4) Manufacturing and Assembly - Group 6

In our manufacturing process, we utilized the 3D printers and the laser cutter in the TIW. For our project, we primarily worked with PLA plastic, super glue, heat shrink wrap, tape, a hot glue gun, and 0.25" thick wood. 

Link System

We used 3D printers to create the links, spacers, and modular axles. The axle was directly designed and used to connect and rotate the linkage. A stopper was made at the end of the axle to prevent the linkage from shifting left and right. Also, in order to connect the axle, a press-fit mate was created with a square extrusion and indent. Through multiple experiments using a 3D printer, the most suitable tolerance of 0.06mm was found. The pair of manufactured axles are able to firmly connect and can be disconnected by applying force. Additionally, for the grounded link (link 1), we created a press-fit hole for bearing placement and created connection points to ground the link with the wooden platform. Finally, in order to smoothly rotate the linkage system to the full range, an appropriate gap must be maintained between the linkages because the rotary axle and the linkage must not collide (seen in the design process section). For this purpose, linkages were connected by printing spacers of 1mm-2mm-4mm.

Figure 1. Male and Female parts of the modular axle.

Figure 2. Grounded Link 1 where the top left hole is big enough to press fit a bearing.

To assemble the link system, we used the previously determined axle lengths and spacer sizes to optimize the assembly. Using the modular axles, we were able to string through the components in the following fashion: Male axle->link->spacer->link->Female axle. Figure 3 below visually shows the final assembly of the links, axles, and spacers.

Figure 3. Complete link mechanism assembly

Boat Platform

To manufacture the boat platform, a 0.25" thick wooden board was laser cut into a boat shape with slots to connect the motor stand, pivot stand, and ground linkage. Figure 4 below shows the CAD images of the boat platform and connection parts.

Figure 4. The first image is the slotted boat platform. The second image is the pivot stand. The last image is the motor stand.

For the assembly, we added the connector pieces to their appropriate slot and fixed them in place using a hot glue gun. Figure 5 below shows the different components in the final model.

Figure 5. Complete assembly of the boat platform (ground).

Gears

When manufacturing the gears, we needed to make multiple iterations till we were satisfied with the pinion and gear's press fit on the axle. One main complication was to create a D-hole on the pinion that fits tight enough on the motor to effectively transfer the power. Figure 6 below shows the final prototype gear connection.

Figure 6. Final gear assembly.

Oar

Since the end of the oar rotates around the pivot, the angle between the output of the linkage system and the connection part of the oar keeps changing, so a ball and socket joint was required. The first plan was to design the ball and socket joint directly, and the ball as shown in Figure 7 was manufactured at the end of the oar. However, since the oar is thin, the ball was designed to be even smaller, and when it was printed and checked for strength, it was too weak, so another method was sought. Our next plan was to use a thread to connect the two ends since this allows the angle of the connection part to be freely changed (Figure 8). However, when connecting with a thread, it was difficult to match the centers of the two ends, resulting in severe tolerance. So, the last method suggested was connecting the two ends by tightening them with a heat shrink tube. By using a tube, two parts can be firmly connected by heat and the centers of the two parts can be matched. The elasticity of the material can then be leveraged to allow free rotational motion between the oar and the link system (Figure 9).

Figure 7. CAD model of a ballpoint for a ball and socket joint.

Figure 8. Failed attempt at using thread to connect the oar.

Figure 9. The final prototype of the oar-link joint.

Pivot

The pivot system was manufactured using a 3D printer and was designed so that it may slip on the pivot holder at the necessary point to create the optimal oar stroke. To attach the pivot, we used super glue and set it in place with the pivot holder (Figure 10). The oar is then connected through the pivot using its press-fit modular connection.

Figure 10. Pivot connection on the pivot holder.