The first sketch of our project
This blog chronicles our time spent working on the midterm project where we were asked to build a mechanical model. After a while spent brainstorming, we were inspired by the toys that move a ball up a slope through a series of steps. We decided to turn this type of movement into an Indiana Jones themed diorama. Taking inspiration specifically from the scene where Indiana Jones almost gets run over by the boulder, we set out designing some Adobe Illustrator files for our low fidelity prototype.
Our model features the combined movements of numbers 90 and 96 from “507 mechanical movements”. Our model has a row of 6 offset cams driven by a hand crank. Resting on those cams are 6 cam followers. Each of these cam followers are shaped like steps with sloped tops so that the boulder always falls into the next step. The top step is also sloped to guide the boulder towards the ramp. Once the boulder reaches the top, it falls into the ramp where it rolls until it hits Indiana Jones. Indiana Jones is on a weighted pendulum mechanism with a water jet cut flag on his back. The boulder hits the flag, knocks over Indiana Jones, and then Indiana pops back up and the boulder continues back around the corner to the steps for it all to happen again.
Low Fidelity Prototype
Video of the low fidelity prototype
Close up showing the cam and cam shaft. This part failed first in the cardboard prototype, so we made sure to upgrade for future iterations.
We used laser cut cardboard to construct our low fidelity prototype. This Prototype was designed to test the functionality of the stair step mechanism. After the files were laser cut, we assembled them used masking tape to hold it together. This model functions as well as it could be expected to and gave us a great proof of concept and inspired up to move onto higher fidelity materials.
Medium Fidelity prototype
Video of the medium fidelity prototype
A slight oversight was made when designing the files. These holes got left out.
The medium fidelity model add a couple key features. Mainly an enclosed ramp for the boulder and a middle panel to hide the stair mechanism from the from of the diorama. The medium fidelity prototype was made from laser cut wood. To make the boulder, we brainstormed materials that were both the right size and weight. Marbles would be too small and too heavy whereas the puffball from the low fidelity was way too light. We ended up hammering a tinfoil ball so that it was both dense and smooth. This led to a boulder that was the perfect weight and could be whatever size we needed.
This is a partially assembled view of the medium fidelity prototype. In it you can see how the ramp comes above the doorway on the top door.
A failure with the medium fidelity model was that there were some missing holes on the files we designed, so we used a drill and chisel to add them for this model and changed the files for the high fidelity model. We also had slightly misaligned the part of the model where the boulder rounds the corner after the ramp and goes back to the steps. After some troubleshooting, we found that a small triangular piece of would could be lodged in the corner to guide the boulder into the right spot. Another flaw with this prototype was the wooden shaft which the cams rest on was made out of a weak section of the plywood and it had the tendency to twist under the torque. An improvement we made to this prototype and carried over to the final model were the bearings inserted on the shaft edges and the upgrade of the handle. Before the handle was just wood and the shaft spun in a laser cut hole in the side panels. This led to a lot of friction and unpleasant operation of out model. Once we added the bearings there was a drastic reduction in force needed to spin the handle.
High Fidelity Model
Video of the medium/high fidelity prototype
We noticed that the ramp the boulder rolled down was very short and the boulder didn’t have enough momentum to knock over Indiana Jones. So, for our final high fidelity model, we extended the diorama by 6 inches. While this led to an almost total redesign of the laser cutting files, in the end it was worth it. We took this time to also update the files with all of the edits from the previous iterations. We changed the steps to make them a lot lighter by simply cutting a rectangle out of all of the 6 individual squares that make up each step. Once the files were all laser cut, we noticed a few small adjustments that were easily fixed with another round of laser cutting.
The slope was cut too low on this first iteration of the high fidelity. This was fixed with a new line and a re-laser cut part. The burn marks are from the laser cutter. The speed was a little too slow.
One of these issues was that the curve on the front panel was too low and dipped below the ramp. Another issue was that the boulder, once it has rolled down the ramp, got stuck going around the corner. We fixed this by adding a bigger wedge in the corner and changing the angle of the ramp slope. One minor issue with this model was with Indiana Jones himself. We attempted to laser engrave him, but something went wrong with the Illustrator files and we were not able to laser cut him out. We ended up using a Dremel tool to clean up the edges and get a clean outline for Indiana Jones. We assembled the whole model and verified the functionality of everything by securing the edges with painters tape. Once we were satisfied we took all the pieces out to the loading dock to give them a nice coat of brown stain. We also gave the boulder a coat of gray to take away the shine of the tinfoil. Then we reassembled the pieces again to check that it all still worked and took off the front panel to give it some more post processing. While Izzie worked to secure all other pieces with wood glue, Benji cut out stencils of some dinosaur fossils, rocks, and grass the add to the final piece. Then we vinyl cut out a whip and a hat to further symbolize Indiana Jones and secured the front panel.
front view of the high fidelity prototype. The vinyl cut whip and hat can be seen on the front along with a stencil/spray painted dinosaur fossil and the name plate.
In conclusion, we are both proud of the effort we put into this mechanical model. From the first brainstorming session all the way to placing the finished model on the ENGI 210 table, we worked hard to make the diorama come to life. While we are happy with the way it turned out, there are a couple things we would update or change if we ever did this project again. First of all, I feel like we focused a little too much on the main mechanism of the stairs and kind of neglected the movement of Indiana Jones tipping over. We could have balanced our time in this sense better. In the end, Indiana Jones didn’t spring back up like we wanted him too, and the boulder would still get stuck around the corners. Looking back, I feel like we should have implemented a living hinge into the corners of the design. The would solve the issues of the boulder getting stuck on the sharp corners.
Cost Analysis
Material Cost:
- 3 sheets of 2’x3’ ¼’’ plywood – $13.47 per unit (Lowes), total of $40.41
- 4 sheets of 2’ x 2’ ¼’’ plywood – $8.98 per unit (Lowes), total of $35.92
- 2 sheets of 2’ x 3’ cardboard – $22.99 for pack of 5 (Amazon) total of $9.20
- 2 35mm diameter bearings – $6.99 for pack of 2 (Amazon) total of $6.99
- Spray Paint – Negligible amount
- Vinyl – Negligible amount
Total: $92.52
Labor Cost
Izzie and Benji spent 30 hours working on this whole project, including prototyping, cutting, assembling, and post processing. Because this project is majority wood, we chose to use a Houston carpenter’s hourly wage, which is $21/hour, this comes out to a total of $630 for labor cost.
Total: $722.52
