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Eggtimer Quantum Altitude

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Crazyrocket

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I built an Eggtimer Quantum and was testing my new e-matches with it and I noticed that the ASL reading on my phone is registering -263 feet. I know my real ASL is around 70 feet. Does anyone think this is an issue or is it ok to fly it. I'm worried that the Quantum may arm too high or the main may open very low and cause some problems.

Thanks!
 

markkoelsch

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I cannot answer. It would seem to be a calibration issue. I am not certain, but does the device register launch as a change in altitude versus a change from zero? That would be a question for cerving.
 

Buckeye

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I built an Eggtimer Quantum and was testing my new e-matches with it and I noticed that the ASL reading on my phone is registering -263 feet. I know my real ASL is around 70 feet. Does anyone think this is an issue or is it ok to fly it. I'm worried that the Quantum may arm too high or the main may open very low and cause some problems.

Thanks!
Probably not an issue, but I am not sure about the negative value. Barometric altimeters can be off by 500' when sensing the ground level. AFAIK, they use the Standard Atmosphere model at Standard Day conditions - something that rarely happens in real life.

The baro alts measure the change in pressure and convert to change in altitude to give you the AGL measurement. We assume that is good enough for our hobby rocket application.
 

r66astro

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Not sure about Egg have 3 not built yet. Most are referenced at 29.92 standard at 59 degrees f. It can report at the ground neg or pos depending on your pressure at that time. I assume it uses it as reference to base from. So not matters.
Bill
 

Crazyrocket

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The pressure was 30.39 that was my concern. I have an email into Chris to see what he thinks.
 

PiperCPO

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I noticed the same thing and contacted Cris about it. Here is my question and his answer below:

I had a question regarding the ASL Altitude readout. Both units are showing values between -72 and -55 when the page refreshes. I know that my house is 134ft ASL. Why is there such a error in both units and within the same range? I disconnected and reconnected my phone’s wifi to each after each sat on my bench powered by my bench power supply. I had assumed that it would eventually settle out after a few minutes of sampling , but they didn’t. Is anything wrong? I have attached screen shots, one from each of my Quantums.

Here is his reply:

Brad:

The ASL altitude is dependent on temperature, and the temperature sensors take awhile to settle down... maybe 30 minutes. What's really more important is the relative AGL altitude during flight... and that's pretty much independent of what ground altitude it shows.

The ASL altitude gets updated over time after arming, so it tends to be more accurate during actual launch conditions. When it's not armed, what you're seeing is the last reading, with no filtering. That's why it might vary, and it will be more accurate outdoors than indoors.

Cris


After a couple days I powered my Quantums up again and things were close to normal.

Brad
 
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Crazyrocket

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Thanks for the information. It was pretty cold so maybe that was the problem. I will hook up ematches to them and let it sit for awhile.
 
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