Batteries

[jfro]

I'd highly recomend keeping on that path with the voltage part, the heavier the load the less pack i like using up to give a margin in the flight envelope like your doing

We fly epics on gens ace and see almost a volt in sag, i'll fly it down to about 21.5 at about 6 minutes and land at 22.3-22.5 ish, half packs used. my hex has a bit less sag with all the same but u series stuff, and i do about the same numbers,,,,, were on 20 amp hours of 6s in pairs parralel

the math for a c rating is suppose to be c rating times capacity equals continuous amp rating.... 10 amp hour 30c pack is 300 amp service...

doing pairs of packs vs single packs is a huge weight difference and cutting every gram is the best way to go... nothing in excess

Please let me know if this is somewhat correct.

#1 8 Tiger u5 motors have a rating of 20 amps at 100% throttle with 16" 5.5 props. 8x 20 = 160 amps draw.
Their max rated draw is 30 8x30 = 240 amp draw. max

The new 10,000 mah Multistar has a 10c rating with a max of 20c for 10 seconds. 10cx10amp hr = 100 amps
20cx10amp hr = 200amps

Conclusion, these batteries would not be enough for a 8 u5 motor MR.

#2 4 Tiger u5 motors 100% throttle 16" props 4x20 = 80 amps
max amp of motor 4x30 = 120 amps
The new 10,000 mah Multistar has a 10c rating with a max of 20c for 10 seconds. 10cx10amp hr = 100 amps
20cx10amp hr = 200amps
Conclusion, this would be enough for a 4 u5 motor MR.

#3
Tiger u4 motors on a hex w/ 15" props 100% throttle 15' props 6x17.2 = 103.2 amps
max amp of motor 6x30 180

The new 10,000 mah Multistar has a 10c rating with a max of 20c for 10 seconds. 10cx10amp hr = 100 amps
20cx10amp hr = 200amps

Conclusion. Kind of on the edge, but maybe ok if c rating is not fudged and full throttle on 15" props is just for a few seconds. Kind of close on this?


Would appreciate some feedback as to if I'm doing the numbers right.

Thanks in advance............

 

[R_Lefebvre]

Why on earth would anybody engineer a system based on the maximum amperage rating of a motor?

For example, I'm currently using KDE 2814XF 515 motors on my quad. Rated at 24A each. That's 96A. I'm using a 8000 mAH battery rated at 10C. 80A continuous. Ooops, the battery can't deal with it...

No.

The reality is that the motors draw 3.125A in a hover. 12.5A total. They're only drawing the battery at 1.6C. That is completely fine for the battery. Maximum amperage rating of the motor is completely meaningless in this calculation.

If I were to give it full throttle, the motors will draw 16A each, 64A total, still less than 10C. And the reality is that you'll never ever have them all at 100% throttle, highest would be 80%, so only 51A total, which is only a 6C rate. Totally fine.

doing pairs of packs vs single packs is a huge weight difference and cutting every gram is the best way to go... nothing in excess

And this... are you suggesting not to use 2 packs in parallel? Sorry, but I have to strongly disagree. The weight difference is not that much. But importantly, it offers redundancy on your power supply. If one battery goes open cell, as they sometimes do, you're done if you only have 1 battery. With 2 batteries, the system voltage drops, you see it, and land.

The only time I use single batteries is on cheap quads.

 

[kloner]

if one pack goes open cell in a 2 pack system being wired parralel does nothing, other than drag the whole setup down anyways. only reason to run 2 packs is to give more amperage rating..... and leaves a break point because of the ability to not plug both packs in and fly, ie systems setup to count on both packs be it plugs, battery rating, whatever..... i've done it several times, it's what made us go to manadatory check lists, none the less not everybody can get that extreme

 

[R_Lefebvre]

No.

If one cell goes open, the entire pack becomes invisible to the rest of the power system, and nothing happens except now you're flying on a single battery. And if you've designed everything right, you'll still be able to land safely.

If your craft design is marginal, such as flying at 80% throttle and 5-10 minute flight times, then yes, it'll probably come down anyway as the remaining battery won't be able to handle the load. But that's not how I build my machines.

 

[kloner]

we've had one major crash on set, it was attributed to blowing a cell and the whole thing wigged out..... came down like a bag of rocks so however your running it and thinking somethings better there, good luck

You'd be surprised how a few grams can change everything. on a disco 20 grams is 3 minutes of flight time

 

[R_Lefebvre]

I don't know what your setup was. But I can tell you when I build a system, it will survive it just fine. And on my quad, 20g is about 15 seconds of flight time. Should be about 2 seconds on a 20lb Octocopter.

 

[Motopreserve]

R_L: my question would be whether the amp draw ever spikes to a higher level than we expect on burst up, or any sudden Burt of throttle given a "what if" scenario. I had a situation not long ago where the battery must have sagged toward the end of flight, and while it began to decend somewhat rapidly I was pushing up toward full throttle to control the rate of descent.

Later, when I checked the superx flight log it showed that most of the 6 motors had been near 99%. While this may have been shorter than 10 seconds, I'm not sure if want to push that calculation too close....

 

[jfro]

R_L: my question would be whether the amp draw ever spikes to a higher level than we expect on burst up, or any sudden Burt of throttle given a "what if" scenario. I had a situation not long ago where the battery must have sagged toward the end of flight, and while it began to decend somewhat rapidly I was pushing up toward full throttle to control the rate of descent.

Later, when I checked the superx flight log it showed that most of the 6 motors had been near 99%. While this may have been shorter than 10 seconds, I'm not sure if want to push that calculation too close....

My earlier post was meant to infer something on the order of do you push the published calculated amps and have some overhead? Do you trust the manufactures numbers or wait for real world confirmation?

When I bought ESC's for my 3515's and 3520's, I used the 100% throttle %'s plus some for headroom. I did not use the max amp number. I've had no problems, but I do not fly fast. I am more of a drifting/filming guy.

 

[R_Lefebvre]

At 100% throttle, they will not draw more than whatever it is they draw at full throttle with that prop. It's the prop in combination with the motor that determines maximum load. Any given motor will have different max amp draw depending on the propeller that's mounted on it. The maximum amperage rating from the motor vendor has nothing to do with this at all, that is just the maximum rated amperage for the motor before the windings start to melt. If you stick too large of a propeller on your motor, the load will be too great, and the amperage will go over the maximum rating, and you'll damage the motor. This is why these things are engineered as a system.

Now, during transients, as the motor is accelerating, obviously it will draw more. But we're looking at the constant load here, not the transients that are only in effect for 1/10th seconds.

 

[Motopreserve]

Jfro: I don't rocket around either - it really would be for a worst case scenario that I would want to know how these new batteries (and any battery) reacted. I don't think I'd ever come close to pushing the limits during normal flights, but I've had a few hairy moments - and that's when the Multistar batteries would show their mettle.

R_L: totally get the concepts. I have based my conclusion on the published data that KDE has provided for my motor/prop combo (excluding prop brand variables). If I pad calculation a bit - these are running close to max on the 100% transients that "may" occur. Also, this is all based on KDE data - and I will getting some of my own as soon as Bart forwards me some motors for testing. It would be interesting to throw one of these new batteries on the thrust/watt tester to see how they perform. Obviously not real world - but may provide some further insight.

 

[R_Lefebvre]

We really need to look at specific numbers here, because this is getting confusing. Too much hand-waving.

From what I have seen, people in the pro film industry are pushing the limits, and not designing reliable power systems. The whole aircraft design is not robust because it's too close to the edge. So we get into these problems. They're simply trying to lift too much weight, with machines that are too small. Yes, you can lift a Red Epic with an octo with 18" propellers, but it's not efficient. That results in pushing the design limits of the available motors, ESC's and batteries.

Anyway, all I know is the batteries are working fine for me, because I'm well within their design specs at about 1.5C continuous, and maybe 5C maximum. I also like to "pad" things, usually to a factor of 2:1. The problem is when trying to fly a 20+lb machine on 18" props, there's no room left to pad.

 

[Benjamin Kenobi]

We really need to look at specific numbers here, because this is getting confusing. Too much hand-waving.

From what I have seen, people in the pro film industry are pushing the limits, and not designing reliable power systems. The whole aircraft design is not robust because it's too close to the edge. So we get into these problems. They're simply trying to lift too much weight, with machines that are too small. Yes, you can lift a Red Epic with an octo with 18" propellers, but it's not efficient. That results in pushing the design limits of the available motors, ESC's and batteries.

Anyway, all I know is the batteries are working fine for me, because I'm well within their design specs at about 1.5C continuous, and maybe 5C maximum. I also like to "pad" things, usually to a factor of 2:1. The problem is when trying to fly a 20+lb machine on 18" props, there's no room left to pad.

Totally agree! Lots of overhead is a great thing. :nevreness:

 

[Motopreserve]

Totally agree! Lots of overhead is a great thing. :nevreness:

I too agree - headroom and padding is the best piece of mind. My specific rig could draw 102A total at 100% (based on MFG published data for my motor/prop) if I had to nail it. If the superx data log is to be believed - I've actually hit 99% for a prolonged period (can't say exactly how long - but it felt like forever). Unfortunately I was not data logging so I have no corroboration between my physical throttle spike and the amp draw.

Either way, the 100A would be fine for me 99% of the time - if the battery data/spec is correct.

 

[fltundra]

Oh! They didn't have anything bigger than 6A I think when they first released them (I looked only 2 weeks ago!). Nice. 10A would be plenty for me - I was even thinking 8A. Especially if I ran 2 for 20A is be sitting pretty

so you have not experienced any premature voltage sag or drops end of flight???

None! 15 flights so far.

 

[stevemaller]

We really need to look at specific numbers here, because this is getting confusing. Too much hand-waving.

From what I have seen, people in the pro film industry are pushing the limits, and not designing reliable power systems. The whole aircraft design is not robust because it's too close to the edge. So we get into these problems. They're simply trying to lift too much weight, with machines that are too small. Yes, you can lift a Red Epic with an octo with 18" propellers, but it's not efficient. That results in pushing the design limits of the available motors, ESC's and batteries.

Anyway, all I know is the batteries are working fine for me, because I'm well within their design specs at about 1.5C continuous, and maybe 5C maximum. I also like to "pad" things, usually to a factor of 2:1. The problem is when trying to fly a 20+lb machine on 18" props, there's no room left to pad.

My big octo is relatively efficient in the configs I fly. I'm using Mikrokopter electronics, so I have exhaustive data logging.

My copter is an X8 with 500mm booms on a Cinestar-like hub. I have the full MK stack including the "Double Quadro 2XL Cool" power board, KDE 4012 motors and T-motor 16" CF props, and a MōVI M5.

What I see on my machine is a current draw at hover of about 58A with the GH4 (AUW about 22 lbs.) and a draw of 67A at hover with the 5D Mark III (23 lbs). I'm using dual Tattu or Pulse 10000mAh LiPos. The highest current draw I've seen in a full-out climb (not that I generally do that) or an arrested descent is about 110A. In a normal flight for filming purposes, the copter consumes almost exactly 1000mAh/minute, giving me a 15 minute flight time with 25% reserve (although I usually fly 8-10 minutes).

 

[kloner]

that's a similar draw i see with a skyjib with 3520 and my 1100 hexacrafter with u7..... then with an epic we get up towards 100-120 amp draws... both have a similar draw, the u7 just have half throttle to hover with epic, jib is running at 60-65%

 

[R_Lefebvre]

My big octo is relatively efficient in the configs I fly. I'm using Mikrokopter electronics, so I have exhaustive data logging.

My copter is an X8 with 500mm booms on a Cinestar-like hub. I have the full MK stack including the "Double Quadro 2XL Cool" power board, KDE 4012 motors and T-motor 16" CF props, and a MōVI M5.

What I see on my machine is a current draw at hover of about 58A with the GH4 (AUW about 22 lbs.) and a draw of 67A at hover with the 5D Mark III (23 lbs). I'm using dual Tattu or Pulse 10000mAh LiPos. The highest current draw I've seen in a full-out climb (not that I generally do that) or an arrested descent is about 110A. In a normal flight for filming purposes, the copter consumes almost exactly 1000mAh/minute, giving me a 15 minute flight time with 25% reserve (although I usually fly 8-10 minutes).

What voltage are you using? 4S or 6S?

I'm assuming 6S, in which case, you're using 132 Watts/kg to hover. You're not efficient unless you're under 100. My quad does 90 W/kg.

The issue is you're lifting 10kg on about 0.51 m^2 of disk area. Or 19.6 kg/m^2

Compare that to my quad, which is 2.099kg on 0.456m^2. That gives 4.6 kg/m^2.

This means that to fly, your props must accelerate the air to a much higher speed than in my case. That is less efficient. There's no way around this rule unfortunately.

 

[stevemaller]

What voltage are you using? 4S or 6S?
I'm assuming 6S, in which case, you're using 132 Watts/kg to hover. You're not efficient unless you're under 100. My quad does 90 W/kg.
The issue is you're lifting 10kg on about 0.51 m^2 of disk area. Or 19.6 kg/m^2
Compare that to my quad, which is 2.099kg on 0.456m^2. That gives 4.6 kg/m^2.
This means that to fly, your props must accelerate the air to a much higher speed than in my case. That is less efficient. There's no way around this rule unfortunately.

6S, yes. I've been wondering why there aren't good mid-range "efficiency" motors out there. I guess T-motor is coming out with the U6, which may provide the kind of profile that'd come closer to your ideal numbers.
What do you recommend that would achieve the numbers you have for your quad when lifting the kind of weight I fly?

 

[R_Lefebvre]

6S, yes. I've been wondering why there aren't good mid-range "efficiency" motors out there. I guess T-motor is coming out with the U6, which may provide the kind of profile that'd come closer to your ideal numbers.
What do you recommend that would achieve the numbers you have for your quad when lifting the kind of weight I fly?

That's sort of my point. The only thing you can do to reach my numbers, would be to use much bigger props, which would require a much bigger frame. It's a natural law, that the biggest determinant of efficiency is the disk loading, weight/area. You won't get meaningful increased in efficiency from your power system. You can get a little bit more, but not compared to disk area. Actually, I was frankly surprised you're even getting 132W/kg. That's pretty good with that weight.

 

[stevemaller]

That's sort of my point. The only thing you can do to reach my numbers, would be to use much bigger props, which would require a much bigger frame. It's a natural law, that the biggest determinant of efficiency is the disk loading, weight/area. You won't get meaningful increased in efficiency from your power system. You can get a little bit more, but not compared to disk area. Actually, I was frankly surprised you're even getting 132W/kg. That's pretty good with that weight.

I'm curious what you would do to fly a 8-9 pound payload (gimbal, camera and FPV gear)?