For my project, I wanted to work on a project that really interested me; I’ve always had a fascination with cars and the mechanics of engines. So, I decided that I wanted to show a combustion cycle like that inside your car’s engine. I started with a few sketches:
I’ve had a lot of experience with CAD, so I decided it would be much easier to build up a solidworks assembly to make sure all of my geometry made sense. I used geargenerator.io to create all my gear teeth geometry, and imported those dxf files into solidworks, and overlaid them over a cylinder at the gears respective bite radius. After talking with Dr. Wettergreen and the TAs, we decided that my initial valvetrain representation was likely non-viable, requiring simplification to a simple rotational motion. While this new motion does not perfectly mirror the action needed in the combustion process, it is much more simple and better within the scope of this project. Some assorted images of the assembly are below:
Low Fidelity:
From here, I made a couple of cardboard cutouts, which allowed me to better understand if everything was going to work and to what scale the project would functionally be.
From these cardboard cutouts, I learned that it would be good to go bigger, so, as Dr. Wettergreen and the TA suggested, I doubled the size of the entire project. This was done by importing all DXF file cutouts into illustrator at 200% size. My initial hole diameter was 0.25in, which became 0.5in, so I just decided to use 0.5in dowels instead.
Medium Fidelity:
Next, I made my medium fidelity prototypes; these consisted mainly of laser cut wood, as I decided my greatest hurdle would be friction and cardboard simply cannot simulate plywood friction to the degree I needed. First, I did a basic gear wall cutout, as well as the main drive gears. Then, I made a geneva drive to test out the state change mechanism. From these, I learned a lot: all my gears needed to be spaced out a bit more, my geneva drive geometry was incorrect, and needed to be redone, and that all of this was probably going to work. Some photos from this stage are below:
High Fidelity:
Next, I began to work on my high fidelity prototype. I was pretty sure everything was going to work, and the final deadline was quickly approaching, so I organized all my parts into a few batches, and went to cut them all out. All parts cut here ended up on the final prototype, with the exception of the base plates because, in sketching in solidworks, I added box holes for the width of 2 layers of wood, this was then doubled in the process of laser cutting, and using 8 total widths of wood would be both wasteful and look bad. These were correctly resized and recut. From here, I did an initial test fit.
This first assembly required a lot of work. Many of the pieces appeared to be warped, and I had measured my holes according to a dowel in which the diameter seemed to be significantly smaller at the end, requiring a fair bit of time spent dremelling all the things. Next, I did the finishing steps on all components. Finishing consisted of a 230 grit sanding, stain (dark walnut), 2 clear coats, 400 grit light sanding, and 2 more clear coats. From here, I sanded the exterior a little more, as I wanted this project to look more like a weathered work piece, rather than some perfect model straight from the factory, this is because of two reasons: first, that the stain was never going to look uniform on this wood, and second, in order for this project to perform smoothly, I knew that I was going to end up messing up the surface coats either way; I thought it better to lean into a more rough, handmade look.
After the final sanding, I applied a healthy coat of butcher block oil. I decided to use the butcher block oil after I found that friction was still a major problem after clear coats and final sanding; at first, I found both the cutting board oil and butcher block oil as shown below, I was hesitant to use the butcher block oil, as it was a more viscous fluid, and from my experience, butcher block probably has a higher friction surface coating than cutting boards. I tested the two on an extra piece of stained, clear coated wood from my box project, then selecting the butcher block after inspecting the results.
I also used the vinyl cutter to cut a stencil with which I used black spray paint to put on some arrows to indicate the intended operation direction.
From here, I reassembled the entire prototype and did a basic function test:
Noticing that it worked too well, I attempted to break it… (call it a high speed test.)
Conclusion:
Overall, this was a very enjoyable, yet difficult project. I’ve had a lot of prototyping experience, but have spent surprisingly little time working with wood or a laser cutter. I realized that at first, I was worried about every single thing when operating the machine, however, by the last day of work, I didn’t really think anything of setting up the laser cutter in the morning, then editing cuts on the fly, and getting perfect work pieces. If I were to do this project again, I would work more on the original design, especially to get vertically reciprocating valves. I would also take more care in each step, there are many flaws in each part, either due to flaws in my process, or because I didn’t want to take the time to make another from scratch after something uncontrollable happened (like how some of the teeth of the gears fell apart during first sanding, or were dropped in moving around).
More pictures of individual parts:
Slide Deck: Slide Deck
Costs:
- Material:
- Plywood: 3 sheets @ $9.15/sheet = $27.45
- Wood Glue: 1 bottle @ $3.47/bottle = $3.47
- Super Glue: 1 bottle @ $6.97/bottle = $6.97
- 1/2 in Dowel: 2 sticks, 1/2″ x 48″ @ $2.21/stick = $4.42
- 1/4 in Dowel: 1 stick: 1/4″ x 48″ @ $1.11/stick = $1.11
- Stain (Dark Walnut): 1/2 pail @ $9.78/bottle = $4.89
- Butcher Block Oil: 1/8 bottle @ $9.98/bottle =
- Clear Coat: 1 bottle @ $9.98/bottle = $9.98
- Black Spray Paint: ~$0, just 2 sprays from the bottle
- Total: $49.56
- Labor:
- Solidworks assembly: 9 hrs @ $30/hr = $270.00
- Laser Cutter Operation: 4 hrs @ 15/hr = $60.00
- Vinyl Cutter: 1/2 hrs @ $15/hr = $7.50
- Assembly: 12 hrs @ $15/hr = $180.00
- Total: 25.5 hrs | $517.50
- Machine Costs:
- Laser Cutter: 4 hrs @ $25/hr = $100.00
- Vinyl Cutter: 1/2 hrs @ $10/hr = $5.00
- Total: $105.00
Overall Cost = $672.06
