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Thread: ARTS and ARTS2

  1. #1
    Join Date
    19th June 2017
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    Vacaville, CA
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    ARTS and ARTS2

    So I picked up so Ozark Aerospace items, and I finally got to fly them. I used the ARTS as primary and ARTS2 as back-up. They worked great and I got some great data out of them.

    But I have one question. Why does the accelerometer altitude differ so much from the barometric alt? The baro alt is what I had simmed the flight at. But the acc alt is almost double.


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    Eric Hamilton, NAR, TRA
    SARG, LUNAR
    Level 1, Estes Argent, H115DM
    Level 2, Scratchbuilt 2.6", J270G

  2. #2
    Join Date
    26th October 2016
    Posts
    156
    Can't help with the question but for future reference, the "ALT" key + "PRT SCN" key will copy the current window to the clipboard which can be pasted into a blank Paint file. This would provide better images for people to look at and lead to better answers.

    NAR level 2: Mad Cow Super DX3

  3. #3
    Join Date
    18th March 2009
    Location
    Wisconsin
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    3,829

    ARTS and ARTS2

    The accelerometer might be measuring distance traveled to apogee- not altitude. Did it weathercock?


    Sent from my iPhone using Rocketry Forum
    Mark Koelsch
    Tripoli 6155 L3
    Owner of http://www.rocketryfiles.com/
    Editor of http://www.thrustcurve.org/
    Member of the Tripoli Motor Test Committee, and keeper of the motor file

  4. #4
    Join Date
    26th November 2009
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    5,246
    The Arts 2 'was a very nice unit and even had an egg finder type GPS to go along with it. I picked up a GPS to go along with my Arts 2 and for folks who had the money in 2007 it was the cat's meow. Kurt

  5. #5
    Join Date
    15th February 2009
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    North Texas
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    Accelerometers are notoriously poor for altitude measurements as they integrate motion to determine distance. Any errors accumulate over time and if you have weathercocking or other issues they also confuse the true reading. Even worse its possible that even after deployment they can still experience positive Gs and think they are still gaining altitude. A payload bay spinning under a drogue for example.

    I would not even bother with the accelerometer altitude since the barometric will be so much more accurate. This is true pretty much regardless of brand of altimeter that offers both measurements.

    I like the ARTS 2 and use one on some my larger rockets.


    Tony
    why do people put so much stuff in their sigs?

  6. #6
    Join Date
    19th June 2017
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    Vacaville, CA
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    Thanks for the replies. I do have the ARTS GPS that has an ARTS on top of it. But it is a little big for my rocket avbay. I probably won't use it since I went the eggfinder route. I might just put that whole system in the yard sale section.

    Sent from my VS988 using Tapatalk
    Eric Hamilton, NAR, TRA
    SARG, LUNAR
    Level 1, Estes Argent, H115DM
    Level 2, Scratchbuilt 2.6", J270G

  7. #7
    Join Date
    5th March 2009
    Posts
    525
    Quote Originally Posted by Eric View Post
    So I picked up so Ozark Aerospace items, and I finally got to fly them. I used the ARTS as primary and ARTS2 as back-up. They worked great and I got some great data out of them.

    But I have one question. Why does the accelerometer altitude differ so much from the barometric alt? The baro alt is what I had simmed the flight at. But the acc alt is almost double.


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    Three questions:

    1) Did you launch vertically?

    2) Was the rocket stable during ascent

    3) What was the temperature?

  8. #8
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    Quote Originally Posted by Larry Curcio View Post
    Three questions:

    1) Did you launch vertically?

    2) Was the rocket stable during ascent

    3) What was the temperature?
    1, The launch rail was with in a degree or two of vertical.

    2, It went strait up, and leaned over at the very top.

    3, Started the day at 60*. Might have got up to 70* . Calm 2-3 mph winds.
    Eric Hamilton, NAR, TRA
    SARG, LUNAR
    Level 1, Estes Argent, H115DM
    Level 2, Scratchbuilt 2.6", J270G

  9. #9
    Join Date
    5th March 2009
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    525
    Quote Originally Posted by Eric View Post
    1, The launch rail was with in a degree or two of vertical.

    2, It went strait up, and leaned over at the very top.

    3, Started the day at 60*. Might have got up to 70* . Calm 2-3 mph winds.
    Then it looks all bent outa shape

  10. #10
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    Quote Originally Posted by Larry Curcio View Post
    Then it looks all bent outa shape
    What looks bent out of shape?

    Sent from my VS988 using Tapatalk
    Eric Hamilton, NAR, TRA
    SARG, LUNAR
    Level 1, Estes Argent, H115DM
    Level 2, Scratchbuilt 2.6", J270G

  11. #11
    Join Date
    5th March 2009
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    525
    Quote Originally Posted by Eric View Post
    What looks bent out of shape?

    Sent from my VS988 using Tapatalk
    The data is (are) all bent outa shape. Calibration? (The ARTS units are self-calibrating.) Wrong orientation? (Self-calibration gives you a lot of latitude there. Dobut it.)

    Are the barometric data credible?

    -Larry (Out of practice in this realm) C.

  12. #12
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    19th June 2017
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    Vacaville, CA
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    I would think both units being out of calibration at the same time would be odd. Because they both gave the same kind of altitude curve. The barometric altitude is what I had simulated. So I believe it. Both the ARTS and the ARTS2 are oriented in the correct direction.

    This is my first time flying an altimeter with an accelerometer. Click image for larger version. 

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    Sent from my VS988 using Tapatalk
    Eric Hamilton, NAR, TRA
    SARG, LUNAR
    Level 1, Estes Argent, H115DM
    Level 2, Scratchbuilt 2.6", J270G

  13. #13
    Join Date
    15th February 2009
    Location
    North Texas
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    Eric - I don't think any of the accelerometer based altimeters do a good job of recording altitude. They are not very reliable at detecting apogee for the same reasons they don't calculate altitude correctly. Your plots look very similar to the ones I've gotten not only from my ARTS, but whenever I've tried plotting accelerometer based altitude. Almost universally they greatly over estimate the altitude.

    For deployment events and altitude, barometers are hard to beat. But I like knowing what else goes on during the flight, like motor burn duration, stress caused by ejection charges, pieces bumping into each other, etc. Accelerometers are great for that additional kind of info.


    Tony
    why do people put so much stuff in their sigs?

  14. #14
    Join Date
    5th March 2009
    Posts
    525
    Quote Originally Posted by Eric View Post
    I would think both units being out of calibration at the same time would be odd. Because they both gave the same kind of altitude curve. The barometric altitude is what I had simulated. So I believe it. Both the ARTS and the ARTS2 are oriented in the correct direction.

    This is my first time flying an altimeter with an accelerometer. Click image for larger version. 

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    Sent from my VS988 using Tapatalk
    It looks almost like 1 g isn't being subtracted from the acc data. Something is horribly wrong. Can you post the exported data (i.e.; not just the graphs.)

  15. #15
    Join Date
    20th January 2009
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    655
    You can read the sensors when connected to the Data anylizer in diagnostic mode. What does the accelerometer read? (orient the arts in launch direction).

  16. #16
    Join Date
    7th February 2009
    Location
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    There are two calibration factors for the acceleration.

    The 1G value which is subtracted from all readings during flight is calculated each flight prior to launch.

    The sensitivity (ADC counts per 1G) is calculated using the GUI (so the manual says) and stored in the altimeter.

    One of these is out of whack. You can't do anything about the 1G offset but you can recalibrate the altimeter. Correcting existing flight data may or may not be possible.


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