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Old Oct 09, 2012, 12:46 AM
If it broke, i probably did it
United States, NV, Las Vegas
Joined Jul 2012
53 Posts
Quote:
Originally Posted by flyingdogfilms View Post
Hey little Dietr just needs to fly.

One thing I'm curious about which I've seen very little information on is the power consumption of the different flight boards. I originally started with the KK board and when I moved on to the multiwii I saw a noticeable drop in flight time. I'm curious how MK Naza HF and all the others would stack up all other things being equal.
Flying dog,

Would it be possible to run a data logger between your power supply and your flight board to see what kind of amperage draw you have at the board?
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Old Oct 09, 2012, 12:52 AM
If it broke, i probably did it
United States, NV, Las Vegas
Joined Jul 2012
53 Posts
Jsey,

I see where your going with your reply and I will admit that I may have jumped the gun about being "blown off" or feeling like I wasnt getting any "positive feedback". To me it just seemed as though dudes were chiming in to tell me that I was dumb for even thinking that it could be accomplished. I may be a rookie but Im not shy about asking the questions that hopefully some of the experts can help me with. Instead of spending countless hours researching and clicking from one webpage to another, why not just ask the experts, you guys.. Thanks for putting me back in check and hopefully you can share some knowledge on how I can further my endeavor.

Thanks,
Dietr
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Old Oct 09, 2012, 02:41 PM
Registered User
Australia, NSW, Mt Hutton
Joined Jul 2007
144 Posts
Just think of it as
Weight is evil - less flying time
the more weigh eg batteries the bigger the props needed to lift it - the bigger props need bigger motors - more weight added and so on it goes
a circular arguement
its then a matter of finding a happy balance
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Old Oct 09, 2012, 04:03 PM
If it broke, i probably did it
United States, NV, Las Vegas
Joined Jul 2012
53 Posts
Quote:
Originally Posted by joeb56 View Post
Just think of it as
Weight is evil - less flying time
the more weigh eg batteries the bigger the props needed to lift it - the bigger props need bigger motors - more weight added and so on it goes
a circular arguement
its then a matter of finding a happy balance
Exactly, now the key is to break the circle.. I am gonna try and run two 8000mah 4s packs to begin with at roughly 1.8lbs a piece. If I get good results then I am definetly going to consider going to two 4s 11000mah packs at roughly 2lbs a piece. I am going to start with a single data logger on one motor just so I can get a feel for what the motors are doing then I hope to eventually run a logger on each motor to see how different flight regimes draw different amps..

Dietr
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Old Oct 09, 2012, 04:27 PM
Posted as eflightdude 06-07
United States, IL, Peoria
Joined Aug 2012
133 Posts
Quote:
Originally Posted by Dietr777 View Post
Exactly, now the key is to break the circle.. I am gonna try and run two 8000mah 4s packs to begin with at roughly 1.8lbs a piece. If I get good results then I am definetly going to consider going to two 4s 11000mah packs at roughly 2lbs a piece. I am going to start with a single data logger on one motor just so I can get a feel for what the motors are doing then I hope to eventually run a logger on each motor to see how different flight regimes draw different amps..

Dietr
Your max flight time, for a given frame, as it relates to batteries, is given when the weight of your battery or batteries is one-half the ready to fly weight of the quad. Less then that, and you are below max capacity, more then that, and you have to lift more weight then the energy you gain. For the proof, look at this thread: http://www.rcgroups.com/forums/showthread.php?t=1733300 Go down to post #8 for the mathematical formula showing this. Post nine shows a graph of a quad showing flight time vs mAh, and the peak of the curve is just about where the battery matches the weight of the rest of the quad (14,000 mAh, in this case).

I found another thread about efficiency in general, 89 posts long, and I mainly just skimmed it and bookmarked it for later. It may be of use, it talks about other things then the batteries, because although good quality batteries and matching the weight to the weight of the rest of the quad is important, there are other important topics. Motors are more efficient as a certain speed/loading. Propeller size matching and other factors. ESC efficiency. Motor speed, pack voltage (3s, 4s, 5s, ..), and so forth. http://www.rcgroups.com/forums/showthread.php?t=1719368.

Those are the only things I had saved in regards to long flight times, which are of interest to me as well. However, I myself cannot yet implement them, as I have not yet built a quad. I have an order place, and it got to New York on the 3rd or so, and last I knew it was still sitting there (USPS tracking is down right now). Hopefully my research was able to help you.

Now I'm curious. If the max battery size for longest flight time always equals one-half the weight of the quad, for a given frame, then what happens with a heavier or lighter frame? You raise or lower the weight of the battery to match, but there is more or less weight, respectively. Hmm...
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Old Oct 09, 2012, 05:24 PM
Don't drink and fly
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646 Posts
Just remember, the bigger they are, the harder they fall. S800's falling only 1-2 meters seem to shatter on impact. 18,000 mAH 6S battery would be about 6 pounds, so roughly 12 pounds aircraft. That's almost a bowling ball.
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Old Oct 09, 2012, 05:45 PM
If it broke, i probably did it
United States, NV, Las Vegas
Joined Jul 2012
53 Posts
Jsey,

Dude, I am in the same boat.. Thanks to the chinese festival and holidays my stuff has just finally departed from NY.. Running some quick numbers here is where I am at weight wise:
Hexa 700mm Frame: 400g
Six motors (70g per): 420g
Six ESC (30g per): 180g
AR8000 receiver + TM: 30g approx
props: 80g
two data logger (17g per): 34g
Wookong flight controller: 150g
Power distro board: 100g approx
Other (wire, misc) 100g approx

Total airframe: 1494g approx or 3.3 lbs approx

8000mah batt (845g per): 1690g or 3.7lbs
11000mah batt (825g per): 1650g or 3.6lbs

Total approximated weight will roughly be 7 to 8 lbs while stripped down.

So here I have 2 batteries that out weigh my initial frame setup. But I will be getting 16000mah or 22000mah respectfully. Are you saying that I will lose flight (max efficiency) time because my battteries arent equal to half of the hexa weight?

I would think that a lighter frame would draw less amps. Now granted I am adding a lot of battery weight which will increase the amp draw due to weight. The video posted earlier in this thread with the 62 minute flight time showed the guy using two 11000mah packs on a very small quad and not doing any real maneuvering. My assumption is that yes amp draw goes up but huge mah numbers give you back time and then some.

Thoughts?

Thanks,
Dietr
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Last edited by Dietr777; Oct 09, 2012 at 06:37 PM. Reason: correction
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Old Oct 09, 2012, 09:10 PM
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Colorado
Joined Oct 2004
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So the total weight of your hypothetical craft is 8lb. Your power system will need to produce at least 8lb. of thrust to keep in the air (hovering). Assuming a quad configuration, each motor/prop needs to produce 2lb. thrust minimum. What is the power (iow, current draw based on battery voltage) the motor/prop combo needs to produce this amount of thrust? Unless you have some idea what this number is, you are flying blind.
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Old Oct 09, 2012, 09:45 PM
If it broke, i probably did it
United States, NV, Las Vegas
Joined Jul 2012
53 Posts
850g per motor is the spec. Im guessing thats on a 4s with the recommended 9x6 props. There will be 6 motors combined to produce approx 11.2 lbs of thrust. The max amps is 23.2 and the max power is 243W per motor (again i believe this is based on the 4s config). Im still learning lipo calculations and kv calculations but I think these should be sufficient for initial testing.
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Old Oct 09, 2012, 09:59 PM
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Colorado
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Ok, here is another way to look at it. Your larger battery (22000maH, 4S) will supply 44A for 30 minutes. That is 7.3A (44/6) per motor. The motor is rated at a theoretical 850gm. thrust (with a 9x6 prop) while drawing 23A. So the question is will the motor/prop combo deliver 605gm (2lb/6) of thrust at a (maximum) of 7.3A for you to get 30 minutes of flight time. Doesn't look like it will. What do you (or perhaps others who use similar sized craft) think?
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Old Oct 10, 2012, 06:49 AM
Posted as eflightdude 06-07
United States, IL, Peoria
Joined Aug 2012
133 Posts
Quote:
Originally Posted by Dietr777 View Post
Jsey,
So here I have 2 batteries that out weigh my initial frame setup. But I will be getting 16000mah or 22000mah respectfully. Are you saying that I will lose flight (max efficiency) time because my battteries arent equal to half of the hexa weight?

I would think that a lighter frame would draw less amps. Now granted I am adding a lot of battery weight which will increase the amp draw due to weight. The video posted earlier in this thread with the 62 minute flight time showed the guy using two 11000mah packs on a very small quad and not doing any real maneuvering. My assumption is that yes amp draw goes up but huge mah numbers give you back time and then some.

Thoughts?
Yes, that's what I'm saying. More battery capacity gives you more energy storage (mAh), but only to a certain point, and that point is around (probably not exactly) where the weight of the batteries is half the weight of the entire quad, ready-to-fly. Yes, you gain more storage, but at a certain point the amp draw to lift the weight negates that extra storage ability.

Sometimes it's helpful to think of extremes to understand a concept. Think about adding so much weight your motors can't produce enough thrust to get it off the ground. What's your flight time? Zero, of course. Well, think about taking off weight until your quad just barely flies. Motors are screaming at full power, you're pulling huge amounts of current. What's your flight time? Very little. As you take off more weight the motors draw less and less power, so you need less capacity for a given flight time. It doesn't matter were this weight is coming from though, the batteries or the quad, right? If you have a lightweight quad and add a ton of batteries, it still can't take off. If it can barely fly it won't fly for long cause even though it has a ton of capacity, you're draining the batteries at an insane rate just to stay up.

So now that we've done that, let's skip to the other extreme. You've got the same nice, lightweight quad as before, only this time you take all the batteries off. If you have no battery weight, your flight time is, again, zero. Notice now, we have zero on both sides, both too light and too heavy, so we have to have a curve of some sort in between them. If you add a small battery, assuming it's big enough the current draw doesn't burn it up, you have a short flight time. This is due to not having a large capacity for energy storage. You add more batteries, your flight time does up. But it doesn't go up in a straight line, each additional battery gives less flight time then the one before it did, because the current draw goes up faster then the energy storage is added. Say you get 5 minutes on one battery. Add another of the same size and you should get 10, but you don't, you'll get maybe 9 minutes of flight. Add a third one, and instead of 15 minutes, you may get 12. Add yet another one, and while you should be at 20 minutes because of the capacity, you may only get 14 minutes. This can't continue forever. For this, I'm just saying that each battery gives one less minute then the one before did. Let's put my completely hypothetical scenario in a better way:
  • 0x batt: 0 minutes
  • 1x batt: 5 minutes
  • 2x batt: 9 minutes
  • 3x batt: 12 minutes
  • 4x batt: 14 minutes
  • 5x batt: 15 minutes
  • 6x batt: 15 minutes
  • 7x batt: 14 minutes
  • 8x batt: 12 minutes
  • 9x batt: 9 minutes
  • 10x batt: 5 minutes
  • 11x batt: 0 minutes
Again, this is all just hypothetical, but does it make sense? Note how adding the 6th battery did not increase the flight time. Now, the current draw increased so much with the additional weight, that the extra capacity did no good. The next battery took away a minute of flight. Then all the way at the bottom we get to battery number 11, and it can't even take off anymore. Lets graph this:

Notice we have a nice curve. But does this make sense? I was doing a hypothetical situation, anyhow. Well, let's see:


Source post: http://www.rcgroups.com/forums/showp...75&postcount=9

Hmm, my situation gives the same sort of curve as the real-life test graph. Does this help you understand?

Also, note on the test graph, that going from 10 Ah to 14 Ah only gave 3 more minutes of flight, yet the initial 4 Ah gave 24 minutes of flight, or you can say that 29% of the max capacity gives 57% of the max flight time. This here lies the problem with getting the absolute longest flight time. With a heavy quad, it's expensive. With a light copter, who cares? Have the weight isn't much money in batteries. But with a heavy one, like the one in the graph, 4 Ah is what, at least $25, and that gave you your last 3 minutes of flight time?

The thing you want to do is to try different capacities, and while I'm sure they won't be exactly spot on with these mathematical calculations and graphs, I'm also sure they will be pretty close. I'm planning on doing my own real-life graph to show other people who have problems, as soon as I have my own quad and enough practice and batteries to do so. Good luck, keep us updated!

P.S. By pretty close, I mean take a look at the 62 minute quad. It was 2400 g ready to fly, and the batteries were 1680 according to maxamps.com, which is 69% of the ready to fly weight of the quad. Would he have gotten more time had he put in less capacity? Who knows, but at his level experimenting gets pricey, he had $300 batteries, and had two of them, so he paid $600 for those batteries. Trying lots of similar sizes would get pricey, fast. But he probably tweaked it a lot in other ways, too. Just think of it as possible room for improvement.
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Old Oct 10, 2012, 08:20 AM
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Miami, FL
Joined Jul 2003
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@jseyfert3

I just have to say, that was an excellent post!

-dave
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Old Oct 10, 2012, 01:20 PM
Posted as eflightdude 06-07
United States, IL, Peoria
Joined Aug 2012
133 Posts
Quote:
Originally Posted by dalbert02 View Post
@jseyfert3

I just have to say, that was an excellent post!

-dave
Thank you. It took a while to do, but I had time to spend since I don't have the parts to build my quad yet.
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Old Oct 10, 2012, 02:52 PM
If it broke, i probably did it
United States, NV, Las Vegas
Joined Jul 2012
53 Posts
Jsey,

The simplistic breakdown is perfect. I think I will just have to data log and crunch numbers until I find the proper config. At least now I have a good starting point to build from.. Thanks for all of the good info and I will keep you posted as the build and testing moves forward. I think my power systems should be in by the end of the week and then I dont expect to see my hexa frame until the end of the month. On top of all that, we just had our first kid so she is absorbing a lot of my time..

Thanks again for the info,
Will talk soon,
Dietr
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Old Oct 26, 2012, 01:30 AM
If it broke, i probably did it
United States, NV, Las Vegas
Joined Jul 2012
53 Posts
Atg 700

Gents,

Here is the first pic of my new ATG 700 that I have almost completed.. Got some 4S 8000MAH lipos in that I am going to try ang hang on this bad boy.. I will keep you posted on how she does..

Dietr
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