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I'm currently working on a project and trying to sense the thrust being output by an ion thruster.

Right now I am using a faraday cup to measure the Ion count and figuring out the thrust by this reading, but I'd like to have another sensor to check and verify the faraday cup. I was thinking to use some sort of small fan and using the rotation of the fan to figure out the thrust. It's a low amount of thrust so I don't know how practical this idea would be but I did think of two potential options:

  1. Use a small computer fan and remove the electronics from inside of it with the exception of the stepper motor. That way as the fan turns it generates a current from the moving fan and thus I can measure the current to get the speed then go from there to get the thrust.

  2. Just use a fan with nothing inside and use an external encoder/laser and just count the amount of times a marked blade passes by the laser each second.

Any option seem reasonable, or are there better ways of approaching this?

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  • \$\begingroup\$ What are you thinking will spin the fan? The ions themselves? Air affected by the ions? Either way your test seems unrealistic - typically an ion thruster is for spacecraft usage so a test more realistic than monitoring the ions themselves and calculating from that probably requires a vacum chamber. You don't need a displacement pendulum to measure thrust, you can (for a range of values) use a load cell in the mount. \$\endgroup\$ – Chris Stratton Nov 26 '15 at 17:42
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Typical thrust-test for rocket engines is: mount engine on a pendulum, fire the engine sideways and measure pendulum deflection. Use trig functions and pendulum-bob-engine mass to calculate milliNewtons.

To avoid excess deflection, add more weight to the pendulum. Of course the pendulum-rod and connecting cables have to have insignificant mass compared to the pendulum bob.

Similar: use a "horizontal pendulum" based on a springy flexible material clamped down at one end, mount the engine on the other end, then fire the thrust upwards or downwards.

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  • \$\begingroup\$ I'd go with this suggestion, but right now the thruster is being held in a static position so I am not currently able to put the thruster on a string due to how the design is currently set up. \$\endgroup\$ – FrankerZ Oct 18 '15 at 0:01

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