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I have a science project about how different propellants affect the thrust of an Ion engine so I have 2 questions: 1 How can I measure the thrust of a diy ion engine ( technique or tool that I need to buy any solution is welcome)

2 is there a way for me to test other propellants other than N2 in the air (where to get the gases and a setup to test it)

Any other suggestions to add value to my research is very welcome Thanks

The test ion engine will look something like the one shown in https://makezine.com/projects/ionic-thruster/

enter image description here

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  • $\begingroup$ Hi, I've added a link to the image that you mentioned in your comment. The more information you put into your original question, the better the answers might be. Welcome to Space! $\endgroup$
    – uhoh
    Commented Jan 31, 2019 at 5:39
  • $\begingroup$ Put a wind mill in front of it. $\endgroup$
    – Muze
    Commented Feb 1, 2019 at 4:45
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    $\begingroup$ Hello, welcome! I've taken the liberty of editing the title (pending approval) to be more specific. I hope I have preserved your intent. Also, your second question, about testing other propellants, would be better asked as its own, separate question. Unlike a web forum, which is pretty free form, the stackexchange sites encourage us to have just one good question per question. $\endgroup$
    – Wayne Conrad
    Commented Feb 1, 2019 at 15:40

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since you are doing it for a science project I would recommend you to read this paper which summarizes the standard techniques that are employed in the thrust measurement of electric propulsion devices.

https://arc.aiaa.org/doi/10.2514/1.B35564

https://www.researchgate.net/publication/316444395_Recommended_Practice_for_Thrust_Measurement_in_Electric_Propulsion_Testing

The thrust produced by your planned engine (from image) would be pulsed and very low, furthermore thrust to weight (of engine) ratio will be small to mount the engine directly on some weighing scale. You will need some kind of thrust balance if you opt for direct thrusts measurement. Or a baffle plate and a calibration mechanism should also work. It all depends on how much accurate you want the measurement to be.

If you want to experiment with different propellants, you will have to put everything in an enclosure, preferably vacuum tank, to exactly differentiate the thrust produced because of the propellant(vs the air/N2). Most of the chemistry labs will have access to these gases, I recommend trying inert gases like Argon, they are the EP industries choice.

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  • $\begingroup$ Thank you very much for your suggestion but I have one other question about the experiment with other gases. Other than obtaining the gases I don't know which measuring tool can be used to measure the thrust in the vacuum tank. $\endgroup$
    – Vegeta sama
    Commented Feb 7, 2019 at 15:33
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    $\begingroup$ As already mentioned earlier, try reading that paper it lists the methods used to measure thrust. If you are only concerned about what sensor to use, you have to use S-type load sensor or LVDTs or baffle plates but they all generate only voltage signal which is meaningless, so you would need someway to calibrate that voltage into thrust with some known masses. Go through the paper once and if you have questions, I will be around. $\endgroup$
    – MyTwoCents
    Commented Feb 7, 2019 at 15:37
  • $\begingroup$ Thank you but The bigger problem in this case is how to make measurement inside the tank. Because first of all the engine needs to be connected to the power supply and I can't imagine how can we connect the power supply to a power source and at the same time have our engine inside the tank. $\endgroup$
    – Vegeta sama
    Commented Feb 7, 2019 at 16:25
  • $\begingroup$ There is something called vacuum feedthroughs, you can buy it directly or make yourself, if you want to jingle jangle it you can make a hole pass the cable and pour silicon over the hole from both sides, sealing the vacuum inside!! Similar way you can pass the cables for sensor, make sure you make keep some distance between the power cables(put it through another hole) so as to avoid electronic interference with power cable. Try to get shielded cables. Don't hesitate to ask any more questions, I am here to help. $\endgroup$
    – MyTwoCents
    Commented Feb 7, 2019 at 23:48
  • $\begingroup$ Hi sorry To bother you but I really need your help.So while talking with my teacher about the things we need for the project. He thinks that we can't do it because the high voltage power supply first of all is lethal second (and this what matters for me) the vacuum chamber's shell is small and can't contain the engine and the pipes that transfers electricity would melt under the high voltage here are 2 pictures of the vacuum chamber and if there is a way to overcome those problems I would be very grateful drive.google.com/file/d/1e0ow8Nl1H70DWbsgcNDvQc3PQheBbq8t/… $\endgroup$
    – Vegeta sama
    Commented Mar 6, 2019 at 20:36
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I'm knowledgeable on your first question: To measure the thrust of any engine, you're going to have to build a thrust test jig. Look to people in the RC hobby on how to build one of these, they do a lot of propeller and motor testing.

A typical propeller thrust test jig would look something like this:

Oscar Liang thrust test rig

When the prop pushes the air, the lever arm presses down on a scale, where you can read the force.

If the thrust you're producing is too low to measure on a rig like this, you could hang the thruster on a pendulum and measure deflection to calculate force. If that's not for you, you could find a frictionless slide (magnetic or air cushion) and measure acceleration of the thruster to determine force. Many school and University physics departments have such slides.

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  • $\begingroup$ Thanks a lot for your answer However I missed a critical detail. The diy Ion engine is fixed And it looks something like this goo.gl/images/txaLRF $\endgroup$
    – Vegeta sama
    Commented Jan 30, 2019 at 22:59
  • $\begingroup$ Hangingg the entire rig from a fine wire in a vacuum chamber and then hoping there is enough deflection to measure seems like your best chance. It'll need to be in a vacuum chamber to work anyway, and ion engine thrust is so low that you're not going to measure it more directly $\endgroup$
    – Steve Linton
    Commented Jan 30, 2019 at 23:39
  • $\begingroup$ @SteveLinton this uses the ambient atmosphere (i.e. air!) as the reaction mass, so the vacuum chamber is a non-starter. Have a look at the newly-added link in the quesiton $\endgroup$
    – uhoh
    Commented Jan 31, 2019 at 5:37
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    $\begingroup$ @uhoh. Ok very different kind of ion engine. Hadn't realised that $\endgroup$
    – Steve Linton
    Commented Jan 31, 2019 at 7:02
  • $\begingroup$ @SteveLinton have a look: Troubleshooting a DIY Ion Thruster Unless the nails are very very sharp, there may be no thrust at all. $\endgroup$
    – uhoh
    Commented Jan 31, 2019 at 7:10
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Since the thrust is going to be minuscule, your best option would probably be a torsion weight. A horizontal bar suspended by the middle on a wire, engine rig on one end, counter-weight on the other so that the bar remains horizontal. A small mirror attached to the weight and a laser beam (just a laser pointer) shining on it and reflected onto a scale located a considerable distance from the rig. As the rig turns with the thrust of the engine (twisting the wire) the reflected point of the laser moves across the scale indicating the deflection angle.

Calibrating the setup will be rather tricky as you'll need to apply a known force comparable to that of the engine, and measure the deflection. One option could be a piece of thread with a small weight (<1 gram) using a roller to convert the vertical pull to horizontal. And of course no air currents... even your breath is enough to completely change the measurements.

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Analytical scales measure with accuracy in order 0.1 mg or about when the engine itself could weight close to a hundred g. Direct the exhaust straight upwards and weight with power on and power off - the thrust is the difference. With digital scales, you probably can measure remotely, away from high voltage. Do not know, maybe some could work in vacuum.

https://www.mt.com/ch/en/home/products/Laboratory_Weighing_Solutions/Analytical.html for instance.

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  • $\begingroup$ Range of weighing scale is far off the real problem. There will be an issue of feeding the power to the thruster and also data acquisition from the 'scale'. The thruster will need some kind of mount(like a wooden frame from the magazine article) which will add more weight. Also, the sampling frequency of these devices will affect the resolution and accuracy of the measurement. $\endgroup$
    – MyTwoCents
    Commented Feb 9, 2019 at 9:46

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