torque • Controls • Hardware • Wiring Diagram • Control Scheme • Logistics • Cost • Schedule • Conclusion 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. 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

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

  9. 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

  10. 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

  11. 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

  12. Design Overview Final Design: Variable Position Cam & Follower Speaker: Nick Schwartzers

  13. Assembly Views Speaker: Nick Schwartzers

  14. Assembly Views Speaker: Nick Schwartzers

  15. Assembly Views Speaker: Nick Schwartzers

  16. Assembly Views Speaker: Nick Schwartzers

  17. Sub-assemblies Speaker: Nick Schwartzers

  18. Control Speaker: Nick Schwartzers

  19. Follower Speaker: Nick Schwartzers

  20. Input Speaker: Nick Schwartzers

  21. Case Speaker: Nick Schwartzers

  22. Design Analysis Speaker: Tom Gentry

  23. 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

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

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

  26. Excel Parametric System Model Speaker: Tom Gentry

  27. Isight Capabilities Speaker: Tom Gentry

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

  29. Lift Curve Speaker: Tom Gentry

  30. Kinematics Speaker: Tom Gentry

  31. Cam Profile Speaker: Tom Gentry

  32. Output Analysis Speaker: Tom Gentry

  33. Output Analysis Speaker: Tom Gentry

  34. Output Analysis Speaker: Tom Gentry

  35. Design Outputs Speaker: Tom Gentry

  36. Spring Force • A spring is used to keep the follower in contact with cam and must be capable of applying a force equal to inertia force. F - mfg - S(X - xo) = mf Af F = contact force, mf = mass of the follower, Af = acceleration of the follower. Neglect gravity Speaker: Tom Gentry

  37. Efficiency • Major Contributions: • Kinematics ~.5% • 2 Chains ~2% each • 2 Gears ~5% each • Friction Losses ~2.5% • Spring Energy ~1.5% • Total Efficiency ~83% Speaker: Tom Gentry

  38. Losses Speaker: Tom Gentry

  39. Efficiency Speaker: Tom Gentry

  40. Gear Ratio Low Gear (1:1) High Gear (3.5:1) Speaker: Tom Gentry

  41. Output Analysis – Gear Ratios and Torques Speaker: Tom Gentry

  42. Stress Analysis

  43. Roller Follower Selection Stud Bending Stress Cam Contact Stress Follower Bearing Fatigue Max Allowable stress of 100 kpsi given by manufacturer 48.288 Kpsi Calculated Factor of safety= 2.07 Speaker: Andrew Shaw

  44. Contact Stress Max Contact Pressure Principle Stresses Speaker: Andrew Shaw

  45. Contact Stress cont. Assumptions: Operating at nearly max load (very conservative) Using the minimum radius of curvature (conservative) Constant contact No buckling Speaker: Andrew Shaw

  46. Contact Stress cont. Satisfactory factor of safety, for worst case scenario. Speaker: Andrew Shaw

  47. Material Selection Speaker: Andrew Shaw

  48. Sprag Clutch DIN 6885.3 Standard Keyway Speaker: Andrew Shaw

  49. Follower Arm Stress Critical plane at the end near fillet. Factor of safety=1.47 Speaker: Andrew Shaw

  50. Follower Arm Stress Fatigue Life: 340 hours (assuming no coasting) Max Deflection: .009 in. Speaker: Andrew Shaw

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