For our school’s Residence Exploration Period , we built a swinging carousel ride. Our goal was to create a safe and fun ride that will attract people to come live at our dormitory (freshman get to chose what dorm they want to live in after exploring all the dorms). The ride is human powered (two people walk around the platform and push) and can seat up to four riders. The seats are attached 7.5 feet from the center, but the riders spin out farther as #Yolo spins due to centrifugal force.
The ride is broken into 3 main parts. The base stand that the large pipe sits in. This is also connected to the main platform. The platform that the pushers run along. The rotating top that contains the swings. This is connected to the pipe with bearings.
Pictures By –
Amartya Shankha Biswas
Step 1: Design
The purpose of the base stand is to prevent the pipe from tipping over during operation or when the riders are getting on or off. Ideally, people of close to the same weight would sit opposite each other on the ride to prevent huge imbalances and torques. We realized that it wouldn’t always be loaded in perfectly ideal conditions, so we designed it to be able to withstand a 250lb-f difference in load at 1 rotation/4 seconds.
The base consists of 4 main 4x4 spokes and 8 sets of diagonal braces (one large and one small diagonal brace on each side). We had to balance size and strength constraints when designing the diagonals. The bigger the diagonals, the stronger the base. However, if we made them too big they would either hit each other or the base platform. We decided to use 2 of each of the following diagonal braces:￼
Each brace is made of 2 2x6 pieces of wood screwed together. The spokes are each 8ft 4x4s (We chose that length because that was the cheapest length that would be long enough to make the spokes).
In the design, there are three big failure modes. The buckling of the central post, the bending of the central post due to uneven loading, and the bending of the bar on top.
%% Define constraints for column calculation
E = 29e6; %PSI
F = 1000; %Pound
SF = 2; %safety factor
K = 1; %Column effective length factor
L = 3*12; %inch. Unsupported length
Calculating for buckling failure
%% Using a known column radius, solve thickness
R = 1.5;
t = F*SF*(K*L)^2/(pi^2*E*pi*R^3)
To support our load, the central metal pipe has to be at least 8.5411e-04 inch, which is not very much. We ended up ordering a ~1/8 inch thick metal pipe, so it is extremely solid.
Bending of Column
F1 = 400; %Loading by one person
L1 = 72; %inch. length of beam on top.
maxStress = (F1*L1*R)/pi*R^3*t; %maxStress should be less than 1800 psi
The max stress on the column should be less than 1800 psi. In this uneven loading scenario of 400lb, the stress is only 39.6389 PSI, much less than max possible value.
Step 2: Getting Materials
Bill of materials:
12 2x6x8ftto be cut down to make the diagonal braces
2 47.75inx61.75inx.75in thick OSB
2 47.75inx68.75inx.75in thick OSB
2 95.75inx47.75inx.75in thick OSB
18 46.5in 2x4
6 58.75in 2x4
6 51.50in 2x4
4 13ft 2x6
4 60in 2x6
4 16ft 2x10s
12 8-foot 2x6s for diagonals
¾ inch stock aluminum
Steel Pipe - 13ft O.D = 3 inches
Sliding adjustable Miters saw
Drills with driver bits
Hole saw + mandrel
Step 3: Construction! (The Base Stand)
Long pipes are more expensive to ship than they are to buy. Luckily, there is a pipe supply store about 10 minutes from campus (Metropolitan Pipe and Supply in Boston). So we walked over there with a motorized dolley and purchased a 13 foot long metal pipe.
Step a: Cut all the wood. We have a sliding angle-adjustable chop saw which we used to cut all our wood.
Step b: Screw together the 8 diagonal braces. Each brace consists of 2 2x6 trapezoids which much be attached to each other.
Each brace is made of 2 2x6 pieces of wood screwed together.
Step c: The spokes are each 8ft 4x4s (We chose that length because that was the cheapest length that would be long enough to make the spokes).
Two 6-foot long 2x10s are used to construct a box for the pipe. 2x10x10" pieces with 3 inch holes cut into the center are used to constrain the pipe. These cuts can be made using a holesaw.
Step 4: The Base Platform
The base platform:
The purpose of this platform is to give runners a smooth surface to walk on (the ride is outside on somewhat uneven ground) and to give the riders a nice point to get on and off from (the corners of the platform are the right distance from the center to allow the riders to get on and off easily.
The platform has 12 legs which are each made of 2-ft long 4x4s that support the entire assembly. The inner and outer squares are constructed of 2x6s, and 2x4 joists (yellow) are used for further bracing. Pieces of .75” thick OSB are used to make the actual part that people step on.
Underside view of a solidworks model of the platform.
Closer view of part of the underside of the platform. The places where the 2x4 joists come together are where there is a seam in the OSB. This prevents there from being any cantilevered OSB sections.
Step a: Cut all the wood to length. We used a chop saw for everything except the OSB and a circ saw for the OSB (a jig saw would also work well on the OSB).
Step b: Build the outside and inside 2x6 frames
Step c: Attach the corner legs to the frames so that the frames are free-standing
Step d: Align the two frames so that they are concentric
Step e: Add in joists marked in red (this attaches the frames to each other and ensures the concentric relationship remains
Step f: Add in the remaining joists
Step g: Add in the remaining legs Screw these into the 2x4s and 2x6s in the same manner that the other legs were attached.
Step h: Brace the legs Use scrap 1x3s left over from a different project to brace the legs. Each leg should be braced in two perpendicular directions. Even though the 4x4 leg and the 2x6 that the leg is being braced to is coplanar, because wood is so bendy (especially 1x3s), this doesn’t matter. The braces are necessary because without them the 4x4s are only held in with 5.5 inches in one direction (the width of a 2x6 piece of wood) and 3.5 inches (width of a 2x4) in the other, which is a very small lever arm compared to the 2 foot long length of the leg. The braces prevent the 4x4 legs from breaking off from the frame if there is a large moment applied to them.
Step i: Attach the platform to the pipe base This prevents the platform from sliding around if the runners run too fast along it. The weight of the platform is enough to keep it mostly in place, so these attachments don’t have to be all that sturdy. _________
Step j: Add in the OSB deck to the top of the joists When attaching the OSB to the deck, make sure that all the edges of the OSB rest on the platform joists and that the OSB is not cantilevered out in any location. The OSB could break if someone jumped hard on a cantilevered unsupported section because it is not nearly as strong as the 2x4s.
Step k: (Optional) Add in carpeting on top. We recently acquired some carpeting, and decided to use it to carpet our ride. The carpet was cut with an exacto knife, which was time consuming and ruined several blades. There are probably much better methods to do this. The carpeting was attached to the OSB using a staple gun, which works very nicely.
The platform got pretty dirty during the construction process, so we decided to give it a thorough vacuuming at the end.
Step 5: The Spinning Top Part 1: Bearings and Holes
Creating the Mounting Billet:
#YOLO has a thrust bearing on top, and it order for it to rest on top of the metal pipe, a cylindrical billet is milled to create a resting for the bearing. A 3 inch diameter aluminum stock is cut into a 3 inch section. Afterward, a bevel is cut out from the top of the billet, and the bottom half of the billet is cut down until it is the size of the inner diameter of the metal pipe.sprinkler pipe.
Bearing Mounting: #YOLO has one thrust bearing and two radial bearings. The bearings are pressed fitted into an aluminum plate .75” thick. The aluminum bar is precisely cut to have a hole .05” smaller than the diameter of the bearing. The bearings are placed in an ice bath while the aluminum bar is heated up over a grill. The bearings are then heavily encouraged to fit into the aluminum bar by hammering it on top of a flat surface..
Step 6: Lighting
Cutting a hole for wiring:
To power the LEDs on the device, wires run from the bottom to the top of the device inside the hollow metal pipe. A small hole is cut in the pipe using a dremel cutting disk.
The LEDs are synced with the spinning speed of the device. As #YOLO spins faster, the LEDS changes color faster or “more rainbowy” (as our designer put it). The spinning speed of the device is measured by an accelerometer placed at the edge of one of the spinning arm. An arduino acts as the central brain reading the accelerometer and controlling the signal to the LEDs.
Step 7: Operation
The ride supports up to 4 riders at the same time, and it’s recommended that the ride is evenly loaded. Four people sits in the hanging seats, and two people pushes on the vertical bars. As #YOLO gets to max speed, determined by how fast the two people can push it, the pushers duck down and let the ride continue to spin. The pushers should be careful to stay low to avoid the pushing attachments swinging around and hitting them in the back of the head. The ride is actually quite frictionless and will take a long time for it to come to a full stop. As the ride slows down to a manageable speed, the pushers stand up and push in the opposite direction of the spin to act as a brake.