IV-Manufacturing and Assembly

As described in the Design Process section previously, this mechanism has already gone through several iterations using various materials and components for each part. 

Rough Layout and Tangible Model

A major setback of computer simulation was the "planar" element of PMKS. Unable to see the physical collisions and connections needed for a mechanism, I opted to create a simple model of the six links using balsa wood. I began prototyping with some balsa wood that I found at the Co-Op when the laser cutters were down. The joints are made from a post and screw pair shown below. Found at ACE, these fasteners have a smooth surface for joint rotation and come in various lengths for spacing out the joints. Lock nuts and bolts were also used to give a bit more flexibility in spacing the joints.

Screw and Post

Drilling holes caused the balsa to crack, so instead I burned them in by heating a screwdriver on the stove and gently poking it through. These joints moved smoothly, but the prototype was not functional since several joints came in the way of the motion of the links, as can be seen in the picture below.

Laser Cut and Accurate Prototype

The outcome of this prototype was a second prototype made on the laser cutters after they were fixed. I purchased more screws and posts of varying lengths. The links were cut from ¼” plywood and spacers were made from ¼” acrylic to allow smooth motion. Additionally, the crank input (link 1) had to be separated like a crankshaft to allow the “piston,” link 3, to move freely. This meant that both sides of the split crank had to move at the same time and maintain their position relative to one another. While welding or some sort of epoxy would be ideal for this, it would not be adjustable and could be problematic later on. Instead, I used lock nuts on a 2” machine screw to secure each side of the crank in place on the screw, while leaving a space for link 3 to rotate without restriction.

Finally to ground the mechanism a 6th link was made as a clamping point. Overall, I am pleased with the mechanism, it is not as smooth as I had hoped for because there is some tolerance in the length and thickness of the joints and links, which results in small gaps and wobble. However, I sanded down some laser cut washers to fill these gaps as best as possible. The longest link in the mechanism is just over 5,” which results in a “step height” of 1” at the peak of the arcing path drawn above.

Please see the video of this updated prototype below: