Phantom 3 out of control at 81 mph and no wind!
- Thread starter Adam Herron
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I steel think the battery could be bad. But there are other facts, such as the battery did recover. So I would try a test flight in a safe place.
alokbhargava
Premium Pilot
Battery seems to be ok as its capable of delivering huge current pulses. Question is why do we see current pulses: either motor tends to stop or main controller / ESC problem
Meta4
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If you are wanting to find out the cause of your incident the flight data stored in the app is very helpful.
Go to https://www.phantomhelp.com/LogViewer/Upload/
Follow the instructions to upload your flight record.
Come back and post a link to the report it provides and someone here might be able to analyse it and give you an understanding of the cause of the incident.
The first crash I had with P3P, it was banged up but not as bad as that. My camera was OK, so I put a battery in and I could not get it to bind with the transmitter. When I opened it up There was a plug torn out of the main board. The board is ruined. No good. I think you may find the same thing.
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Again?
Did you fly over that same building that caused your last fly away? It'd be good if you could get your .DAT from the carcass.The compass error is addressed below. I don't know that much about motors and the amount of current they draw. But, is it possible the current seen in this flight is "normal"? There are 3 current spikes to values roughly around 50 amps. But these are each associated with motors being commanded to the max value. This plot shows the first spike (blue line). The other two are similar.
The compass error precedes this motor/current behavior.
The blue line goes from 0 (normal) to non 0 (compass error) at about 24.5. The current (orange line) starts rising more than a second later and spikes 5 seconds later.
The "compass error" is actually a disagreement between observed and expected values. I don't know the root cause of that disagreement in this flight but you can see it happening here.
Yaw (blue line) is a calculation based on IMU measurements, mostly the gyros, but then corrected by the accelerometer data and to lesser degree the magnetometer data. It's the value you see in the GO app and when the .txt or .DAT is converted to a .csv. magYaw is calculated directly from just the magnetometer data. They were in agreement until about 20 seconds but then start to diverge. At about 24 they were enough different that a compass error is declared. There was a similar behavior with the velocity based on GPS data vs velocity based on, I think, IMU data.
@Adam Herron do you have a video from this flight that could be used to help determine which of Yaw and magYaw is correct?
The compass error precedes this motor/current behavior.
The blue line goes from 0 (normal) to non 0 (compass error) at about 24.5. The current (orange line) starts rising more than a second later and spikes 5 seconds later.
The "compass error" is actually a disagreement between observed and expected values. I don't know the root cause of that disagreement in this flight but you can see it happening here.
Yaw (blue line) is a calculation based on IMU measurements, mostly the gyros, but then corrected by the accelerometer data and to lesser degree the magnetometer data. It's the value you see in the GO app and when the .txt or .DAT is converted to a .csv. magYaw is calculated directly from just the magnetometer data. They were in agreement until about 20 seconds but then start to diverge. At about 24 they were enough different that a compass error is declared. There was a similar behavior with the velocity based on GPS data vs velocity based on, I think, IMU data.
@Adam Herron do you have a video from this flight that could be used to help determine which of Yaw and magYaw is correct?
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No i didnt record the flight, after about a few seconds I knew something was wrong and was only worried about getting it back. I do remember seeing that thing lean like crazy. Maybe that is where my speed came from.
Tonight I took it back out in a field and there were no problems at all.
Tonight I took it back out in a field and there were no problems at all.
A few things; first of all, I suspect the magyaw going negative is the same converter bug that caused negative amps. If you where to make those values positive, then the charts looks much more reasonable.
Secondly, on the first chart, amps do not correlate with commanded motor speed. The amp peak occurs 4-6 seconds after the motorspeed peak and when motors are already back to normal speeds.
This is not correct. The tell tale sign of weak battery is that the voltage will sag much more than with a healthy battery when drawing a certain current. And since in a multirotor the flightcontroller (through the esc's and motors) actually commands power (watts) from the battery to achieve its desired motion, this creates a little feedback loop: the lower voltage requires an even higher current to get the power required by the flightcontroller/esc, so current goes up further, causing a weak battery's voltage to sag further. Its this feedback loop that I suspected could cause the compass to throw errors, as high currents can easily distort the magnetic field.
I'll look in to the logs further tomorrow to see what I can find.
Secondly, on the first chart, amps do not correlate with commanded motor speed. The amp peak occurs 4-6 seconds after the motorspeed peak and when motors are already back to normal speeds.
This is not correct. The tell tale sign of weak battery is that the voltage will sag much more than with a healthy battery when drawing a certain current. And since in a multirotor the flightcontroller (through the esc's and motors) actually commands power (watts) from the battery to achieve its desired motion, this creates a little feedback loop: the lower voltage requires an even higher current to get the power required by the flightcontroller/esc, so current goes up further, causing a weak battery's voltage to sag further. Its this feedback loop that I suspected could cause the compass to throw errors, as high currents can easily distort the magnetic field.
I'll look in to the logs further tomorrow to see what I can find.
The reason that I had asked for the video is to determine which of the Yaw or magYaw is correct. But, heading can also be determined by using the thrust angle derived from motor speeds and the direction of travel derived from successive GPS locations.
Looking at the interval between 30 and 35 seconds. The thrust angle is close to 0; i.e. the P3 is flying forward along it's X axis. The direction of travel is about 110 degrees.
In that same interval magYaw is about 110 degrees. But ,Yaw is -68 degrees.
Clearly, the IMU's calculation of Yaw is in error and the heading derived just from the magnetometer data is correct.
I'm still thinking about what would cause this. The FLY195.DAT file you submitted shows a gyro drift rate of .438 degrees/sec. (Am I correct in assuming that in that "flight" the P3 didn't move after about 38 seconds) That's pretty high. Mine is around .03 degrees/sec after doing an IMU calibration
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When you used the second battery, did you restart every thing in the proper order.
If I do not start in the order of RC - AC - APP there is sometimes no data present in the sensor screen.
I always check the sensor screen before takeoff. But one time I forgot and I got the yaw,compass and speed errors.
I was lucky to get it back. Haven't made that mistake since.
So when I switch batterys, I shut down in reverse order and restart everything in order again. Might be overkill but it doesn't take long.
What bugs me about your log is the battery readings.
There have been some cases on this forum where members did not have the battery latched in properly.
Most were fatal. But some did get them back. Maybe a possibility?
You cant say that. You assume its flying along its X axis, nose forward. It could just as well be travelling sideways or backwards for that matter. The magnetometer will measure the angle between the 'front' of the quad and magnetic north. To compare that to the GPS ground track, you would have to factor in the quads tilt and pitch to determine if its flying nose in, sideways or whatever.
I know i didnt shut the app down when I put in the second battery but Im sure that I had the GPS ready when I took off the second time. I checked the battery when it got back and it was secure.
Actually, I can say that.
The thrust angle is computed from motor speed data making it relative to the AC. A thrust angle of 0 means that the back two motors have the same speed and is greater than the front two motors that have the same speed. That would cause the AC to pitch down with no roll and move forward along it's X axis. Direction of travel is computed from successive GPS locations. Taken together these two values can be used to determine the AC heading, aka yaw.
magYaw is a vector computed from the magnetometer data. Since that vector is in the AC's frame that vector is rotated into the XY plane of the inertial frame depending on the roll and pitch of the AC. I.e., the resulting value of magYaw is independent of the AC's roll and pitch.
I know all of the above because I wrote the code to do these calculations. These fields are documented here.
Of course any crosswind will affect the thrust angle/direction of travel calculation. But, all I'm doing here is determining which of Yaw and magYaw is correct.
You had a question about the current measurement delay relative to motor commanded data. I also questioned this but noted the same occurs with the 2 burst motorStart sequence. There is probably more to the story than I need to know at the moment but that story would start with noting that motor data is at 200 Hz while battery data is at 1 Hz.
A difference in motor speed causes a constant rotation around any of the 3 axis, it does not result in a constant (pitch) attitude. Equal motor speed theoretically results in a constant attitude (roll/pitch/yaw) at a constant speed and heading. Flying forward at 50 degree pitch attitude backwards or sideways at full speed, all 4 motors will run at the ~ same speed. Only a change in attitude requires a temporary difference in motor speed.
If I understand what you're saying, you conclude an attitude based on relative motor speed. You cant do that. There is no correlation between them. Thats like concluding the direction a car drives by looking at the steering wheel. All you can say is that the heading will remain constant when the wheel is centered, and will change when its not. But its not heading north east just because the wheel is slightly to the right.
Similarly, if you fly a quadcopter in acro mode (which the phantom doesnt have, but bare with me), stick neutral results in equal speed for all motors - Im simplifying and ignoring external factors. The quad will happily continue flying forward, backwards, sideways or upside down with all 4 motors running at the same speed. A "thrust angle" as you call it would correspond to a stick input in acro mode in any direction, which will cause a difference in speed between front/back or left/right which results in a constant roll or pitch rotation for as long as there is a difference in speed; until its upside down and back again and upside down again. Well, or hits the ground
But you can not tell attitude/orientation from motor speed, or vice versa, without accelerometer data, the quad can not maintain and has no idea of its own attitude relative to the world. It can only detect and cause changes relative to where it was before.Or Im misunderstanding what you're saying.
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