Let us decipher. Let us calibrate. Let Us Drone.

You thought flying your new Phantom would be a delightful experience, but then you hear “calibrate the compass”, “calibrate the vision sensors”, “calibrate the IMU”, oh come on! Fret not, all this calibration talk is usually just that, talk. There is certainly a time and place for calibrating, but if done right, 99% of the time you’re with your drone will be spent flying.

So, the million-dollar question: when should you calibrate the IMU on your DJI drone? DJI does not make this information clear in their user manuals, but they have suggested in multiple forum posts and tutorial videos to calibrate the IMU if the app prompts you to and/or if you notice any erratic behavior with your drone.

What is an IMU?

The inertial measurement unit (IMU) is an electronic device that measures the specific force (speed), angular velocity, and attitude of your DJI drone. This is done by using a combination of the following sensors:

Accelerometer- I could give you a technical definition but it’s my goal for you to make it through this post without yawning. Simply put, the accelerometer detects your drones acceleration.

Gyroscope- Detects your course, pitch and roll angles and allows you to hover with that precise stability we all love so much about our DJI drones.

Barometer- Detects changes in height.

Thermometer- I won’t insult your intelligence by giving you a proper definition of the word “thermometer”, but I will say that the ambient temperature at which you calibrate the IMU is very important as your drone will need to warm up to that temperature before future flights. Some have taken extreme measures by putting their drone in the refrigerator before calibrating, but DJI states that room temp is advisable.  

When should I calibrate the IMU?

As noted above, DJI’s answer about when you should calibrate the IMU has been ambiguous. Below, I have provided instructions and linked videos where DJI tells you exactly how to calibrate the IMU, but they haven’t been great about telling us when to. When asked directly on the DJI forum, the administrators have given conflicting answers. Fortunately, we have a strong drone community with thousands of members who have millions of combined hours of flight time. All of this experience has enabled us to bring together our combined knowledge on this topic.

Curious as to what they would say, I emailed DJI regarding this very subject, and here was their reply:

“In regards with your Question: When should I calibrate the IMU on my Phantom 4 Advanced? Answer: You can calibrate the IMU after unboxing the the aircraft, or after updating the firmware, if the warming up procedure takes too long, or when there is an small error encounter like the aircraft tilted in the horizon. you can do the IMU calibration if there is a problem with the balance of the aircraft during flight , if the aircraft is balance, stands still when it hovers.” -DJI representative 

I was hoping the “you can” would be a “you should”, but I’ll take what I can get. We have to take into consideration the language barrier as well, where the specific meaning of words often gets lost in translation. With that being said, they got back to me on the same day and proceeded to ask further questions about the IMU and any problems I was experiencing. Good job, DJI.

The following is a list of occasions when it’s recommended to calibrate the IMU, according to DJI representatives, web resources, and forum contributors.

• If the DJI Go or Go 4 app tells you to. If there is only one time when you choose to perform a calibration, this would be it. If the app is telling you to, you may also notice alternative red flashing lights on the drone which can indicate an IMU error. Don’t panic if you see flashing red lights though, as this also indicates a low battery. But hey, that’s another good reason to land soon.
  
• If you notice the drone hovering at an angle when there is little to no wind, or it drifts without your input. The cause of the aforementioned behaviors may be something completely unrelated to the IMU, but calibrating the IMU would be a good step when diagnosing the cause.
• After a crash or a hard landing. Sensors may be jarred in such an event, in which case a calibration would be smart.
• When you first receive the drone. All of the sensors on your new DJI drone come pre-calibrated, but your new Mavic or Inspire had quite the journey getting to your front door. We’ve all seen those videos of porch cameras capturing delivery drivers doing their best Joe Montana impression with packages.
• After a firmware update. I personally don’t calibrate the IMU after every firmware update and have never had an issue with it, but some swear by this practice.

When should you not calibrate the IMU? If it ain’t broke, don’t fix it. After reading this post I’d hate for you to walk away telling yourself “well shoot, maybe I need to do an IMU calibration”, just because you never have and it seems like something people do, at least occasionally. You do not need to calibrate the IMU before each flight; that would be redundant and unnecessary. If you don’t currently fall into one of the above categories (unless you’re in the “when you first receive your drone” category), then keep your fingers away from that calibrate button.

How to check the IMU’s status

If you’re curious about the current status of your drones IMU, you can check this by going to main controller settings>advanced settings>sensors. You will see the “accelerometer bias” and “gyroscope bias” with bars underneath each that have one of these three colors: green (excellent), yellow (good) or red (poor). If the bias value is too large with either sensor, red or yellow will be present in the bars; in which case an IMU calibration would be appropriate. But remember, the app will give you a notification if you need a calibration whether you’re on this sensor screen or not.

How to calibrate the IMU

Calibrating the IMU is a relatively quick and painless process, usually taking about five minutes. The two most important things to remember when calibrating are to make sure the drone is on a completely flat surface, and calibrate the drone in a cool environment. Since the IMU is what tells the drone what is level, calibrating it on anything but a level surfaces can cause some serious aerial instability. You can get a free “level” app on your phone or tablet if you don’t have one lying around the house. I used the one called “Bubble Level for iPhone” and it worked great. Whatever temperature you calibrate the drone at is the temperature the drone will have to warm up to before each future flight. Some have resorted to chilling their drone in a refrigerator before the calibration as to ensure quick warm-up times, but the risk of moisture and extreme temperature changes by the fridge has DJI and I recommending that you calibrate the drone while in a cool location indoors.

There may be slight variations with each DJI drone model, but here are the quick steps to calibrate the IMU.

1. Place the drone on a flat surface (don’t forget to use that level).
2. Let the drone cool down to the room temperature.
3. Make sure the battery is at least 50% charged.
4. Open the DJI Go or Go 4 app.
5. Power on the controller.
6. Power on the drone.
7. Click on the following: Main controller settings>advanced settings>sensors>calibrate IMU>start.
8. Follow the onscreen instructions (you will be required to tilt the drone in various directions).
9. After the calibration is complete, restart the drone.

Here are video tutorials to walk you through the calibration process with different DJI drone models:

Spark-  https://www.youtube.com/watch?time_continue=59&v=z_pfcHyHFm8

Phantom 4 series- https://www.youtube.com/watch?v=xC1mqmQHRgs

Mavic Pro/Pro Platinum- https://www.youtube.com/watch?v=guD8qFRRv-c

Mavic Air- https://www.youtube.com/watch?v=x36WO2OnIaY

Inspire 1- https://www.youtube.com/watch?v=LSnrCx35CG0

Inspire 2- https://www.youtube.com/watch?v=x57DWy0xyRU

Trevor’s Take

If you take away anything from this post, let it be that the most important thing you can do is to listen to your drone. These highly technical flying machines are engineered to give the operator a sign when something is off. Whether it’s a warning on the app or a tilted hover, take your time to investigate the problem; and if it’s an IMU in need of some calibrating, you now know where to start. Ever have any IMU problems while flying your drone? I’d love to hear about it in the comments section below!