Idea

Our initial idea for this project was something amusement park/carnival themed. We thought of doing a carousel or a ferris wheel before we settled on doing a rotating swing ride. This idea seemed more plausible with our level of mechanical understanding and also felt like a more novel fair ride-themed project compared to those we had heard of others doing. 

 

Gate 1

Our first step was to decide which mechanical movement was required for the swing ride. Our first idea was to use #26 (gears that are perpendicular to each other), but we realized after submitting Gate 1 that simple spur gears (#24) would work for what we wanted, so all subsequent work was based on this design. After drafting rough sketches of the idea we were going for, we were able to see which pieces we would need to incorporate and how they’d interact with each other. 

Sketch from submitted gate 1 depicting right angle gears, prior to our shift to simple spur gears 

 

Gate 2

Our next step was to model the ride with low-fidelity models. We used cardboard and wooden dowels to show how the gears would work and how this would allow the desired swing rotations. We found gear designs online (after a little trouble with online gear generators that weren’t free) at https://evolventdesign.com/pages/spur-gear-generator. We brought these into Adobe Illustrator in order to separate them and modify the dimensions to fit our design better. When deciding the parameters for our gear design using the gear generator, we decided to choose numbers of teeth for each gear that aren’t multiples of each other so that the gears wouldn’t wear out by interacting with the same teeth each rotation. 

We determined that the gear attached to the handle should be larger than the smaller gear so one rotation of the handle by the user would lead to a faster rotation of the actual swings, which would be tied to the rotation of the smaller gear. We also chose not to add swings to the cardboard prototype because we decided it wasn’t necessary to display the movement of our model, and the cardboard would be too flimsy. 

Gate 2 submission, showing gear and central rotating hub mechanisms with laser cut pieces from cardboard

 

Gate 3/ Final Design 

After the second gate, we moved to high-fidelity materials like wood, steel wire, and metal. We cut out two sets of gears so we could double up and improve the gear integrity. After cutting, we tested if the gears could rotate properly and they did! We also cut out a central rotating hub, where the swings would attach at the top of the ride. We chose not to laser cut holes we’d need to attach dowels into and instead to hand drill or drill press these holes. We did this so we could tailor the hole size to the dowel size based on what was needed (looser for rotating or snugger for attachment). We then used wood glue to stack the two sets of gears and the rotating hub. 

Stacked pieces bonded with wood glue drying while clamped to secure position

When we were designing our gears and choosing their size with Adobe Illustrator, we considered how we wanted the gears to be attached to the full system. We decided to keep the gears in a box with some open circles in the top that both the dowels attached to the central rotating hub and the handle could stick out of, as these were the components that require full rotational movement outside the confines of the box. To achieve this, we used en.makercase.com to define a box size that was compatible with our gear designs, so the gears could spin freely within the box. Similar to the laser cutting assignment, we measured the kerf using a kerf box and exported the box sides. In the top panel, we added two circles, one for each gear, with a diameter smaller than the diameter of the gear but great enough that the support dowels of the smaller gear and the handle of the larger gear could readily stick through and rotate fully. Our first attempt printing this design failed, as the fingers were inexplicably misaligned by a considerable margin. We re-did the process of exporting the box, only keeping the circle cut-out shapes from the previous iteration, and confirmed the fingers aligned visually before re-printing the box. This print worked, so we were able to proceed. We then assembled all of the box but the top, as we needed the top away to assemble all other pieces that were to be added to the box. 

Misaligned fingers in first box laser cut attempt

Box assembled completely except top piece (partially seen in back right)

Next, we decided on the dowel size we wanted for each of the components where dowels would be added. We decided to use a thicker dowel for the center of the gears that the gears could rotate around, and to use this thicker dowel size for the handle as well as it would individually be subject to more forces. For the support dowels that would link the smaller gear to the central rotating hub, we opted to use four thinner dowel pieces, as the symmetry and number of dowels meant that the forces could be balanced and the thinner and therefore lighter dowels would lead to less rotational inertia for our ideally fast-spinning pieces. 

We then decided to identify all the drilling points and drill bit diameters we wanted for drilling holes in the gears and central rotating hub. We knew first that we needed to find the center of the gears and central rotating hub as an origin for determining the hole positions. To find the center of the circular central rotating hub, we utilized the law of geometry that the perpendicular bisector of a chord of a circle goes through the center of the circle. Therefore, we marked several chords on the circular shape, drew out their perpendicular bisectors, and identified the approximate center based on where the perpendicular bisector from each chord intersected. We used this same principle to find the centers of each gear. Since we knew the teeth of the gear would lead to challenges finding a perfect perpendicular bisector, we used only the inner circle of the gear- areas where the teeth weren’t protruding- to define chords and find perpendicular bisectors. For the larger gear, we only needed to cut the center exactly, so only marked this spot for cutting. Note: my (Juliana) phone died around this point so several of the below processes unfortunately couldn’t be photographically documented (I was working without Ini here), but extensive typed notes allowed me to document the process with words instead, albeit this was a suboptimal solution. For the smaller gear, we needed to cut the hole in the center for rotating, and also four holes at 90 degree angles from each other equidistant from the center, as these would be the support dowel spots. We needed these holes cut from the central rotating hub as well, with the same distance from the center so the holes would align (ideally) perfectly. We used a protractor and ruler to measure these spots out, and mark them on the small gear and central rotating hub. We used the drill press to cut out the center holes for both gears with a larger bit size, allowing for rotation about the center. We used a slightly smaller drill bit size and a hand drill to cut out the hole in the larger gear for the handle dowel, in order to achieve a more snug fit with the larger dowel size. Note: this same drill bit size was later used to drill holes in the bottom of the box for the larger dowel to be secured, similarly aiming to achieve a snug fit with this dowel size. We then used a smaller bit size to drill the holes for the support dowels in the small gear and central rotating hub; the bit size we used achieves a snug fit with this dowel size.

Geometric law utilized to find center of circle in this project, diagram from Mathematics-Monster.com

Chords of approximate inner circle of gear utilized to find center, this process was repeated multiple times to converge to a more accurate center point

An error was made while testing drill bit sizes, as a hole was accidentally drilled into the top piece of the box after it was mistaken for a piece of scrap wood. To fill this hole, a mixture of wood glue and sawdust was used, which resulted in slight aesthetic loss but maintained the function of the piece. Since the function was maintained, we decided to use this fix rather than printing a new box top in order to prevent wasting wood (the piece is quite large). During post-processing, sanding over the wood glue and sawdust spot resulted in the flatness of the surface being maintained, so no lasting harm was done.

Blemish due to drilling error can be clearly seen after post-processing as a darker spot in the wood that didn’t absorb spray paint as readily

With all holes drilled except the holes for swing attachment which we tackled later, we decided to next determine how to add the gears to the box and position them with respect to each other. First, we laid the gears next to each other so they visually aligned and were centered in the box. We marked the center of the larger gear, and drilled this hole out and inserted the dowel for rotation. We were not sure if there was an optimal strategy for deciding how far apart to place the center of the second gear, so we spoke to Hayden. He explained the concept of diametral pitch and pitch circle diameter, and helped us estimate the pitch circle diameter of our two gears. We then measured the pitch circle diameter of each gear, halved these values, and added them together to get an estimate that 8 inches apart was an optimal distance between gear centers. 

Diagram depicting that the optimal distance between gear centers is the radius of  the pitch circle of each gear added together (pitch circle labelled 2, pitch circle diameter labelled 1), image credit: KHK Gears 

After confirming that this distance indeed achieves continual rotation of both gears, we drilled out the second gear center position into the bottom of the box. We then cut the dowels using a bandsaw to form the center dowel posts for each gear, the handle, and the four support dowels for the central rotating hub. At this point, all of the wooden pieces were ready for assembly except the central rotating hub, so all pieces were sanded with the orbital sander, except the sides of the box, which were too challenging to unassemble and not structurally strong enough to withstand orbital sanding. These sides were hand-sanded.

Using the orbital sander to post-process the large gear

Status of project following completion of all functional woodwork (except swing attachment points being added to central rotating hub), top still lies loose on box here as assembly was not done

Next, we needed to set up the swings and how they attach to the central rotating hub. Since we had mistakenly sanded the central rotating hub and the pencil-marked center spot, we used geometry to re-calculate the center point as described above, and also used a protractor to draw lines through the centers of the support dowel holes that were all 90 degree angles from each other, tracing all the way to the edge. Then, we used a protractor to draw out all the lines that were 45 degrees from the 90 degree lines, splitting the circle into 8 pieces of approximately identical size. Based on the dimensions of our swings, we marked the spots 0.5 cm and 1.4 cm from the edge on each of these 8 lines for drilling the holes for swing attachment. We hand drilled these 16 holes with a very small bit size, so there were two attachment points for each of the eight swings. After drilling, we re-sanded this piece with an orbital sander.

Central rotating hub with marked spots for drilling swing attachment sites

To attach the swings to the central rotating hub, we used a thin steel wire rope, which is a similar material to what we’ve seen in actual carnival rides, and also weighty enough to remain fairly straight during rotation. For each attachment wire, we tied a knot in the wire above a small metal nut, which was too wide to fall through the corresponding hole in the central rotating hub. The nut was not used for fastening, but rather simply as a wider object as beads were not available in the OEDK (to our knowledge). An identical method was used at the opposite end of the wire to attach the swing.

Thin steel wire rope and small metal nuts were used to attach the swings securely to the central rotating hub

To make the swing, we first designed the swing seat in Adobe Illustrator. Since the design was fairly basic, we just created the design using the rectangle and circle shape tools in the software, making sure the design was perfectly symmetric. We then used the water-jet cutter to cut these shapes, as due to the small holes in our design we needed a machine with greater precision than the plasma cutter would afford us. We decided to cut our 8 swing pieces from a thin aluminum sheet so that the swings were light (reducing the risk of potential injury). The waterjet cutter lost three of our swings into its abyss during our first cut. (They were nowhere to be found even after sticking a whole arm into the water >.<) Despite this, we came in the next day with renewed energy and vigor to cut the rest of the swings out.

With all of the functional pieces now ready for assembly, we first decided to spray paint the outside of the box, the gears, and the central rotating hub to fit with the carnival theme we were aiming for with our project. We chose a black spray paint base, with streaks of orange, red, yellow, blue, and whatever else our heart desired. We spray painted some of the posts red, blue, and orange to add color and others black as a contrast.

Carnival-theme spray paint was added to all visible surfaces (except decorative handle attachment detailed below)

After the spray-paint had dried, we assembled all the functional pieces. The rotation posts were added first into the holes in the bottom of the box. Then the gears were added. Next the handle dowel was stuck into the larger gear, and the four support dowels were added into the smaller gear. Heavy washers or other hollow metal objects found in the miscellaneous bin were added around the rotation dowels on each gear, sitting on the gears, which was suggested by Hayden to keep the gears weighted down and properly spinning during rotation. The top of the box was then at last added to complete the box structure. Finally, The central rotating hub with the swings attached was secured to the opposite end of the four support dowels.

As a last piece for our project, we decided to add a decorative (not functional!!!) attachment to the top of the handle dowel, deciding to use a car design again to fit with the carnival ride theme. First, we vinyl-printed a red sticker of a car outline. Then we laser-cut the same car design (but slightly bigger) for the sticker to attach to. Similar to the gears and central rotating hub, we cut out two copies of this car outline and stacked them using wood glue so the attachment wouldn’t be as flimsy. We then drilled a hole in the car using the bit size that allows snug attachment to the larger dowel, added the car attachment to the top of the handle dowel, and stuck the red vinyl sticker onto the wooden car, thus completing the project. A nameplate was added with Velcro to give information about our project, and the work areas we worked on were cleaned up.

Cleaned workspaces we each worked on last (Ini- left, Juliana – right)

Completed project!!

 

Cost Model

Cost Type	Cost	Price	Source	Quantity	Total
Materials	1/5 inch plywood, 4 ft x 8 ft	$25.78/sheet	Home Depot	~24 sq. ft.	$19.34
	3/8″x 48″ dowel	$1.26 each	Home Depot	1 dowel	$1.26
	1/2″x 48″ dowel	$2.18 each	Home Depot	1/2 dowel	$1.09
	aluminum sheet metal (0.125″ thick), 0.5 in. x 12 in sheet	$18.72	OnlineMetals.com	entire sheet	$18.72
	1/8 in. x 50 ft. Galvanized Uncoated Steel Wire Rope	$19.97	Home Depot	16 feet	$6.39
	Sand Paper orbital (15 pack)	$9.97	Home Depot	2/15	$1.33
	M4 nuts (10 ct)	$0.60	DIY HIFI SUPPLY	32 nuts	$1.92
	Spray paint	$5.98	Home Depot	2 cans total	$11.96
	Vinyl sheet (12″ x 12″)	$0.98	Expressions Vinyl	1 sheet	$0.98
Labor	Woodworking Operator	$21/hr	ZipRecruiter	3 hours	$63
	Laser cutter operator	$17/hr	ZipRecruiter	.75 hour	$12.75
	Metal machine worker	$21.6/hr	US Bureau of Labor Statistics	0.5 hr	$10.8
	Prototyping Engineer	$36.5/hr	Indeed.com	2 hr	$73
Overhead	Facility Cost (Machine Time)	$40/month	The Maker Barn	1 month	$40
	Adobe Illustrator license	$22.99/month	Adobe	1 month	$22.99
Design	Engineering and Development	$90/hr	ZipRecruiter	1 hour consult	$90

Total: $375.53

Material costs were somewhat significant in this cost model, due to the large range of materials used combined with the lack of wholesale pricing, but with better suppliers the cost per unit for most materials would be expected to decrease considerably. Due to the range of skills employed to make this product, a wider range of employees are needed to complete each skill set, driving up labor costs. We also anticipated that the prototyping engineer would be more involved in such a project due to its multifaceted nature, and as the prototyping engineer commands higher hourly pay, this drove up labor costs. However, the prototyping engineer’s hours would not scale linearly with increased production, and with increased production some tasks, especially for the woodworking operator, could be run in parallel driving down labor costs per unit. The laser cutter operator could also produce several pieces in parallel, but doing so would require multiple laser cutters to be run at the same time which could increase safety concerns. Some tasks necessary for the completion of this project did not clearly fit into the category of one of these worker types, when that was the case, we by default added the expected time to the woodworking operator who we anticipated would be more involved in the assembly of the completed product due to a versatile skillset. With increased production, facility costs would be expected to increase drastically due to the number of machines needed to fabricate our product, which would all have to be rented or bought, which would be a significant expense. Since Illustrator is on a monthly subscription model, with increased use for prototyping different designs, the cost per product made would be expected to decrease considerably. As this project, while more complex than previous assignments in the class, is still not overly-complicated from a technical perspective, we did not anticipate needing increased technical consulting beyond a default one hour appointment. The cost of the engineering and development consultant would therefore also not increase with increased production, contributing further to a decreased cost per unit.