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Advanced How often should I do the IMU and Compass calibrations?

Discussion in 'Phantom 3 Help' started by Dylan227, Jul 22, 2015.

  1. Dylan227

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    So far, for my first two or so flights, I have calibrated the compass each time. I haven't calibrated the IMU since the quad was unboxed this morning. I had a slightly hard landing in the grass on one of my flights , but no damage at all. I was wondering if it is recommended to do a IMU calibration after that landing. I understand that you should calibrate the compass when visiting new flight areas, but how far do they need to be apart? Should I do it when flying on fields in different towns? States? My worry is that I have heard that calibrating the compass too much will lead to a bad calibration.

    Thanks!
     
  2. msinger

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  3. Meta4

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    If you are within 100 miles of home, there should be no need to recalibrate the compass.
    It's not that doing it too often will give a bad calibration, but that it introduces the potential for a bad calibration. A common example is calibrating close to steel reinforcing in concrete.
     
  4. RoyVa

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    You asked about re-calibrating the IMU.
    Recalibrate after any major software upgrade
    Recalibrate if the bird has been shipped via commercial transportation
    Recalibrate when you have continuous drifting or the craft won't stabilize after a couple of flights.
    Recalibrate after any major hardware changes
    Why is IMU important..

    IMU( Inertial Measurement Unit = Accelerometer + gyroscope + compass)
    Roll, Pitch and Yaw. Gives stabilization Without almost any drift.
    The IMU is an electronic sensor device that measures the velocity, orentation and gravational forces of the Quadcopter.
    These measurements allow controlling electronics to calculate the required changes in the motor speeds.
    It's a combination of 3 axis accelerometer and a 3 axis gyroscope and a 3 axis magnetometer (compass) for better Yaw control.
    The accelerometer measures acceleration and also force and measured the downward gravity force. As it has 3 axis it can work out the orentation of the quad.
    The gyroscope measures angular velocity, in other words rotational speed around the 3 Axis.
    A magnetometer (compass) measures the direction and strength of the earths magnetic field. The sensor can then determine which way is north and south. The pole locations are then used as a reference with the Yaw angular velocity around the gyroscope to calculate a stable Yaw angle.
    With proper IMU calibration your copter know where it at, which way is north and can hover without a lot of drifting. It allows for the motors to adjust so she can pretty much sit still while hovering.
     
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  5. Russ

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    I am a new P3P owner/pilot, I have read different threads about compass calibration and most of them give different answers. I live in Malta, which is 17 miles long and 9 miles wide, does this mean that I will only have to calibrate the compass only once, because I will be flying within such a short area, or should I calibrate the compass, before every flight, as other people have suggested. I go through all the pre flight checks and one of them is compass calibration, I do not want any fly aways or crashes, because I have not covered all the checks. I am sorry if this question has been asked and answered before, but any help or advice will be greatly appreciated. Thanks in advance.
     
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  6. Mordor

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    NEver too much to ask. I live in POrtugal......but everytime i fly i calibrate the compass..

    IMU calibration was done only 1, before the first time on a cool morning and completly flat zone.

    They say isn`t need for the same zone.......but if it was me, and if turning off the battery from P3, i would calibrate again just in case....

    Maybe same poweruser with more experience can share some thoughts about it!
     
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  7. bbfpv

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    The consensus is unless you're traveling more than a few hundred miles from the last calibration point, compass calibration is not necessary. It's a sensor after all, so why inadvertently introduce more noise than is necessary.
     
  8. Mordor

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    Well......anyway...i just have one battery, so only 18 minutes of fun, and them home :((( :;;;;
     
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  9. Monico Garza

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    From the information I read you should calibrate the compass every single time you fly. It's advised that if you travel more than 50+ miles from your home point you should recalibrate your compass. I do it everyTime before I fly. I have never had a problem calibrating the compass and I do not think that doing to many would hurt anything. I would like to know little bit more on this also because some people don't do it very often but other people do it all the time
     
  10. bobmyers

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    How often should I do the IMU and Compass calibrations?
     
  11. Meta4

    Meta4 Moderator
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    This has been much discussed in many threads here and pretty well every thing has been said many times.
    You can read a few recent threads here:
    Calibrate every time I fly | DJI Phantom Forum
    Compass Calibration Required | DJI Phantom Forum
     
  12. Monico Garza

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    Understand thanks
     
  13. RoyVa

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    Read above about the IMU calibration. Here is compass info:
    Why Calibrate?
    Compass calibration is important to safe, controlled flight. It compensates for changing background magnetic "noise", a.k.a. magnetic inclination and deviation (not to be confused with declination). Inclination and deviation that isn't corrected through compass calibration will cause inconsistencies between GPS and compass that can result in "toilet bowl effect", a swirling motion that can cause the Phantom to fly out of control.

    What is Magnetic Inclination and Deviation?
    Magnetic deviation is a horizontal variation that comes from the Phantom itself and the equipment you have installed on it as well as the magnetic makeup of the area you are flying in (again not to be confused with declination). Sometimes the deviation will be insignificant, but other times it can be big enough to cause you to lose control. Inclination is a vertical magnetic variation that shifts depending on where you are.

    Warning Signs
    The Phantom can detect when the compass is providing extremely poor (implausible) data. This typically occurs if you place it near a strong magnetic field or do not calibrate it properly. It will flash red and yellow lights and will not start the motors when this happens. Unfortunately, it can only detect this in extreme conditions and you can still fly with really bad compass data if you're not careful.

    Another important safeguard is the compass mod value. This is the total magnetic field as measured by the sensor. You can check this with the Phantom Assistant software. According to DJI, it should be above 750 and below 2,250 but ideally it should be between 1,000 and 1,700. Between 1,200 to 1,500 is very good. Check it away from magnetic influences. If it reads very high or very low, check it again in a different location. If it is still off, it could be magnetized and need degaussing or it could be damaged.

    What Does Calibration Actually Do?
    Calibration measures the magnetic fingerprint of the surrounding area. By turning the compass 360 degrees, the Phantom can see where the compass reading doesn't smoothly increase or decrease. It uses this information to build an adaption table so that when the Phantom turns during flight, the reading is smooth and linear.

    When Should I Calibrate?
    You do not need to calibrate before every flight and in some cases you definitely should not calibrate. That doesn't mean you shouldn't ever bother doing it. It only takes one time for it to go very wrong. The most important aspect of compass calibration is making sure the magnetic "noise" around your Phantom is consistent between calibration and during flight.
    • DO Calibrate
      • If you go to a new location that is a good distance (i.e. >100 miles) from the last place you calibrated the compass.
      • If the terrain has changed significantly i.e. going from prairie to mountainous.
      • If you change any equipment on your Phantom.
      • If you just installed new firmware.
      • If you just degaussed your compass (BTW, don't degauss unless you are absolutely positively sure you need to).
      • If you have taken all the precautions to make sure there are no localized magnetic fields near you.
    • DO NOT Calibrate
      • If you're in an urban area surrounded by concrete, buildings, and hidden or overhead power lines / pipes / etc.
      • If you're on the beach or on a boat.
      • If you're in immediate proximity to metallic objects or anything magnetic.
    • Pre-Calibration Checklist
      • Everything used in flight should be powered up during calibration, e.g. GoPro, tracker, etc.
      • Remove all metal from within 5 - 10ft radius, e.g. watch, phone, belt buckles, coins, controller, etc.
      • Calibrate on grass or dirt and not on concrete, asphalt, in or on a building or structure.
      • Calibrate on a level surface if possible.
    • How to Calibrate (P1 and P2. P3 check the manual.)
      • Power up your Phantom and accessories as normal.
      • What for the Phantom to complete home position and heading recording (2 sets of green flashes)
      • Flip S1 five times between the top two positions. Check to see the Phantom lights are solid yellow.
      • Pick up the Phantom and turn it smoothly and steadily a full 360 degrees until the lights turn solid green.
      • Point the front of the Phantom straight down and repeat until the lights turn off and resume normal flashing.
        Note: Don't be concerned if your gimbal reacts poorly to being face down, keep turning as normal.
      • Optional: power off and restart Phantom.
      • Enjoy your flight!
    If for any reason, you do not complete any of the above steps smoothly and evenly, restart the process.