Wheelchair Dynamic Center of Gravity (D-COG)

Kyle Mobley, BMEGarrett Spiegel, BMEAndrew Lossing, ChBE

Advisor: Dr. Mark Richter, President

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

Background

1.6 – 2.2 million wheelchair users in United States alone1

146.8% increase in wheelchair related injuries in U.S. from 1991 to 20031

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

Background (cont’d) Most users cannot climb hills greater than

8% grade for more than 30 feet [2] Necessitates user folding to maintain

stability. Leads to discomfort and greatly increased effort.

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

Basic Design Questions

Seat or Axle movement? How will it move?

How is the movement controlled? How far does it need to move?

How will it stay in place? How is it designed?

Feasibility - upgrade possibility

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

Seat or Axle Movement? Axle Movement necessitates overcoming

weight at wheels’ point of contact Seat Movement is much more feasible

Similar to movement of driver or passenger seat in a car

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

How will it move? Seat will move in relation to base

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

How will it move? Use of concave wheels between two bars

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

How is the movement controlled?

8° decline biases seat in forward direction Releasing seat results in forward motion User can further facilitate motion by

braking Rear wheel propulsion naturally resets

COG to original position

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

How far does it need to move? Choosing tippiness is a “compromise

between risk of rearward instability and the ability to propel and maneuver easily”.3

Shorter wheelbase = more tippy = COG backwards Longer wheelbase = less tippy = COG forwards

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

How far does it need to move? (cont’d)

Determinations: 20% COG change necessary for desired

effect 4 inches of axle (or seat) movement

14 14.5 15 15.5 16 16.5 170.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

Wheelbase Length (inches)

Cen

ter

of

Gra

vity

(%

ove

r re

ar

wh

eels

)

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

How will it stay in place? User controlled clamping brake pads

When brake released, seat is free to move Clamping brake/guard holds seat in desired

position, keeps seat on track

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

How is it designed?

Altering pre-existing base design to conform to our specifications Dimensional constraints Brake/Stopper placement Roller placement

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

Future Directions

Complete design with SolidWorks Build prototype

Have parts manufactured Metalwork/Construction

Test/Revise prototype

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10

References

1. H Xiang, A-M Chany, G A Smith. 2006. “Wheelchair related injuries treated in US emergency departments”. Injury Prevention. 12:8–11.

2. “ADA Wheelchair Ramp Specifications”. Mobility Advisor. http://www.mobility-advisor.com/wheelchair-ramp-specs.html

3. “Guidance on the Stability of Wheelchairs”. March, 2004. MHRA. DB2004(02).

Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10