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

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

Hill Holder

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

• 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

Shaft Design

Axle to Wheel Attachment

• Spline exists in wheel• Not a standard spline size• May end up cutting keyway into wheel

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

• 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

S = 60200 psiF = 0.375 inY = 0.426 for 64 teethDP = 16V Disregard for low speeds

W = 601 lbf of allowable tooth load

Roll Back Distance Calculation

• 64 Teeth• 22” wheel diameter• 69” circumference• 69”/64 Teeth = 1.08”