1. Physical Prototype

1.1 Iteration 1: Drawings

We began by drawing the individual linkages and labeling each link and important angles. In the Project Proposal we proposed a 7-link mechanism. During the kinematic analysis step of this phase, we found 7 links were causing the velocity equations to diverge, so we reduced the number of links from 7 to 6.

1.2 Iteration 2: Cardboard

We used the drawings and initial kinematic analysis to quickly cut our links out via cardboard. We secured the links together with screws and nuts. We left out the CAM device at this stage to showcase the mechanism design. Our cardboard prototype showed a range of motion that matched closely with the results of the kinematic analysis, which enabled us to proceed to a higher fidelity prototype.

1.3 Iteration 3: CAD

We created a 3D design based on the knowledge gained from drawings and cardboard prototype iterations. The mechanism’s range of motion proved to be acceptable relative to the link lengths. In this phase, we discovered that the length of the CAM needed to be precisely controlled to maximize the motion of link 1, the “foot link” while preventing its collision with other links. After this testing, we chose to leave the CAM out of this prototype build. We will include it in the final build when we include the motor.

1.4 Final Iteration: Laser Cut Acrylic

We cut the 6 links out of acrylic based on the CAD design and assembled them using nuts and bolts as joints. We attached a torsional spring across links 3 & 4 using zip ties. The resulting motion was mostly satisfactory and closely matched previous analyses. 

1.5 Lessons Learned

1. We need a spring with a higher K-constant to generate sufficient force to lift the body off of the ground.
2. The spring mounting system must be robust to ensure minimal movement of the spring related to links 3 & 4.
3. The CAM shape and size must be delicately designed in such a way that it fully extends the spring while also quickly getting out of the way of the spring action.
4. A foot is required between the end of link 1 and the ground to provide stability and potential an additional compression spring.
5. We need to replace the nuts & bolts with rods & bearings to reduce friction and prevent loosening at the joints.

2. Bill of Materials