Calibrating table

Dobmatt · Mar 27, 2016

Embarrassing as it is, I'm getting dizzy during ritual compass calibrating dance. It comes with age, trust me. Add less-than-perfect, off level dancing floor (rocks, roots, tall grass etc.) and you'll fall helplessly, trying to protect $5K bird. Ouch ... Long story short, I've build MFCT (Multipurpose Field Calibrating Table) ...

It's equipped with 3-point adjustable feet and spirit level, rotates smoothly like a bar stool (in better bars, however) and - of course - it's of non-ferrous construction. I'm not sure I'll drag this thing everywhere I go, but when flying in remote places it may prove to be very useful. Any comments - critical or not - will be appreciated ...

The Editor · Mar 28, 2016

Dobmatt said:
Embarrassing as it is, I'm getting dizzy during ritual compass calibrating dance. It comes with age, trust me. Add less-than-perfect, off level dancing floor (rocks, roots, tall grass etc.) and you'll fall helplessly, trying to protect $5K bird. Ouch ... Long story short, I've build MFCT (Multipurpose Field Calibrating Table) ...

View attachment 7508
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It's equipped with 3-point adjustable feet and spirit level, rotates smoothly like a bar stool (in better bars, however) and - of course - it's of non-ferrous construction. I'm not sure I'll drag this thing everywhere I go, but when flying in remote places it may prove to be very useful. Any comments - critical or not - will be appreciated ...

Ummmmm... I applaud your lateral thinking on this one but why when you can do a compass calibration after a firmware update (always recommended,) and not have to do another one until months later?
The 'compass dance' thing really isn't necessary every time you change position you know.
Have a read over the forum and you will see my reasoning behind this and why doing so can actually be a BAD thing.
I think most people are now following a practice which I advised and I haven't heard of a single issue.
As long as you check your mods before every take off you will be fine.
I like the table though.

Mad_angler1 · Mar 28, 2016

Now an IMU cal table is what i need especially the amount of them I end up doing sometimes.

Nice work though fella

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Phatzo · Mar 28, 2016

i share The Editors opinion. but nice work. at the end we'll be selling to DJI for the thing we invent for us with their stuff to finally work well... lol

edit: with the new calibration method with the nose to the side you should make an add on to place the AC on the side...

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timax · Mar 28, 2016

I need to read over the forum about this also as I do a calibration for each location and like you get dizzy doing it. Today when in an industrial estate it took some time to calibrate. I think that turntable on a plastic camp table would be great in the back of my car.

seanmclean · Mar 28, 2016

I mean, that's clever but totally unnecessary.

If you have good compass readings, just fly it. Get one good one and be done with it. I've traveled over 3,000 miles without recalibration.

seanmclean · Mar 28, 2016

Whatcha got clipped onto the arms?

Dobmatt · Mar 28, 2016

seanmclean said:
Whatcha got clipped onto the arms?

That's the part of my amphibious drone mod, had nothing to do with the calibration table ...

Dobmatt · Mar 28, 2016

F...k, I was suspecting that this is an overkill. Interestingly, the official DJI instructions still loudly and clearly recommends compass calibration at every new place. Gee, what a messy environment I've stumbled in ...

Dobmatt · Mar 28, 2016

timax said:
I need to read over the forum about this also as I do a calibration for each location and like you get dizzy doing it. Today when in an industrial estate it took some time to calibrate. I think that turntable on a plastic camp table would be great in the back of my car.

BTW non-ferrous (aluminum legs), portable and foldable table is not easy to find. I'm in the process of looking around for such ...

Dobmatt · Mar 28, 2016

Phatzo said:
with the new calibration method with the nose to the side you should make an add on to place the AC on the side...

Gee, another new revelation I've never heard of ... What's the advantage, would you elaborate pls?

Dobmatt · Mar 28, 2016

[QUOTE="The Editor, post: 98069, member: 1807"
The 'compass dance' thing really isn't necessary every time you change position you know.
As long as you check your mods before every take off you will be fine.[/QUOTE]

Than why DJI clearly, loudly and stubbornly recommends this stupid procedure at every new location? What do you mean "mods", where are they to check and what to look for, please elaborate.

The Editor · Mar 28, 2016

My previous threads/posts are all over the forum if you care to use the search facility together with technical details as to why DJI's 'advice' is wrong.
However, I will repost a previous explanation I have made from an old thread (again).........

OK, so, by calibrating your compass you are giving it a reference point for the magnetic declination in your location/part of the world. If that calibration is done for example standing next to a car you may well get the compass to calibrate but the large metal object has changed the flux value of the true declination. The compass does not know this though and blindly believes it has a good reference to go on.
When you take off and get clear of 'the car' or whatever influenced you calibration the compass now only has the Earths magnetic field acting upon it. This means that its reference is out of whack and it cannot do it's job correctly by providing the offset between magnetic North (compass) and True North (GPS). There is now conflicting data being processed by the FC (flight controller) which will now try and correct the 'error' that it sees - result ever increasing circles (TBE) and an integral wind up scenario takes place whichcan cause an inexperienced pilot to crash.
This can be avoided if it ever occurs by the way by switchingto P-Atti mode since that switches out the compass and GPS and relies on IMU and barometer data only to maintainaircraft attitude (but there will be no positional hold obviously).
DJI's instructions to 'calibrate everytime you change locations' is a bit of cover themselves type of statement and of course they are assuming that every calibration is an accurate one (which of course we know it isn't).
So what happens say, if you followed DJI's instructions to the letter and calibrated your compass and got a goodcalibration. Then flew, had a great flight, then landed and walked say 300 yards to another location but unknown toyou there was an old car burried underneath where you thenput the Inspire down? If you followed DJI's instructions you would calibrate again except this time you would be takinginto account the burried car. As soon as you took off your compass values would be wrong since we know thatmagnetic declination does not change significantly in 300yards!
However, if you simply walked that 300 yards, put your Inspire down and checked the compass mod values prior to take off you would see they were outside of optimum range (1400-1600) and you should be thing "Hmmmm....that's not right because I have only walked 300 yards. Something is causing this". If you then picked up the Inspire, moved it a few feet (outside the influence of the car) then checked the values again you would see they had returned to normal - without recalibrating.

Dobmatt · Mar 28, 2016

The Editor said:
My previous threads/posts are all over the forum if you care to use the search facility together with technical details as to why DJI's 'advice' is wrong.

That makes perfect sense, The Editor Sir! Thank you for your time and effort. By checking mods you mean IMU calibration page>Advanced, right? And the compass readings should be within 1500 value, correct? Sorry for being too cautious, I can't afford messing with this issue and see my bird flying away without even saying Goodbye...

The Editor · Mar 28, 2016

Dobmatt said:
That makes perfect sense, The Editor Sir! Thank you for your time and effort. By checking mods you mean IMU calibration page>Advanced, right? And the compass readings should be within 1500 value, correct? Sorry for being too cautious, I can't afford messing with this issue and see my bird flying away without even saying Goodbye...

Yup - absolutely correct.
The compass values will fluctuate but as long as they are in the 1500 ball park you are good to go.
While you are in that screen ALWAYS check all the mod values.
The Gyro (when the Inspire is at rest sitting on the ground) should be at 0.00
The Accelerometers when on the ground should be pretty much 1.00 but a range of 0.99-1.02 is acceptable.
Remember, if for any reason your aircraft seems to be flying erratically or exhibiting TBE (Toilet Bowl Effect) switch immediately to P-Atti and you will regain control of your aircraft.

Dobmatt · Mar 28, 2016

The Editor said:
Yup - absolutely correct.
The compass values will fluctuate but as long as they are in the 1500 ball park you are good to go.
While you are in that screen ALWAYS check all the mod values.
The Gyro (when the Inspire is at rest sitting on the ground) should be at 0.00
The Accelerometers when on the ground should be pretty much 1.00 but a range of 0.99-1.02 is acceptable.
Remember, if for any reason your aircraft seems to be flying erratically or exhibiting TBE (Toilet Bowl Effect) switch immediately to P-Atti and you will regain control of your aircraft.

... and the very last question (I promise) about this compass issue: I have a large metal garage on my property, sort of shed for my house boat. Do you think it may screw-up compass readings when taking off from - say - 15' away?

seanmclean · Mar 28, 2016

Dobmatt said:
That's the part of my amphibious drone mod, had nothing to do with the calibration table ...

This sounds far more interesting!

The Editor · Mar 28, 2016

Dobmatt said:
... and the very last question (I promise) about this compass issue: I have a large metal garage on my property, sort of shed for my house boat. Do you think it may screw-up compass readings when taking off from - say - 15' away?

Yup definitely
I would calibrate well away from it (middle of a park/field etc).
You may then find that if you place the Inspire down near the garage it throws out the compass mod values. Once you get airborne it will be fine but imagine if you calibrated near to the garage.....you would think everything was ok but once up in the air and clear of it the magnetic influence of the building the compass would actually be skewed and not calibrated correctly for that geographic location.

Dobmatt · Mar 28, 2016

seanmclean said:
This sounds far more interesting!

It's in development, must test it first and the waters around are still frozen ...

Dobmatt · Mar 28, 2016

The Editor said:
Yup definitely
I would calibrate well away from it (middle of a park/field etc).
You may then find that if you place the Inspire down near the garage it throws out the compass mod values. Once you get airborne it will be fine but imagine if you calibrated near to the garage.....you would think everything was ok but once up in the air and clear of it the magnetic influence of the building the compass would actually be skewed and not calibrated correctly for that geographic location.

Of course I'm not talking about calibration in proximity, this must be performed in the park nearby. I'm talking about taking off and landing near my metal shed. Is it too risky and better not to wake up devilish spirits in it, or not to worry having the bird calibrated somewhere else?