How would you build a giant turntable or merry-go-round for the physics classroom? I was recently sent a discussion among teachers from the Exploratorium’s Teacher Institute on this very subject. It reminded me of the summer before my senior year of high school, when I took a physics class at Caltech with a juggling grad student who looked a lot like Jesus. Our best lesson of the summer? He took volunteers to a nearby park to see him and his pal juggle on a roundabout, and a few of us got to join him on the rotating platform. He gave us a playful metaphor to understand the alphabet soup of the calculus-rich vector exercises we did in the classroom.
Back to this teacher’s query. Ben posed the original challenge:
Our physics teacher and I have been fantasizing about having a large turntable on which students could explore a variety of concepts. Ideally we would like a surface around 3 or 4 meters in diameter that will stay flat, turn smoothly, support three or four high school students, and be sturdy enough to survive the wear and tear of years.
Have any of you built a large turntable for class demonstrations?
I would appreciate any plans, suggestions, or cautionary tales. It’s a long-term goal. We’ve been going round and round (so to speak) about size, materials, safety, bearing setups, used vs. new, placement etc.
Mandy suggested our oversized spin-art machine, but Ben needed something a bit slower. He defined it more clearly:
We want the students to study motion on a rotating surface, from various perspectives. I’d like to use it to demonstrate the Coriolis effect, for example.
We would like students to be able to sit on it, throw and roll balls between them, and film the ball’s motion from on, above, and beside the surface, both moving with the surface and not moving with it.
It needs to be strong enough to support them, and large enough to be able to observe the motion of objects moving above the surface for some distance.
Ellen Koivisto of Asawa School of the Arts in San Francisco chimed in with a clever, STEAMy suggestion:
Talk to your theatre teacher/s and tech people. Turntables have become common set items again in recent decades (after Les Miserables). They were often built for Victorian melodramas, then fell out of favor with the rise of movies and kitchen sink naturalism.
I’m doing a show right now that uses a relatively small turntable — 11′-6″ in diameter. There are three concentric rings of casters that take the weight. I believe it’s two layers of 1/2″ ply, laid perpendicular to each other and glued together. One person can push it with their foot, or there are pole holes so a person can stick a metal pole into the hole and pull the turntable around. It moves smoothly and easily.
I did a show once with an 18′-diameter turntable. That required more people to move and bigger casters, but it was lovely to work on. I haven’t done a motorized turntable yet, but there’s tons of info on making and using them in technical theatre magazines and websites and books.
Caren Kershner similarly suggested checking in with the old Creede Repertoire Theatre in Creede, Colorado about how their three stages mounted on a turntable function.
While looking for images for this post, I found this detailed how-to on how Texas A&M’s Scene Shop built this rotating stage turntable for its production of Th3 B3ggar’s Op3ra.
Raleigh McLemore had lots of ideas:
My first thought was that you could build off of a platform like a playground merry-go-round. Some simple welding or carpentry might be all that it takes to either remove the uprights or add structure to them to build a platform that a student could safely stand on. You are working with bigger kids and some of the cheap (about $750) small structures may not have enough carrying capacity. Larger built spinning structures are heavy and expensive (around $2K). Outside chance your local parks department might have a broken one, or one that is in storage after a playground change up.
Another idea might be to start with a junkyard car wheel and wheel bearing. A front wheel kingpin might be pretty cheap and could be located vertically in a strong base with the wheel and bearing slipping over the kingpin to become a center to the car wheel spinning on it horizontally. Not sure how it would happen, but I’m sure the car wheel would be a very strong point to begin to weld or assemble a wooden structure upon. I haven’t thought it through very far but I would start with buying a wheel with a wheel bearing(s) and a kingpin if they were reasonably priced.
If a kingpin doesn’t seem right then I would look for an appropriately sized shaft to support the wheel and bearings. Perhaps even a hardwood axle could be fashioned although first thoughts seem to me that it wouldn’t be strong enough. Any upright axle that could be located into a solid plywood base would get you started. The junker car wheel bearing would fit upon the upright axle, the wheel would then be the spinning base of the structure. Done correctly you should have a stable spinning base. The platform couldn’t be too heavy or unbalanced, or it would wiggle and wobble. Putting additional support wheels around the outside of the large spinning platform might make the platform more level and add to stability.
Seems a bit elaborate, but I suppose you could use a dryer motor and belt to spin the wheel by mounting it on the plywood base at a distance to put tension on the horizontal spinning wheel using the dryer belt. You need guards and a speed control for this. What with the variable loads this could be a mess and deserves a lot of thought unless you can get the junk for free. Done poorly you could have a fire or a short.
Last, I wonder if you could hang something from a rafter/joist support (use rope? wire rope?) and put some good wheels around the outside of the platform so that the center is supported from a high point and the outside edges are held up by the wheels? This might be reasonably cheap if the overhead support is equal to the load. This might not be very smooth or stable for the experiments you have planned. Not sure how you would have a smooth controlled motion without a rail to guide the wheels. You wouldn’t have a clear center with this, the support rope popping out of the center of the platform.
Raleigh wrote again a little later to reminisce about his time working the Funhouse “Joy Wheel” at San Francisco’s old Playland at the Beach.
This thing was a very large flat, slick, spinning disk with about 20–25 folks climbing on, sitting as close to the center as they could squoosh. My job was to control the speed and spin the disk as fast as it needed to go to spin the folks off and have them slide hopefully to the padded wall and away from the spinning wooden platform. It was lots of fun until folks frantically grasped others and took off a large clump of people who slid off together. The resulting crush of humanity wouldn’t fly off of the disk completely and over and over again somebody would get jammed into the edge of the wheel, unable to move away due to the others being pushed against the wall. I had a “panic stop” button but it really didn’t stop the device very quickly when I hit it. Very gruesome injuries would sometimes occur, never life-threatening, but bloody. My job was to clean that up too.
When the midway had no customers, and I was free to move about the site freely, I used to roll stuff across the slick Joy Wheel surface, pour water at different places and occasionally even be able to anticipate where my experiments might exit the wheel. I remember thinking that somehow if I threw a dart in the air over the spinning disk the dart would begin to rotate with the spinning wheel before it hit…it is still surprising how much I want the disk to alter the trajectory of the dart, although I know it can’t.
From Raleigh’s description and the photo at the top of this post, I’m finding myself wishing there were a giant rotating disk in every city. It sounds like such fun! Except the bloody part. If you can’t quite make out the sign in the top of that picture, it reads “The best cure for blues is joy. Get cured here” (Also, who else thinks that might be Raleigh in the picture?)
We now turn to the Maker-verse. Have you built a large rotating disk? Can you share plans and tips for building it?