Plastic Beach - Traveling Water Wave Machine

[rhizotron]

Plastic Beach - Traveling Water Wave Machine

I've been pondering this idea for a while and I've finally put together a design for experimentation. My goal is a machine to create traveling waves in aquarium like wind-driven waves in a natural body of water. These differ from the kind of water movement generated by reef aquarium wavemakers as they would have rhythmic crests & troughs and directional movement down the length of the enclsoure.

With a search you can find several videos with machines achieving this for educational and scientific purposes, or just for fun. But none of the ones I have seen really integrated the concept as a display aquarium with livestock, plants and other ecosystem features.

Here is a really interesting video from MIT with clips showing sand ripple development in a large wave tank...




Most of the examples I have seen used a hinged paddle at one end of the enclosure and actuated with a servo motor or other mechanism. For my project I wish to make the most efficient use of the limited lengthwise space in a glass tank, while also designing the machine as an appealing kind of kinetic sculpture. So I opted instead for a cam & follower mechanism with a stepper motor supplying power. Here's the whole deal in operation with the 6-gallon bookshelf tank...

Here's another example with a wave machine that works in a similar way with a wedge-shaped paddle...




I have an idea in mind for a sloping 3D-printed beach to break the waves at the tank far end, but for now I've just piled up these lava rocks. They work OK. Without some kind of physical dissipation, the energy will just bounce back to the middle of the tank to create standing waves...

There are some cool ideas to explore with wave height, length, frequency and other parameters. I have this microcontroller + stepper driver set up with a rotary encoder and LCD display to toggle the motor on & off and control other signals. Luckily I got some help with this because I'm really not great with code and electronics...would have otherwise taken me forever to figure out...

I'm going to run this for a week or so and then design a version 2.0 with smoother operation (I hope) and nicer fit & finish. This is most likely going to be a brackish water system with moderate salinity and appropriate organisms. I'll explain some more of that later on as I get it organized.

 

[Nox.]

Cool Idea, following!

 

[CoastalTownLayabout]

Reef crest near the end of tank with a spillover zone behind it to dissipate wave energy might be your best bet. Would be great to see a two inch barrelling peak in a reef tank.

 

[rhizotron]

Cool Idea, following!

Thanks!

Reef crest near the end of tank with a spillover zone behind it to dissipate wave energy might be your best bet. Would be great to see a two inch barrelling peak in a reef tank.

Yeah there are various interesting things to do with the beach structure at the opposite end of the tank. A heater and small filter could be hidden underneath. You could also get (rather slow) one-way, wave-driven flow through filter foam with an opening at the top of the slope.

Does anybody have very good results uploading video clips? Is there a file extension that works best? I tried with .mov, but couldn't get that to load.

 

[Devaji]

Reef crest near the end of tank with a spillover zone behind it to dissipate wave energy might be your best bet. Would be great to see a two inch barrelling peak in a reef tank.

yes but can our aquariums handle such a wave over weeks, months and years? IDK but it would be cool for sure.

 

[rhizotron]

yes but can our aquariums handle such a wave over weeks, months and years? IDK but it would be cool for sure.

Energy in sloshing waves could certainly be a problem for the seams in a taller enclosure, but this tank is 8" tall and I don't intend to fill it with more than about 3.25" of water. I think it will be OK.

 

[Devaji]

Energy in sloshing waves could certainly be a problem for the seams in a taller enclosure, but this tank is 8" tall and I don't intend to fill it with more than about 3.25" of water. I think it will be OK.

yeah I wss thinking on the classic 24" tall tanks. love the idea!
do keep us updated!

 

[rhizotron]

yeah I wss thinking on the classic 24" tall tanks. love the idea!
do keep us updated!

The main reason I'm keeping the water so shallow is that I'm as interested in the idea of sand ripples as much as anything. Deeper water would require a proportionally longer sloped beach to dissipate energy, thus leaving less footprint area for sand.

Here's a pic to show the cam & follower mechanism. I looked at several different ways of transferring the rotational motion to linear motion and this seemed like the simplest and most compact solution. The cam is just a circle that spins off-center. I considered adding springs to return the follower during the up-stroke, but instead incorporated the second follower on top so the stepper wouldn't also have to push against springs.

 

[Gumbies R Us]

I like the idea!! can't wait to see where it goes from here

 

[rhizotron]

I like the idea!! can't wait to see where it goes from here

Thanks so much! Updates on the way pretty soon.

 

[rhizotron]

I designed and built the Version II with several improvements:

1. The span thingy (?) between the two pushrods now has a spring connection which is much better.
2. The new cam is egg-shaped, so it completes the extension motion in 1/4-revolution, rather than a whole 1/2-revolution like the simple off-center circle shape. The important effect here is that the machine can create higher amplitude, but longer wavelength waves without such fast rotation.
3. Instead of a second follower above the cam, a length of elastic returns the follower assembly after each extension.
4. They're not really essential, but I incorporated polymer linear bearings for the pushrods and I like how they look.

I need to work on the stepper + driver torque and heat problems. I'll have to study the field-oriented control (FOC) concept some more because that looks like the most effective solution.

The router gave me some trouble and I wasted some material with a couple of bad jobs, but I think I figured out the problem.

 

[rhizotron]

A little more progress...

I improved the support post with a piece of 80-20 integrated into the shelf frame and this looks much better—don't know how that didn't occur to me originally.

Also wired up some lighting with four little 1-watt downlights that I had here on-hand. This should be enough light for the small easy semi-aquatic plants to be scaped into the beach area.

Stepper motor is updated with a bigger Nema 17 variant for more torque. I still need to get the little 4-wire connector to plug into the driver, so I was not able to fire it up tonight.

 

[rhizotron]

Here it is set up again with the new lighting and a quick aquascape too...

I'm going to add a couple of plants as emergents on the far left side. There is a 3.5" net pot filled with stones there in the spot I saved for them. I think I might combine a mat of vining Hydrocotyle with a mini Calathea or other more erect plant. ..

 

[rhizotron]

Here's another concept I wonder about for adapting as a planted aquascape....




Instead of a long linear aquariumlike I am using with the wave machine, I would build a ripple setup with a broad and shallow square tank. This is a 24" X 24" X 8" enclosure currently housing another project....

I really like this tank shape. The view in through the top of the water is such a pleasant, natural perspective.

As with the wave machine, a ripple tank mechanism could serve as an energy source supplementing the water filtration for water movement and model ecosystem health. Ripples in the water surface would provide an additional kind of kinetic sculpture interest, while they would also reflect onto the ceiling and wall surfaces with the aquarium light source.

 

[rhizotron]

I've been thinking about the ripple tank idea some more as a continuation of this project. Ripple tanks are often used in physics classrooms, so it's pretty easy to find details and a number of kits online as well. The basic setup is most often a shallow enclosure filled with just a few cm of water and with a paddle that vibrates or actuates to create the water ripples.

(Attribution: https://en.wikipedia.org/wiki/Ripple_tank#/media/File:Simple_ripple_tank.svg via Wikimedia Commons)

The most essential difference between this device and a wave tank is that the waves are of very short amplitude. The ripple tank may also have a clear enclosure bottom for projecting the ripple patterns with a bright light source. Most ripple tanks are square in shape, while wave tanks are more linear to allow for longer wave travel.

Ripple tank paddle motion is usually achieved with a small attached DC motor spinning an asymmetrical "eccentric" mass which causes the assembly to take a short hop with each revolution. Other designs may use an electromagnetic vibrator driven by a sine wave signal generators. While this kind of setup is more costly than the simple electric motor-driven paddle, you could say it has more conceptual appeal. The electromagnetic vibrators are also kind of interesting devices and could thus serve as a visible hardware element as part of the whole display.

Here's a really interesting video showing a ripple tank with this kind of wave generation.



The spring steel ring transferring the energy to the paddle in this configuration could be an additional sculptural feature of interest. Notice also that the mechanism can cause quite significant water movement, another compelling feature of both wave tanks and ripple tanks adapted as aquarium display; this is a way to energize the system with modes of water movement more natural than air bubbling or electric pump impellers.

 

[rhizotron]

I got this aquascaped with a few plants. This is just a Spathiphylum, a Calathea and some Bacopa monnieri I had on-hand and put together riparium-style in a 4" net pot. Bacopa stems will grow some more to cover the pot while also dampening the wave energy.

There are some pretty cool ways that this could be combined with living aquaecapes. Here's a few ideas:

1. Wabi Kusa, with a few lave stones in front and around the sides to disperse wave energy.
2. Syringodium, Ruppia or other Seagrasses to represent a sandy flat with a saltwater setup.
3. Aegagropila linnaei Marimo Balls rolling back and forth with the waves, just as they do in nature.
4. Laguncularia, Rhizophora and other Mangrove plants.
5. Stony Corals forming a barrier reef.

My current favorite idea for expanding this idea is with a brackish Mangrove setup housing a few trees along with some Cyprinodon, Fundulus or other estuary Killifish. This would require a bigger setup. The little tank I have here is just a 6-gallon and holding only about two gallons of water. Something with a 12" X 48" footprint like a regular 55-gallon could work well as a larger enclosure to include fish.

 

[rhizotron]

I found something really interesting with slo-mo video showing the machine generating two waves with each stroke. I had previously assumed this was caused by resonance since there is still some sloshing with waves bouncing off the far end of the tank. But the slow-motion video shows the second, slightly smaller wave formed by the paddle up-stroke; with the paddle quickly lifting up into the air, energy just fore and aft join to create a neat second wave somewhat smaller than the main wave.

This kind of wave generation could probably be corrected with a modified cam shape. With a cam flattened on one side, but with a round semi-circle on the opposite side, the up-stroke will be more gradual and probably less likely to generate this second wave. However, it also looks like the second smaller wave is deepening the trough for the next main wave to make a taller wave with more amplitude. So I'm just going to leave this as it is for now.

I probably won't leave it up for long, but you can see the slow-mo in this post on my Instagram, Swipe to the fourth frame for the video....

 

[rhizotron]

I hung up the microcontroller + stepper driver with my bracket assembly. The smaller unit above is the LED driver/buck converter for my other project on the top shelf. I still need to fit another controller, air pump, relay and power connections onto the T-track. It will be a tight squeeze with a lot of wires

More video...

 

[brandon429]

so technical and amazing, wow

I don't recall seeing things like that on forums very often at all/ever

 

[rhizotron]

so technical and amazing, wow

I don't recall seeing things like that on forums very often at all/ever

Thanks for stopping by!

I hope to make some more headway this weekend. I have so many little parts to fabricate and round up.