IV. Manufacturing and Assembly - SK

Manufacturing

Links

Manufacturing my mechanism was the most difficult part of this project. Since I built everything at home, I had to cut every piece by hand.

To build my links, I used 11/32-inch thick plywood that I purchased from Home Depot. I started by cutting out rectangular pieces with the link length and a 1-inch thickness. I used a circular saw to cut out my links, which made the process easier compared to using a hacksaw. Then, I filleted the ends and drilled 1/4" holes for the joints. To make the slotted link, I cut out a slot using a Dremel with a small circular saw attachment. I wrapped the inside of the slot with duct tape to reduce the friction. Adding the duct tape surprisingly reduced the friction against the slotted pin. For the slider, I cut a 4.95-inch piece of 2x4 wood and attached small pieces of plywood to act as guards. A picture of all four links are shown below:

Figure 1. Wood materials used to build links and housing.

Figure 2. Individual links of my mechanism.

I ultimately lengthened the slot in the slotted link to increase the mechanism's range of motion.

Housing

To build the housing of the links, I used standard SPF 2x4 wood planks that I purchased from Home Depot. I cut out three different posts: one to hold the motor, one to hold the slot pin, and one that acts as the slider for the sliding block. I cut out these posts using a circular saw. For the motor housing, I originally attached the SparkFun servo motor with a U-bracket. However, the motor proved to be too weak, so I attached a TIANKONGRC servo motor by screwing it into the wood post. For the slot pin housing, I screwed in a 4-inch lag screw to serve as the slot pin. For the slider post, I attached two parallel 2x4 planks to act as a slider. The sliding block translated between these two pieces. Surprisingly, there was little friction between the sliding block and slider post. I attached all the posts to a base 2x4 piece with L-brackets and nails. Below is a picture of the housing:

Figure 3. Housing unit for the link assembly. The motor used in this figure was not used in the final design.

Assembly

To assemble my mechanism, I used a series of bolts, nuts, and washers to connect my links together. Every link was connected using at least one nut, bolt, and washer. The washer reduced the friction between the links, which made the motion smoother. Since some of the links would rub against each other during rotation, I spaced out the links using nuts and washers. This prevented the links from hitting each other during motion. I also screwed in the input link to the servo motor with a 1/8" screw. This screw needed to be held on tightly or else the motor would not effectively rotate the input link. Below is a picture of how the washer, nuts, and bolts were assembled to connect the links:

Figure 4. Series of washers, nuts, and bolts to connect the links.

Below is a picture of the final assembly of the links:

Figure 5. Final assembly of the links.

Below is a picture of the final mechanism assembly:

Figure 6. Final assembly of 5-bar mechanism