4. Manufacturing and Prototyping (ALAG)

Manufacturing and assembly of our prototypes all used the resources in Texas Inventionworks, which includes 3D printing and laser cutting. We would like to thank Texas Inventionworks, as well as our TIW teacher assistants Victor Guzman and Ashwin Hingwe for their help.

For our prototyping process, we first began with prototyping the arm mechanism. Once that was completed, we added the claw mechanism.

Our first prototype developed was a proof of concept for the arm mechanism, as shown below. Each of the structural components was fabricated out of 3mm- and 6mm-thick wood through the laser cutter. We used ¼ inch dowels to mimic pin joints, and at this stage, neither the motor nor the claw were attached. Although we knew that our arm was geometrically valid, we wanted to handle a physical prototype to experience how our mechanism functioned under gravity, identify areas of insufficient clearance, and determine whether or not there were any obvious toggle points that we would need to account for in subsequent iterations. We moved the input link manually to watch the position profile of the point of connection for a claw. This was a quick prototype to determine that the design made in MotionGen is viable. From this prototype, we were able to confirm our mechanism design. 

Our second prototype was a more robust version of the first. See the Solidworks images, pictures, animation video, and explanation video below. This prototype also consisted of laser-cut wood links, like the first prototype, but also featured upgraded components such as metal shafts and collars, ball bearings, thrust bearings, 3D printed spacers, and a motor. This prototype also had a place-holding, non-functional claw to help visualize the final mechanism. The purpose of this prototype was to create a model that successfully functioned the way we imagined our final machine to operate, identify areas of unwanted friction, verify tolerances of both the frame and the claw, and visualize how the claw would function. From this, we confirmed that our design is viable and that the links all connected smoothly based on our design. However, we did notice the hitch in the arm as it moved from each side. We believe that this was due to three things. First, we recognized that this could be due to the out-of-plane wiggle room between the slotted link that connects to the claw and its accompanying pin. To fix this, we planned to 3D print spacers and fasten them with a lock collar. Secondly, we believed it to be due to the rusted-over bearings, and so we planned to use new bearings and linkages for our final design. Finally, we thought it to be due to the weight of the claw being shifted from one side of the origin (see Solidworks images below) to the other, as touched on in the explanation video.

Once we felt confident in our arm mechanism, we moved on to prototyping a claw. To develop a functioning claw with a ratchet mechanism, we first added mounting points for two springs on the bottom of the claw. These springs are pretensioned such that the default position of the claw is closed. As such, the claw can clamp down on any sized object that can fit between the jaws. To open and hold the claw in position without automatically closing, we attached a ratchet mechanism that only allows the jaws to open. In practice, as the claw travels to the object-releasing side, a lever attached to the ratchet and input link will be engaged, driving the claw open. Once the claw travels to the object-grabbing side,  a lever attached to a spring-tensioned ratchet foot can be engaged to allow the claw springs to rapidly close the claw around the object. To ensure a secure grip on the object, the jaws are angled inwards and feature a high-friction rubber surface. Our final prototype was also the first prototype of the claw. Due to the time constraints of the semester, we were not able to iterate on this claw design. A more detailed description of the final prototype and the claw prototype can be found in section 6, “Final Design and Demonstration.”