Aluminum

[J.James]

I just cant picture all that much of a need for any one to be needing to do much IMU calibrations in the field. Its not like and IMU calibration any thing that needs to be do to often as it is.

But as far as a metal table goes it should not effect the imu being that metal should not change or interfere with inertia sensors tho it can mess with your compass even if not magnetic metal. But only intill you take it off the table or fly it and get a few few away from it.

 

[BlackHawk388]

This has already been mentioned by one person, but I'm going to make it plain as day.

If you have an aluminum table, run a magnet all over it to ensure all hardware and plates are aluminum as well.

People here can go crazy making huge assumptions about IMU calibrations and taking off from a purely aluminum table, but if it has no ferrous metal in its framing or hardware, there is no way for aluminum to mess with the compass or anything else.

See aircraft electronics and how they're mounted. You HAVE to use aluminum hardware, retaining clips, so on a so forth.

 

[Monte55]

Well, no one has answered my question. Either they won't or just don't know. How would an aluminum table affect IMU calibration? Even a wooden table like a park bench has nails, screws, or bolts to hold it together. People are always willing to give information as though it is a fact but can't back it up. Nothing new really.

 

[J.James]

Even a wooden table like a park bench has nails, screws, or bolts to hold it together.

and how would nails screws or bolts effect the inertial measurement unit aka the IMU ????

 

[Monte55]

That's what I want to know. If a wooden table with ferrous screws or bolts won't, how would an aluminum table do it.
I'm just trying to learn here but can't seem to get the answers. Does this apply to all Phantoms or just the P3

 

[Louis_Eng]

I do my calibration on my slate pool table, and when the weather is bad i can have a game or two☺

 

[BlackHawk388]

Well, no one has answered my question. Either they won't or just don't know. How would an aluminum table affect IMU calibration? Even a wooden table like a park bench has nails, screws, or bolts to hold it together. People are always willing to give information as though it is a fact but can't back it up. Nothing new really.

I'm not going to go out and buy an aluminum table just to prove it. Here's what you can do though.

I use a wood table in the field. It's a simple little thing held together by, GASP! steel screws.

At home I have a very old, rectangular wood table that has zero metal hardware. Everything is made with various dovetail joints and glue. Don't know how it was made since I'm no carpenter, but it works and is very stable. Made moves with me through my Army years. I easily level it with a quarter under the two left side legs. I use it as my "master" IMU calibration area.

I recorded my IMU X, Y and Z numbers as well as the MOD number.

Took my small wood table and laptop to a field site to check for any electrical interference from nearby power lines. Leveled that table as well.

The figures for X, Y and Z, as well as MOD were within just a few digits of each other.

Did the DJI dance and it hovered just as expected from 5' up to 150'.

If you hover over certain areas of the IMU calibration page in the Assistant software, it will give you the accepted values for each reading. Mine are WELL within tolerance.

Now that I've written out some instructions for you, please go answer your own question about your table.

 

[Monte55]

I'm not going to go out and buy an aluminum table just to prove it. Here's what you can do though.

I use a wood table in the field. It's a simple little thing held together by, GASP! steel screws.

At home I have a very old, rectangular wood table that has zero metal hardware. Everything is made with various dovetail joints and glue. Don't know how it was made since I'm no carpenter, but it works and is very stable. Made moves with me through my Army years. I easily level it with a quarter under the two left side legs. I use it as my "master" IMU calibration area.

I recorded my IMU X, Y and Z numbers as well as the MOD number.

Took my small wood table and laptop to a field site to check for any electrical interference from nearby power lines. Leveled that table as well.

The figures for X, Y and Z, as well as MOD were within just a few digits of each other.

Did the DJI dance and it hovered just as expected from 5' up to 150'.

If you hover over certain areas of the IMU calibration page in the Assistant software, it will give you the accepted values for each reading. Mine are WELL within tolerance.

Now that I've written out some instructions for you, please go answer your own question about your table.

Well, that was a lot of typing not to answer my question.

 

[BlackHawk388]

Well, that was a lot of typing not to answer my question.

I've negated your question. In my first post, I stated that since aluminum isn't going to cause magnetic interference, there are no worries. Then, you came back again asking someone to answer your question to which I replied that a wood table held together by steel screws, ferrous material, doesn't affect my IMU calibration one bit. Also, the instructions I mention will help alleviate anyone's worry about the type of table they're using if they would just exhibit a little personal responsibility, initiative and effort.

Since the OP hasn't replied with the answer and more people are making WAG's about the subject rather than expressing the details of their own personal experiences, I made it clear how people can figure it out.

But hey, you go on with your bad self.

 

[Monte55]

What is a WAG? Not trying to argue with you but so many say so much crap here, I don't know what to believe. I only post what I know is fact by my own experience. Still don't have an answer to my question.

 

[Fplvert]

What is a WAG? Not trying to argue with you but so many say so much crap here, I don't know what to believe. I only post what I know is fact by my own experience. Still don't have an answer to my question.

Wild *** Guess.

But the real answer is the P3 has to be started to perform an IMU calibration. If there is a ferrous metal or magnetic field near the birds compass, that can cause erratic flight.

The OP was asking about using an aluminum table for IMU calibration in the field. I don't know how level or vibration free something like that could be, but as long as it had no steel or magnets, it wouldn't mess up the compass.

I remember a UK Member who put his P2 next to the subwoofer in his trunk. Next flight he crashed an uncontrollable Phantom. So I'd say this compass concern would apply to all the Phantoms, but the P3 especially seems prone to compass errors.

 

[johnv]

Wow i just wanted to know if it would have an affect? I was pretty sure that the table wouldn't make a difference but it cant hurt to ask. And the table is stable. Now I'm questioning my wood cabinet door? It only has 24 gauge pins for the glue up but... Oh well ill just put the thing in the grass.

Thanks for all the response.

jv

 

[BlackHawk388]

What is a WAG? Not trying to argue with you but so many say so much crap here, I don't know what to believe. I only post what I know is fact by my own experience. Still don't have an answer to my question.

As mentioned, WAG means Wild *** Guess.

I will never post ********. If I don't know, I'll either feel sorry for the person or, post nothing at all.

I do not tolerate ANY conjecture in aviation related things. Not much in car related things either. Come to think of it, not much in computer related topics. But those are my areas of experience, education and passion.

I spent over 8 years in Special Operations Aviation and learned, more than anything, to only speak and offer opinions on what I know and am able to offer good advice on.

I hold two degrees in Aviation Engineering and Technology as well as Maintenance. Seven years of education in total. I'm FAA certified with a full A&P license to work on anything from a Cessna up to the newest airliners and all manner of rotary wing aircraft in between. I've also obtained a degree in Computer Information Technology, an additional two years with my basic two year education having been completed already, with a bunch of time writing review articles for online publishers, being a moderator for Maximum PC magazine forums for 7 years as well as time in the field building systems from the home power gamer to home servers onto small business servers and dummy terminals. I should also mention building WAN's for the Army in Iraq as well as being responsible for a Battalion's worth of aviation computers in addition to the job of being the Blackhawk Quality Control NCOIC at the same time.

I also have an associates in English Writing although, both of my skills, being Math and English, took a hit when I had brain surgery in the right, front Parietal Lobe due to a blast injury.

Finally, I was ASE certified in GM vehicles for Cooling, Manual transmissions, drive line, engines, A/C and Electrical before I went into the Army and began my Aviation Career. If I don't know it from first hand experience or, cannot gain sufficient knowledge from researching proven methods and practices, I'll find out before I open my mouth and insert foot.

Now that the pleasantries are out of the way, know this. I will not give concrete advice about anything unless I'm 110% sure about it. Otherwise, I will typically add the caveat that I could be wrong or, that I might be having an "off" day.

Still, I am amazed at the amount of people who will not go out of their way to learn something on their own. Either too lazy or too blase, it doesn't matter.

I am always willing to admit when I'm wrong even though I detest it when I am. When I am wrong, it means I didn't do my due diligence in researching with my experience. I am too competitive in many ways, but Aviation simply isn't one of them. WAY too much at stake for that.

Having said ALL of that, I'm only human and as such, I'm a ******* at times.

 

[NHBIRDDOG]

I bought a nice folding Aluminum framed camping table with a melamine top (Wood Flour & Resin) from "****'s Sporting Goods" and I use it all the time for taking off and landing with no compass problems. Because it's for outdoor camping it has little or no ferrous metal in it. I wouldn't use it for IMU calibration but it seems to have no effect on my compass.

 

[acherman]

I gotta ask: what has any ferrous or other metal surface got to do with an IMU calibration? The thing measures inertia, gravity. He's not asking about calibrating his compass, so magnetism has no bearing. [emoji6] I do my IMU calibrations (2 so far) on my table saw - precision ground cast iron, with a 1/4" piece of plywood I shim for perfect level. Don't get much more ferrous than that. My P3P flies flawlessly, super stable, no tilted gimbal. Magnetism should not have anything to do with the IMU or gimbal. I would not hesitate to do an IMU calibration on any stable surface - wood steel, aluminum, fiberglass, concrete with rebar.

 

[TAZ]

I gotta ask: what has any ferrous or other metal surface got to do with an IMU calibration? The thing measures inertia, gravity. He's not asking about calibrating his compass, so magnetism has no bearing. [emoji6] I do my IMU calibrations (2 so far) on my table saw - precision ground cast iron, with a 1/4" piece of plywood I shim for perfect level. Don't get much more ferrous than that. My P3P flies flawlessly, super stable, no tilted gimbal. Magnetism should not have anything to do with the IMU or gimbal. I would not hesitate to do an IMU calibration on any stable surface - wood steel, aluminum, fiberglass, concrete with rebar.

The very simple answer is the definition of an IMU does not strictly limit it to the inclusion of only an Accelerometer and a Gyroscope. The IMU chip utilized on the Phantoms board includes a Magnetometer (compass) for error correction, so conditions that would normally negatively affect a compass, can negatively affect the included IMUs calibration calculations.

Less simply, an addition of a Magnetometer is the difference between what is referred to as a 6 DOF (Degrees of Freedom) IMU, and a 9 DOF IMU. Looking at the IMU calibration page, you can see we in fact have 9 variables being calibrated, Gyro XYZ, Accelerometer XYZ, and Compass XYZ, with associated mod values. That's the best indication that you don't want to tip, spin, jostle or magnetically interfere (in even minute ways) with a Phantom while it is calibrating its IMU.

And even less simply, all solid state accelerometers and gyroscopes have errors over time (due to temperature changes and something called Gyro Drift, for example). During IMU calibration (no change in gravity, no change in attitude, no change in acceleration, no change in direction), data from a fixed reference point of one fixed sensor is used to correct tolerance errors of another. The 3 systems (gyro, compass, and accelerometer) provide all the data needed to make an attitude and heading reference system (AHRS), with associated corrections as a function of time that is calculated during a calibration. And, at least during an IMU calibration, it's not as much about the compass pointing in the right or wrong direction, it is the importance of the compass pointing in a fixed direction, so the gyroscope readings can be measured and correctional tables be populated to compensate for errors like gyro drift. Due to inescapable but measurable errors over time like gyro drift, the raw attitude data will always indicate the gyro is yawing over time, even while it is not. Providing the consistency of a stable compass reading during calibration over the same time interval can then calculate the corrections needed during actual flight introduced by these errors.

So back to simple again, just as you COULD put your Phantom on an unstable table during an IMUs calibration of its accelerometer, it wouldn't be a problem as long as you didn't bump, tip, or cause vibrations of it....you COULD place it in upon a ferrous material, as long as the ambient EMI isn't messing with the compass reference readings used to correct for errors like gyro drift. However, just as an unstable table is more likely to introduce vibrational variations, a ferrous material is more likely to amplify magnetic variations, thus creating erroneous corrections in the AHRS tables. Varying EMI is very difficult to observe, predict, or control, and is environmentally influenced, so of course you don't wish to introduce conditions (ie, no magnetic field altering or amplifying ferrous materials during IMU calibration) that might exacerbate this.

The importance of the IMU compass (providing a fixed reference point for IMU system error correction) during IMU calibration, should not be confused with a Compass Calibration, in which one is additionally calibrating the compass for geographically located variations of compass heading corrections.

 

[acherman]

So is the compass pet actually built in to the IMU? And if so, then why is an external compass (in the leg) required? And why have a separate compass calibration procedure? I feel like when doing an IMU calibration it is only working on the gyro and accelerometer values, and not compass. Again, I have performed 2 calibrations if the IMU, both times sitting on a table saw with a large heavy steel top. I have had zero issues with stable and level flight in over 60 flights. But, that is just my experience, others may be different.

 

[N017RW]

You are correct about the P3 compass actually being physically separated from the IMU and the related calibration observations..

 

[SteveMann]

So is the compass pet actually built in to the IMU? And if so, then why is an external compass (in the leg) required? And why have a separate compass calibration procedure? I feel like when doing an IMU calibration it is only working on the gyro and accelerometer values, and not compass. Again, I have performed 2 calibrations if the IMU, both times sitting on a table saw with a large heavy steel top. I have had zero issues with stable and level flight in over 60 flights. But, that is just my experience, others may be different.

I'm with you on this. I've never seen anything that says there is a magnetic compass in the IMU.
to the OP: The IMU as stated above only measures inertia. How far and how fast the Phantom moves. You can do an IMU calibration from a steel battleship or the wood floor of your house. All that matters is that the surface is perfectly level.

 

[taroh]

Don't do compass calibration at magnetic place.
Compass calibration is not IMU calibration.
Aluminum is never magnetic.
+)____________
???

What the important is, DO IMU calibration at flat place. It's ok in house (inside house is not suggested by DJI to calibrate compass)... more flat place than outdoors, and fridge (what guys favor) is nearby.
Technically compass maybe included in the part of IMU, but I guess DJI separated "compass calibration" because it's hard to find a place inside house without magnetic, or perfectly flat place outdoors.