James Stanley

Coriolis fountain

Sat 29 April 2023

I have an idea for a cool-looking water fountain. It's based on the coriolis force, which is where an object travelling in a straight line appears to be travelling in a curved line when viewed from a rotating reference frame.


Imagine one of those lawn sprinklers that has angled nozzles that spray jets of water as they spin around in circles:

Now imagine the arms are made longer, and the jets are more powerful, and the angles and motion are controlled so that the jets of water land exactly where you want them.

In fact, you don't have to imagine, because I made a simulation.

Check out my simulation here

It's not super easy to control (the angle controls, in particular, are confusing) but you can make the jets loop around and return to the nozzle they came from, or all cross in the middle, or do several spirals before returning to the ground, etc.

First implementation

I don't know if I'm ever going to actually build this, but for a proof of concept we could mount the Coriolis fountain in a small paddling pool.

We'd put a raised platform in the centre with a large gear on it, fixed in place. There would be a frame on top of this platform which is able to rotate around the centre. The frame would be driven around the gear by a motor mounted on the rotating frame, something like this, from my robotic telescope mount:

The speed of the motor would be radio-controlled. Obviously it needs to be waterproof.

The rotation axis would be hollow, and a submersible pump would go down it to be submerged in the water in the paddling pool. It doesn't matter that the pump rotates with the frame, it still pumps. The output of the pump splits into 3 (or however many) and runs off down the arms to the nozzles. The nozzles have 2-axis control via radio-controlled servos.

Then we just need to put a battery and an RC receiver on the rotating frame, and the whole thing can be controlled remotely with normal RC gear. Since both the pump and the drive motor are located on the rotating frame, none of the cables or hoses need to pass through rotating fittings.

We could add per-nozzle flow rate control by having a (strong?) servo motor clamp down on the hose to limit the flow.


Once the concept is proven with manual radio control, we can look at automating the control. In increasing order of complexity:

  1. the rotation speed and nozzle angles could be set manually and left alone
  2. we could have a small number of preset patterns and the system cycles between them either on a timer or on command
  3. we could have animated patterns, where the nozzle angles or rotation speed can vary over time

Probably we'd want a microcontroller onboard the rotating frame to control the animations. And we'd either want some power cables running to the frame through slip rings, or maybe solar panels if we can tolerate it not running when it's not sunny.

And it would be cool to make it a permanent installation in a big pond or something. Sadly I don't have anything suitable. Do you have a big pond or lake? Do you want a Coriolis fountain? Email me, let's talk. I would love to help you make a Coriolis fountain.

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