Intro: Make an Underwater Instrument in Your Favorite Shape: Hydraulophone From Shopbot CNC Routed Marine Plywood
Steve Mann with Max Lu, at Autodesk Pier 9:
We're inspired by the boat building tradition along the shores of the San Francisco coast.
So let's make a really nice marine-inspired housing (basin) for the hydraulophone (underwater pipe organ).
Our instrument is in the shape of a sea shell, but you can design any shape, such as a maple leaf (like the one on the Canadian flag), or a boat or ship-themed shape.
The housing helps save water, by efficiently capturing and recirculating the instrument's water.
Step 1: CAD: Design the Overall Shape, and Create Layers for It.
The key to great design is collaboration.
Fusion 360 is a great way to bring collaborative ideas to reality.
In the past we've used Solidworks, and shared designs across several of our locations, MIT, Stanford, Toronto, etc., and this has been problematic. For example, we send out a Solidworks file to 2 different collaborators who each make revisions and send back. Then we have to merge them, and quickly we get a mess.
Fusion 360 is like a Google document for CAD, in which we all see and share and edit the same file online.
Here we can collaborate and come up with a design we like.
Step 2: CAM: Toolpath Visualization
Fusion 360 also does great CAM (Computer Aided Manufacture) for toolpath design, etc., allowing us to make the design a reality.
Here we use the Shopbot CNC router to cut out our patterns from marine plywood.
Marine plywood is commonly used in boat building, and what we're building is a lot like a boat.
Step 3: Cut Out the Layers on a CNC Router (e.g. Shopbot)
Once the shape is designed, it is time to cut it out.
Before cutting, make sure the design is checked carefully.
For example, be sure to have a nice deep bilge for the instrument's recirculation pump.
Step 4: Design for Hydraulic Efficiency and Water Conservation
Two important design principles pertain to hydraulic efficiency and water conservation:
- Capture as much of the water as possible for recirculation: design the housing big enough that most of the stray water returns to the catchment area. Notice how we expand in the direction where most of the splash goes.
- Design so that the instrument can run on a very small amount of water. For this to happen well, be sure to construct a nice deep bilge. I drilled the bilge by hand in order to optimize its location carefully, in context of manually holding and positioning the recirculating pump (a submersible bilge pump). Drill halfway through from one side, then turn over the piece, and drill halfway from the other side. If done right, this gives you nice clean edges without splintering. Just like in a well-designed boat, the bilge is the lowest point in the vessel, and ensures the water collects efficiently.
In this design, notice how one of the T-nuts for the legs is in the bilge. This requires sealing to prevent leaking, and represents a good tradeoff between water efficiency and strength of the base.
Step 5: Laminate the Layers Together to Make the 3D Shape
The layers are glued together using Titebond III,
with a sufficient number of clamps to keep them solid for 24 hours before disturbing.
Use enough glue that some is seeping from every crack.
Step 6: Make a Support Base Conforming to the 30 Inch Standard Spacing
The instrument sits on a base which should be large enough that it won't easily tip over.
The shape of the base should be such that a user has a convenient place to stand.
Two pipes are used for the support base.
The standard spacing for most hydraulophones is 30 inches center-to-center between the two legs.
If you conform to this standard, you will find it easier to swap instruments and also to install them in waterparks and playgrounds and match existing mounting hardware.
There are two standard sizes for pipes: 1.5 inch schedule 40 IP (International Pipe) thread, and 2 inch schedule 40 IP.
Of these two sizes, the 1.5 inch is the more commonly used in hydraulophone installations.
Step 7: Finish and Assemble
Finishing was done using sandpaper by hand, with no sanding block.
That produces a nicer result (though takes a bit longer) than an orbital sander or other electric sander.
Begin with medium coarse (not too coarse) paper.
Number 60 is a good place to start.
Then advance to finer and finer paper.
Two coats of tough transparent floor paint was applied to the bottom.
A nice thick coat of West epoxy to the top... inside the bilge, throughout the basin....
Get the expoxy right the first time!
Epoxy does not stick to already cured expoxy!
Finally, put legs on.
Here some 1.5 inch NPT (National Pipe Thread) pipes and flanges were used.
Be sure to apply anti galling compound so the pipe threads don't seize up, otherwise it will be hard to disassemble for transport later.
You'll need 4 flanges: 2 for the instrument and 2 for the base.
Use stainless steel T-nuts in the base, and stainless steel screws....
Step 8: Be Creative!
Here we decided to expose the innards, but in a creative and tasteful way using transparent hoses to show the natural beauty of the water. The transparent hoses, when filled with water, function like cylindrical lenses, and catch the light in a very beautiful way.
The open design also makes the instrument easy to clean and service.
The pump is the heart of the instrument.
The parts of the instrument that require service are the filter (e.g. requires cleaning if a lot of people with dirty hands are using the instrument, or if leaves and branches and other debris collect, etc.), and the pump.
Over the years, it has been our experience that the most common point-of-failure in hydraulophones is the pump. By leaving the pump exposed, we can quickly replace it if it fails. Also we can change the pump size for different occasions, such as a big concert with an 1100 GPH (Gallons Per Hour) pump, versus a tranquil ambient instrument at around 500 or even 360 GPH.
Step 9: The Proof Is in the Pool
You'll know if your instrument is a success. If it is constantly surrounded by happy people having fun, you'll know you've got a great design.