Altus Metrum Easy Mini issue

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Walldiver7

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I fly redundant flight computers about 95% of the time. Today, I was reviewing the data from two EasyMini computers that took a ride in my DarkStar to somewhere around 10,500'. Both EasyMinis started logging data above 500'... thus skewing the final apogee report. I own 6 of these EasyMinis and I've noticed several of them, on occasion, having this same issue. These two that I use in my DarkStar are now consistently starting above of 500'. Anyone else having this issue with their EasyMini flight computers?
 
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mpitfield

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I fly redundant flight computers about 95% of the time. Today, I was reviewing the data from two EasyMini computers that took a ride in my DarkStar to somewhere around 10,500'. Both EasyMinis started logging data above 500'... thus skewing the final apogee report. I own 6 of these EasyMinis and I've noticed all of them, on occasion, having this same issue. These two that I use in my DarkStar are now consistently starting above of 500'. Anyone else having this issue with their EasyMini flight computers?
This is a timely thread. I am just buttoning up a sled for a new build and I am using the EasyMini v2.0, running 1.6.8, no redundancies. What version hardware and firmware are you running?
 

Walldiver7

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This is a timely thread. I am just buttoning up a sled for a new build and I am using the EasyMini v2.0, running 1.6.8, no redundancies. What version hardware and firmware are you running?
These are both v 1.0 computers and they were both running 1.5. Due to your question, I just flashed them to 1.6.8. Are you EasyMinis marked v 2.0? I didn't know that AM had released a new version of the EasyMini...??
 

StanO

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I used my EasyMini-v1.0 in 2014 with Software version: 1.3.0.1 and it recorded AGL at "0" on the pad. At apogee it was within 70' of the Raven3 max altitude of 6200+'
 

mpitfield

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These are both v 1.0 computers and they were both running 1.5. Due to your question, I just flashed them to 1.6.8. Are you EasyMinis marked v 2.0? I didn't know that AM had released a new version of the EasyMini...??
No my bad it is v1.0 as well, I was looking at one thing and typing another. I would be interested to know if updating your firmware has any appreciable effect on the phenomenon. Can you report back on your next flights?
 

Walldiver7

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No my bad it is v1.0 as well, I was looking at one thing and typing another. I would be interested to know if updating your firmware has any appreciable effect on the phenomenon. Can you report back on your next flights?
I will do that. Our next launch is the first Saturday of April, so it will be a while. I'm hoping that the update will cure those affected. I was going to attach the latest flight file showing what I've experienced, but I guess it's been too long since I've been on TRF; I've forgotten how.
 

mpitfield

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I will do that. Our next launch is the first Saturday of April, so it will be a while. I'm hoping that the update will cure those affected. I was going to attach the latest flight file showing what I've experienced, but I guess it's been too long since I've been on TRF; I've forgotten how.
Hit the "Go Advanced" button then "Manage Attachments" upload your attachment in one of the supported formats, zip should work if the format you have is not supported natively. Having said that I have not tried to do this for anything other than .jpgs for a while and even photos I am using BBcode and Flickr these days, plus I hear about upload issues from time to time from other TRF members.

But give it a try anyway as I would like to see the data.
 

Walldiver7

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Hit the "Go Advanced" button then "Manage Attachments" upload your attachment in one of the supported formats, zip should work if the format you have is not supported natively. Having said that I have not tried to do this for anything other than .jpgs for a while and even photos I am using BBcode and Flickr these days, plus I hear about upload issues from time to time from other TRF members.

But give it a try anyway as I would like to see the data.
Well..... The uploader just doesn't seem to like the Altus Metrum eepro type files....... so no luck on that.
 

mpitfield

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Well..... The uploader just doesn't seem to like the Altus Metrum eepro type files....... so no luck on that.
It says it supports .zip files, so if you compress it first with the .zip extension then you should be able to upload it. No guarantees as others are reporting upload issues, however that would explain why you are having issues with the .eepro extension.
 

markkoelsch

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It says it supports .zip files, so if you compress it first with the .zip extension then you should be able to upload it. No guarantees as others are reporting upload issues, however that would explain why you are having issues with the .eepro extension.
The forum software allows certain file types. If a file is not in the approved list you cannot upload it. I am not sure Eepro is an accepted file format. Likely not by default.
 

keithp

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I fly redundant flight computers about 95% of the time. Today, I was reviewing the data from two EasyMini computers that took a ride in my DarkStar to somewhere around 10,500'. Both EasyMinis started logging data above 500'... thus skewing the final apogee report. I own 6 of these EasyMinis and I've noticed several of them, on occasion, having this same issue. These two that I use in my DarkStar are now consistently starting above of 500'. Anyone else having this issue with their EasyMini flight computers?
I think this can be explained by how the firmware works, and that the reported height values are AGL.

As you may know, EasyMini uses a Kalman filter to track the state of the flight. This takes the raw barometric data to update the "state" of the flight, which is contained in three values: height above ground, vertical speed and vertical acceleration. One piece of a Kalman filter is a predictive model of how the underlying system works. In our case, we've got Newtonian physics as a pretty darn good approximation of rocket flight; given the previous height/speed/accel, you can estimate the next state by simple arithmetic.

Because we don't know when the motor is going to be lit, or how it will burn, the EasyMini Kalman filter makes a rather rash assumption -- that acceleration is constant. This is a really good model when trying to estimate when apogee occurs, but not so hot when the motor starts burning. The barometric data is quite noisy, especially when under thrust or accelerating through mach, so the Kalman filter takes quite a bit of convincing whenever the acceleration changes.

EasyMini assumes that the rocket is flying once the Kalman filter value for height is greater than 20 meters (about 66 feet). As the Kalman filter takes a while to adjust to the fact that the motor is burning, it is only slowly adjusting the estimate of the height of the airframe, and the reported Kalman values will lag the actual airframe state by a long time.

To avoid filling up the eeprom with ground data, EasyMini doesn't start logging flight data until it figures out that the rocket has left the pad. It does save 160ms of data from before the launch detect, so you'll see that much data, then the 'boost' line, and then the rest of the flight.

EasyMini records the raw barometric pressure value during flight, not the cooked up Kalman values, so what you see in AltosUI is what the pressure sensor actually recorded. This lets you see the Mach transition effects, along with changes in internal pressure caused by ejection charges. EasyMini also records the barometric pressure at the launch pad, which allows the ground software to compute AGL values for all of the logged flight data. That's how you see the flight start 500' above the ground; it's not that your rocket started the flight from that height, it's just that the data recording didn't start until the rocket reached 500'. I've reviewed a couple dozen EasyMini flight logs and see boost detect at anywhere from 30' to 800', as you'd expect, it depends on how much acceleration the airframe is under, and could also depend on the size and shape of the static ports on the ebay.

I don't think there's anything "wrong" here, just that the boost detect is taking a while, which is normal. If you want more flight data recorded, adding an accelerometer to the system makes the Kalman filter much more responsive as it can quickly adapt to acceleration changes. I reviewed another several dozen TeleMetrum flights and all of them start at 0 AGL.
 

mpitfield

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I would go with Keith's explanation.

On a side note, nice flights! What size drogue are you running?
 

Walldiver7

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Keith,

Thank you for explaining this! I've noticed that when flying my other EasyMinis, they start up from 60' to 80'. The Openrocket sim for this flight was, at best, 9,800'. Since the recorded apogee was 11,296' on the #1685 Easymini, with a starting agl of 730', should I subtract 730' to get a more accurate apogee figure? The Telegps recorded (via the downlink) an apogee of 10,902'. My reason for asking, is that we have contests on a regular basis and I need to know that I am not taking unfair advantage of my competition when one, or both, of my EasyMinis starts recording at a higher AGL than the usual 60 to 80'. I think I'll include my MicroPeak on the next flight.
 
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Walldiver7

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I would go with Keith's explanation.

On a side note, nice flights! What size drogue are you running?
You noticed the descent rate..... ha! Well, I was flying with an 18" drogue, and the Main never came out. The shear pins didn't shear. This was a new batch of shear pins and I think they are suspect in this event. Fortunately, my Darkstar came out just fine.... and that's another testament to flying with a tailcone.
 

keithp

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Keith,

Thank you for explaining this! I've noticed that when flying my other EasyMinis, they start up from 60' to 80'. The Openrocket sim for this flight was, at best, 9,800'. Since the recorded apogee was 11,296' on the #1685 Easymini, with a starting agl of 730', should I subtract 730' to get a more accurate apogee figure? The Telegps recorded (via the downlink) an apogee of 10,902'. My reason for asking, is that we have contests on a regular basis and I need to know that I am not taking unfair advantage of my competition when one, or both, of my EasyMinis starts recording at a higher AGL than the usual 60 to 80'. I think I'll include my MicroPeak on the next flight.
You can treat the reported height as accurate. EasyMini is carefully recording the barometric pressure on the ground by averaging a lot of samples and using that to figure out AGL during the flight. I'd suggest looking at the data recorded after landing and see if that looks reasonable. And, I don't think you'll be surprised to hear that MicroPeak has the same Kalman filter and launch detect algorithm, so it will do something similar, although the lower sample rate will mean that the pre launch-detect data will cover more time.

Make sure you go download the data from TeleGPS -- that will be the most accurate value you can get as it won't depend on atmospheric conditions.
 

Walldiver7

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You can treat the reported height as accurate. EasyMini is carefully recording the barometric pressure on the ground by averaging a lot of samples and using that to figure out AGL during the flight. I'd suggest looking at the data recorded after landing and see if that looks reasonable. And, I don't think you'll be surprised to hear that MicroPeak has the same Kalman filter and launch detect algorithm, so it will do something similar, although the lower sample rate will mean that the pre launch-detect data will cover more time.

Make sure you go download the data from TeleGPS -- that will be the most accurate value you can get as it won't depend on atmospheric conditions.
Thanks for all the information.... Will do on the download of the TeleGps data.
 
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