Introduction
For our midterm project, Daniel and I decided to construct a race track that includes both an incline and a flat portion. Each track has a car with a distinct design, and this project incorporates mechanical movements 12 and 24. This blog post details the process by which we arrived at our final prototype, including descriptions from each gate check-in, a cost analysis of the final model, and the failures and successes of our project.
Gate 1
At first considered many ideas; however, we decided on a race car track with an inclined and flat portion, which involves moving two cars up the track with movements 12 and 24 (From 507 Mechanical Movements). The vehicles would be pulled up the ramp by a thread (at this stage, we thought of a string or fishing line as the thread) guided by a pulley at the other end of the track. The user could operate this model by utilizing gears and a crank. The crank rotates about the same axle as the smaller gear. We decided to employ a 2:1 gear ratio to increase the torque the smaller gear provided to the larger gear at the beginning of the race, where more torque was necessary to help the cars travel up the ramp. This gear would then cause the larger gear to rotate about another axle that contained both the larger gear and a spool contraption (with a larger diameter than the axle) responsible for winding and unwinding the thread that pulled the cars up the ramp. Another thing we considered while designing this model was the longevity of the mechanical system; we wanted to minimize any unnecessary strain or wear and tear on the gears. As a result, we decided to incorporate a dowel system, which enables the user to move the cars back to the starting position following the completion of the race without turning the gears and thus ensuring they undergo no unnecessary wear and tear. This design involves drilling a hole through the spool and the axle on which the spool rests. Then, inserting a dowel into this hole, the three components, the axle, spool, and dowel, move as a rigid body. But once the race is finished, the user can take out the dowel, detaching the three components and allowing the user to move the spool, unwinding the thread without the rotation of the gears, because the spool lies on the same axis as the axle; however, due to the larger diameter of the spool, it can move freely. Then, once at the string location, the user could insert the dowel into the hole and recommence the race.
At first, we anticipated designing a track that was adequate in size. Still, upon the completion of our low-fidelity prototype, we realized that the box was too small for our liking, so we decided to increase the dimensions of the box from 9″ x 4 1/2″ x 6″ to 12” x 8” x 6”
Gate 2
For gate 2 of the project, we constructed a low-fidelity prototype of our design using cardboard for the main frame and wooden dowels for the axles and gears.
To get the press fit shape for the cardboard, we used https://www.makercase.com/ for the general box design with two dividers. However, we edited the original design in Illustrator to create the inclined front. We used the laser cutter to make the cardboard parts. When assembling the box, we made minimal measurements and worked on a cut-as-needed basis. One problem we identified was how the gears moved along the axle and did not stay in place. To fix this in the low-fidelity version, we made the spool the same size as the walls and added curled metal wire to act as a spring and keep the large gear pressed against the wall. Another problem was that the string was not staying on the spool when we rotated the gear system. We noted this down for future versions as something we would need to fix.
Gate 3
We cut all of our materials (including the aluminum piece) for gate three and assembled the components. The box came together through a press fit. We also post-processed the aluminum piece by first filing it and then sandblasting. Unfortunately, the hand crank did not work as intended because the small gear still needed to be glued to the axle. We intentionally left this step until the end, as once the gears were glued to the axle, it would become much harder to change anything. However, manually turning the spool worked as intended, and the stand-in “car” moved up and over the ramp.
Final Prototype
For our final prototype, we completed all the post-processing required. Following the feedback from gate three, we decided to smooth the cranking motion further and enhance the overall presentation of the model. We did this by meticulously sanding the axles and the frame portion of the truck to minimize any rough edges or unwanted debris. Then we glued the box together using wood glue to ensure the press fit did not come undone. Once the frame was glued, we began to finalize other aspects of the model, such as gluing the axle upon which the pulleys rested and the name plates on the back side of the model. While the model dried, we constructed our small cars by cutting out pieces from a 2″ x 2″ lumber in the desired length we wanted for the vehicles, and using the same wood, we cut out wheels. Then, we constructed the cars using various tools in the OEDK, painted each vehicle with a different vinyl, and then put them all together. Once that was done, we decided to finalize the remaining section of the model, which included gluing the axles, gears, cranks, and the spools (and passing leather thread through the spools). We then decided to stain part of the track using a dark walnut wood stain we found in the OEDK. After all was said and done, we had a working model! That displayed mechanical movements 12 and 24, incorporated vinyl, metal pieces, and post-processing techniques.
Cost Analysis: For Final Prototype
Labor: $580
80 hours (At Texas minimum wage) = $580
Equipment: $50
Maker Space (One month membership, includes all the tools and machines used to construct this project) = $50
Materials: $60.68
Aluminum (Two 1/4 inch 2″ x 1″) = $0.95
Dowels (Variety Pack) = $9.99
Plywood (2.5 2ft. x 2ft.) = $20.75
Spray Paint (Blue and red spray paint) = $15.90
Wood Stain (Dark walnut) = $8.17
Leather Cord (One roll) = $1.00
Vinyl (12 square inches from a 1584 square inch roll) = $0.08
Lumber (2″ x 2″ lumber for the wooden cars, used one foot) = $0.37
Wood Glue (One entire bottle) = $3.47
Total Cost = $690.68
Improvements
-We should have verified dimensions before assembly. As a result, we devoted a lot of time to sanding and recutting material to acquire a proper fit.
-We should have stained the frame of the track before gluing.
-We could have incorporated wall bearings to minimize friction between the axle and the wall.
Conclusion
This midterm project, alongside the other homework assignments assigned thus far in the semester, has provided great insight into the procedure and technique for designing and constructing our designs. Although there were shortcomings and unforeseen challenges with the project’s construction, we are satisfied with the final prototype and excited for the upcoming projects.
Cleaned Workspace
After using every space in the OEDK we left a clean and organized environment.
