Having no idea what the power transmission is in the area, such as number of phases and frequency, compass frequency (if not analog), and sampling frequency of the data, it's hard to tell anything from the frequency of the "harmonic". Having said that, why would the vehicle drift as opposed to yaw in the presence of a disturbance?
First flight fly away....P3A crash...
- Thread starter TmoneyF
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No idea....if you follow my whole train I have not definitively concluded anything, below is a kind of summary...
1. Compass calibration seemed pretty normal
2. 18+ satellites and solid GPS signal, since the track of the aircraft is known the Phantom had GPS the whole time.
3. Phantom drifted with no input from RC, up to 7 MPH with no input from RC....that is pretty fast....
4. The compass data shows a harmonic that increases as it approaches the powerlines, this is the only anomaly I can find.
5. The drift was not in the direction of the wind, which rules out ATTI mode...
So to me the question is why didn't the Phantom compensate for or cause the drift. It needs compass and GPS to hold position and since GPS is known good that leaves either compass or a problem with the flight controller. I would hope a compass error would cause an alert, but maybe the Phantom was just confused. I am still looking, but so far the only thing I found is the compass anomaly although it doesn't seem large enough to me to cause the drift away....but I got nothing else...maybe @Luap will find more....
@TmoneyF,
It sounds like you are exchanging it so don't mess that up, but would be interesting to see if it flies ok somewhere else. When you get your replacement I personally would not fly at the same spot....but I am also curious if it would happen again. I might try moving mine near some powerlines to see what happens to the compass - not while flying just holding it and approaching them...not sure when I would have time for that though....
And then there is a video like the one below which makes me think it was not related to power-lines....maybe something else was messing with the compass....I have not seen a compass signal with that period fluctuation before....
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I have just joined this forum and I find it fascinating and full of great info for a rookie like myself with regard to my new P3A. I have been caught up in this unfortunate accident that happened with Timothy and his P3A. I am also very impressed with the flight and activity of same analysis carried out by "TheRealNick" - great work. Since I am in the vibration analysis business I would like to add some thought to this thread and especially after reading all the postings and analysis information along with viewing the video of the incident.
Timothy, you mentioned the wind was parallel to the power lines and the highway - the fact you remember this indicates it was of a fair presence as to velocity of same. Your flight path (intentional or not) was then perpendicular to the wind direction and the "drift" mentioned by Nick was also in that direction. After watching your video a few times and seeing the erratic behaviour of your P3 it brought to mind the serious presence of a possible "low level wind shear" and another anomaly called a "sinkhole" - both of which are destabilizing wind effects that can create exactly the type of behaviour you experienced with your P3.
When defining the effect of wind shear and a sinkhole (effect from wind shear and objects obstructing wind travel) they create sudden changes of direction and a very fast loss of altitude with any flying vehicle regardless of size or speed and especially in something this weight, configuration and size. This may help with your analysis Nick when considering the unexplained drift and the direction being opposite to the wind direction while under the influence of wind shear. I have seen the results of wind shear when it has acted upon stationary objects as a "forcing frequency" that is equal to or close to the natural frequency of the object effected - combining the "forcing frequency" with the "natural frequency" of any object - especially a light flying object such as the P3 creates "resonant activity" that does crazy things with respect to vibration and velocity of same which in turn would make handling the P3 under those conditions near to impossible.
When experiencing such activity (especially a very fast loss of altitude) from wind shear and/or sinkholes the best approach would be to power up the motors as quickly as possible to resist the downward pressure that reduces altitude extremely fast and can help you remove your craft away from the kind of behaviour you experienced during this anomaly (if in fact it was present) to avoid catastrophic results. I know Timothy, much easier said than done.
One final note here with respect to low level wind shear activity and in particular the sinkhole effect - this is created for the most part by interference of low and ground wind travel that is obstructed by objects such as buildings, trees, hedge rows, power lines and even parked vehicles (low level wind shear). All the posts I have read and videos I have watched as to safe flying of these units all mention going to clear unobstructed areas - for me it was a given as I am well aware of anomalies such as described here not to mention I am most definitely a rookie when it comes these units. Unlike and unfortunately for yourself Timothy, I did have a non-event first and 2nd flight and I loved it.
I noticed it was snowy where you were flying Timothy and not sure what air temps were at the time - however when flying in very cold temps it wouldn't take long for a prop to freeze up and possibly crack as a result of slight vibration or contact - any crack in one or more props would also create serious erratic behaviour (not unlike that of low level wind shear) as a result of an unbalance at the rotating elements. Of course you were not flying for very long so it is doubtful this had any effect on the behaviour of the P3 - unless it was outside longer than just the take-off and flight time. Just thought I would add this FYI with respect to the negative effect vibration can have on these units. I am planning on doing some "shaker testing" on my unit to identify the natural frequencies present - then some slow motion stroboscopic studies on the props in flight to identify if any forcing frequencies from the rpm of them can effect the unit as a whole. No doubt this has all been part of the R&D long ago - but being in the vibration business makes one curious.
The DJI Inspire 1 is calling my name - but not until I am well versed in the flight of this P3A I have now - I know I am going to love this hobby. It is of great comfort knowing there are people around like you all on this forum who are offering their expertise with regard to safe flying along with tips etc. As stated, your in-depth analysis of the flight path etc. Nick is most impressive. I have been making notes and copying info as related to compass calibration (great layout on that from I think it was Ian (taco guy) another impressive posting there. Thank you to all and I hope I have contributed a little towards this thread and the subject of same.
Sorry guys - a bit of a novel here- won't happen again!
Timothy, you mentioned the wind was parallel to the power lines and the highway - the fact you remember this indicates it was of a fair presence as to velocity of same. Your flight path (intentional or not) was then perpendicular to the wind direction and the "drift" mentioned by Nick was also in that direction. After watching your video a few times and seeing the erratic behaviour of your P3 it brought to mind the serious presence of a possible "low level wind shear" and another anomaly called a "sinkhole" - both of which are destabilizing wind effects that can create exactly the type of behaviour you experienced with your P3.
When defining the effect of wind shear and a sinkhole (effect from wind shear and objects obstructing wind travel) they create sudden changes of direction and a very fast loss of altitude with any flying vehicle regardless of size or speed and especially in something this weight, configuration and size. This may help with your analysis Nick when considering the unexplained drift and the direction being opposite to the wind direction while under the influence of wind shear. I have seen the results of wind shear when it has acted upon stationary objects as a "forcing frequency" that is equal to or close to the natural frequency of the object effected - combining the "forcing frequency" with the "natural frequency" of any object - especially a light flying object such as the P3 creates "resonant activity" that does crazy things with respect to vibration and velocity of same which in turn would make handling the P3 under those conditions near to impossible.
When experiencing such activity (especially a very fast loss of altitude) from wind shear and/or sinkholes the best approach would be to power up the motors as quickly as possible to resist the downward pressure that reduces altitude extremely fast and can help you remove your craft away from the kind of behaviour you experienced during this anomaly (if in fact it was present) to avoid catastrophic results. I know Timothy, much easier said than done.
One final note here with respect to low level wind shear activity and in particular the sinkhole effect - this is created for the most part by interference of low and ground wind travel that is obstructed by objects such as buildings, trees, hedge rows, power lines and even parked vehicles (low level wind shear). All the posts I have read and videos I have watched as to safe flying of these units all mention going to clear unobstructed areas - for me it was a given as I am well aware of anomalies such as described here not to mention I am most definitely a rookie when it comes these units. Unlike and unfortunately for yourself Timothy, I did have a non-event first and 2nd flight and I loved it.
I noticed it was snowy where you were flying Timothy and not sure what air temps were at the time - however when flying in very cold temps it wouldn't take long for a prop to freeze up and possibly crack as a result of slight vibration or contact - any crack in one or more props would also create serious erratic behaviour (not unlike that of low level wind shear) as a result of an unbalance at the rotating elements. Of course you were not flying for very long so it is doubtful this had any effect on the behaviour of the P3 - unless it was outside longer than just the take-off and flight time. Just thought I would add this FYI with respect to the negative effect vibration can have on these units. I am planning on doing some "shaker testing" on my unit to identify the natural frequencies present - then some slow motion stroboscopic studies on the props in flight to identify if any forcing frequencies from the rpm of them can effect the unit as a whole. No doubt this has all been part of the R&D long ago - but being in the vibration business makes one curious.
The DJI Inspire 1 is calling my name - but not until I am well versed in the flight of this P3A I have now - I know I am going to love this hobby. It is of great comfort knowing there are people around like you all on this forum who are offering their expertise with regard to safe flying along with tips etc. As stated, your in-depth analysis of the flight path etc. Nick is most impressive. I have been making notes and copying info as related to compass calibration (great layout on that from I think it was Ian (taco guy) another impressive posting there. Thank you to all and I hope I have contributed a little towards this thread and the subject of same.
Sorry guys - a bit of a novel here- won't happen again!
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TheRealNick, I just noticed your post on the near miss of power lines and your comments related to same. I do think and agree with you as you mentioned in a previous post the power lines and interference with the compass is a real possibility. The magnetic field surrounding those and the 60hz line frequency which has also been measured at 120hz (2xfl) from my perspective has to have a negative effect on any electronics near by. Unless the Phantom products have some kind of magnetic shield preventing this - there is no way it can't effect it.
I meant to ask in the previous post I put up if data produced via flight includes or has access or information from accelerometers on board as to the amount of vibration that was present during the flight. If that unit was caught up an effect from "low level wind shear", the vibration present at it would likely be very excessive if any resonance was present. You are far more versed than I as to the internals of these units so I can't just make an assumption as to vibration having a negative effect on the compass - what say you as to that possibility?
I meant to ask in the previous post I put up if data produced via flight includes or has access or information from accelerometers on board as to the amount of vibration that was present during the flight. If that unit was caught up an effect from "low level wind shear", the vibration present at it would likely be very excessive if any resonance was present. You are far more versed than I as to the internals of these units so I can't just make an assumption as to vibration having a negative effect on the compass - what say you as to that possibility?
There is tons of data available, the phantom has 3 axis accelerometers, 3 axis gyros, GPS, compass, calculated velocity, motor commanded, motor actual, motor load, all four controls, flight mode, status list, and many others. If you follow the earlier link to @BudWalker datconverting tool. You can get all the data from .dat files too. @BudWalker has made all this analysis possible!! Thanks!!!
I don't think it was a vibration as I do not recall any patterns in the accelerometers, but I may look again. I think the compass is a sensor with no moving parts, but not sure there as well. There was no unexplained drop in altitude. The flight seemed to go this way:
He was hovering and rotating and then after ending rotation all of a sudden without control stick input the Phantom moved to the right across the street accelerating. About 3 secs after that he applied full down and full back to try to recover , this caused the start of a normal decent and back. While trying to recover the sticks triggered CSC which turned the motors off. The question to me is why did that drift start?
@TheRealNick, really cool analysis of this event and thank you for helping calm my nerves that I didn't initiate that drift. The replacement should be here tomorrow. I will for sure not fly here again just in case. I will do a pre flight just as I did before but will walk the copter over near the power lines. Will load that .dat in a few days
If you're gonna use the P3 gather more data could you please do this. Get as close as you can. From what's been posted it seems that you can't get close enough to duplicate the conditions where the compass event occurred. Since the signal was not evident at this distance we'll need to gather more data and attempt to "pull the signal out of the noise" with some signal processing techniques
Use a cardboard box, or something else to elevate the P3, and leave it for one minute without touching or moving it. Then repeat this in several different orientations. The reason for not touching or moving is that the interference may be caused by an electric field and could be evident in the gyros and accelerometers as well as the compass.
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I had no idea these units had that much on-board and were able to store all that retrievable data as per operation and flight - thank you for further insight. With the unexplained (thus far) movement (drift) and acceleration across the street I am in agreement as to compass issues. However not a compass issue with regard to a fail or a software issue but possibly a sudden destabilizing wind travel creating Aerodynamic instability and increased vibration that would have an affect on the compass stability and operation.
The vibration could have come as a result of the "low level wind shear" I mentioned in a previous post?? This effect or "sinkhole" effect would create a very short burst of increased vibration that may have an effect on compass, hence uncontrolled drifting - perhaps the data will support this, however I would think we are talking split seconds or milliseconds as to time and identifying it on low resolution plots might prove to be be difficult.
One last bit of food for thought on this relates to another anomaly called "vortex shedding", whenever wind bursts exceed the minimum wind speed and is forced around any objects (trees, houses, buildings even hedge rows), vortices are formed on the back side of that object - the Phantom may have passed through this and experienced Aerodynamic instability allowing the Phantom to drift - even if only for a short yet quick distance - regardless of the presence of vibration or not. If this scenario existed the effect would over-power the Phantom mechanically and cause it to change direction. I believe after reading about so many "unexplained" fly-aways others have experienced the elements of Mother Nature plays a fairly large part.
Nick - your 'RCFA" (root cause failure analysis) is to be commended - you are doing a great job - I'm only adding a couple of thoughts in the hope of helping you with the unexplained drift.
p.s. Tim - great news on the replacement Phantom and all the very best of luck with your future flights.
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Wow Bud, your data converting tool etc. is amazing as to producing the analysis material - fantastic. I agree with the possibility of the electro-magnetic interference and your tests may just prove that. Just a thought - perhaps during the testing outside he could do what you have suggested then perhaps cover the Phantom with a box to somewhat insulate/isolate it and note the difference in your analysis. Looking forward to the findings and results of same. I am learning so much from this forum - Thank you.
ianwood
Taco Wrangler
Had to skim a couple of the posts so forgive if it's already been stated:
- Power lines: if calibration was done near them, that would be bad. Flying near them on a good calibration shouldn't be an issue unless they are very high voltage regional lines.
- RF from trucks? No.
- The oscillation in the compass at take off is not good. Not sure what that would be.
- Looking at 3 axis data from calibration can tell you the right motion was done but can't tell you what was in the vicinity of it at the time.
After pondering and pondering, I think I am going with the flight controller malfunctioned as my opinion. Even though the compass had some weirdness, the yaw of the craft was correct. All the information the flight controller had was accurate, it just didn't do anything with it. It uses the compass to determine yaw and heading, and by Luap's video and data the yaw and heading were correct during the drift....I am curious what the yaw looks like in a compass error .dat file....
I've recorded how calibration was logged for this thread's flight, bottom video, and another user calibrating his P3, top video.
If you watch the 3 Phantoms in the top video calibration looks like how it should be done. But the bottom looks very odd?
If you watch the 3 Phantoms in the top video calibration looks like how it should be done. But the bottom looks very odd?
I think you only have step 2 of the compass calibration in the bottom. I also noticed that the opposite x/y value went high between the two....so then I noticed the top one looks like the Phantom is face up for the second part, I thought it was supposed to be face down. The top one looks well done...except the top/down thing but I could be wrong....
Below are the ticks I used for my plots...
Step 1 112171 - 119971 -matches below leds perfect
Step 2 119972 - 127057 - not sure of exact end....but looked for y mod to return to normal...
and below is the log:
106579 : 8575 compass calibration init!
106627 : 8579 [LED] changed: normal led
112171 : 9041 [LED] changed: mag calibration: step0
119971 : 9691 [LED] changed: mag calibration: step1
137839 : 11180 a:0.962877 b:1.138082 c:-109.035965
137839 : 11180 d:-172.226746 e:-1.057873 f:-229646.765625
137839 : 11180 t1:240320.625000
137840 : 11180 sx:3.059819 sy:3.002488 sz:3.264243 bx:-166.815155 by:-268.522583 bz:-1.517
137840 : 11180 2 steps compass calibration : 1
@TmoneyF if you do as @eaglegoaltender suggested could you keep a log that will show when the P3 was covered. Please do all the uncovered measurements first and then all the covered measurements second. It'll be clear from the .DAT when the P3 is moved to a different orientation but it may not be clear when it gets covered. Thank you.
ianwood
Taco Wrangler
X and Y should be orthogonal, so between the two calibrations I think one of them had the Phantom face down/up and the other had it with the rightside/leftside down....I need to check when I get home...I think x is forward and y is to the right....or it is swapped in the data between Luap and I....I used Bud's latest datconverter. When I checked the charts I only made sure that the values started and ended at the same point going through the same range and that on step 2 x or y went to a value close what z was during step 1....
Watching Luap's video it seems to look like @TmoneyF had it right side down....I am not sure what this would do.
@TmoneyF,
Does that match your recollection for part 2 of the compass calibration?
Watching Luap's video it seems to look like @TmoneyF had it right side down....I am not sure what this would do.
@TmoneyF,
Does that match your recollection for part 2 of the compass calibration?
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I've found powerlines cause major interference in the past. It caused one of my first major crashes so i stay weeell away from them
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Gents - To satisfy my own curiosity, I started to play around with identifying natural frequencies and the force frequencies associated with the Phantom 3A. As I was doing some spectral live time viewing I noticed a significant increase in the "noise floor" of my spectrum whenever the accelerometer I was using was anywhere near the Phantom Radio Controller and in particular nearest the USB cable and connectors. The noise floor had a kind of roll to it, like a pulse and was intermittent - but none the less present.
This got me thinking of this thread again with respect to any EM interference or transmitted signal degradation from the controller to the Phantom either during calibration or in flight. The noise generated is a "broadband" noise and I am wondering if this activity falls within the operating frequency range (2.4 GHz) of the controller and as such can't be filtered out.
Question: Wouldn't this degrade the SNR (signal to noise ratio) the Phantom sees and have an effect on sensitivity?
I did a little research on USB 3.0 cables and connectors and found they do emit 2.4 GHz interference but only to the ISM band (I'm not sure exactly what that means (ISM) - any help on that will be appreciated). Speaking from what I saw on my spectrums the noise floor was very broad/wide band and that in my opinion, might have a negative effect on a lot of other devices to include radio transmitters, GPS etc. Considering the Phantom (receiver) - the further away it gets from the controller, it stands to reason the weaker the signal.
Question: Is it possible the signal is further compromised with EMI from the USB 3.0 link between the controller and device?
Question: During calibration, could the USB 3.0 EMI interfere and/or compromise with that process as relative to the compass?
I tried shielding the accelerometer with EMI shields I use in the field when needed and the noise floor activity was reduced on the plot - I shielded the USB cable and both ends and again the noise floor was reduced. I'm not saying this is in anyway positive proof of any EMI I was picking up since the noise floor when first noticed was intermittent and it could have been I wasn't seeing it when shielded due to that. I didn't have another USB cable that would fit to test that out - will grab one tomorrow and try it out.
Question: are the USB ports in the controller 3.0? And if so, does that revert to 2.0 with the appropriate 2.0 cable?
I may be "grasping at straws" here with my comments - especially being new to this forum and Quads but how else can one learn if not for asking questions or commenting. I am intrigued with this thread and the subject of 'fly-aways" in general from other sites that I have visited as to the "how's" and "why's this happens.
Simply replacing a Phantom for example, that was damaged in a crash is not the final answer as to the cause of the crash and the beauty of this forum is how people care, spend the time and endeavour to find the answers!
This got me thinking of this thread again with respect to any EM interference or transmitted signal degradation from the controller to the Phantom either during calibration or in flight. The noise generated is a "broadband" noise and I am wondering if this activity falls within the operating frequency range (2.4 GHz) of the controller and as such can't be filtered out.
Question: Wouldn't this degrade the SNR (signal to noise ratio) the Phantom sees and have an effect on sensitivity?
I did a little research on USB 3.0 cables and connectors and found they do emit 2.4 GHz interference but only to the ISM band (I'm not sure exactly what that means (ISM) - any help on that will be appreciated). Speaking from what I saw on my spectrums the noise floor was very broad/wide band and that in my opinion, might have a negative effect on a lot of other devices to include radio transmitters, GPS etc. Considering the Phantom (receiver) - the further away it gets from the controller, it stands to reason the weaker the signal.
Question: Is it possible the signal is further compromised with EMI from the USB 3.0 link between the controller and device?
Question: During calibration, could the USB 3.0 EMI interfere and/or compromise with that process as relative to the compass?
I tried shielding the accelerometer with EMI shields I use in the field when needed and the noise floor activity was reduced on the plot - I shielded the USB cable and both ends and again the noise floor was reduced. I'm not saying this is in anyway positive proof of any EMI I was picking up since the noise floor when first noticed was intermittent and it could have been I wasn't seeing it when shielded due to that. I didn't have another USB cable that would fit to test that out - will grab one tomorrow and try it out.
Question: are the USB ports in the controller 3.0? And if so, does that revert to 2.0 with the appropriate 2.0 cable?
I may be "grasping at straws" here with my comments - especially being new to this forum and Quads but how else can one learn if not for asking questions or commenting. I am intrigued with this thread and the subject of 'fly-aways" in general from other sites that I have visited as to the "how's" and "why's this happens.
Simply replacing a Phantom for example, that was damaged in a crash is not the final answer as to the cause of the crash and the beauty of this forum is how people care, spend the time and endeavour to find the answers!
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Ugh so sad to hear these stories. Its sort of like when you buy a product, rave about it, highly recommend it, and somebody takes your advice and buys one... only to get a dud and be disappointed, and you feel like the bozo. Very sad. Well I'm sure DJI will make it right and your next one will be great.
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