1. Wheelchair Dynamic Center of Gravity (D-COG)
Kyle Mobley, BME
Garrett Spiegel, BME
Andrew Lossing, ChBE (Not present)
Advisor: Dr. Mark Richter, President
GARRETT
Lossing, Mobley, Spiegel D-COG Senior Design

2. 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
GARRETT
Lossing, Mobley, Spiegel D-COG Senior Design

3. 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.
GARRETT
Lossing, Mobley, Spiegel D-COG Senior Design

4. 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
GARRET
Lossing, Mobley, Spiegel D-COG Senior Design

5. 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
ANDREW*No ability to brace against ground with feet.
Lossing, Mobley, Spiegel D-COG Senior Design

6. How will it move? Use of concave wheels between two bars
Bars will move in relation to each other
Lossing, Mobley, Spiegel D-COG Senior Design

7. 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
Momentum/inertia
Lossing, Mobley, Spiegel D-COG Senior Design

8. 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
*Tested by altering wheel base, but final design maintains wheel base and simply shifts user.
Lossing, Mobley, Spiegel D-COG Senior Design

9. How far does it need to move? (cont’d)
Determinations:
20% COG change necessary for desired effect
4 inches of axle (or seat) movement
ANDREW
Lossing, Mobley, Spiegel D-COG Senior Design

10. How will it stay in place?
User controlled clamping brake pads
When brake released, seat is free to move
Clamping brake holds seat in desired position
ANDREW
Lossing, Mobley, Spiegel D-COG Senior Design

11. How is it designed?
Altering pre-existing base design to conform to our specifications
Dimensional constraints
Brake placement
Roller placement
KYLE
Lossing, Mobley, Spiegel D-COG Senior Design

12. Future Directions Get assistance with AutoCAD Build prototype
Welding, Metalwork, Construction
Test/Revise prototype
KYLE
Lossing, Mobley, Spiegel D-COG Senior Design

13. References
1. H Xiang, A-M Chany, G A Smith “Wheelchair related injuries treated in US emergency departments”. Injury Prevention. 12:8–11.
2. “ADA Wheelchair Ramp Specifications”. Mobility Advisor.
3. “Guidance on the Stability of Wheelchairs”. March, MHRA. DB2004(02).
ANDREW
Lossing, Mobley, Spiegel D-COG Senior Design