My Heavy Lift U8, Pixhawk - Sweep heads South


A successful build of my heavy lift quad copter.

Thanks especially to William Cox and Steve Keep - it is now flying a lot smoother.


  • Pixhawk
  • U8 motors
  • 70A ESC
  • 10S 8Ah (2 * 5S)
  • 28" Carbon fibre props
  • Aluminium frame
  • Weight (no payload or batteries) 4.1kg
  • Water resistant
  • Lunch box :-)

Successful flights:

  • 5 minute test flight at 12kg
  • 24 minute down to 3.57 volts per cell


  • Loiter stability - everything stable except loiter
  • Needs a larger box

Attached is my parameters. I read a lot about people not sharing parameters. And these need a lot of work, but here they are... shared...

In the next 4 weeks it should be flying down in Antarctica doing some radio tests to wave buoys and photos of sea ice floes.

Sweep 2014-10-22

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      • Yes 3.2. Yes same parameters (change GPS_TYPE_2 = 1; recalibrate accels and both comapss) however I did not enable any of the EKF filters - will look into that tomorrow.

        • but I think filter fusion improvement depend on AHRS_EKF_USE = 1

  • Scott

    We have a X8 with U8 170 kv  27 x 8.8 CFs

    Using 6S Desire Power Lipo  20,000 mAh

    Have had several crashes so far. 

    We are guessing that using auto trim for these heavies may not produce the best results.

    Last incident was in loiter mode. 

    Flight data file is under analysis, but we are guessing that the roll and pitch rates are too high such that the motors can't accelerated fast enough to hold altitude in high roll/pitch rates. 

    Be careful   

    BTW we are shooting for 1 1/2 hr flight time with GoPro and gimbal  3 batteries. 

    • Do you have a picture :-) Sorry to hear about the crashes. Lower KV motors, especially how efficient these are, tend to spin very low and I have had a stop - one stopped due to sync issues you might end up in reverse or just slow to start. One suggestion I have had given to me is to keep the minimum throttle up so there is a higher spin, more chance of recovery. See what your logs say.

      1.5 hours will be impressive. Although if efficiency is key, why not go for a octo instead of X8? 

      When I get more batteries (my other two sets are already on site) I plan on putting in a pair, ie: 16,000 Ah at 10S. That should give me an hour, but probably not 1.5. My 25 minutes was with my payload (about another 2kg), which will be the same weight as no payload but full batteries.

      • Can't figure out how to get a picture loaded. 

        We are taking losses with coaxial props, but we have removable arms and can pack in shipping box. 

        We wanted to keep the size down. 

        AUW to date is ~ 45 lbs   No issues on motor heating. 

        On the throttle we have found that we can't fly at empty payload weights.  Throttle too low for control.  Ok

        add more batteries. 

      • Moderator

        Great looking build Scott, I find X's easier to fly than + its just a personal orientation thing. Don't think there is any performance difference, could be wrong often am. I bet the cold down there will improve the bite and hurt the batteries.

  • I just tested your parameters on my machine (performing first the changes for type X frame) and behaves very well in stabilize and AltHold. It has been a indoor test because here it's night, tomorrow I will try to test it outside with loiter.

    Thanks again.

    • Great Fran. Today I will be trying 3.2 & reducing the P in Loiter from 1.00 down to 0.8 or even 0.6 to try improving Loiter.

  • With that high voltage, are you sure you need 70A ESCs? I couldn't see you drawing that much power.

    • T-Motor now recommend only using their new 80A ESC on the 100KV U8 motors. They are rated up to 12S (Battery and motor). Also when I researched other builders of U8 motors they all used a similar size, smallest being about 50A.

      But now I have built it, I have not got anywhere near those numbers. I don't currently (could be joke in there) know the max current during full power, but I suspect only around 120Amps total, or 30 amps per ESC. 50 therefore should be fine. Lots to learn and test. What size would you have used?

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