Design & CAD

When beginning the design process, we knew we wanted to use pieces that are available off of the shelf as much as possible. We broke it down by each major subsystem; the slider crank for the piston and the belt drive for the cam shaft. 

Here is a basic list of components used from off the shelf to help manufacture the device:

1) Cylinder housing (3" pvc pipe)

2) Standard nut sizes such as fastener callout size 3/8-16" with 9/16" external width and 9/16" hex bearings to match. However, we couldn't obtain hex nuts with 9/16" ID and had to opt for 11/16" which we had to order extra-wide nuts for (Something we were hoping to avoid by utilizing conventional manufactured sizes in the first place).

3) Threaded rod to match fastener size, and arbitrarily 2x4 wood to build the base with.

4) A toothed belt for sizing the distance between the pulleys along with pulley indent sizing.

After finding these parts on McMaster, we imported the CAD designs and started to mock up our project. 

To find the link lengths for the slider crank that is apart of the piston mechanism, we did a kinematic analysis. The analysis is further explained in the kinematics and motion analysis. Once we found the link lengths, we designed the device accordingly. We attempted to design based on manufacturing the device. This incorporated things like material selection, dimensioning, and the steps used to manufacture certain components. For example, when designing the crank shaft, we wanted to do it in pieces to allow ease of manufacturing. In addition, using things like a 3D printer and laser cutter, also influenced other features to be designed a particular way.

Here are a few pictures of the device and components as we went through the design process:

Figure 1: This is the initial revision of our design. In this design, we noticed it would be difficult to manufacture due to weird sized of rods and complex geometry.

Figure 2: This is the first and second iteration of the second revision of the device. We added supports on both sides and designed based on manufacturing. we also added a crank for the crank shaft. 

Figure 3: Here are pictures of the cams. The intial design on the left was causing the valves to move side to side. The design of the cams was changed to be more circular to aviod this problem as seen in the middle picture. A valve tip as seen on the right was added to the valve for a larger surface area for the cams to catch.