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?

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Mhh.. seems to be a big motor. :)
I think you have to carry a lot of accu power to drive such motors some minutes.

Yes Thomas,

 

I am running it with a 4400mah 5 Cell 18.5 V lipo. It should give me in the vacinity of 15 + minutes. The motors are Pulso 2820/14 Motors with  a DLU70A+ ESC

Whow, real good motors. Would be interesting how much they will really lift,
but if I'm honest I've no idea if we can add the power, so I will leave the discussion now (and make place for more competent users ;)
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 :-)
what is the c rating on the battery... you could over discharge quickly with that much amp draw.
It is a Thunder Power Pro Power 30C 30C continuous/ 60C Burst (132A/264A)
Are you sure about your numbers ? your battery is a 4.4Ahr 18.5V so it's 81.4 watts per hour. Your motor producing 2000g thrust at say 5g/watt efficiency will draw 400 watts and 4 will draw 1600 watts. So your flight time at this thrust will be 81.4/1600 hours or 3.05 mins and you will be pulling 86 amps, a tough ask for your battery.

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).

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

www.ecalc.ch

wow that link calculator is good man!

 

Tks for that Roman

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

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.

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