I’ve got some excellent feedback on our latest article Spoilers! from Chris on our internal chat (Discord) where he came with following comment:
I must admit that I closed my eyes when the RPM ramped up at the end, expecting to see a plastic shower! Oh yeah… and do you happen to know the RPM they spin up to?
Chris Drake
… while he instantly followed on that with his typical call for action and got a spectrum analyzer to check that RPM from the video using the Spectral View application. Output out of it surpassed all my expectations, that result looked … colorful.
Luckily Chris immediately provided his commentary – “Most of the test was at 3700hz, ending with a ramp-up to 5200hz (that’s the strongest of all the harmonics anyhow) – not sure if that’s the motor speed, or the rate at which the blades pass by. Multiple those out, and if it’s near 5000 – that’s the motor speed. If it’s wrong by the number-of-blades, then I’ve picked up the wrong thing.”
Chris also noted that common phone Mic’s only can go up to around 20khz, and his phone has a max sample rate of 48khz (making it unable to record anything about 24khz at all), so it’s inconclusive as to what that line maxing out at 5200hz means (it might be a harmonic of something unrecordable).
Of course he also came with some cool suggestions for improvements. For the reference, this is how our propeller looks like today (Chris’ rendering).
.. and now this is a how the most efficient for 2kg (20N) at 20,000 rpm should look like based on his calculations.
While they look quite different, you can see that that “pitch” is not that different. Luckily Chris confirmed that with:
… which is actually pretty close to what you’ve got.
Chris Drake
Thank you Chris! Glad that we are not completely off the scale with this! And I clearly learned something new. 🙂
