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Entire System PowerPoint Presentation
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Entire System

Entire System

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Entire System

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  1. Entire System

  2. Gradual Grade

  3. Braking System • Avid BB7 Disc Brakes • Controlled by bicycle brake handles • 160mm discs • Offers more control and less wear than rim brakes • Easily adjustable braking force • Wear items easily and inexpensively replaced • Normal state is disengaged

  4. Braking System Mounts • Mounting disc • Threaded onto end of shaft • Used as lock nut to allow shaft to spin with disc • Caliper Mount • Bent sheet metal • Located with hole in frame • Caliper attached via bolts through spacers

  5. Hill Holder

  6. Ratchet System • W.M. Berg Ratchet and Pawl • R16S20-64 • 4” PD, 64 Teeth • Can handle ~600 lbf • Roll back distance of ~1 inch

  7. Pawl System • Sheet metal arm • Locating slot for vertical motion • Spring pin at top • Used for engaging locking feature and for handle • Pawl is press fit onto end of arm • System weight will provide force to lock pawl in place

  8. Shaft Design

  9. Axle to Wheel Attachment • Spline exists in wheel • Not a standard spline size • May end up cutting keyway into wheel

  10. Moving Axle Backwards • May need to move axle backwards • Provides more room for brakes • Larger bearings can be used • Should not impact ergonomics • Similar bracket already exists on chair

  11. Advantages to Design • Very little modification to frame needed • Should work for many chairs • Easily removed to return to regular chair • Uses purchased parts where possible • Shaft and pawl mount need to be made • Wear items easily replaced

  12. Holding Force Calculation S = 60200 psi F = 0.375 in Y = 0.426 for 64 teeth DP = 16 V  Disregard for low speeds W = 601 lbf of allowable tooth load

  13. Roll Back Distance Calculation • 64 Teeth • 22” wheel diameter • 69” circumference • 69”/64 Teeth = 1.08”