Throttle "Dead Stick" Position in Loiter

I had a scary experience today using loiter. I had the quad about 3 metres off the ground and switched from Loiter to Stabilize and the mid throttle position did not provide enough thrust so the craft came to ground too fast for me to adjust. Fortunately it was soft grass underfoot and although it landed heavily it landed on all four feet and everything is ok.

My question is; how do I move the loiter "dead stick" position from 50% throttle closer to the 70% throttle I need to hover so that the next time I switch from Loiter to Stabilize the quad does not drop from the sky!

I am using Pixhawk, 3dr Quad X4 with a Taranis.



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  • A quick google search and J-Drones had this to say about the motor:

    ArduCopter specific motor for heavier payloads, This motor is designed for 12x45 Propellers 

    Motor features:

    • Size: 28 x 36 mm
    • Shaft: 4mm
    • RPM/V: 880 Kv
    • Prop: 12x45
    • Batt: 2-4 S LiPo
    • Weight: 72gr
    • Cables: 35cm/18 AWG
    • Accessories: bullets, propeller adapter, shrink tubes

    Tested thrust: 

    Power out put from ESC, 3S LiPo, 12x45 Propeller
    25% 50% 75% 100%
    1.5 A
    6.1 A
    14.2 A
    20A A

    Even the 3dr site says this motor is designed to run 11 and 12 inch props. So why do they sell the Quad kit with 10's?


    • SoI bought the 11 inch APC MPR series props but they don't fit on the stock 3dr motors. The hub is too thick for the prop shaft :/
      So then I bought the 11 inch APC SloFlyer series and they have the throttle mid position much closer to the mid stick position. Which is fantastic! Thanks everyone!
  • Anybody have a recommendation on what props I should replace the APC 10 x 4.7 SF and SFP's with? I was thinking Carbon Fibre props would be nice - not so flexible, might help to keep vibrations down? I am getting a little jello in my footage but I might be able to tweak that in the gimbal settings.

    Thanks again for all of your advice!

  • Have you set your THR_MID parameter correctly? If that is done properly, the quad hovers at 50% throttle.

    • Is there a calibration for that?
      • I found the thr_mid wiki, and made a "hover" flight to examine the log. I notice my hover point is much higher than normal - around 750... The thr_mid setting will only go as high as 700... My quad must be too heavy? I am running a 4000mAh Turnigy nano tech battery, Minim OSD, 433MHz Telemetry, Pixhawk with GPS/Compass module and an X8R Receiver as well as a Video system with a Turnigy 1.3 Nano Tech battery, Quanum Ubec, Tarot 2-d Gimbal, Go Pro Hero 3+ Black, Immersion 25mW Transmitter.

        Logs of machine attached:


        • Sandy,

          Your copter is significantly underpowered.  You'll need to improve its lift performance.

          It's probably possible via a change to your props.  Put the appropriate details into Ecalc and see if you can change the props to get your hover at around 50% throttle

          • Just to add to this, if you can't match up Ecalc to your specs without a premium account, I'm happy to help.  Just add the AUW, the prop specs and the battery voltage.

            • @ Matt, Thanks, I was thinking of some carbon fibre props - what do you think? Or do you think I should go up a size to the 11x4.7?.

              I'm willing to try a different battery too - maybe moving from a 3s to a 4s battery will help?

              I am not sure about E-Calc. It does not have any of the hardware I am using in it (3DR stock DIY Quad Kit 880Kv motors and 20 Amp SimonK ESC's), so how can it be accurate? It doesn't even have the battery I am using (Turnigy Nano Tech 3S 4000mAh 35-70c). The machine weighs 2.2Kg's total including battery etc.

              • Yeah; eCalc isn't perfect but it gives a good indication on performance.  I ran the numbers on your existing setup (making a few assumptions) and got this:


                It's not exact, but eCalc tends to be conservative.  I'd say it's close enough to match your specs.

                I then changed to 12x45 props and got this:


                Which is far superior.  Also, the above numbers are based on a full battery.  The hover performance decreases to 47% on a 'normal' battery.

                The closest I could get to a 50% hover seemed to suggest a 12x40 or 11x60 prop.

                Whilst changing to 4S will almost certainly help, a replacement set of props is far cheaper and should achieve similar results.

                Make sure you test it carefully after the changes but I think a solution is easily achieved.

                Good luck.

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Aug 25