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

The Problem  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  ADA (Americans with Disabilities Act) regulations specify no more than a 1.1º cross slope

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+/-1.1 Nm. 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):

The Solution  A locking pin 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  Upon activation, pin snaps down and interlocks with lower plate due to spring loaded potential

Current Design Lever Base (Side View)

Current Design Lever (Top View)

Current Design Pin Housing (Lateral View)

Current Design Pin Housing (Axial View)

Current Design Rotor (Axial View)

Current Design Summary  One tapered pin locking housing and bottom plate together  Spring-loaded (release and return)  Engaged (uncompressed) – 1.4 in.  Disengaged (compressed) – 0.8 in.  Stroke length – 0.6 in.  Tethered to lever via bike cables which screw into pin  Bike cable length adjustable via M9 bolt  Spring force can be varied  Lever placement adjustable  Mechanically simple

Issues  Cost of working model exceeded three times initial estimate  Solves problem  Necessity of locking mechanisms on both wheels  Mechanism inadvertently activating  Reliability - Mean Time Between Failure (MTBF)  Ease of use  Warning of hazards  Add-on difficult

Work Completed  Designed and machined all parts of full-scale working model  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) and machinist  Submitted NCIIA proposal  Established project website  Dismissed initial design (housing with axial and radial teeth)

Present Work  Completing newly designed model  Attaching bike cables to pin  Assessing effectiveness of locking mechanism on a variety of cross- slopes  Determining appropriate spring constant for loading spring  Verifying calculations and considering other circumstances that may potentially affect those calculations  Determining optimal composition of heat-treated torsional spring pin of final model

Future Work  Analyze design effectiveness  Optimize handle position  Re-design model and make adjustments accordingly  Implement device alterations  Quantify new force distribution  Construct beautified diagrams for final poster