Drone goes up, doesn't come down.

HiFlew my hex x a few days ago and it flew great. Over 50 mph and very stable. Pixhawk came out of an Iris+. DJI e310 kit.The following day I was getting compass errors. Calibrated it several times and it was okay. Took off and it was very shakey. Then it just went up and would not come down. The battery was low so it only got to 300 feet all before it came down.I reconfigured it as a quad because two motors burned out.I put on a new pixhawk mini and had issues with the motors not spinning right on px4 firmware. Motor spun according to the pitch of the uav. Put on ardu 3.4 latest stable and motors were working good.Flew around for a while at 40 feet. Quad was very shakes again.Suddenly it started going up. This time it had more battery remaining. Went into land mode. Still going up. Rtl still going up. Althold same thing.Looking at the thr in it was at minimum. Thr out was at max.Battery gave out around 12000 ft.Any ideas what could be causing this or what to check for?Regards

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  • Thanks




    Gary McCray said:

    Hi David,

    I like 4 in 1 ESCs too, but you do need to ensure that sufficient air gets past them to prevent their overheating, in particular on the metal plate (heat sink) side. It is probably better to install them on at least 1/4" standoffs, rather than stuck flat against the frame.

    That said, I doubt they like -40 either and their internal components are almost certainly not actually rated for it.

    In electronics we tend to worry most about over heating, but in reality, most electronic components are not even rated for zero degrees and many will have problems as sub zero temperatures drop lower.

    As  more and more multicopters are flown in colder environments, no doubt this will be addressed more fully, but for now it is a minefield you have to sort out largely on your own.

    I might add, most of the plastics and resins used in the frames become extremely brittle and break much more easily at those temperatures as well, including CF and G10.

    Best,

    Gary

  • Hi David,

    I like 4 in 1 ESCs too, but you do need to ensure that sufficient air gets past them to prevent their overheating, in particular on the metal plate (heat sink) side. It is probably better to install them on at least 1/4" standoffs, rather than stuck flat against the frame.

    That said, I doubt they like -40 either and their internal components are almost certainly not actually rated for it.

    In electronics we tend to worry most about over heating, but in reality, most electronic components are not even rated for zero degrees and many will have problems as sub zero temperatures drop lower.

    As  more and more multicopters are flown in colder environments, no doubt this will be addressed more fully, but for now it is a minefield you have to sort out largely on your own.

    I might add, most of the plastics and resins used in the frames become extremely brittle and break much more easily at those temperatures as well, including CF and G10.

    Best,

    Gary

  • Thanks for that info. It sounds like I need to look at different mounting hardware. Not sure what can be done about the electronics unless it could be heated by the battery. The change in temperature over the flight duration might make it even worse. It's pretty rare to see those kind of temps but -15 or so is fairly common.

    Strange thing with a quad that flew well at -40 did not fly very good at 26 to 28 F. It would start out good and then it would drop altitude suddenly appearing to be underpowered. Sometimes it would even bounce off the ground. But most if the time it would regain altitude before it hit the ground. It would reach a point where it could not move at all and had to be flown back. There was wind but it did not appear to be the cause of this. Eventually the power module / 4 in 1 esc burned out.

    Regards
  • Hi David,

    In short yes, -40 can easily be really excessive.

    Most of the IC's used in the FC's are not rated for that low a temperature and their performance is likely to be incorrect.

    In particular, the sensor IC's - all of them can be drastically affected by too low a temperature.

    Also you're battery really hates being that cold, it is only the self heating from high discharge rates that lets it work at all.

    Also, any silicone or rubber shock mounts you use for gimbal or flight control stabilization cease to work effectively at that low a temperature.

    There are special silicones and plastics that will continue to work, but they are not commonly available or used.

    Rob Lefebvre (number one DIYD heli guy) actually operates his high end helicopter in this temperature range a lot, but he is a true expert and fully understands and compensates for the problems encountered.

    Basically, -40 for most of us is just a recipe for a crash.

    Best,

    Gary

  • Thanks for the input. It was apparently a damaged motor.

    How about cold weather? Is -40 too cold for autonomous flying? I was flying in -40 for a couple of days but most of the time it has been above 0 F.

    Regards
  • Just a thought, the baro is a mechanical diaphragm and it is definitely sensitive to vibration.

    Basically the vibration was throwing off all your sensors, at leas baro, gyro and accel and that means the FC was reading invalid conditions on almost all channels.

    Basically the FC tries to protect you from performing a throttle off and crash maneuver by ensuring the motors have enough throttle to hover or descend slowly.

    But if all the sensors are inputting nonsense, it just keeps trying to compensate.

    And compensating for nonsense produces - nonsense!

    Lots of things can cause compass errors, motors or iron or high amperage circuits too near the compass IC for instance, but it is the one sensor that probably didn't pay too much attention to the vibrations.

    You really need to fix the vibration problem(s) before even bothering with the rest of it.

    Bad motor shaft or bearing maybe.

    Best,

    Gary



  • Mike Boland said:

    The copter had real problems with compass variances and EKF in the red.

    A lot of vibration as well which either contributed or raised the issues.

    When it comes to EKF problems it is out of my area.

    You will probably get better answers by posting on the Ardupilot Forums



    Thanks for the info. That's what I was thinking. Once I gave it enough throttle to create the vibration it started increasing itself.
  • Thanks for all the information. I am certain something happened to the frame or one of the motors when it crashed the first time and that time it was in stabilize mode but for some reason the throttle went wide open at takeoff. I was only testing the hover time at that point and there was white out conditions so I really could not see it after a couple of seconds. The day before it flew perfectly.

    It does look like once I opened the throttle past a certain amount it gradually started giving itself more and more lift as the vibration increased.


    The wind was around 25 on the ground but as it got up around 10,000 feet it seemed like the wind got it so there is no telling where it came down. Probably blew at least 1000 feet. Where ever it is its covered in snow.

    Regards
  • I didn't look at your log, it is most very likely a vibration issue. Let me explain. Most of the vibes are in the Z axis (up & down) on a multi-rotor, for what ever reason, it just is. The Z axis is different than the X or Y because it fells the force of gravity. The accelerometers have a max value of +/- 16 g. They are constantly vibrating +/- a certain amount and this vibration is filtered out to get an average reading. The amount of the vibration is usually more much more than 1 g. If the vibration surpasses 15 g you will get clipping. This is when the accel reading is more than+/- 16 g. Since we are normally at 1 g, when the vibs are greater than 15 g we exceed 16 g on one end and this data is lost. The - g is 14 when the + g is 16 and so the altitude calculator is getting bad data on one end where it exceeded + 16g. This makes the copter's EKF to think that it is falling down quickly. It chases the false altitude solution and climbs. This revs up the motors and makes the vibration worse, and well you saw the result. 

    Did you have stabilize mode set up? In stab mode altitude doesn't mater, you control the throttle directly and you could have got it down. Learn to fly in stab mode. Check critical thing live vibration levels and clipping (exceeding 16 g). Mission planner does this for you. Think about were that machine fell to from 1200 ft. and consider yourself lucky. Read the wiki again, please.

  • The copter had real problems with compass variances and EKF in the red.

    A lot of vibration as well which either contributed or raised the issues.

    When it comes to EKF problems it is out of my area.

    You will probably get better answers by posting on the Ardupilot Forums

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