I built a QAV400 that flies well and records smooth video. I'm getting 10 minute flights using 5200mAh LiPo batteries.

I want longer flight times.

My Plan:

  • Create a baseline using a standard battery.
  • Reduce the weight of the "dirty" frame by 200g, maintaining strength and rigidity.
  • Design the new, lighter frame to allow for 10" props (current limit is 8").
  • Reduce the weight of the "clean" frame by 50g or more.
  • Replace the original 1100kv motors with more efficient, lower kv motors.
  • Document the performance of various prop/motor combinations.
  • Find other ways to reduce overall weight/increase flight time.

Goal: To achieve 30 minute flight times while maintaining good flight performance.

I've been following posts by Forrest Frantz who currently holds the Guinness record for Longest Electric RC Multicopter Flight at 97 minutes!! He has some great threads with tons of info, especially this one on Building Copters with Round Tubes...

I'll be posting detailed notes and photos of each step...

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QAV400 Baseline:

My quad's AUW is 1894g with the following gear:

  • Lumenier QAV400 frame
  • APM 2.6 flight controller with uBlox GPS/compass kit
  • 3D Robotics telemetry radio
  • FrSky X8R 2.4GHz receiver
  • QAV Quick-mount 2-axis brushless gimbal
  • GoPro HERO3 camera
  • Lumenier CS-600 FPV camera
  • SmartFPV RCCC V2 remote camera switcher
  • MinimOSD
  • ImmersionRC 5.8GHz 600mw Tx

Here's a photo of my current configuration:

If you want to know anything about how I got to this point, you can visit my build log here:


Baseline Battery Tests

I recorded a few flights using two different batteries to confirm a 10 minute flight time using roughly 4200mAh from a 5200mAh battery. For my next test, I removed the gimbal and GoPro camera (260g) and I also used a lighter, 3300mAh 4S battery. Because there was no gimbal or GoPro up front, the CG (center of gravity) was off quite a bit. To fix this, I added a 100g counter weight to the front.

My total weight savings: 260 + 175 - 100 = 335g.

335g is roughly 18% of the original weight.

If I removed weight somewhere else and was able to use the 5200mAh battery, I would have 12 minutes of flight time (a 20% increase). With everything else being equal, is weight savings directly proportional to flight time? I don't know the answer to that question but I'll be doing more tests to find out.

QAV400 Components - Weight Reference

QAV400 frame: 375g
- "Dirty" (lower) frame: 260g
- "Clean" (upper) frame: 115g

APM 2.6: 16g
3DR Ublox GPS: 17g
GPS mast with hardware: 20g

Lumenier CS600 camera: 15g
QAV board camera mount: 11g

GoPro HERO3 camera: 75g
Gimbal assembly with layer lens: 185g

X8R module (Rx, anntena stand): 25g

FPV module (Tx, OSD, switcher): 68g

(6) 9" servo cables: 24g

(4) Lumenier FX2216-9 1100KV: 304g
(4) Lumenier 30A ESC: 128g
(4) Graupner props, washers, nuts: 42g

3DR telemetry radio w/antenna: 25g

"Rib Bones" plastic landing gear: 36g

Lumenier 3300mAh 4S battery: 328g

Lumenier 5200mAh 4S battery: 503g

Robert - Remarkable.  Wish everyone could document like this.  There are a lot of QAV onwers out there that will directly benefit and will get other standard frame users thinking.

So base ship is 1.87 kg with a 5200 mAh battery?  This will be so fun to watch.

Robert, I follow your proyect, I'm in the same line with my firs cuad, up now I reduced 200 grs and obtain much better vibrations level with Forrest help, now I'm in pause for harvest time and waiting more efficient motors, when I return I'm going to try to make a post like yours to change experiences; Thank's

I think you would be better off just going right to the 540 arms if they will fit the 400 frame.  I increased my qav500 from the 500mm to the 540mm arms to be able to use 12 inch props.  Motors I am running are 40mm 620v pancakes.  Prior to the arm/prop change I was running 10x5.5 props and using about 18 amps at hover with gimbal/gopro/full fpv gear/5000mah pack. I also used 4000mah pack and there was virtually no difference in flight time because carrying the heavier battery was too far above the efficiency zone on my motor prop combo.  With the 12 inch props the hover amperage has dropped down to 10-12 amps for the same setup.  If you put similar size motors to I am using, and up the battery MAH to 8-10000 you might get close to 30 minutes, but you will have to find somewhere to either strap the second battery or figure out how to hold a larger one than will fit in the area designed for it.  I was going to try the multi star 6000 mah size and see if it will fit.  I am using the 8000 size on my hex and they have been working really well.  I am getting an easy 15 minutes with plenty to spare and using 23-25 amps in hover on that machine.

I obtained aprox one minute for extra weight that lost, interesting to see if you have similar results.

This is great.  we can see what different people tried and the result. thanks for sharing Hal.

As a general rule of thumb, duration will increase with the percent change in prop size.  So if the prop was upsized from 10 to 12, there would be a 20% increase in duration.  So the 33% drop in amp usage you experienced was also due to using a better 12" prop.  Well done.

I think the outsize gain also had to do with the low kv motors.  On my hex I am using 720 kv and there is not nearly the difference in gain between 10/11/12 inch props.  I had to push to much power through the low kv motors to get the thrust needed with 10 inch props.  With the 12 inch props the motors now operate in a much more efficient amperage range.  I dropped my throttle mid from about 650 to 450.  That is a very large change.  On the hex there is almost no difference in power draw between 11 and 12 inch props.  RPM is lower with the 12 inch to achieve the same thrust.  But the amperage is higher, and in the end it all equals the same power draw.  One thing this also shows is how important matching the kv of the motors is to the planned propellor size.

I have 15*6.5 props on my Tarot cuad and hover at 70%, I have 17*5.5 props, if I try with them I have the chance to have good results with 460 Kv motors ?

in general, the lower the KV, the larger the prop it can efficiently throw.  only way to find out is try.

Yess,  I'm going to try :)

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