Midterm Mechanical Model by Kathy and Ellena: DROWINING CAPYBARA?!?!

For the past month, we’ve been working on both the designing and the building of a mechanical model. It’s been our first time working with mechanics and elements such as gears, so the learning process was both challenging and fun!

Process:

Firstly, we looked at the 507 Mechanical Movements website and noted down a few movements that seem both feasible and interesting, and during this process the ones that we’ve noted down were mechanical movements #24, 122, 125, 131, 138, and 222. Combining that with the examples of projects from the previous years that we’ve seen in class, we settled down with using movement #138. Below is a picture of our main mechanical movement and the previous project that we referred to.

After that, we made a few sketches about how we wanted to custom the design with consideration of the flowing movements. We had the idea of either doing a road trip theme or a swimming theme, and we ended up settling down with the swimming theme with a little capybara in the center. To make it more stable, we also decided to make two rows of cams instead of just one row, since we decided to do rectilinear waves instead of circular ones.

Moving on, we started making the laser cut files in Rhino, since it was easier to draw accurate dimensions and also keep in consideration the thickness of the wood we had, which turned out to be 1/5 inch. Here are some of the files we made using rhino and on the right side is a drawing of the model from plan view that we used to calculate the distance between pieces and the dimensions of pieces with consideration of wood thickness.

After having the files, the next step was laser cutting a low fidelity model for the first gate. We unfortunately weren’t able to successfully cut the cardboard pieces because the laser cutter set on fire while we made sure that we used the correct settings.

After that, we had to move on and start cutting the ply wood pieces for the final model. This time, the laser worked fine and we made sure to do test cuts and focus it very carefully and thankfully nothing happened. We made sure to tape the pieces onto the board before removing them from the laser cutter, since we have many small pieces for the cams that need to be kept in place in order for us to find them and know where they are. For the cams specifically, we also made sure to score the outline of the cam before it, which would help us make sure that the two cams would be perfectly mirrored and that the movement would be coherent.

The next step was the assembly and the sanding of the laser cut pieces! It mostly went very smoothly, because Rhino is very accurate with the considerations of material thicknesses and sizes, we didn’t have any problems fitting the pieces together, everything went pretty smoothly!

It all worked well until we clamped it together and tested how it worked. The cams were clogged and not moving at all, only slightly left and right. We observed and concluded that it might be the following issues:

There was too much friction between both the surfaces of the feet and the cams due to the laser burn since we didn’t get to sanding yet.
The holes for the feet were too loose, which causes the feet to move left and right too much.
The width of the feet is too narrow and it’s going against the cams at certain points.
We don’t have a finish yet.

With these, we edited the file for the platform and feet and re-cut them using the laser cutter. We also asked the TAs during our second desk crit and were told that we could try to use graphite, or lubricant as our finish, which would significantly reduce the friction.

With the new pieces, we sanded all of our pieces to reduce friction on the linear motion. Additionally, the bottoms of the feet had to be a little bit rounded to prevent the feet from getting stuck on the cams. Then, we coated them with a dry film lubricant that both prevents grit and grime from sticking onto the wood and reduces sliding friction. Then, we used the paste finishing wax to finally finish post processing. There is not much of a color difference, but the texture was definitely smoother and the motion was more functional. These methods of decreasing friction between the feet and the cams were pivotal in making our machine function.

Next, having known that the mechanism works, we worked on the wave pieces. they were sanded and spray painted light blue. We sprayed, waited 20 minutes, and repeated this 4 times to fully and evenly cover the waves with spray paint.

We assembled all of the pieces together layer by layer. The first layer involved putting the dowel through the first layer’s holes and gluing on the stoppers on either side of the side strips. Next, using the clamp to structure the bases, we inserted the feet into the smaller holes. It was crucial to make sure all of the feet were straight to make sure that the waves were level. We were able to clue on our spray painted water waves onto the top of the feet after the layers were inserted onto them. After assembling the basic structure of the machine, we used a hand saw to cut off excess of the dowel piece and sanded it afterwards to make it clean.

Next, for the handle, we waterjet cut our metal piece. We drew the new handle with another capybara on Adobe Illustrator making sure that the hole size was consistent with the wooden dowel’s diameter, and utilized the waterjet cutter. After cutting the piece, we post processed the handle with a sandblaster to make the surface smooth. We glued the metal piece with 2 stoppers on both ends to make it stick on the dowel, and let it dry for a while for the rotational movement to happen. The excess dowel on the handle was also hand sawed off and sanded to make it smooth with the stopper. After drying the glue, we were finally able to see the full motion of the waves with the rotating capybara handle!

Final pictures and videos of the project!

Workspace before and after cleanup:

Link to Slideshow

Cost Estimates:

1/5″ plywood sheets 24″ x 24″: $7.28/piece x 3 = $21.84 (home depot)
1/4″ wooden dowels: $0.20/dowel x 2 = $0.40 (amazon)
1.5″ x 2.5″ metal piece: about $1.75 (home depot)
Vinyl Sticker: about $0.49 (amazon)
Sand Paper: about $5.50 (amazon)
Lubricant (Dry Moly Lube): $12.50 (amazon)
Spray Paint (including clear coat): $5.98/can x 3 cans = $17.94 (Walmart)
Finishing Wax: $17.18 (amazon)
Waterjet Cutter: $31.83/hour x 0.5 hours = $15.92 (waterjet)
Laser Cutter: $120/hour x 2 hours = $240 (practical machinist)
Vinyl Cutter: $1.50/minute x 15 minutes = $22.50 (geekifynic)
Labor as a Design Engineer: $29/hour x 20 hours x 2 people = $1160 (zip recruiter)

Total: $1515.82