CSM -- Initial Approaches and Prototyping

We decided to begin prototyping in SolidWorks with a fourbar mechanism that would give us the motion we wanted to relocate a reversing wheelchair onto a curb. The aim was to have the mechanism vertically elevate and horizontally translate a wheelchair in a continuous, smooth manner. Because we anticipated that the wheelchair user would operate the mechanism most conveniently with the wheel, the fourbar mechanism was designed so that the crank or input link would have full rotational movement, i.e. a Class I Grashof linkage. Taking into account approximate locations and dimensions of the parts of a wheelchair, the relevant linkage lengths were varied until the desired motion was captured. The CAD concept drawings are shown below

With the skeletal design in place, further design in SolidWorks was necessary to integrate the concept with our expected build materials. A rough approximation of a 1:4 wheelchair with the relevant dimensions was 3D printed, and the initial iterations of our mechanism linkages were lasercut in the MakerStudio of the ETC for convenience of prototyping.  

This project had two main prototypes prior to our final presented prototype. Images and a video of the first prototype are shown below. 

 The first iteration had a few issues that required improvement. One primary problem was that upon retraction, the pushbar link interfered with the curb and was not able to reset back into its initial resting state. Another issue is that the current design for the pushbar raised the wheelchair too high above the curb. Upon returning to the ground, the wheelchair user would be subjected to a high incline angle which introduces a safety hazard and discomfort to the user. To address these issues, a second iteration was designed. The images and video are shown below. 

The second iteration is inspired by a crank-slider mechanism, providing a smooth and controlled motion to translate the wheelchair. The pushbar is redesigned to align with the ground during its period of contact so as to prevent the wheelchair user from tipping excessively. The guide slot link provides a path for the pushbar so that it is introduced when needed but does not interfere with the curb during retraction and the motion is relatively compact. This design fulfills the basic requirements of the curb scaling mechanism concept but still required a couple of improvements. Firstly, a separate mechanism is anticipated to engage the curb scaling mechanism via the wheel. Because the wheel would have to lock with the crank link throughout full rotations, the current design of the guide slot component is inadequate and interferes with this possibility. Consequently, the slot will have to be shortened at the top and lengthened at the bottom to further accommodate for a full range of motion by the pushbar. Furthermore, a new pinning location for the guide slot link is required.  

Shown below is a list of materials requested for the project and final prototype.