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Understand Calibration - No Toilet Bowl Effect

Discussion in 'Pro/Adv Discussion' started by Bret Lucas, Jul 10, 2015.

  1. Bret Lucas

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    Read this and apply... Your wandering P3 will stay rock solid. Check out the Calibration Checklist at the bottom.

    Calibrating the Phantom 3 Compass

    [Moderator Edit - This is from http://www.phantompilots.com/threads/compass-calibration-a-complete-primer.32829/ by @ianwood]

    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 magnetised 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
    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.

    [Moderator Edit - End Quote]

    Pre-Calibration Checklist

    ️ Position Phantom on non interference level surface
    ️ Power up Aerial Booster, Controller, Device, Phantom
    ️ Remove all metal from within 5 - 10ft
    ️ Confirm Device is in Flight Mode and all Apps are closed
    ️ Open DJI Pilot App and allow App to engage with Phantom
    Wait for the Phantom to complete home position and heading recording (2 sets of green flashes)
    ️ Push Calibrate button on App and follow instructions as follows
    ️ 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 green flashing.
     
    #1 Bret Lucas, Jul 10, 2015
    Last edited by a moderator: Jul 10, 2015
  2. TonG

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    What is the relationship between GPS and the compass and why should the phantom fly away if the compass is not well calibrated?
    After all the other consumer based GPS equipment like car navigators and the like you never have to calibrate and they still working fine and correctly. The don't get confused by the magnetic interference of a car.

    When a Phantom wants to fly away will tuning to Atti-mode prevent this behavior because I have red several treads that this will not work.
     
    taroh and acherman like this.
  3. Bret Lucas

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    The Phantom works on a 3 dimensional platform. Rather than argue the point, just try it. And understand the concepts above... or don't. Your call.
     
  4. TonG

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    I don't argue. I try to understand the how it works.
    You haven't answered my question about car navigators etc, who will functioning correctly in a hostile magnetic environment. And what about the atti-mode?
     
    ScottyT likes this.
  5. RoyVa

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    Goes along with IMU calibration
    IMU( Inertial Measurement Unit = Accelerometer + gyroscope + compass)
    Roll, Pitch and Yaw. 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 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. Without proper IMU you can have drifting, floating or even experience a fly a way.
    Proper IMU calibration is one of the most important functions for your quads sensors to bring her back to the right place, presuming that you got satellite lock and home lock.
     
    gbc bs likes this.
  6. EKPhantom

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    Bret Lucas and RoyVa: Best posts I've seen in a long time! INFORMATIVE. THANKS.
     
  7. rwakins

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    Great info guys! I'm tried to fly in my neighborhood trice and my P3P went crazy both times, is it due to me calibrating around houses, I also had it setting on pavement?
     
  8. rwakins

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    Another question, where do you guys get this info you shared, I haven't seen any sources of info with that good of details.
     
  9. coenjaerts

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    I have been flying with a very stable P3P ever since i bought it. Even after the FW upgrade I did not experience any of the issues that others have seen. Yesterday however I had to calibrate the compass three times before the result was OK. I moved a few meters the last time I did it. Maybe some interference due to the environment. After that it flew like before!
     
  10. coenjaerts

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    Very good information guys! These are the informative posts that other (inactive) members are looking for!
     
  11. TonG

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    Thanks for your reply but it still leaves my questions open.
    First: IMU calibration influences stability over 3 axes. I has nothing to do with location. GPS does that job, and as far as I know and I'm certainly not a expert it does not need a external compass for location determining . I think the compass is there for determining temporary changes in horizontal directions and in which direction the nose of the phantom is pointed. But it might be possible that a badly calibrated compass may influence the GPS readings because the corresponding electronic systems of the Phantom will interfere.

    As fa as I know simpel navigation systems don't have a compass and certainly you never have to calibrate them. Does the I-Pad cellular has a compass, because pilot-app gives correct direction-indications without even being connected to the phantom or the transmitter Why I don't have to calibrate my I-pad even when I use it in my car as a road navigator. My car never flew away, sorry, drives away, sorry again, send me in a wrong direction!
     
  12. dmcgrew

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    Just curious, why can't you calibrate on a beach? I calibrated this week about 1/4 mile from a beach and had no issues. Is it something with the sand?
     
  13. ianwood

    ianwood Taco Wrangler
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    @Bret Lucas, when your post is a verbatim copy of someone else's, you might want to credit the person who wrote it. Which in this case would be me! :rolleyes:

    http://www.phantompilots.com/threads/compass-calibration-a-complete-primer.32829/

    See above.

    Simple answer, other consumer based products don't fly. In a car, the compass serves heading functions only. In the Phantom, it serves as a reference to the gravitational vector as well.

    That would be your problem. Do not calibrate on pavement. Ever.

    Sand often contains ferrous material in it. 1/4 mile is a pretty safe distance! ;) As long as you're not on it or right next to it, you should be fine.
     
    Bret Lucas, unclejas and Wayne Coutts like this.
  14. TonG

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    Strange answers. You should explain why. First. Why should you not calibrate on pavement, because of the possibility electric cabling underneath.
    Second; for my calibration I should fly a 1/4 mile upwards since according tho the geography I'm living above sand grounds only separated by a 40cm layer of humus.
     
  15. ianwood

    ianwood Taco Wrangler
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    Pavement often has sub-surface ferrous material in it. And sometimes, the pavement itself is ferrous too. Granite is a good example of a surface you should avoid. As for sand 40cm below the ground, that shouldn't be a factor.
     
  16. gbc bs

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    Great write up!!! very helpful!
     
  17. gbc bs

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    Also a great report!!
     
  18. rwakins

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    If you shouldn't calibrate on a beach, why does the DJI training (how to fly) video show him on a beach calibrating a P3P?
     
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  19. rwakins

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  20. robert velez

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    Lol, good catch @rwakins! Didn't realize he was calibrating on a beach. I guess it depends on location too as I was able to calibrate on a beach with no issues on flight.