An ion thruster is a type of electrical propulsion system used for spacecraft propulsion capable of creating thrust by accelerating ions. Back in June 2015, I remember seeing this demonstration for the first time on Makezine, by Alexander Reifsnyder. I thought it was amazing for its scientific value and at the same time quite easy to build, so me and Hugo thought we could make our own version of it, using 3D printed parts.
The project isn’t exactly an efficient engine, but more of a scientific demonstration of the ion thruster working principle. That said, it won’t launch of the table but it will create a steady flow of air without using any moving parts, which is interesting.
In terms of materials the project is quite straightforward, all you need are some nails, copper tubing or couplings, an high voltage power supply, wires and something to build the structure.
Alexander suggests the use of copper plated nails, which I presume is to increase electrical conductivity. There are many ways to do that, personally I used a very simple method I found on instructables, which only uses some old oxidised copper coins, salt and lemon juice or vinegar. So, I grabbed some iron nails and cleaned them up with a wire wool to remove any oxidation.
And then put them into the solution, one at a time:
Soon enough I had a copper plated nail:
During the process you might need to replace the coins, because this works best with oxidised coins. During the process they will loose that layer of oxidation and the process stops working. It’s also a good idea to add more lemon juice or vinegar and salt every once in a while.
After a while I got all the copper plated nails I needed:
Keep in mind that this method only adds a very thin layer of copper to the nails, so any scratch will easily remove it.
For the tubes, I used an old copper pipe with a 2cm diameter and cut it into 5cm pieces.
Then I started designing the structure. Since we have a Lulzbot TAZ 4 3D printer in eLab Hackerspace, I thought I could use 3D printing to make it more appealing:
So I used Tinkercad to design the entire structure.
If you want to build your own, I made all parts available on Thingiverse. Even though I used a large 3D printer like the TAZ4, I’ve made sure all parts are small enough to fit most printers.
Then I started printing the parts and testing everything in place:
For the high voltage supply, I had an extra NST (Neon Sign Transformer) from my Tesla Coil, so I used that. It has a 9kV, 50mA output. Be very careful working with high voltage, you must know what you’re doing, because it can kill you!
It’s possible to use other HV supplies, like a flyback transformer from a CRT or something like that.
As soon as I had enough parts, I tested the project:
And it was working great!
Eventually I had all the parts printed and it was finished. I even added an emergency button to fire up the transformer, which always makes everything more exciting!
Now for the explanation, the copper plated nails and the copper tubes serve as electrodes:
The nails must be positioned exactly on the geometric center of the copper tubes. This way, ideally, the distance between the tip of the nail and the surface of the tube is always the same:
The high electric field around the nails will ionize the surrounding air, which means it will become electrically charged and will be attracted by the opposite electrode, the tubes:
This will create almost invisible tiny beams of plasma. As the ions reach the tubes, the charges will be attracted to them but the neutral particles already gained momentum, creating a steady flow of air.
As you can see, the nails are placed on the center of each tube:
There are several things that have influence on the efficiency of the system, for example, the voltage applied to the electrodes, the precision of the placement of the nails on the center of the tubes, making sure all distances between them are the same, perfect cut tubes, having the surface perpendicular to the nails, and of course the distance between the electrodes, which must be put right before it starts creating an electric arc.
By the way, even though I designed the structure with a slider to adjust the distance between the electrodes, don’t ever to it with the power supply on, it’s way too close to the electrodes and it can be very dangerous. So be sure to turn everything off before adjusting the distance through the slider!
If an electric arc is created, the circuit will be closed through that arc, therefore there won’t be any other beams of plasma, and there won’t be a flow of air. Electricity always follows the path of least resistance:
However it does allow for some amazing photos:
I had the opportunity to take this project to Lisbon Maker Faire 2015, for which it was awarded the prize “Best in Class” of science!
Now just a small note, in space there is no air to ionize, which means this project, as it is, wouldn’t work, so how do they do it in space probes? Well in space it’s injected a noble gas like xenon, keeping the spacecrafts from using solid fuel, making this method more efficient and more appropriate for longer travels. But still, the working principle is still the same!
Here is another video of the complete demonstration, even with some arcs at the end:
High Voltage transformers are very dangerous! Don’t try this yourself if you don’t know how to work with high voltage safely!