How do you calculate quadcopter lifting capability?

I am planning to build a Quadcopter for some time, I have all the required gear and an airframe completed. Before I start assembling the entire quad I would like to know what the lifting capability will be when complete.

I know that one motor with a 2 blade prop will lift 2Kg whithout any hassle at approximately 70% power (thrust test, not in airframe). Does this mean that for a quadcopter I can assume that four motors will lift 8Kg @ 2Kg per motor or is there some other calculation to accomplish this?

Replies

•  Can someone help me with this for amp draw http://diydrones.com/forum/topics/trouble-with-a-hex-voltage?xg_sou...

• I have a standard 3dr quad, with gimbal, telemetry,850kv motors , 3,300 mah lipo, 20amps esc, 1047 props
Total wight is 2100grs, I am very disappointed with flight time and also lifting capability , it hovers at very hight throttle, and is difficult to control when it goes down even at low vertical speed .

The way it is now is almost useless, then I know I have to decrease weight to solve all the other problems, but what is the fun of taking all the equipment out, then the questions is , what is the logical way to go , ? , bigger props , 4s instead of 3s , larger motors , ?
Or just quad was a mistake and should go to exa.?

Thanks,
• Developer

You should calculate lift at ~50% throttle. In other words the copter and payload should hover at 50% throttle. The reason for this is that the copter needs a lot of thrust headroom to maneuver properly. You also get very short flight times if you push the system to much.

• Roman Hofstetter is on the money with www.ecalc.ch - it's probably more accurate, because it lets you configure theoretical payloads. You'll get more accurate results if your motors and props appear in the list, and that your battery specs (particularly weight-per-cell) are reflected correctly.

Note: some frames have a "thrust per arm" limit. eg: www.quadframe.com.

• hmmmmm...

i am using 330 size Brushless Outrunner, 1400kv motor and

Thunder Power 2700mAh 2S 7.4v 25C battery.... can any1 say wat vl be the thrust and lift

• wow that link calculator is good man!

Tks for that Roman

• I know it's an old topic, but for all those finding it with google or anyhow, here another link:

www.ecalc.ch

• You use THIS to find out how much thrust you should have mathematically.

Then you need to make sure those motors going flat out are within your ESC capabilities.

Then you need to make sure that your batteries can be discharged as fast as 4 of those motors flat out.

If you get a no from any of these you cannot do it.

Combining the thrust from all four motors is not like 4x thrust of one. The turbulence created by each motors wake will interact and sap some of this thrust. Dependent on far to many factors to establish an accurate answer (as quite a few are environmental) you should make a safety combined thrust 80% of 4x motors. Also you should realise that thrust decrease with altitude (less air to push means less thrust).

Propeller Thrust Calculator
• Assuming your power grid will be able to feed them all at once (what is that, 40 A each?), then yes, you multiply by 4 :-)
• Mhh.. seems to be a big motor. :)
I think you have to carry a lot of accu power to drive such motors some minutes.

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