1. Wheelchair Dynamic Center of Gravity (D-COG) Kyle Mobley, BME Garrett Spiegel, BME Andrew Lossing, ChBE Advisor: Dr. Mark Richter, President Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

2. Background 1.6 – 2.2 million wheelchair users in United States alone 1 146.8% increase in wheelchair related injuries in U.S. from 1991 to 2003 1 Lossing, Mobley, Spiegel http://www.bme.vanderbilt.edu/srdesign/2009/group5/ D-COG Senior Design 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

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

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

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

6. 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 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

7. 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 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

8. 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 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

9. 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 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

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

11. 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 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

12. 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 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

13. 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 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/

14. 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 2009-10http://www.bme.vanderbilt.edu/srdesign/2009/group5/