Materials requested for project.
Part | Price | Quantity | Notes | Status |
|---|---|---|---|---|
| 8 mm retention rings | 20 | From Slider-crank mechanism | Ordered; Received | |
| 8x16x5 mm bearings | 20 | From Slider-crank mechanism | Ordered; Received | |
| Aluminum plate stock (12” x 12” x ¼” plate stock) | $30.51 | 1 | 8975K142 (McMaster-Carr Part No.) | Ordered; Not Received |
| Aluminum stock (¼” x 1” x 48” bar stock for links) | $12.28 | 1 | 8975K596 (McMaster-Carr Part No.) | Ordered; Received |
| Rotary shaft 200 mm x 8 mm | 2 | From Slider-crank mechanism | Ordered; Received | |
| Rubber lining (1” x 18”) | $6.47 | 1 | 9023K82 (MacMaster-Carr Part No.) | Ordered; Received |
Above are concept drawings for the mechanism. In reality, the curved pushbar will have two points of contact with the ground and will cause the wheelchair to not be perfectly level through the motion. Two cycles of the motion may be needed to get the wheelchair fully on the ledge.
An issue to consider for the project is the scale of the final prototype or presented class product. A life-size scale for a wheelchair presents difficulties in obtaining the required materials for construction and testing, and we may look into a reduced-size model for a prototype. Another issue is the separate mechanism for engaging and operating the curb scaling mechanism, which would be necessary for a complete, functioning attachment. The scope of the whole attachment may conflict with the class timeline, but because the two mechanisms are fairly independent, a single presentable mechanism with the conclusion of the class can be manageable. A final prototype might be the curb scaling mechanism, which would demonstrate translating a wheelchair or model from the ground onto an elevated platform.
By testing our first designed model with a scaled down curb, we encountered a critical problem when going through the motions of the mechanism. As seen from the videos above, once the mechanism was over the curb and the mechanism needed to be retracted, the coupler interfered with the curve and thus preventing the desired motion to be completed. This led to the necessity of redesigning the mechanism.
For our second prototype, a slider-crank mechanism was implemented where the slider was a curved slot which guided the direction of the coupler and thus allowing for the appropriate retraction of the mechanism.