1.  Heat-treated torsional spring pins allowing for more vertical flexibility.  While highly adjustable, the current lever is a bit bulky for the aesthetically-concerned wheelchair user. It performs adequately in distributing force and can be easily activated by a geriatric patient. It would be optimal to preserve the mechanic functionality of the current lever while streamlining its design into a smaller, more sexy form.  Currently the barrel/bullet caster distribution is approximately 90%/10%. In 10 years, industry experts project a complete reversal of this trend. Adapting the cross-slope compensation mechanism to bullet casters would be a worthwhile endeavor in anticipation of shift. Attaching a bracket to one of the legs could be a temporary makeshift solution until a new mechanism is devised. The two-caster cross-slope compensation mechanism is effective in mitigating the involuntary veering from straightforward motion of the wheelchair. ADA (Americans with Disabilities Act) regulations specify no more than a 1.1º cross slope on public walkways. However this goes unheeded for construction purposes or in private environments. Currently wheelchairs do not have a mechanism to prevent involuntary veering on cross-slopes. Thus subjects are forced to apply more torque on one wheel to maintain straightforward motion. Due to a large target market (more than 1 million manual wheelchair users in the United States), a lucrative solution is in order. BACKGROUND MECHANICS CONCLUSION FUTURE DIRECTIONS RESULTS Cross-slope Compensation for Manual Wheelchairs AA Abraham 1, D Dar 1, MC Moore 1 Advisor WM Richter 2 1 Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee 2 MAX mobility, LLC  Add-on application to existent wheelchairs  Cost-friendly (<$150 per mechanism)  Aesthetically appealing  Lightweight (<1 lb. per mechanism)  Mechanically simple  Robust, durable  Must withstand 7.3 N*m torque - calculated downhill moment on 6° cross-slope, mean plus standard deviation (5.2+2.1 N*m) DESIGN CRITERIA DEVICE METHODS  Considered various locking mechanisms and constructed prototypical mockups  Opted for the single-pin design because of its simple design and clean appearance  Mechanical mechanism (as opposed to electrical) eliminated the necessity for a source of power  Decided on a lever mechanism utilizing bike cables  Tethered pin is attached to an adjustable lever (via mounting bracket and/or retractable M9 bolt on top of pin housing)  Built two mechanisms (one for each front wheel) to determine the necessity of the dual-locking mechanism  Effectiveness of mechanism functionality evaluated on a 3° cross-slope (safety factor of 2.7)  One thrust followed by coasting at ~5 mph  Data acquired a distance of 6 ft from origin The final design includes a locking pin mechanism that restricts rotational movement of a front wheel. It forces the wheelchair to travel in a single direction without deviation. It is applied only when the subject deems it necessary. Upon activation, the pin snaps down and interlocks with the lower plate due to a preceding spring loaded potential. The mechanism is initiated by a lever, transmitted via a bike cable through a sleeve, which attaches to the top of the pin housing. The released cable allows for the spring to move a stroke length of 0.6 in., pushing the pin down through the rotor. Figure 3. Image of the cross-slope compensation mechanism. Figures 1,2. Illustrations of wheelchair user encountering cross-slope. Figure 4. Forces involved in pin deployment. The normal force of the rotor on the pin provides the torque preventing the wheel from turning. The gravitational force acts at an angle on a cross-slope. Figures 5,6,7. Lateral views of the pin housing. Figures 10,11. Axial views of the pin housing. Figure 12. Sketches of the lever base.Figures 13,14. Views of the lever. Figures 8,9. Lateral views of the pin.  Implementing a cross-slope compensation mechanism that employs more than one pin with interlocking radial teeth that allow for vertical movement and axial teeth which provide locking function. Figure 17. Axial view sketch of a proposed multi-pin locking mechanism.  Results show significant decrease in path deviation with cross-slope compensation mechanism engaged  Usage of both pins show increased functionality, as compared to one-pin deployment  Significant difference between direction of cross-slope explained by uneven condition of wheelchair frame (a used cambered basketball chair subjected to multiple impacts)  Approximate cost of $100,000 per 1000 units Figures 15,16. Graphs of path deviance among different pin usages.  Both pins disengaged (0°): 4.6 ± 2.726 in.  Both pins disengaged (3°): 11.6 ± 3.161 in. (sloping left) & 9.6 ± 2.525 in. (sloping right)  Left pin only (3°): 1.65 ± 1.029 in. (sloping left) & 8.3 ± 1.513 in. (sloping right)  Both pins engaged (3°): 2.6 ± 1.542 in. (sloping left) & 3.35 ± 1.916 in. (sloping right)