Machine Design

This two-week assignment tasked my classmates and I to work on a group project to design and fabricate a machine. After a round of brainstorming followed by a democratic voting process, we decided to build a robotic etch-a-sketch machine!

You can follow these links to learn more about the overall project, and see the machine in action. What follows is my specific contribution to the group project.

I took on the challenge of designing the housing that would hold the etch-a-sketch as well as the two drive motors and wheels. I started with the rough sketches we made on the white board. This gave me the general sense of where everything needed to be located.

Then I gathered together 3D models of the "purchased" parts. I imported STEP files of the etch-a-sketch and stepper motor that my classmates built, and then used SolidWorks Toolbox to generate the bearings, screws, and gears we needed.

With these items in place, I could start to design the geometry that would tie them all together. I knew that I wanted to laser cut the final design, so I broke things up into panels and used tab-in-slot as well as snap fit joints to align and hold everything together. Generally speaking, these joints performed well, but we did push a few of the snaps too far and they broke off. In the future, I'd consider altering the shape of the snaps, or better yet, build the assembly out of a more flexible material such as HDPE.

I designed the housing in SolidWorks 2018 as a multi-body part and included a few key variables for material thickness and clearance that I can quickly change to produce a design that accommodates any material.

I created a SolidWorks drawing of all the parts, saved it as DXF, opened it in Adobe Illustrator to tweak the line thickness and color, then sent it to the Trotec laser cutter.

With the pieces all cut, I began assembling them. I had to pay close attention to the assembly order as some pieces could only go togehter at a specific time. For example, the threaded rod had to go in after one side wall was assembled, but not after the second side wall, as it needed to be "trapped" in the housing.

The overall housing went together really well, but I learned that I allowed a bit too much clearance above the etch-a-sketch, so it felt floppy when the housing was inverted. I tweaked a few dimensions in SolidWorks and onlly had to recut a few of the pieces to snug up the fit.

I also designed a latch that I 3D-printed. It's job is to hold the etch-a-sketch snuggly in the housing and maintain inward pressure so the drive wheels stay in contact with the etch-a-setch knobs.

I'm happy with what we could accomplish as a team in these two short weeks. As it stands now, our machine runs off of instructions (g-code) that we manually write. We started to investigate software that could translate any image into g-code for our machine, but didn't have enough time to realize that dream. Perhaps one day we (or some other adventurous FabAcademy student/group) will take on this challenge and robotically etch-a-sketch an image of Neil!