Safe location to calibrate IMU?

[Xenomorph]

Hey all! Just have a simple question for those of you who have successfully calibrated the IMU on your Phantom 4. What is a safe location to do it? From what I've been reading it has to be on a level surface and away from electromagnetic objects. Does this mean it's safe to do it indoors? Only reason I'm asking is because I can find a 100% level surface inside my home with no problem however finding something that 100% in the backyard may be an issue. Can I calibrate the IMU inside if the tv, microwave, lights etc are all turned off? Or should I work at creating a level surface in my backyard? What have you all done? Thanks everyone in advance!

 

[msinger]

There is no requirement for it to be done away from electromagnetic objects. It should be done inside on a level surface that won't be disturbed during the calibration process. You could technically do it outside, but it'll be tougher to find a suitable location.

 

[GMack]

I did it once in the kitchen and got some "Electrical Interference Detected" warning. Can't recall if it was the IMU or the compass, but I took it outside after that.

I leveled a patio table and used that for a while. Then I decided to make something I could use for the IMU and compass and try and make it repeatable and portable. Found some wooden Lazy Susan turntable at "Bed, Bath & Beyond" for $15 and a bubble level and 1/4-20 3" long nylon screws for leveling from Home Depot and this thing was born with a bit of old red oak and some garage work:

 

[jiggyb21]

I always do it on the kitchen table, on a shimmed, level piece of plywood. Level corner to corner on a square. Foolproof.

 

[Trmills]

I found by checking with a Spirit level, that my office desk is dead level. Great place to calibrate the IMU following an update. As for the compass, I calibrate that on site before each flying session.


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[alokbhargava]

IMU calibration can be done on kitchen table if it's Leveled. See that there are no vibrations and level is checked with a 10-12" leveler at least to get better accuracies. Also note that aircraft should be colder than the expected minimum ambient else it would take long time to warm up.


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[Shep]

Gmac- love it!


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[RémyHeli]

And once your happy with IMU calibration setup, you can take the opportunity to calibrate the gimbal right after the IMU.

Hey, quite surprised to see that for the P4 Pro DJI changed the procedure to calibrate the IMU by introducing steps and putting the bird in various new positions, even upside down!?. Probably for better acuracy and workaround case when surface is not perfect level.

Just to highlight process is different or I'm missing something?




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[John Locke]

I did it once in the kitchen and got some "Electrical Interference Detected" warning. Can't recall if it was the IMU or the compass, but I took it outside after that.

I leveled a patio table and used that for a while. Then I decided to make something I could use for the IMU and compass and try and make it repeatable and portable. Found some wooden Lazy Susan turntable at "Bed, Bath & Beyond" for $15 and a bubble level and 1/4-20 3" long nylon screws for leveling from Home Depot and this thing was born with a bit of old red oak and some garage work:
View attachment 71938

Being exactly level is not required for compass calibration, as implied with your lazy susan with bubble. For the compass, it's more critical to be out away from anything metal, in an open field is ideal. Not in your back yard (unless you're on a farm, or just have a huge back yard).

 

[rocketflyer]

Being exactly level is not required for compass calibration, as implied with your lazy susan with bubble

I'm also not sure if a lazy susan for IMU calibration is a good way to do it unless it can be locked in place or has enough friction so it doesn't move during the process. I find a spot away from things like washers so there's as little vibration as possible.

 

[jiggyb21]

I'm also not sure if a lazy susan for IMU calibration is a good way to do it unless it can be locked in place or has enough friction so it doesn't move during the process. I find a spot away from things like washers so there's as little vibration as possible.

Looks to me as if the lazy Susan is upside down.

 

[GMack]

I'm also not sure if a lazy susan for IMU calibration is a good way to do it unless it can be locked in place or has enough friction so it doesn't move during the process. I find a spot away from things like washers so there's as little vibration as possible.

The three white nylon screws screw down onto the concrete for the leveling part much like a tripod. It doesn't budge for the IMU part, and you can put a long torpedo level across it to check (I did and found the bubble circle needed to be adjusted a bit once it was glued down and the new circle is blacker in the photo!). I just drilled the tap three holes and tapped the wood with a 1/4-20 tap for threads, coated them with Super-Glue, dried, and re-tapped so they are the nuts to the nylon leveling bolts. Same process if you built an RC plane for attaching the wings (Hobby shops also sell those long nylon bolts for that.).

For the compass, I back the nylon screws out and spin it. Backstop (dowels) slips in and is the right height to keep it 90 degrees down and it will not change as when I spin it myself. That makes it repeatable with a greater degree of accuracy than me spinning it by hand. I've gotten my phone's compass off by 180 degrees at times by spinning it so I figured the drone might need something better than me to spin it.

Fwiw, the underside of the L.S. turntable thing is also wood, just half the diameter. Pivot is some small screw in the middle.

 

[Xenomorph]

Just calibrated the IMU, gimbal and compass out back. I did it in the center of my backyard. I have an acre lot so it's very spacious where the calibration was done. Said it was all a success!

It's like 40* here in the north east US. First I charged everything up and created a level surface in the backyard while I let the Phantom get cold. Then after the Phantom was out there for an hr I plugged in the full battery and calibrated.

 

[rocketflyer]

The three white nylon screws screw down onto the concrete for the leveling part much like a tripod

I completely take back my original comment!

 

[Pirate63]

GMack, I borrowed your idea, but decided to just use it for compass calibration. I have a very level shop floor I use for IMU calibration.

 

[AlecW]

I assume your taking that outside to do the actual compass calibration?

 

[Pirate63]

I assume your taking that outside to do the actual compass calibration?

Outside, in a nearby field.

 

[AlecW]

Outside, in a nearby field.

I thought that but you never know, I'm sure someone has calibrated a compass in a shop before

 

[rocketflyer]

There is a fair bit of metal in that lazy susan that *could* throw the calibration off?

 

[Pirate63]

There is a fair bit of metal in that lazy susan that *could* throw the calibration off?

Yeah, kinda wondered about that.