I was out practicing a shot i am trying to get over a bridge in San Diego today, when the little devil tried to get away from me. I was able to bring it back safely and land without incident, but im glad i wore my brown boxers. I should have known better than flying on Friday the 13th. Any help figuring out what happened will be much appreciated. C8 MK Board 2x 8000mah quadropower in parallel 360 Gimbal with cx760 Im attaching my gpx file and the video link to vimeo.
G'Day Darren, What were you doing when the bird tried to get away, I can see in your log file that your compass was out of whack, part way through the flight and you low battery alarm came on at the same time in the flight, and from the replay that looks like the same time you had the moment. The GPX file shows a fairly large change in the magnetic field between line 260 and 265 ... compass maybe? Some one with more brain cells and experience than me can probably get a lot more out of the data. Cheers Chris
Well, it definitely appears that you had a close encounter with a bird. At about :23 in, this appears at the top of the frame...or maybe it’s the aforementioned bridge ghost. Either way, it could have literally knocked you off course. Probably lucky for both of you that it didn’t get nicked by a prop. Or maybe it did...
Other than the magnetic disturbance I did not see anything too alarming to cause that. I noticed some wind variation in the video in some of the trees. You are kinda of flying in a bowl. Sometimes light winds where you are at can be amplified in certain spots. The bridge and surrounding trees causing causing some mechanical turbulence. All these obstacles including the bridge truss structure can cause eddy currents and as the air rotates around different structures. It the same concept as water flowing through a stream at slow rate but than gets disrupted by a boulder or a branch. Just like water masses that can opposite direction under current air behaves the same, where you see small whirlpools. The same principles apply to air masses. My guess is you got caught in some turbulent air that was moving faster than the surrendering air mass.
Glider pilots call it rotor, or curl-over. Other pilots probably use similar names. It can be quite severe depending on the amount of wind shear (the difference in speed between the upper and surface winds) or the terrain. Andy.
Hi Guys, Thank you very much for your replies. I went back about five flights and noticed that all gpx files had a Mag error in them. This leads me to believe that it could have been turbulence of some sort. The only nagging question is, would turbulence of that nature spin me around and knock my yaw out of wack before carrying the C8 on its journey? That is what you saw Steve. The black object you saw coming into frame at the top right corner was my FPV cam on boom 1. The whole thing happened so fast, but the first thing that happened was the copter yaw'd to the right and then it took off on me. On a side note, is there any possibility of a 5.8 ghz transmitter interfering with my gps unit if it is too close? Thanks guys,
I have never seen mine do a full 360. I have seen it do an un-commanded 45 degree yaw due to turbulence. There are not a lot of things we don't understand about the aerodynamics of these things. I propose it is possible from the fact that the autopilot commanded an aggressive power increase that it could have been in response to a shear. If the air was disrupted over the copter this could have caused a pressure differential that the copter sensing on one side. It powers up to keep the altitude steady, but if the airflow over the propellers is not efficient it could be that the system was not able to keep up with the demand. Typically these things have priority for stabilization. 1. Maintain altitude if altitude hold is on. 2. Maintain the commanded attitude. 3 maintain the heading. Sometimes they may sacrifice heading of the copter from un-commanded bank or roll. One hypothesis is that an abrupt change in wind occurred and effected one side of the copter. The copter compensates to keep level and increases power for altitude. Then the combination of a unstable heading indicator could have caused some confusion causing the rotation. As the copter is rotating the disrupted air is transferring to the other motors caused the situation to be exacerbated and continued the yaw. Once it finally found the original heading the long way around it stabilized and allowed you to fly back. The TV transmitter can cause disruptions in the compass as well other things. A couple ways to know for sure is to take it out to a field away from any EM interference including your cell phone and fly the copter for a bit say 30 seconds to minute with the 5.8 off. Land disconnect the main power and reconnect it to allow for a new GPX file. Then fly again with the TX on. Another way to know is take a handheld compass to the copter and see how much magnetic field is being created. If the TV transmitter is causing disruption then I recommend you calibrate the compass with the TX on. It will normalize the compass to the field that the TX is creating when it's on. Possibly move the TX to the rear of the AC. Either way it is good to calibrate the compass with as much dirty signals as possible to get the most normalized field. Of course keep in mind that the compass will have an error in the opposite direction if you fly with the TX off. It could be just the environment you were flying. Lots houses around there and other potential sources for a magnetic disruption. Another thing to look at is the motor performance under demand. See if a rapid accelerated climb within reason starts to cause some yawing this could mean a motor is not operating efficiently as well. Shaun
Absolutely second this, easiest way to see if you have one or motors tilted is to be hovering and go to full throttle, if all motors are level it will go straight up, if one or more are slightly angled you will be going straight up in circles.
You can also hover the copter about 2 meters away from you at eye-level and easily see if the prop "discs" are canted over. If you put the copter on PH and AH, you can yaw through a full 360 and take a good look at each prop disc with respect to the others. Andy.
Thank you Very much for your help. Ive tested and re tested everything today and all looks great. Nothing funky and no warnings. Flies like a charm. I guess i underestimated the power of turbulence. Cheers.