For our BIOE 677 midterm project, we were assigned to create a physical mechanical model based on one of the existing models in 507 Mechanical Movements. This project demonstrates a simple mechanical mechanism that ties together the topics and skills we have learned in the course thus far including woodwork, post-processing techniques, laser cutter, plasma cutter, and water jet cutter. We decided to create a self-feeding marble machine.
PRELIMINARY/CONCEPTUAL DESIGN
This marble machine would be manually operated, where the user turns a crank attached to a gear. The machine’s mechanical function is simple, a big gear attached to a crank (input) that drives a smaller gear.
Both gears would contain several holes (or pockets) on their faces to hold a marble as it travels from the bottom to the top of the gear, where it would exit onto the track and begin its descent following the track design. At the end of the track, the marble would be directly led to the bottom of the small gear where it would be fed into one of the pockets to be carried to the top. Once at the top of the small gear, it would exit onto a ramp that would take it directly to the bottom of the big gear where it would be fed into one of its pockets to be carried to the top of the track and begin its descent downwards again.
The track would begin as a series of zig-zags, where the marble would fall down to the next level at the end of each straight away. Once the marble exits the top of the big gear, it would follow a decline straight away ~7″ long. At the end of the straightaway, the marble would fall down to the next level – another decline straightaway ~7″ long in the opposite direction. At the end of the second straightaway, it would fall down to the next level, another straightaway ~8” long going back in the original direction. At the end of the third straightaway, it would fall onto another straightaway ~5” long. This fourth straightaway would be orthogonal to the first 3 straightaways, and it would transition into the spiral path. Finally, at the end of the spiral, the marble would roll down the home stretch, an ~8” long straight away to the bottom of the small gear, where it would be fed into the pocket(s) to begin its journey back to the top of the track.
MECHANICAL MODEl
We decided on a simple mechanical design, a small gear driven by a big gear, and chose mechanism #24 from the examples in 507 Mechanical Movements.
SKETCHES
We decided to make the big gear ~ 8” in diameter and would contain 8 pockets. On the other hand, the small gear would be ~5” in diameter and would contain 5 pockets.
Gears, Front and Back boards, Ramps10.13
We had many design tracks in mind, but we all considered the complexity of some of the tracks. But we settled on a track design that would consist of zig-zags, level changes, straightaways, and the star of the show, a spiral!
Low/Medium-Fidelity Prototype
The low-fidelity prototype was constructed with cardboard, wooden dowel rods, and hot glue. We used the laser cutter to cut out the main mechanic function. We did not build the track in this prototype for several reasons including time constraints and we had not decided on a track design at the time. Here we verified that the mechanical function worked properly and could be further implemented using medium-fidelity material
The medium-fidelity material was constructed solely with wood components. We used the laser cutter to cut out our parts. This time, we cut out the track but we did assemble the track in this prototype because of time constraints. This prototype worked and allowed us to think about how we would assemble the track for our final product. 
HIGH-Fidelity Prototype (FINAL PRODUCT)
The high-fidelity prototype was constructed with wood and metal components. The final product was mostly true to our original design plans with a minor alteration to the marble track (discussed below). The marble shelves within the gears were sanded to have a downward slope on the outer side of each circle (relative to the center of the gear) and the inner side of each circle had an outward slope. This allows the marbles to consistently enter the gear at the bottom and exit the gears at the top. The track was supported by a series of half-inch wooden dowels that were glued to custom connection strips as well as to the foundation. The base, frame, and dowels were coated with a wood stain.
VIDEO DEMONSTRATION
CHALLENGES
We struggled a lot with the “zig-zag” portion of the track. Assembling the track from the bottom, up, we realized that there was not enough vertical space for the zig-zags because you need to leave at least half an inch of clearance for the marble to pass under. We decided to pivot by creating a unidirectional stair-stepping track instead. This allowed us to still include an interesting design that worked with our space limitations.
POWERPOINT
Midterm Project Presentation (1)
Cost analysis
$15 / hour labor x 70 hours (between two people) = $1050
10 sqft of ¼” Plywood = $12
1 sqft ½” aluminum sheet = $20
Wood Glue = $3
Wood stain = $5
First marble machine cost: $1090
The total time required to completely assemble an identical marble machine will drop significantly after the designs and material specifications have been determined. An estimated 4 hours for printing and assembling will be required for future products, costing $60 in labor. Reducing labor costs by almost $1000 will make the product capable of being more reasonably priced. Furthermore, buying materials in bulk will reduce the price by another $10-20 per machine.
Following marble machine cost: $80
Overall we learned a lot about the whole designing and manufacturing process. We believe our project was a success because we worked really well together and made sure that we were on the same page throughout the process.
