Week 8 Deliverables

Assisted Living Facility Visit Talked with elderly who are currently using walkers, a few who were using the same model as the one we have Sitting down and standing up use same motion, they wanted something that would simulate the arms of a chair They like squishy handles

CAD Drawing

Linkage Design Geometry was used so that the lever would go exactly 90° and the handle would go exactly 80°

CAD Drawing

Materials Selection All components analyzed using 1015 steel as the building material, which was found to have the one of the lowest yield stresses of most steels May elect to change material selection pending cost-of-materials analysis Aluminum Alloy 2014-T6 is relatively cheap, has a higher yield stress, lower weight, possible material for construction

Strength of Materials Stress related to bending moment Shear stress 2 shear locations 2 nd moment of inertia circular cross section These values were then compared to the materials yield stress

Strength of Materials 1015 Steel2014-T6 Aluminum Yield Stress315 Mpa400 Mpa Stress Analysis Bending StressShear Stress Handles94.32 MPaN/A Bolts for handlesN/A7.01 Mpa Leg support56.5 MpaN/A Other analysis done was using the stress caused by the compression of the beam, this was used to find the minimum radius of the support beam for the stopper; r min =0.78 mm

Handle Analysis Handle Bending Stress Bolt Shear Stress

Leg Support

Stability During Operation Most reliable solution is to fix the stopper/brace assembly in one position In order to prevent tipping when a 200 lb force is applied to handles, the stoppers must extend 20 cm from the rear legs (in perpendicular direction)

Safety Factor To enhance safety consideration, as many “worst-case” scenarios as possible were used in the analyses. –Force location –Materials choice –Component construction Average weight of men and women, ages 20+ is 165 lbs Factor of safety = 200 lbs/ 165 lbs Factor of safety = 1.21 > 1

Tipping of Walker Largest problem, required the center of mass and all forces involved during use ΣM was taken about the front leg If this moment was found to be less than or equal to 0, then the body did not tip

Tipping Centroid Assumed all members were equal weight Center of mass was found to be (24.50 cm, cm) about the axis shown in the following slide

Centroid Because all components were assumed to be the same weight, the total weight of the walker was applied to the centroid of the body

Tipping

Part Files