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 (<$150)
Aesthetically appealing
Light-weight
Mechanically simple
Robust, durable
Must withstand 7.3 N*m of downhill torque
“The total weight of the wheelchair and user SD was kg. The percentage of the total weight located over the rear wheels was found to be 84.4%+-6.4%. Wheelbase length was 37.3+/-3.5cm. The downhill moment resulting from the 3° slope was calculated to be 2.6+/-1.1Nm. Similarly, the downhill moment on the 6° cross slope was calculated to be
5.2+/-2.1Nm. The data were found to be normally distributed (significant at .19).”[1]
1. Richter, W. M., R. Rodriguez, et al. (2007). "Consequences of a cross slope on wheelchair handrim biomechanics." Arch Phys Med Rehabil 88(1):

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. Current Design Hand lever activation/deactivation controlled by user
When activated, the pin snaps down and locks with lower plate due to spring loaded potential

6. Current Design
Hand Lever
(Top View)
Hand Lever Basic Look
(Side View)

7. Current Design
Caster + Pin Holder
Caster (Top View)

8. Current Design Summary
One pin locking two plates together
Spring-loaded
Clean appearance
Mechanically simple
Add-on easy

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

10. 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

11. Present Work Completing mock-up model for new design
Attaching bike cables to pin
Waiting for expert machinist to finish production of model
Determining appropriate spring constant for loading spring
Determining optimal composition of heat-treated torsional spring pin of final model

12. Present Issues
Cost.
Actual prototype cost approximately 3x the initial estimate.
Weight
Hand lever
Aesthetically pleasing
Hand lever ugly?
Ease of use
Test entire system

13. Future Work Test manufactured device Analyze design effectiveness
Optimize handle position
Re-design model and make adjustments accordingly
Implement device alterations
Quantify new force distribution