I am putting together a few gifts for friends who are all in education. I want to make a line of interesting desk/shelf toys that are hard to source nice versions of but simple to make.
Today, I’m going to mock up a Pendulum Wave. It’s a very straightforward kinetic build with some well defined maths that should make it easy to customize. I’m looking forward to just executing a plan instead of having to figure out all of the interesting bits myself
While being straightforward to build, the pendulum wave has some interesting maths backing its function. That math ends up defining the lengths of each pendulum as well as the time it takes before the patterns “reset”
Here is a video from the excellent Nighthawkinlight describing the pendulum wave and how we can make our own: https://www.youtube.com/watch?v=08ueDogNkP8 (There are plenty of other videos as well, including another by Nighthawk which describes the sculpture in more detail)
First things first, let’s build a proof of concept before investing a bunch of time in design. Hopefully it goes well, because I’d love to make one of these out of some interesting materials. Brass and walnut is never a bad combo
My proof of concept is just going to be some wooden dowel with holes drilled and a few nuts suspended by string. I’ll report back when that’s done.
Sidenote
This line of gifts was inspired by this post: To Julien…the physics nerd 🤓
I’ll be making that exact item for a physics teacher in a post coming soon…probably
Lessons learned:
Clear line is interesting. It’s also really annoying to work with.
Hot glue is nice but it takes forever compared to just getting off the couch and drilling holes
Being lazy AND stubborn makes for a bad combination.
I think I might use the calculator for the first & last, the fine tune in between.
The challenge now being how to do that. Being a musician my mind goes to stringed instruments, (piano & guitar). A guitar string is held in place by a tapered pin in a bridge hole
Curious what line you are using. Also, as a fisherman… clear lines have some stretch. Fluorocarbon stretches the most, monofilament has less stretch. Braided line has no stretch, but is not available in clear.
So it’s actually pretty elegant, the curve is necessary to set the timing of each pendulum swing.
Say the first pendulum swings 60 times in one minute, the second should swing 61 times in a minute, the third at 62 times, and so on.
So long as the center of masses are all the same, they all start at the same height, and they hinge from the same point, the only force acting on them is constant and also the same across them all (gravity). That just leaves one variable to play with in setting the timings of each swing, string length
Another note is that the lengths in the calculator are from the hinge point at the top to the center of mass of the weight. So to get it just right, you’ll need to account for the size of your weights when cutting the strings.
I’m thinking something like the guitar taper pin since it seems pretty straightforward and easy enough to service if necessary. It also provides an almost point contact as a hinge so you don’t have to worry about the radius of an edge like you would on a piano setting. (Though aesthetically, a piano setup could look incredible)
The lines I used in the test is from a hidden seam sewing kit. It’s probably just thin fishing line and almost certainly has some stretch.
Another important string aspect is in the mounting strategy. With just a single mount point the weight is free to swing any which way. While this works, it means you have to be pretty accurate in how you stage and drop the weights, else they start to smack into each other
Seems most folks use another mount point to better constrain the motion.
Upon watching the prototype, my wife said “Wow, that’s super cool! I can’t wait to see one that really works!”
Which is a great sign for the project overall but a terrible endorsement of my prototyping skills
Also looks like we’re making a slightly larger one for the father in law. He’s an avid (and frankly, exceptional) pool player.
A bit of brainstorming with the led to:
A mini pool table, maybe 2’ long, as the base.
The mini pool balls as the weights.
The cues as the rods and supports.
Interesting timing…I have a rear-view mirror hanger of the spaceship Serenity from Firetly and currently have it hung with monofilament with three points of support. They definitely have taken a (non-uniform) stretch and I’m thinking about retrofitting glass fibers, which would be available in deconstructing a piece of FG tow material from a local fiberglassing supplies company.
And then there is fused silica, as in fiber optic cores…
And thank you for introducing me to this concept, Tyler.
Nerd on!
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WillAdams
(William Adams (Carbide 3D))
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Yeah, you can get them tapped too which might be convenient. Pretty sure they are marketed as things like cabinet pulls
(I was looking at them as an easy ball end for my hard stop )
Drilled 8mm balls (used with 608 skateboard bearing inner rings) are part of the latest (unless there is a latest-er) variation of the DIY spacemouse, to give low-hysteresis linkage between the handle and the joysticks…
But if you end up getting the cheap Chinese drilled balls, you might want to weigh and sort them because, from comments I’ve read, they are not especially close-tolerance and the differing mass could affect the period of the pendulums.
Thank you kindly, I wouldn’t have thought to look up phenolic
I’ll apply these when I start cutting balls and report back the findings (it’ll be in a dedicated gallery post)
