Vent Sensor

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Voyager
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Vent Sensor

Postby Voyager » Mon Nov 27, 2017 10:30 am

Has anyone implemented a vent sensor for their hybrid launches? Usually, you can see the venting occurring, but sometimes it is not that obvious, particularly when your launch tower is 90+ metres away. Yes, I have used binoculars, but it would be more convenient to have a very visible indication, either at the pad, or better still, at the LC position with a wireless link.

I'm sure one of you has sorted this out! I did see a post on TRF (http://www.rocketryforum.com/showthread.php?129000-hybrid-rocket-motor-nitrous-oxide-vent-sensor) that describes one pad-based method.

... and I just found this one! https://www.youtube.com/watch?v=ka6EpxNi-YE
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Re: Vent Sensor

Postby OverTheTop » Mon Nov 27, 2017 11:45 am

I suspect a remote camera watching the vent would be invaluable based on the hybrid launches I have seen. Would take the guesswork out of it fairly cheaply.
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Re: Vent Sensor

Postby SpaceManMat » Mon Nov 27, 2017 12:13 pm

OverTheTop wrote:I suspect a remote camera watching the vent would be invaluable based on the hybrid launches I have seen. Would take the guesswork out of it fairly cheaply.

Might also help take guess work out of various failures as well.
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Re: Vent Sensor

Postby OverTheTop » Wed Nov 29, 2017 8:31 pm

Maybe something like this is fairly cheap. Only need some batteries and an LCD monitor I guess
84883.jpg
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https://hobbyking.com/en_us/quanum-fpv- ... eiver.html

I bet there are even cheaper solutions out there.
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Re: Vent Sensor

Postby Voyager » Wed Nov 29, 2017 9:57 pm

That's not a bad little system OTT, thanks for that. Could be useful in a number of applications.
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Re: Vent Sensor

Postby Voyager » Tue Dec 19, 2017 12:01 pm

OK, I now have a N2O vent sensor courtesy of Jaycar Electronics. I was planning to design & build one, but as I was about to purchase the components from there, I saw their temperature sensor kit which fits the bill nicely.

For those of you wanting to reliably test for venting from their hybrid, the kit link is https://www.jaycar.com.au/economy-adjustable-temperature-switch/p/KC5381. It has a 2 pole relay that can drive a very bright LED and/or a loud beeper. It can also be used to provide remote indication at the LC table.
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Re: Vent Sensor

Postby strud » Sun Nov 17, 2019 7:05 am

Hi Voyager,

Any luck implementing this method?

Wondering if you've come up with a reliable setpoint and target?

Of course the most reliable approach is to monitor the mass delta so you know exactly how much Oxidiser has been transferred. More complex I guess but if you have a wireless GSE system then definitely something to consider adding.

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Re: Vent Sensor

Postby Voyager » Sun Nov 17, 2019 3:57 pm

Hi strud

Yes, I have now commenced a redesign of my hybrid GSE that is based around a wireless Arduino control system. I will be monitoring fill tank temperature, pressure & mass, and flight tank mass & vent sensor, plus ignition. I have designed a load cell arrangement that fits on the launch rail so I can monitor the flight tank mass delta. That, with the vent sensor (plus continuity), will determine flight readiness. I hope to have this completed before the start of the 2020 launches. I will post some details and pics when I have progressed a little further through the development, build and test process.

Looking forward to seeing how your setup turns out. Very impressive work there! Hopefully you might make it down to Ardlethan in 2020.
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Re: Vent Sensor

Postby strud » Sun Nov 17, 2019 4:04 pm

Hi Voyager,

That sounds very comprehensive, should be no doubt where you stand prior to pressing the bit red button :D

I'm planning on having more high level metrics and auto checks with my GSE interface such that when you or someone else is in the process of filling and firing, you are less likely to make a mistake due to a 'rush of blood/adrenaline'.

eg: Set up tolerance band for fill mass + Ox pressure and have a boolean that indicates 'Ox Fill OK' when mass and tank pressure are inside tolerance

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Re: Vent Sensor

Postby OverTheTop » Sun Nov 17, 2019 6:36 pm

Sounds like a nice improvement over the standard hybrid GSE :)
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Re: Vent Sensor

Postby strud » Wed Apr 22, 2020 4:23 pm

Hi Voyager

How is your GSE/Vent monitor going?

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Re: Vent Sensor

Postby Voyager » Thu Apr 30, 2020 8:34 pm

Hi Strud

I settled on an encapsulated DS18B20 sensor https://core-electronics.com.au/waterproof-ds18b20-digital-temperature-sensor.html. It is monitored by the Arduino in the pad box and transmits back to the launch controller. It will mount on the launch rail near the vent, but out of the fin path.
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Re: Vent Sensor

Postby strud » Thu Apr 30, 2020 10:14 pm

Looks great.

Have you settled on thresholds yet?

I assume you get a significant fall when liquid starts coming out, but it must be pretty cool already with the cold gas.

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Re: Vent Sensor

Postby Voyager » Sun May 03, 2020 8:25 pm

I was hoping to measure the temperature curve at our first scheduled HPR launch at Ardlethan in April, but that didn’t happen because of the virus situation. Now it’s looking like our next scheduled launch there in June is probably going to be rescheduled to later sometime.

So, I am looking at setting up a way of safely performing this at home, but living in the suburbs of Canberra isn’t conducive to performing this stuff. Basically, I need to be able to simulate the initial gaseous phase, then the liquid. I can’t even use our low/mid power launch site at Yass because of the current restrictions.

My main concern with using a solid state sensor is that it’s typically rated for about -50C, but N2O boils at about -89C. I have used these sensors before at lower temps in my former occupation, so it’s worth a try. Failing that, I will probably use a PT100 sensor that’s good for lower than -100C.
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