According to Randy the know issue of altitude loss after a high speed run is at its heart a frame issue.This seems to me a very worthwhile discussion to have.Once the majority of us understand this, we will be less likely to muck up other threads.Take it away Randy...

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        • Just ordered 2 of these Zubax GNSS 2 modules with the barometer built in to see if this does the trick. May be easier than incorporating the barometer sensor separately.

          • Any news about altitude loss with Zubax GNSS 2

            • Still waiting for them to arrive.

        • ...or how to connect or use this mag-baro combo

          • Emin, The Zubax unit looks awesome, but then so is the price - dearer than the most expensive pixhawk clone I ever bought (and that was with all the accessories!). As for the GLB link you posted here, I am not certain that this unit is i2c compatible. It certainly doesn't mention it. I have bought two of the i2c 5v baro's so far - one connected to my Pixhawk running the Plane f/w - just hooked into the i2c splitter, and the other one chained to the mag connections on my m8n GPS unit, and both work very well, and at a very cheap cost. The ones I used were off eBay here:

            Its very easy to connect - just 4 connections to chain onto the i2c bus: VCC(+5v), Gnd, SCL, SDA 

            You also would need to be running the 3.4dev Copter firmware (or Plane for fixed wing).

      • Randy,

        Loaded 3.4-dev and have set GND_PRIMARY to 1. I can see the Alt is reading OK, but is it possible to determine conclusively that the Alt reading is definitely being produced by the external (i2c) baro? 

        Update - just back from some flight testing with the above setup and am glad to report that the baro performed flawlessly, and barely any drop in altitude during fast forward flight (where there was a considerable drop previously), so I am very impressed with the outcome.

        To reiterate my solution, I purchased the external i2c baro as per this one Randy mentioned in an earlier post. I installed it inside the GPS puck, connecting it to +5vcc, Gnd, SCL, SDA (I.e. connecting it in parallel with the i2c compass connections of the ublox GPS/mag):


        I placed a square of orange HK foam over this entire side of the unit and re-assembled the GPS Puck - bear in mind that the electronics here is far too padded out to fit inside the puck, so I simply sandwiched it in there and used (a lot of) hot glue as a filler between the two halves of the puck to hold it together. The foam and baro therefore are on the underside of the GPS patch antenna, so I then drilled four 1mm holes through the underside of the puck case allowing the atmosphere through to the orange foam inside - and therefore allowing a buffered air path to the baro. Here's the puck all glued up:

        Z3dNe4xwl48XThHghzATj1uDfLgcR9EbMzAMpb2C19dldjeuPrMCHfDIX5MSDwawg9VDTeQ9acBAvhZEa2YtO3tWz59gmMaE0zuITZ5AyeWkzyGN2uT9lFPa3reW63CVtHr00G9sPKT4Bnhu6dYEoP9wCWdtxUE2pwliTwvZqZTPm7LCoZaxebItsmKv8yP2qlLGe6UYSBbTZTfwMMxrCG4CtfBAIre1_Fv62FM_0o1cIyT6sHUD1Lwet5o2dkV9yW52GhHvM48J6Mnpcs7wRhhmklRK7llOyNA_KbPid58cER2Hz5450WGcozc-GKD2BMJdxggGE3dimHm6dl8ch21-A-oNp-ppjLJ7lLJnisvu_iV7EgckDExLDV0OfCSuAygx-9iyAAfiA6ng8O9-ySldOFnM5iAJnLnWC5myjVec5B9j9iOdkCZp8N5dZwnUIbRfklgPzVJOP72Wakx3GKwGhkI5HSURC0btpImDsg35Y2j9xLvCmgFWz6BIuNx7hW50rz3__ioT3LP_LlSrnFm5dVjBoixye9Eu7ZBfRGtVbDAOcvcjyXrD1z8vFHxvIPNv=w1087-h815-no?width=300and here's the underside showing the breather holes and through the plastic you can just make out the orange foam inside:


        I should add for clarity that the GPS puck is mounted on a pole which allows it to sit only around 4 inches (100mm) above the top of the AUAV-X2 FC, so I am by no means lifting this way above the copter as I have seen others do in this post.

        • Log file of flight using the above setup is attached for reference. Thanks, Paul

          p.s. as I mentioned in an earlier post - wouldn't it be good if these resourceful Chinese manufacturers developed a 3-in-1 (ublox/mag/baro) unit ;-)


  • Moderator

    Is GPS altitude so bad that it can't be used to correct this drop in altitude in the short term?

    • Yeah. If you look at GPS Alt. in your logs you can see that GPS has a huge altitude granularity.

  • Maybe this is too much of a simplification but is the problem basically to let the air pressure change at a rate that would happen via increase in altitude, but not the faster rate that happens from gusts of wind, prop wash etc? IE make the flight controller airtight except for a small entrance

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