4. Prototyping Process

We divided our prototyping manufacturing into three main sections. 

First, we made a prototype of the leg mechanism. Using the CAD model described before, we laser cut one leg mechanism out of 1/8" wood. These were the driver link, the ground link, the connecting link and the leg link. Each link has a smaller hole to fit a shaft in and a larger hole to fit a bearing. For this first prototype, we 3D printed small 5mm diameter shafts. Cutting and assembly were done in an afternoon, and this prototype worked as expected, meaning we were free to move to the second step. 

Laser cutting leg mechanism

Next, we decided to cut the rest of the prototype. This included two leg mechanisms, the main body, and the wheels and their connectors. As before, we used the CAD model to create image files of each link then laser cut them out of 1/8" wood. By then we realized we needed a way to transfer the rotational motion of our motor to the input shaft. Following our principle of simplicity, we decided on a 1:1 gear train. We designed the gears using an online gear generator, then laser cut them out of acrylic. This process took a lot of trial and error, as one of the gears needed to be adjusted to fit over the motor attachment. After multiple iterations, we obtained a gear train that fit perfectly over the motor and shaft. 

Laser cut pieces. Each piece was cut 2 to 4 times, depending on how many were needed for the final design

Laser cut gears. (Left) Unsuccessful prototypes. The inner shape would not fit the motor connector. Every iteration increased the size of the inner shape. (Right) Successful gear train 

Finally, we had to assemble the prototype together. This proved to be the most challenging step, as there were certain unexpected obstacles along the way. The most surprising setback was the 5mm stainless steel shafts we used for the leg mechanism. Its actual diameter did not match the expected diameter, and thus we had to cut and sand the shafts to fit the bearings. This took the longest amount of time, but we were able to successfully connect the leg mechanism with it. The body segments were connected together using L-brackets, and the wheel links slot together into the body. To secure everything together, super glue was put in the wheel link slots, leg shafts, and input shaft gear. 

Prototype during assembly. Note the slot connections between the wheel links and the main body