Manufacturing & Prototype Iterations - Team 9

Overview

Much of the manufacturing was done through laser-cutting as it was both faster and more accurate than 3D printing. The first iterations were made out of wood on a smaller scale, then after the proof of concept was established, later iterations shifted towards using acrylic full scale. This was done to reduce the coefficient of friction between joints, especially since many of the joints were sliding against each other over the full operation of the mechanism. Because of the precise nature of the laser cutter, many of the components were press fit (i.e. bearings and pin joints). 3D printed press-fit endcaps were used to constrain the undesired out of plane motion of the mechanism, and were toleranced through several test prints on the Bambu printers. 

Materials

The structural integrity of the linkage mechanism is vital to the efficiency, strength, and reliability of the mechanism. With the consideration of the mechanism still being in the prototype phase, the material selection had to be within a tolerable range that doesn't go over budget but also effectively demonstrates the mechanisms main purpose. We decided on using 1/4" Acrylic for each of the links and for the base plate since the material was easily available and affordable. The links and base plate had to be the most structurally stable, and so using acrylic plastic allowed for a strong mechanical hold while also remaining lightweight. The next important material selection came in choosing the rods, and so we decided to use 6mm diameter acrylic dowels. The main factor that we looked into for the rods was that they would have little friction so that they could act as proper revolute joints, and so the acrylic dowels did the job effectively. Finally, we utilized PETG for the motor mount and the rod ends since these parts were not to bear high stresses.

Manufacturing and Part Iterations

For the manufacturing process of our prototype, we utilized the resources given to us by Texas Invention works. For the linkage system, since we wanted precise cuts and holes with minimal error tolerance, we decided to laser cut each link and the baseplate. Even with minimal tolerances, we still made test cuts for the links in order to determine how well the acyclic dowels, bearings and the motor point fit. Below is a picture of a very early iteration of the end effector, with one of the first usages of the end caps in this project. Despite the inefficient mechanical advantage, this iteration was a proof of concept for our manufacturing methods. Each of the slots and the joints held up incredibly well to repeated usage and the play between the slot and the pin was minimal. The purpose of these early iterations was to figure out exactly what tolerances we were able to achieve with the machines we planned to use. 

When cutting the links for the final system, we determined that the links lined up fine, but found that the bearings were slightly loose and we wanted them to have a tight friction fit. Interestingly, cutting acrylic produces different tolerances than laser cutting wood does. So we slightly decreased the diameter of the bearing holes by .1mm and laser cut the acrylic again. This resulted in a perfect friction fit, constraining out of plane motion for the mechanism. Another important note is that the acrylic we bought came with an outer paper layer that gave the acrylic a decently frictionless surface. So we decided to keep the paper on when assembling the mechanism as we wanted the links to move as smoothly as possible. Now, for the manufacturing process of the endcaps, we decided to 3D print them out of PETG plastic using the Texas Inventionworks Bambu 3D printers. We created two iterations of the endcaps, the first iteration was exactly 3mm in diameter and fit the dowels really well, however the end caps were not as friction fit as we wanted and would slide off if given enough force. We then decreased the end cap diameter down to 2.90mm in order to create a tighter fit, and this worked successfully as we had to slightly hammer each end cap on the dowels and created a strong hold.

Electronics

The scope of our project only required that the whole linkage system was to be powered by one actuator, and so the only electronics utilized were a 12-V DC motor, two alligator clip wires, and a 9-volt battery. The 12-V DC motor simply slotted into the motor mount and was connected directly to the 9-V battery via the alligator clips. The electronic system still could have some improvements however, like adding a switch and resistor and creating a circuit that allows the user to easily switch the system on and off. The resistor would also act to reduce the current entering the motor and would negate the chances of overheating. 

Bill of Materials:

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