Let me start off by saying I have been searching the discussion boards for some time now and have now found many if any that are building large Quads using the Pixhawk and the U8 Tiger motors. I am a bit of an overachiever and and wanted build and efficient UAV with long endurance. I have put together one using the following equipment.

1200 mm motor to motor frame.

Pixhawk Flight controller.

Castle Creations 50A ESC's 

6s 15C Lipo Battery

U8 Tiger Motors

28" Tiger Props

Taranis 9XD Radio

Here is my problem. I have gone through all of the calibrations from the flight controler, motors, ESC's and the radio. When I calibrated the ESC's by using the flight controller bypass the motors spin up in reasonable increments as i increase the throttle. When I arm the system the motors begin to spin at an idle speed. When I try to increase the throttle there is no change in response from 0% to about 60%. At that point the motors spin at 100% RPM from 60% to 100% throttle. I have contacted 3D Robotics and the technician told me that he would speak to their engineers and contact me back. I know I am impatient but a week later I still have not answer. I am hoping that someone here can lead me to a solution. I am thinking that there may be some problem with the flight controller.

Thanks in advance

Will

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Replies

  • Hi,

    I'm tuning a large quad based on U8 motors.  After a hard tuning process i have a really nice solution for stabilize mode, but I can not find a good loiter PIDs. 

    My setup:

    1100 mm motor to motor. Home made carbon fiber arms frame.

    Quad + configuration

    T-Motor U8 135 kv.
    T-Motor 30A opto pro ESCs.
    28" T-Motor Props
    6s batteries
    Pixhawk
    APM:Copter v 3.1.5
    Tranis + X8R

    you have made ​​some progress in loiter tuning.

    Thanks.

    Fran

    • Fran,

      I feel your pain. Loiter seems to be the trouble when trying to find PID's that will work. Someone has figured it out but they are not sharing. SteadiDrone has it figured out so I'm told. I wonder if the Loiter settings were set similar to the stabilize PID's if that would work. I don't know why Loiter is creating such a problem. The only thing I can come u with is the mass of the motors and props may have a problem slowing down fast enough after making corrections to maintain stability. This may cause the APM or Pixhawk to chase these corrections to the point that it over-corrects itself into these violent oscillations. But I really don't know. I have seen MikroKopter has an ESC that evokes Regenerative braking in the motors slowing them down quickly and as a byproduct allowing a back charging to the batteries. I sure wish someone could help solve this for us. I apparently not smart enough to .do it myself. 

      • Hi, William

        Yes, the solution is out there, I hope someone wants to share it.

        In this thread I share my PIDs for stabilize, and someone suggested me some parameters values. I'll try it.

  • Hi Will

    I have just built a heavy lift, with U8 KV100, T75A ESC, Pixhawk, 1.2m, 10S. Three flights successful since finished on Thursday, and today a crash. Very fortunately it landed in a tree after it came down so minimal damage, not even a prop broken. Very very lucky.

    Just going through my logs now, but my gut feeling is that the little gusts of wind, and no tuning (probably my choice of bad defaults) caused it to oscillate like crazy. I was able to recover 2 out of 3 times, but on the 3rd time, as I brought it lower, it tipped 90 degrees and hit the tree. I think that these motors don't like being stopped completely, and can have sync issues at super low (/0) rpm - so when the oscillation was throwing it left and right almost 45 degrees each way, it eventually hiccupped on a motor start up and crashed.

    My issue related to yours above was initial configuration where I had the ESC configured (even though not supposed to be the default) into Governor mode.

    How are you going with your setup?

    • I sent you an add request. I am at the point of troubleshooting the PID's. I too have had the oscillation issues but only in loiter, in windy situations. I am looking for solutions. I am running this at 6S on the 170KV motors. I don't know if it is the PID's or an problem with the ESC timing or what. I have read that in some setups people are using dynamic motor breaking. Their reasoning is that the motors due to the mass are not able to slow fast enough and this can cause the flight computer to create these oscillations. Truly i don't know. Whatever it is in my case it starts when there are (sometime small) gusts of wind. I have been able to switch into ALT Hold or Stabilize modes and a little increase of the throttle and it will settle down.  

      • Hi William. I sent you my email for a chat.

        I am using 100KV 10S. Lifted 7.2kg the other day, but still oscillated Going to try increasing D tomorrow and fly again, but back down at 4.2kg.

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