Theo Jansen Invents A Faster, Simpler, Wind-Powered Strandbeest

[Theo Jansen] has come up with an intriguing wind-powered strandbeest which races along the beach with surprising speed and grace. According to [Jansen], it “doesn’t have hinging joints like the classical strandbeests, so they don’t get sand in their joints and you don’t have to lubricate them.” It’s called UMINAMI, which appropriately means “ocean wave” in Japanese.

There are only videos of it in action to go on so far, but a lot can be gleaned from them. To make it easier to keep track of just a single leg, we’ve slowed things down and reddened one of them in the banner animation. Those legs seem to be providing a push but the forward motion is more likely supplied by the sails. The second video below shows it being pulled along by the type of strandbeest we’re all more used to seeing.

What follows is an analysis and best guess about how it works. Or you can just enjoy its graceful undulations in the videos below.

How is it all connected together? There are two sets of horizontal beams which span the length of the strandbeest around halfway down the height. These beams are fixed in length and seem to be for constraining the overall length. There are two sets of them, dividing the wave in the middle and possibly done that way to allow the two sections to tilt sideways independently of each other

From the views shown here, it’s clear that the legs are free to slide along those horizontal beams. Meanwhile, the beam along the top is longer but is also flexible, as are smaller segments in between the legs at the bottom. The top beam, however, keeps the tops of the legs evenly spaced apart whereas the smaller bottom segments only set a maximum distance between adjacent legs, while folding up to allow adjacent legs to touch. That’s why the legs come together only at the bottom of the wave.

What makes it undulate like a wave? Here’s our best guess from the videos and without experimenting. As the bottom of a leg catches in the sandy beach, it’s pulled along at the top by the sails, causing its top to pivot forward. While the leg is caught in the sand and is pulled along, it also pulls apart the legs in front of it while compressing the legs behind it. The compression has to exist because the first and last legs appear to be constrained by the middle horizontal beams, preventing all of the legs from being spaced apart at the same time. But that’s all just based on video analysis and could be wrong. What do you think? We’d love to hear your suggestions and even to see your own undulating strandbeests.

We know Hackaday readers like strandbeests since they come up so often. We’ve seen them used instead of a bicycle wheel, built as a ridable 13-foot behemoth, and even a hamster power one.

Thanks to [Jack Buffington] for suggesting this one through our tips line.

25 thoughts on “Theo Jansen Invents A Faster, Simpler, Wind-Powered Strandbeest

  1. Theo Jansen is a true genius to design and build his “strandbeesten” (“Beach animals” in Dutch)
    I’ve seen videos of these for years and I am a true admirer of these contraptions which are simple and ingenious at the same time.
    All just mechanical motion using just rods. This is the kind of art I really can look at for hours.

    1. +1
      Indeed Gijs Noorlander, I have also marveled at his clarity of focus and conscientious attention to detail for years in combination with addressing use of cheapest simple readily available parts as key elements offering all sorts of permutations for others to follow and augment further, my hats off to him, tis beyond me, we all have our things :-)

  2. its just being blown down the beach and the wave motion is an incidental by product, rather than wind driving a mechanism that actually walks, if you look carefully some of the legs near the front are being pushed through the sand at times…

    1. It’s basically re-inventing the wheel. The motion of the legs being pivoted over drives the wave motion, which makes the following legs step forwards to be pivoted over in their turn. Think of it like a row of wheels connected by a chain, except all the wheels turn only a fraction of a turn before they’re lifted off the ground and set back down further down the road.

    2. Yea at this rate his next strandbeest will just be a sled with a sail, not really what i expected from his many remarks on ‘evolving’ his strandbeest’s over the years.

  3. The sand drags the legs in contact with the sand back, forcing them to bunch up and create an arc in the upper spine. Once there’s enough of an arc, it lifts the legs off the sand and propagates forward.

    It looks like one set of legs is attached at the end of each horizontal segment running down the middle, and each such segment creates one cycle of wave.

    The rounded skis at the back and front seem to control the angle of the spine at that point. I’d guess they have enough mass to lift the legs up off the sand when there’s enough curve in the spine, and enough angular momentum to force a more or less sinusoidal pattern in the spine.

    I’d also guess it’s related to the self-walking armatures that mimic the human gait when you send them down a mild slope.

    It’s an elegant combination of forces and timing.

  4. An ode to PVC and tieraps. But seriously now, these creations are great to looks at, the way they move, the gracefulness the simplicity of the movement and then the scale. Really, really nice.

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