GROUP NINEGROUP NINE

Cross-Slope CompensationCross-Slope Compensationfor Wheelchairsfor Wheelchairs

Alexander A. AbrahamAlexander A. Abraham

David DarDavid Dar

Marc C. MooreMarc C. Moore

Advisor: Dr. Mark RichterAdvisor: Dr. Mark Richter

The ProblemThe Problem

Not followed for Not followed for construction purposes or construction purposes or in private environmentsin private environments

Currently wheelchairs do Currently wheelchairs do not have a mechanism to not have a mechanism to prevent involuntary prevent involuntary veering on cross slopesveering on cross slopes

Subjects are forced to Subjects are forced to apply more torque on apply more torque on one wheel to maintain one wheel to maintain straightforward motionstraightforward motion

ADA (Americans with Disabilities Act) regulations specify no more than a 1.1ADA (Americans with Disabilities Act) regulations specify no more than a 1.1ºº cross slope cross slope

Design CriteriaDesign Criteria

Add-on feature to current Add-on feature to current wheelchairswheelchairs

Cost-friendly (<$150)Cost-friendly (<$150) Aesthetically appealing Aesthetically appealing Light-weightLight-weight Mechanically simple Mechanically simple Robust, durableRobust, durable

Must withstand 7.3 N*m Must withstand 7.3 N*m of downhill torqueof downhill torque

“The total weight of the wheelchair and user SD was 88.515.7kg. 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 be5.2+/-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): 76-80.

The SolutionThe Solution

A locking pin mechanism that A locking pin mechanism that restricts rotational movement restricts rotational movement of a front wheelof a front wheel Forces wheelchair to travel in a Forces wheelchair to travel in a

single direction without deviationsingle direction without deviation Applied only when the subject Applied only when the subject

deems it necessarydeems it necessary

Upon activation, pin snaps Upon activation, pin snaps down and interlocks with down and interlocks with lower plate due to spring lower plate due to spring loaded potentialloaded potential

Current DesignCurrent DesignLever Base (Side View)Lever Base (Side View)

Current DesignCurrent DesignLever (Top View)Lever (Top View)

Current DesignCurrent DesignPin Housing (Lateral View)Pin Housing (Lateral View)

Current DesignCurrent DesignPin Housing (Axial View)Pin Housing (Axial View)

Current DesignCurrent DesignRotor (Axial View)Rotor (Axial View)

Current Design SummaryCurrent Design Summary

One tapered pin locking housing and bottom One tapered pin locking housing and bottom plate togetherplate together Spring-loaded (release and return)Spring-loaded (release and return)

Engaged (uncompressed) – 1.4 in.Engaged (uncompressed) – 1.4 in. Disengaged (compressed) – 0.8 in.Disengaged (compressed) – 0.8 in. Stroke length – 0.6 in.Stroke length – 0.6 in.

Tethered to lever via bike cables which screw into pinTethered to lever via bike cables which screw into pin Bike cable length adjustable via M9 boltBike cable length adjustable via M9 bolt

Spring force can be variedSpring force can be varied

Lever placement adjustableLever placement adjustable Mechanically simpleMechanically simple

IssuesIssues

Cost of working model exceeded three times Cost of working model exceeded three times initial estimateinitial estimate

Solves problemSolves problem Necessity of locking mechanisms on both wheelsNecessity of locking mechanisms on both wheels Mechanism inadvertently activatingMechanism inadvertently activating Reliability - Mean Time Between Failure (MTBF)Reliability - Mean Time Between Failure (MTBF) Ease of useEase of use Warning of hazardsWarning of hazards Add-on difficultAdd-on difficult

Work CompletedWork Completed

Designed and machined all parts of full-scale working Designed and machined all parts of full-scale working modelmodel

Researched ADA regulationsResearched ADA regulations Researched wheelchair mechanics (lab visits, journal Researched wheelchair mechanics (lab visits, journal

publications, etc.)publications, etc.) Constructed initial 3-D modelConstructed initial 3-D model Consulted several times with Dr. Mark Richter (Vanderbilt Consulted several times with Dr. Mark Richter (Vanderbilt

University, MAX-Mobility) and machinistUniversity, MAX-Mobility) and machinist Submitted NCIIA proposalSubmitted NCIIA proposal Established project websiteEstablished project website Dismissed initial design (housing with axial and radial Dismissed initial design (housing with axial and radial

teeth)teeth)

Present WorkPresent Work

Completing newly designed modelCompleting newly designed model Attaching bike cables to pinAttaching bike cables to pin

Assessing effectiveness of locking Assessing effectiveness of locking mechanism on a variety of cross-mechanism on a variety of cross-slopesslopes

Determining appropriate spring Determining appropriate spring constant for loading springconstant for loading spring

Verifying calculations and considering Verifying calculations and considering other circumstances that may other circumstances that may potentially affect those calculations potentially affect those calculations

Determining optimal composition of Determining optimal composition of heat-treated torsional spring pin of heat-treated torsional spring pin of final modelfinal model

Future WorkFuture Work

Analyze design Analyze design effectivenesseffectiveness

Optimize handle positionOptimize handle position Re-design model and make Re-design model and make

adjustments accordinglyadjustments accordingly Implement device Implement device

alterationsalterations Quantify new force Quantify new force

distributiondistribution Construct beautified Construct beautified

diagrams for final posterdiagrams for final poster