Hexacopter doesn't want to lift up

Hello everyone!

I'm a newcomer to this awesome world and I'm facing a simple issue (at least I hope so) with taking off.
I'm rebuilding this hexacopter which I got from an university colleague, it's not new and so I assume lots of parameters have been changed.

I checked the hardware, installed the last working firmware (I'm using an APM 2.5) and I went through the calibration procedure. As additional part, I installed the battery module. So far so good. I can read the parameters in Mission Planner and they make sense.

Then, I tried to fly. ESC are calibrated, the copter is levelled, the remote is connected, the Lipo is full charged. If I arm the motors, they run as configured but when I rise the throttle just a little bit they autonomously increase. Moreover, the speed is not the maximum available but at a "lift-up" point at which the drone is still on the ground but if I roll and pitch together, it does jump 20-30 cm. If I try to increase the throttle, it simply stays at that level without any change. It seems as a loop is cutting the power or a parameter is not set correctly.

I'm using 9-inch 3-leaf props with 11,1 V - 2.600 mAh LiPo Battery and a whole weight under 1.6kg, the motors are AC2836-358 880Kv. I run a motor test and they spin correctly and in the right sequence. The props orientation is correct as well as the copter configuration (X). I tried to take off in stabilized mode and all is looking good in the logs. Looking at the voltage from the battery monitor and comparing with a multimeter, voltage and ampere look okay. The only problem I've seen in Mission Planner is about the Terminal: when I connect the board in the Terminal, it gives errors and I can stop it only closing MP with Windows Task Manager.

It's such a shame I can't make it fly. I've been repairing it in the last few months and I've so many projects to do with it.

Thank you guys in advance for your help!



Terminal error.PNG

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  • This morning I tried to fly with all safe modes off and the default parameters. I found for no apparently reason THR_MAX was set at 80 and I put it at 1000 values. It did finally fly and it was really a such great time!

    As I might be expected, all the basic tuning operations have to be done and here I understood why I had had that feeling of auto-increasing in the throttle: first the power was almost completely cut to a very low level, more or less comparable to 3 or 4 throttle steps of the remote control; secondly the "climb sensitivity" was very low, so much that I could increase the speed and actually see it only after few seconds.

    Still, I can't figure out the problem with the terminal.

    Next step will be a sonar and a ground station. Following some pictures of my warrior !

    MyHexacopter (1).jpg

    MyHexacopter (2).jpg

    • Looks like a great vehicle, good luck!

  • Try to adjust THR_MAXIMUM in mission planner set it to 80%.

  • Another thing that you can check is to connect one speed control directly to the receiver.  Then hold onto the copter, advance the throttle.  If the motor increases and decreases smoothly as you change the radio throttle, you know the receiver is sending correct throttle information to the apm.  This would indicate that something is going wrong in the apm.

  • Thank you very much Mark and James for your fast replies. I updated my post, I'm using 880Kv motors and read battery values are okay. I checked the board looking for short circuit and there's no problem about that. I also tried to change the initial motor speed, the one just after arming, and it's actually changed.

    I activated motor log and disabled all fail safe modes and if it still gives problems, I'm going to reset to default parameters ( I'm quiet scared to mess up instead of solving ).

    I'm wondering why the motor speed rises automatically after giving a little of throttle. Is it the same with your copters?

    Thanks again guys, I'll try to fly again in a week and I'll keep you up-to-date. Cheers !

  • Hi Flavio,

    It seems that you have checked most of the likely issues that you should when attempting to diagnose the symptom you are facing. Your props are mounted in the correct orientation and are spinning the correct way and your ESC's are all calibrated to give the full range of output for the range of input they receive. I would enable the MOTORS log and check what Arducopter believes it is sending to the ESCs while attempting to take off. If you are confident that the motor/prop combination is well suited to the task at hand (capable of producing the required thrust - what kv??), then perhaps you are facing voltage sag due to a battery or wiring issue? Do you have a voltage sensor? If everything is still looking OK, perhaps you could verify the APM output to the ESC using a scope (or PWM setting on a multimeter)

  • I have just finished my first hexacopter.  My expertise is intermediate.  Your configuration sounds like it should work, but I am assuming you have reasonable motor size.  I would check the following:

    - save the old parameters using MP, then reset the parameters to default set and re-do the wizard and initial setup including all calibrations

    - recalibrate the ESCs

    - make sure that the RC calibration is done correctly and you are in Stabilize mode on takeoff

    - check that you have not set a failsafe in MP like the throttle failsafe, battery failsafe, or similar

    - try arming the drone with the USB cable attached and watch the flight data, are there any errors, warnings, or strange indications after arming?

    - check your transmitter settings as well and make sure that you have not limited throttle travel or changed the throttle response

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