How do I determine payload?

[adanac]

I'd like to move up to a medium lifter and I'd like to buy a used hex or octo. How do I determine how much something I might see in the classifieds will lift? Would I take the specs listed and use ecalc?

 

[SleepyC]

Motors.

If you look up the motors used most have a voltage/prop chart that will give you the lift capacity at 50% - 100%.

Take the number of motors x the lift capacity at 50% throttle and that will give you the target lift capacity.

I have a QUAD that uses T-Motor U7 490KV motors and 18/6.1" props. On 6S battery power, each motor at 50% should be able to pull 2420 grams of thrust.
So 2420 x (4) motors = 9680 grams of total thrust at 50% throttle. That is 21.34lbs at 50% throttle. So i would want my rig's all up weight (rig, gimbal, cam and batts) to be no more than 21.34 lbs.

Hope that helps!

 

[Quinton]

Motors.

If you look up the motors used most have a voltage/prop chart that will give you the lift capacity at 50% - 100%.

Take the number of motors x the lift capacity at 50% throttle and that will give you the target lift capacity.

I have a QUAD that uses T-Motor U7 490KV motors and 18/6.1" props. On 6S battery power, each motor at 50% should be able to pull 2420 grams of thrust.
So 2420 x (4) motors = 9680 grams of total thrust at 50% throttle. That is 21.34lbs at 50% throttle. So i would want my rig's all up weight (rig, gimbal, cam and batts) to be no more than 21.34 lbs.

Hope that helps!

2420 grams of thrust @ 50% is a serious amount of pull, just looking at those thrust details now.
So whenever you are calculating you would never take the 100% thrust being 5250g and divide it by 2=2625g and multiply that by the number of engines?
I just found that @50% the thrust is usually pretty low, and goes up quite quickly after that.

..On my own thrust calcs for my motors and props I got the following, where you can see a big jump after 50%
50% 110W 4.8A 1060g Thrust
75% 350W 15.3A 2370g Thrust
100% 536W 24.3A 3200g Thrust

 

[SleepyC]

From what I have see in real life work (ie. system not get overloaded, ESC's and Motors stay coolish) and what almost everyone I know does is to set your rig's target weight at the 50% thrust capacity.

Thrust in numbers is cool, thrust in the real world is a different story.

Factor in wind, barometric pressure, altitude, moisture in the air, all of this factors in. SO keeping the AUW of the rig at 50% usually just works.
I honestly never look at the claimed thrust after 50% as I hope to never use it. But having GOOD power in resources can really help out.

I was on a shoot recently with one of my bigger hex's flying a Movi M5. The wind was blowing around 20 mph constantly. The wind all of a sudden stopped and combined with a really strange barometric pressure drop that actually popped my ears, my rig fell almost 10 feet in a split second. Since my rig is right around 50% I was able to push full throttle (in atti mode, so more like full "GO UP") and the rig blasted up the extra few feet keeping my rig from splatting on the ground.

 

[SleepyC]

I saw this on another thread I think the user was "Sk8brd" or something like that but he nailed it.. again all based off 50% thrust:

If you know your auw, you can reference the amp draw figures on the kde spec sheets for your prop size and voltage your using to predict hover time. take your auw in grams-to make it easy then divide by number of motors. this is the amount of thrust per motor you need to make your rig hover. reference the spec sheet for that thrust number per motor using the prop size and voltage your using and look at the amp draw. once you know how many amps per motor are being used to hover- multiply that number by the amount of motors on your rig to get overall total hover amp draw. Then convert your batt mah to amp hours then divide by total amp draw and multiply by 60. this will give you hover time ballpark wise if the auw numbers are correct and spec numbers provided by kde are correct. if the spec sheets are not exact for your auw just use closest figures for ballpark numbers.


here is a theoretical example since i cannot explain things well.lol ..


Say my 450 on 6s w/ 11inch props (auw) is 2760 grams. i divide 2760 by 4 to get minimum thrust per gram i need to lift my craft, ends up to be 690 grams of thrust. 2760/4= 690.


i reference the kde spec sheet chart for 6s with the 11X3.7 prop that i'm using and it tells me i can lift 690 grams at 50% throttle at a 2.9 amp draw-*see 515kv spec sheet w/ 6s and 11prop.
take 2.9amps and multiply by number of motors which is 4 on my quad and that equals 11.6 amps for hover for my rig. 2.9*4=11.6
I'm using a 6s 5000mah batt so i convert to amp hours 5000mah becomes 5.0ah then divide by the total amp draw figure which was 11.6 and then multiply by 60...


what it looks like----5.0ah/11.6amps X 60=25.86 ish min-hover time .


* this is using 100% of the battery so multiply the hover time by .8 to use only 80% of the total mah to keep lipo happy which will give you 20.6ish hover time. this is hover time not flight time, can't predict how heavy on the throttle your going to be during flight, altitude, wind etc these can effect numbers as well as components that also use some mah but this will give you ballpark numbers and has worked for me making predictions on builds and comparing motors. The kde's are great, the computer balancing is a biggie for me as i'm only interested in the end raw video result, jello for me is a no no and the added efficiency and build quality of these motors is icing on the cake.


you can also find your amp draw for your flight if you don't have osd with telemetry by using flight time and mah used. simply take mah used convert to amp hour divide by flight time and multiply by 60- thats your total amp draw for your flight.


ex- my 450 used 4000mah and flew for 20.6 minutes. so 4.0/20.6* 60= 11.6 amps---

 

[Cameraj]

Wow, that a power house of a quad what are you going to lift?camera, gimbal etc?

 

[Bartman]

the only problem with the 50% argument is that some of the flight controllers don't love hovering at 50% and actually do much better in the 60 to 70% range. This has been my experience with DJI controllers, for example.

IMHO.

 

[SleepyC]

GH3/4,Zenmuse and 16,000 - 20,000 may of batt. Rig comes in right at 19 - 20 lbs...
"Maldito Bastardo"


View attachment 19188

 

[SleepyC]

the only problem with the 50% argument is that some of the flight controllers don't love hovering at 50% and actually do much better in the 60 to 70% range. This has been my experience with DJI controllers, for example.

IMHO.

I have had the opposite result.
IMHO.

 

[Quinton]

I saw this on another thread I think the user was "Sk8brd" or something like that but he nailed it.. again all based off 50% thrust:

I hear what you are saying, however if you look at a LOT of users setups, they seem to be using as an example Skyjib x4... lots of people are using motors like U5 or 3515-15 or similar along with 15x5 props/400KV motors etc, and 970g is 50% for the U5, now you multiply this by 8 and on this theory they should only be lifting 7.76KG auw, which really is nothing for a machine like that.
Now the motors you mentioned the U7s really are power horses, and maybe an exception, but if you look at a lot of members setups if you take the 50% thrust rate it would barely be able to get off the ground which is not the case, as these things are usually at least 10-13kg AUW, however if you take the 100% thrust data and half it, it makes a bit more sense..to me anyhow.

 

[Old Man]

Some also use a factor to obtain a relative number with a small buffer. They take the 100% thrust power, multiply X 1.2, and divide by 2 to establish the designed total lift capability at 50% throttle. If basing lift capability on 100% power then that capability decreases as the battery sheds voltage, so you can only lift that amount for the few seconds the battery is at full capacity.

 

[adanac]

Thank you all for incredibly helpful information. This is helping me get to one of the most important things about multi's that has eluded me thus far, which is the battery, motor, prop relationship.

Here's another very fundamental question: I typically hear that one needs at least a 1000 to start flying a DSLR for a decent amount of time. If true, why is that the case. Why not just put larger motors on an 800?

 

[SleepyC]

Depends on what the rig is.

On an Octo, the spacing between motors will limit your prop size.

An 800 Octo would probably be around 12" props max. So it would be pretty hard to get motors and props that swing 12" props to get the lift needed for a dslr.
Or take a 800 Hex, it can support 15" props max. And that with the proper motors can carry a DSLR all day. My HC-800 will lift and carry 9 lbs of cargo for 12 minutes using 15/5 props with Avroto 3520's and 65 amp ESC's.

This is also the reason a lot of guys go to the coaxial rigs. you can have a 700mm X8 and swing 18 - 20" props.

There are MANY other reasons for flat or coaxial but this is one for sure!

 

[adanac]

Sorry, I meant an 800 hex.

 

[sk8brd]

nice quad sleepyc! i'm liking those vulcan frames, nice clean designs and frames are light ..sorry off topic but yeah i too only look at 50% thrust values on spec sheets and work from there i like room if a motor goes to stay afloat.

 

[Buzz_Roavr]

I wonder what my max payload would be then? X4 (8 motor config).

Motors are Torx Power Pro 3536
40A Maytech Esc’s
Props 13x6.5 Carbons

 

[Quinton]

I wonder what my max payload would be then? X4 (8 motor config).

Motors are Torx Power Pro 3536
40A Maytech Esc’s
Props 13x6.5 Carbons

Depends if you are using 3 or 4S lipos, also your actual props aren't on the list but it can give you a good idea..
http://www.rctigermotor.com/html/2013/Professional_0912/46.html

 

[adanac]

If you can get this kind of lift from a quad, why does anyone deal with the extra arms, extra weight, extra size and extra cost of an octo to fly large cameras? Is your quad not half-ish the price of a heavy-lifting octo? Your quad will lift my Scarlet no problem.

 

[Quinton]

If you can get this kind of lift from a quad, why does anyone deal with the extra arms, extra weight, extra size and extra cost of an octo to fly large cameras? Is your quad not half-ish the price of a heavy-lifting octo? Your quad will lift my Scarlet no problem.

Redundancy, you have a motor fail your going down.

 

[adanac]

This is great information but I must be doing it wrong. Based on the formula, the hex listed below should have a max AUW of 4.6kg, yet he's flying 7.5kg for 11 minutes! 6x780g (which is the lift at 50% capacity for that motor) = 4.680kg.

T810 with 3-Axis Gimbal + Canon T2i
AUW: 7.505kg (Canon T2i: 1.17 kg, 2x5000mAh:1.45kg, T810: 3.125 kg, Gimbal with 3s 2200: 1.760 kg)
T-motor MT3515 400kv
2x5000 6s with 14"x8.5 props
Actual Power Used: 7478 mAh, 41.6A, 923.7W
Actual Flight Time:10m 47s
Prorated 80%-Battery-Usage Flight Time: 11m 30s
Current/Power: 6.9A per motor, 154 W per motor
Efficiency: 123.1 W / kg