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(tm) Feasibility competition. Complete feasibility analysis. Fall 2008

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Tech presentation

  1. 1. Symptum Cycles Technical Design Concept Presentation Michael Allan, Mitchell Angus & Vladimir Borisov
  2. 2. Problem <ul><li>Current limitations </li></ul><ul><ul><li>Conventional bicycles have pre-selected gear ratios </li></ul></ul><ul><ul><ul><li>The rider is prevented from performing at optimal efficiency </li></ul></ul></ul><ul><ul><li>Conventional systems are prone to the elements </li></ul></ul><ul><ul><ul><li>Chain slipping </li></ul></ul></ul><ul><ul><ul><li>Damage and wear caused by dirt and debris </li></ul></ul></ul><ul><ul><ul><li>Costly and time consuming repairs </li></ul></ul></ul>
  3. 3. Proposed Solution <ul><li>Create an internal gearbox with a continuously variable transmission </li></ul><ul><ul><li>Eliminate derailleur </li></ul></ul><ul><ul><li>Protect the shifting mechanism from the elements </li></ul></ul><ul><ul><li>Smoother and more reliable shifting </li></ul></ul>
  4. 4. Design requirements & constraints <ul><li>Performance Requirements </li></ul><ul><ul><li>Shifting </li></ul></ul><ul><ul><ul><li>Shifting accuracy at or above conventional shifting </li></ul></ul></ul><ul><ul><li>Power transmission </li></ul></ul><ul><ul><ul><li>Within a competitive range 85-90% (Gordon) </li></ul></ul></ul><ul><li>Physical Constraints </li></ul><ul><ul><li>Weight </li></ul></ul><ul><ul><ul><li>Less then 10 pounds </li></ul></ul></ul><ul><ul><li>Geometric </li></ul></ul><ul><ul><ul><li>Length ≤ 12 inches </li></ul></ul></ul><ul><ul><ul><li>Height ≤ 8 inches </li></ul></ul></ul><ul><ul><ul><li>Width ≤ 6 inches </li></ul></ul></ul>
  5. 5. Considered designs <ul><li>Toric drive </li></ul><ul><ul><li>Fluid needed </li></ul></ul><ul><ul><li>Weight </li></ul></ul><ul><li>Planetary Gears </li></ul><ul><ul><li>Weight </li></ul></ul><ul><ul><li>Bulkiness </li></ul></ul><ul><ul><li>Mechanical complexity </li></ul></ul>(Benitez,2002) (Loewenthal,1983)
  6. 6. Belt Drive CVT <ul><ul><ul><li>Uses one or a combination of variable sheaves to allow the belt to move radially changing the input to output gear ratios </li></ul></ul></ul><ul><ul><li>Advantages </li></ul></ul><ul><ul><ul><li>Mechanical simplicity </li></ul></ul></ul><ul><ul><ul><li>Cheap production cost </li></ul></ul></ul><ul><ul><ul><li>Commonly used design </li></ul></ul></ul><ul><ul><ul><li>Eliminates shift “jerking” </li></ul></ul></ul><ul><ul><ul><ul><li>Increased shifting efficiency </li></ul></ul></ul></ul><ul><ul><li>Disadvantages </li></ul></ul><ul><ul><ul><li>Potential for losses in power transmission </li></ul></ul></ul><ul><ul><ul><ul><li>Belt slip </li></ul></ul></ul></ul>(Stuhler EP 047299A1)
  7. 7. First prototype suggested <ul><li>Based off of a 1970’s patent. The design consisted of two variable sheaves connected by a belt, and moved by a spring to change gear ratios. </li></ul>(Chao USP 3837234)
  8. 8. Design complications <ul><ul><li>Mechanical complexity </li></ul></ul><ul><ul><ul><li>Expensive and intricate parts </li></ul></ul></ul><ul><ul><ul><li>Difficult to predict shifting </li></ul></ul></ul><ul><ul><ul><ul><li>Relies on spring tension to select ratios </li></ul></ul></ul></ul>
  9. 9. Selected Design A variable sheave is positioned on a movable control arm and attached with a friction drive belt to a fixed pulley. The motion of the control arm causes the belt to move radically changing the gear ratio <ul><li>Advantages </li></ul><ul><ul><li>Linear shifting </li></ul></ul><ul><ul><ul><li>Mechanical simplicity </li></ul></ul></ul><ul><ul><ul><ul><li>Lower production costs </li></ul></ul></ul></ul><ul><ul><ul><li>Increased shifting accuracy </li></ul></ul></ul><ul><ul><ul><ul><li>Simplified control function </li></ul></ul></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>Gear range limitations </li></ul></ul>θ
  10. 10. Design evaluation <ul><li>Power transmission test </li></ul><ul><ul><li>Single most important indicator of success </li></ul></ul><ul><ul><li>Shifting efficiency </li></ul></ul><ul><ul><li>Slip conditions </li></ul></ul><ul><li>Shifter force profile </li></ul><ul><ul><li>Actuator specification </li></ul></ul>Pedal attachment Variable Sheave sheave Shifter bar motion Testing set up Friction rollers Force sensor
  11. 11. Next step <ul><li>Actuator design </li></ul><ul><ul><li>Rider input control </li></ul></ul><ul><li>Frame integration </li></ul><ul><ul><li>Geometrical reconstruction </li></ul></ul><ul><ul><li>Frame integrity </li></ul></ul>
  12. 12. The Future <ul><li>Production of diversified friction drive CVT bicycle models </li></ul><ul><li>Rider specific customizations </li></ul><ul><ul><li>Frame dimensions </li></ul></ul><ul><ul><li>Gear ratio ranges </li></ul></ul><ul><ul><li>Special Features </li></ul></ul><ul><ul><ul><li>Handle bars </li></ul></ul></ul><ul><ul><ul><li>Seats </li></ul></ul></ul>

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