Low flight time with Foxtech SS HV 13Ah 6s batteries

ArduCopter
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1

Hi all,
I am using Foxtech SS HV 13Ah 6s batteries and I’m getting significantly lower flight time than expected on my quadcopter. Would appreciate any insights. I would be truly grateful for any insights or suggestions you may have to help me understand this issue better.

Setup and observations below:
Setup:

  • AUW: 3113g, Motors: MN4008 380KV | Props: Tarot 16x5.4, Battery: Foxtech HV 6S 13Ah, 10C | Weight: 1223g Voltage (V): Full: 26.7 | Nominal: 23.7 | Charge Cutoff V: 20.1, Energy Density: 265 Wh/kg, FC: CubeOrange+ | GPS: Here4, Power Module: Standard Power Brick, Voltage Calibration: ±0.5V accuracy, RTL Voltage: 21.5V
  • Issue:
    Flight time is ~20 mins (tested on two Foxtech packs). Estimated time was ~44.5 mins based on:
    ((13 x 0.8) / 14) x 60 = ~44.5 mins
    Average hover current from logs is ~13.9A, and batteries were discharged to ~80%. Logs attached.

Other Tests (same build):

  • Battery 1: Molicell P45B, 13.5Ah 6S3P | AUW: 3207g | Time: ~13 min | Hover Current: ~13.5A
    Battery 2: Molicell P45B, 9Ah 6S3P | AUW: 2690g | Time: ~15 min | Hover Current: ~9.8A
  • I know that molicell voltages can be lowered down to 18.5 V but I landed it at 21V.

Additional Notes:

  • Wind was moderate during the Foxtech battery tests, Current sensor is not calibrated but values seem close, Voltage readings look accurate in logs.

Questions:

  • Could bad soldering somewhere be increasing resistance and causing higher power loss?
  • Any other reason I could be getting nearly half the expected flight time?
  • Is RTL getting triggered early due to voltage sagging?

Logs are in the drive link
Thanks in advance for your help!

foxtexh13AH
foxtexh13AH1502×651 158 KB

2

I’ll reply with what I posted in your other since deleted post:

Before wondering about flight time why don’t you complete the tuning of this craft and calibrate the current sensor? Tuning is poor, there is output oscillation and the Rate Controller looks terrible. Perhaps you will pick up a bit of efficiency by doing so.

And what actual motors are those?

3

I am using Antigravity MN 4006 380KV. Also I am pretty new to tuning it was my friend who tuned the quad. I will follow your suggestions and in a few days will go another tuning round. I have read that current calibration is best at above 10Amp draw, as of now I don’t have a current measurement sensor I will get a watt meter and calibrate power brick.
Motors: https://store.tmotor.com/product/mn4006-kv380-motor-antigravity-type.html
It would be awesome if you could give a few pointers regarding tuning what values or params needs to change. Thanks for reply

4

If you have no experience then use the Methodic Configurator

You don’t need a wattmeter. Use search here for “current sensor calibration” and you will find the procedure posted many times using logged current vs charged current to calibrate the current sensor.

I would guess (from eCalc) that your hover current will be closer to 19amps with the 3113g AUW.

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5

Thankyou, I will go with methodic configurator for tuning. Yes, I had used ecalc to design this quad it shows hover amps as 15.61. I simulated the 13Ah HV battery using the resistance value from logs.

revor_est
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6

4006 or 4008? I think it must be 4008… It is a very good idea to calibrate the current sensor…

Now, one thing I notice is that your copter is very heavy. I have two very similar copters, and one is using 340 kV motors which are inferior to yours (mine are RCtimers), with 16x 5.5 props from RCtimer (which are also inferior to your props). I use almost the same battery, 12 Ah, 6S, 1250 grams. Now, my copter weighs in empty at 1200 grams, so total flying weight is 2.5 kg. But I get close to and slighyl above 1 hour slow flying time.

Now I see that you use Liions, in that case, you can fly them down to 18 V safely, or an indicated voltage of 17 V as absolute minimum.

Most liions tolerate very well discharge down to 3.0 V per cell under no load, or about 2.7 V under moderate load. The way I determine an absolute safe voltage value is this:
With a rather discharged battery, I hover for about 2 minutes, note the voltage for instance 18.5 V, land, and wait for 3..5 minutes. The voltage will recover, to maybe 19.2 V. That is your no load margin, 0.7 V. Then you take the 3.0 V per cell, multiply it by the number of cells, i.e. 6 you get 18 V. From that you substract 0.7 V, so your minimum indicated voltage is 17.3 V. That voltage means that there is no reserve, and copter is about to crash.

If you landed at 21 V (especially under load), you have more than 50 % of energy left in the batteries, how do you know you used 80 %?

Sooo. If you want to increase your flight time:

  • Tune your copter first, that could give a small improvement (maybe 5..10 %) if it is very badly tuned.
  • Fly down to the minimum voltage, but very first thing to do is to verify that your voltage sensor is well, and check the battery data sheet. That will give you much more flight time, maybe even double.
  • For maximum flight time, you should fly slowly, hover uses about 10 % more energy than slow flying at about 20..25 km/h
  • Shave off about 600 grams from your copter… Unless you have some special equipment on your copter, there is no reason to have it so heavy. Sometimes, something which looks cool, futuristic, with high landing gear, a lot of nuts nd bolts, etc. is not always the best choice… A weight reduction is not proportional to the flight time, i.e. if you reduce weight by 20 %, your flight time may increase by 30 %.
  • Finally, your motors are a little bit too small for the copter weight, you would be better served with 100 gram motors which would be much more efficient at higher loading. That could give you another 5..10 %, despite the weight increase.
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