Quadplane won't produce enough power to lift off

I successfully launched my quadplane on a 3S power system. However, 3S system wasn’t enough power for the front plane motor. I then replaced the quadmotors and the front motors will 4S capable motors. Each quadmotor is capable of producing 0.8KG thrust at about 11 amps each (44 total amps). I tested one with a servo tester on the plane and consumed 12 amps at full throttle. My quadplane weighs less than 4 pounds so that should be more than adequate times 4. I’ve recalibrated the ESCs and made test flights. The craft will not lift off. I’m only drawing 12 to 16 amps at full throttle, not the near 44 they should be at full throttle. The logs show one motor near the top on PWM, two in the middle and one near the bottom. I haven’t been able to figure out what is going on. Any thoughts? Thanks.

Mark

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For multi rotors you need to calculate available lift as 50% of max thrust.
The motors will not reach full throttle on the throttle stick, because if they did you would have no extra thrust left for things such as stabilisation.
I believe max thrust is capped at 80% by default for multi’s.

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Highflyer
Beacuse its a smaller frame: Whilst holding down the airframe safely to avoid the props try going to max throttle in Qstabilize mode. Also make sure you have set the right prop/motor config in Q Frame and Type. Either x or h quads should work if your props are spinning the right way. You can also test the motor config by very carefully (wear eye/face protection) holding the aircraft to avoid all the props and throttling up to 50% in qstabilise, and test if the motors try to lift the lowest side when you tilt it by hand. Can you describe the propulsion setup more? The setup sounds a little underpowered.
Regards

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I first flew it with a 3S 2800 Mah using 4 Hobbyking DST 1200s with 10X4.5 props It rose at about 25 to 30 amps. I switched over to DST 700s with a 4S 3000 Mah, same 10X4.5. Now I’m pulling 12 to 15 amps total. 30A ESC in both cases. With the pixhawk out of the way, I can pull 12A per motor with this configuration. I weighed it once and it was between 3 and 4 pounds. I’ll have to check the weight again. I’d say it’s close to 4. Full thrust should be 7 pounds with this configuration. I should be off the ground at about 60% thrust. We did do the tilt test and believe it was correct. I’ll check with the guy holding it to make sure it worked in all 4 directions. I can check frame parameters again but I had them correct earlier and the plane flew on 3S. Thanks.

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Hi Highflyer.
For a quick test reshuffle your ESC connections to the PXH and see if the same PXH outputs always cause the same effect. It would be good to find out if it is actually the PXH or the ESC/motor setup that is the issue. It might be hardware related, like maybe cabling, connectors etc. so maybe try to eliminate that first before going to the PXH. It’s strange that you had it flying on 3S but on 4S it’s not. Unless something on the PXH has changed, it shouldn’t be causing it, as it doesn’t “know” that you’ve changed something. So it should still fly. Do you have a backup of your params when it worked on 3S that you can try? If not do a backup of what you have now so you can get back to what you have currently, then do a fresh reload of the latest 3.6 firmware and do a full recal. Once you have done that you can then use the compare function to see what params are different from stock. Let us know how you go.
Regards.

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I had a little time to tie down the plane and throttle it up. Below is a picture of some of the graphs on the 3S configuration:

I’m flying with a peak of 377 watts up at about 40 feet.

Here is the 4S graph running on the ground at about 250 watts maxed out. Notice channel 8 barely has any PWM.

The plane is heavier than I thought. It comes in at about 4lb, 14 ounces. The 3S version would be a few ounces lighter as I was running a smaller battery. I really haven’t changed any parameters that I can recall other than battery monitor voltage thresholds. I just swapped out the 3S for the 4S configuration.

Mark

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