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Sensor Bias...place on a level surface.

Discussion in 'Inspire 1 Help' started by SkySav, Mar 29, 2015.

  1. SkySav

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    It never fails. I do Compass calibration and find a nice flat place (or so I think) to take off and I get the "sensor bias..." warning. I have to try several other places and often restart the aircraft before I can get in the air. Does anyone else have this much trouble taking off? And it's every single time I fly.
     
    #1 SkySav, Mar 29, 2015
    Last edited: Mar 29, 2015
  2. The Editor

    The Editor Moderator
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    No!.... I have done two IMU calibrations since I got my Inspire.
    One on the day I unboxed it and another one when I upgraded the firmware to .17.......that's it!
    What are your IMU mod values?
     
  3. SkySav

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    I was mistaken. I do the DJI compass dance very time. I have to check my mod values and get back to you.
     
  4. amkorp

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    You really shouldn't be doing the compass calibration every time you fly.

    It is overkill and completely unnecessary. The Pilot app will tell you if the compass needs calibration or you can do it if you have traveled significant distances geographically since your last flight.
     
  5. SkySav

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    The compass calibration is not the real issue. The problem is the "Sensor Bias is too big." And constantly asks me to place in a level surface. I find the best most level places I can in the area I'm in and still gives me three flashing red lights warning me about the Sensor Bias. I have to mess around with different takeoff locations and often times having to restart the aircraft to get it to go green. Do you have this issue?
     
  6. The Editor

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    The level surface reference is connected with IMU not compass, so, I will ask again, what are your mod values?
    Advanced settings, Sensors, right hand column, Gyroscope, Acceleration, Compass - what are those values with the Inspire at rest on a level surface?
     
  7. Wormwood

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    IMU calibration & compass swing are two totally different events!! IMU calibration needs to be done in a quiet place away from any vibration on a known plumb/level surface & done so after the machine has been off for a good period of time so the circuits are cold. I mean don't even walk around the machine while the IMU calibration is running! The compass swing should be done at every flight location but not before a second or third battery at the same location.

    Your compass sensors should be somewhere around:1400-1600 hope for a mean of 1500. This reading will trend in a given direction when exposed to a field. What I mean is watch your readings, normally (1496,1504,1492,1510,1501,1506,1498,so on...) they appear to be somewhat random but nonetheless hover right around a mark say 1500 +\-100. if the compass sensors are introduced or removed from a magnetic field the readings will still seem somewhat random but they will trend in a direction higher or lower. (1496,1505,1499,1508,1500,1515,1502,1513,1522,1514, so on...) the readings will continue to do this until they reach a neutral balance & begin to hover around a number set.

    The IMU sensors on the Inspire are the most sensitive I've seen, simply shuting the door in the same room as you may be running the IMU calibration can ruin the calibration & make you have to recalibrate. Outside, performing an IMU is very easy because of the sun exposure & expansion of material making pops, creaks, also the springs winds will ruin the calibration. So I place my Inspire inside on the kitchen counter when I have the house to myself & the dogs are asleep, washing machine, dish washer, etc. aren't running & it's deathly quiet in the house for 5 minutes. I can't say what exactly it does while calibrating but my guess is, it shuts down each axis, allows it to cool for a minute then powers the specific axis IMU, samples the readings & zero's out the sample. It does this for X,Y, & then Z axis, you can watch you readings 0 out in that order, but who knows for sure.

    Wormwood
     
  8. The Editor

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    You need to be able to hold your breath for 5 minutes as well and....it helps to wear a Hazmat suit.
    I also ask the local police to stop all traffic for a 2 mile radius and makes sure my neighbors do not flush their toilets.
    Any birds in flight should be warned off with a scarecrow. Local schools (closer than a mile) need to be closed for the day as children running about cause problems.
    Please have local farmers slaughter all cattle that are roaming free and spray your garden for all insects and slugs and snails.
    Finally, turn off all lights as the mass of the photons smashing against the Inspire can cause havoc

    If you are sure you have followed all the above instructions you may go ahead and hit 'Calibrate'........

    Sorry....... Couldn't resist !! :p:p:p
     
    inspire909, mdomeny, SkySav and 2 others like this.
  9. DaBone

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    I just put it on a leveled table and switch off the router, so I donĀ“t have any WiFi-signals disturbing the calibration.
     
  10. DaBone

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    Why not? Does it harm the Inspire? Or is it just a waste of time, in your opinion?
     
  11. DCGOO

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    Mostly a waste of time.

    If you get a good compass lock in a location known to be free of magnetic influences, there is a possibility your new compass calibration could be bad, or less accurate than the one you are replacing. Hard to tell what is buried under that new parking lot you just found.

    Honestly, I did the compass dance with mine in an open field several weeks ago, and left it set. Generally I fly in the same local area. I would dance again if I travel a significant distance east or west of home, like to the next time zone. North or south shouldn't matter.
     
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  12. Wormwood

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    Seriously, I almost breathe shallow while it's calibrating. Running a calibration on my machine, if someone shuts the door or the dogs come running thru the room, it fouls up my IMU calibration. It'll either stop as say something about having to redo the calibration or one of my axis will off & my mod will show 1.10 or 0.90 somewhere around that. I thought everyone's was about the same?

    Also I've NEVER had an IMU calibration succeed outside... Guess mine has a shy IMU?

    Wormwood
     
  13. The Editor

    The Editor Moderator
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    +1

    Same here, why run the risk of a skewed compass calibration when you know you have a good one already.
    Magnetic declination only changes when you travel hundreds if not thousands of miles and the more times you calibrate the more times you run the risk of a biased calibration.
    However, the one caveat to this is I AlWAYS check my sensor mods before every flight and even after a battery change. If there was a reading out of whack I would calibrate.
     
    #13 The Editor, Mar 30, 2015
    Last edited: Mar 30, 2015
  14. RolandRSA

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    It is never a waste of time to do a compass calibration, you can't always rely on the app. More the merrier in my opinion.
     
  15. SkySav

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    0.02, 0.98, 1501.91 are the values. Your reply is much appreciated.
     
  16. The Editor

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    In your opinion .
    That's fine, if you feel happy doing g a compass calibration every time you turn round carry on. Whatever floats your boat.
    I on the other hand will rely on reading the mod values from the accelerometers (the same ones you tell me I can't rely on) and will calibrate if the MEMS gyro data is outside of DJI's advised working thresholds.
     
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  17. The Editor

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    OK, I would say you need to run an IMU calibration.
    Your mod values (with the exception of the compass which looks fine) are just outside the recommended numbers that DJI advise.
    Run the IMU calibration inside on a level surface and ensure everything stays VERY still. Although there are jokes above about not breathing etc there is some truth in the advice about not having kids/dogs running around etc as the IMU will pick up vibrations as small as people walking around or doors slamming!
    Run the calibration (should take around 5-6 mins) and my advice is to do it when the craft is cold - i.e turn the Inspire on and go straight into the app and calibrate. Don't let it sit there for a few minutes, do it straight away.
    After calibrating you should get values of 0.0, .99-1.01 and your compass is already spot on at close to 1500.

    Let us know how you get on.
     
  18. RolandRSA

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    Cool
     
  19. RGD

    RGD

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    I finally figured out how to calibrate the IMU thanks to the help from the folks on this forum. Now that I am looking at the mods I would like to know generally what should the numbers be.
     
  20. RGD

    RGD

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    Do you know what IMU stands for.
     
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