Question of battery vs flight time

[NerV-Runna]

Hey everyone

Lets say I have a quad that flies for 20min on 2x 6200mah 3s lipos.
Its lifting capacity is 2kgs excluding batteries.

How much extra time will I get if I add another 2, 4 or 6 batteries?

I know this is a relative question, but im just trying to figure out at what point does the weight of the lipos exceed the extra flying time generated by said lipos.

Thanks :frog:

G

 

[FerdinandK]

Copter-weight:Batteries-weight => 1:2 is a good choice. For the best setup, but this you can calculate based on the used Propeller (and the battery data).

best regards

Ferdinand

 

[NerV-Runna]

So if my platform weighs 1kg, i can put 2kgs of batteries? (Provided the plaform can lift that amount)

 

[FerdinandK]

Yes, that would be a good starting point
what propellers an what copter (quad, hex, octo)?

best regards

Ferdinand

 

[NerV-Runna]

Quad. APC electric 14x6. with Tiger 2814-11 710kv.
<small id="directLink">[url]www.ecalc.ch/xcoptercalc_e.htm?ecalc&weight=2000&calc=auw&rotornumber=4&elevation=1500&airtemp=25&batteries=lipo_6000mah_-_65/100c&s=3&p=4&chargestate=normal&esc=max_60a&motor=tiger_motor&type=mt2814-11&propeller=apc_electric_e&diameter=14&pitch=6&blades=2
</small>[/URL]
According to the calculator, I have a 29min flight time at hover.
If I double up the batteries, it gives me a 59min flight time. This cant be right? Does the calculator not take into account the extra battery weight?

 

[robone]

Yes it does, but you have to put in the weight "without drive" in the drop down menu. So put the weight in without the Batteries, ESC and Motors

 

[NerV-Runna]

Could someone explain how they get 88min flight time with the microdrone md4-1000?
I would postulate its a combination of large motors, large props, high voltage/low current. Would i be correct?

If so could someone supply a xcopter calc link with a 60+min flight time?

 

[owlhh]

What would be a good selection of motors to use go get those long flight times and at what total takeoff weight?

 

[FerdinandK]

88min flighttime was flown with a non-standard battery (you cannot buy these batteries), there is also a russian guy that went for 100min, he used a battery of some military drone.

My personal record is 65min (the setup you find in the video):

@NerV-Runner
You will get approximately 45min with 2kg of batteries (if you copter if fine with the takeoff weight).

best regards

Ferdinand

 

[NerV-Runna]

@Ferdinana: Thats awesome!!! Have you got an xcopter calc link of your setup, coz i cant seem to get the correct figures.

Can anyone post an xcopter calc of a copter they've built where the actual flight time is the same as the calculated flight time?

 

[FerdinandK]

I have my own math, which predicted the flight-time pretty accurate. I trust ecalc for airplaines, but for multicopters I rely more on my tools.

best regards

Ferdinand

 

[R_Lefebvre]

Yes, I was wondering about that. With Ecalc I can't seem to get much over 20-25 minutes max, no matter what I do. Is it accurate at all?

Edit: Huh. Well according to Ecalc, my current setup can't even fly, so I guess that answers that...

 

[jes1111]

eCalc seems to work well for me - but you have to be aware of its few quirks. Certainly it is better to use "Without Drive" in the top line and enter the weight of your craft minus ESCs, motors and batteries.

Long flight times come from large diameter low-pitch props, low KV pancake motors and "low C" batteries (probably 6S). But it's always a trade-off with weight. Look at the PDF brochure (download from their site) for the Multidrones MD4-1000 - the flight time drops off sharply as soon as you add payload (which is limited to 1000g anyway).

 

[R_Lefebvre]

It just doesn't work for mine. It's about 1300gr AUW, quad, 2830-880 motors with 10x4.5 props, 3S-2200 battery. If I do it as "without drive" and a weight of 800g, is says 80% throttle to hover, 5.5 minute flight time. Not true at all. It hovers about 40-50%, and at least 7 minutes.

It gets a little better if I put in my FPV setup, about 1000g on the frame and camera, 4S 5000 battery. It says 65% hover (a little high), and 11 minutes hover (I'm not positive yet, but that's about right).

Anyway, to the original question, there's definitely a case of diminishing returns with the battery weight. If I were to put a second 4S 5000 battery on this setup, it would only fly 15 minutes, but take 80% to hover (which is unflyable, IMO). You can image at some point it would be so heavy it couldn't even lift off. Too bad we can't do something like drop-tanks. Take up a bunch of batteries and deplete them and drop them...

I've also seen a neat idea that circumvents the UAV laws in the US, and gives unlimited flight time. Basically just a "flying mast". A quad that is flying with a tether wire, supplying the power from the ground. It would work just to get a high vantage point for some journalism or something like that.

 

[jes1111]

http://skysapience.com/products/the-hovermast
http://www.iai.co.il/35759-41817-en/BusinessAreas_UnmannedAirSystems_ETOP.aspx

 

[R_Lefebvre]

I can't quite see what you attached. I think it's an example of my setup. But what is the hover percent?

 

[jes1111]

Damn silly image attachment system! Bart!?

As close as I could get with the numbers you gave.

 

[R_Lefebvre]

Damn silly image attachment system! Bart!?

As close as I could get with the numbers you gave.

Ok, that looks pretty good, other than I think the throttle % at hover is high. It's more like 40%. But then maybe that is being masked in the code because there is some rescaling going on. It's no Ferrari in any case. The flight time is almost spot on.