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Entire System. Gradual Grade. 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.

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Braking system
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


Braking system mounts
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



Ratchet system
Ratchet System

  • W.M. Berg Ratchet and Pawl

    • R16S20-64

    • 4” PD, 64 Teeth

  • Can handle ~600 lbf

  • Roll back distance of ~1 inch


Pawl system
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



Axle to wheel attachment
Axle to Wheel Attachment

  • Spline exists in wheel

  • Not a standard spline size

  • May end up cutting keyway into wheel


Moving axle backwards
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


Advantages to design
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


Holding force calculation
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


Roll back distance calculation
Roll Back Distance Calculation

  • 64 Teeth

  • 22” wheel diameter

  • 69” circumference

  • 69”/64 Teeth = 1.08”


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