1. GROUP NINE Cross-Slope Compensation for Wheelchairs Alexander A. Abraham David Dar Marc C. Moore Advisor: Dr. Mark Richter

2. The Problem  ADA regulations specify no more than a 1.1º cross slope  Not followed for construction purposes or in private environments  Currently wheelchairs do not have a mechanism to prevent involuntary veering on cross slopes  Subjects are forced to apply more torque on one wheel to maintain straightforward motion

3. Design Criteria  Add-on feature to current wheelchairs  Cost-friendly  Aesthetically appealing  Light-weight  Mechanically simple  Robust, durable  Must withstand 7.3 N*m of downhill torque

4. The Solution  A mechanism that restricts rotational movement of a front wheel  Forces wheelchair to travel in a single direction without deviation  Applied only when the subject deems it necessary

5. Previous Design Considered  Preliminary model of the caster wheel  Caster features two surfaces separated by ball bearings  Upper contingent smaller than lower contingent

6. Previous Design Considered  Ring with teeth along the radial and axial axes, which surrounds central post  By default, the spring- loaded ring is suspended above the lower surface  When activated, ring snaps down and locks with lower plate

7. New Design  One pin locking two plates together  Spring-loaded  Clean appearance  Mechanically simple  Add-on easy

8. Concerns  Solves problem  Mechanism inadvertently activating  Reliability - Mean Time Between Failure (MTBF)  Ease of use  Warning of hazards

9. Work Completed  Researched ADA regulations  Researched wheelchair mechanics (lab visits, journal publications, etc.)  Constructed initial 3-D model  Consulted several times with Dr. Mark Richter (Vanderbilt University, MAX-Mobility)  Submitted NCIIA proposal  Established project website  Dismissed initial design

10. Nixed Work  Developing caster model with radial and axial teeth  Completing CAD model ourselves

11. Current Work  Completing mock-up model for new design  Welding pin tubing to caster  Attaching bike cables to pin  Consulting with expert machinist  Determining appropriate spring constant for loading spring  Determining optimal composition of heat-treated torsional spring pin of final model

12. Future Work  Manufacture prototype from finished CAD model  Analyze design effectiveness  Re-design model and make adjustments accordingly  Implement device alterations