The EXTRA 300 EXT Build Thread

[Dr. Gonzo]

Like I said earlier, I assumed 12s 5000 785gr x 2 that is an extra 1.75 lbs. What will flight times be on 2600 mah @ 75 amps is 2.08 min (wot and not realistic)? 5000 would be 2.5 @120a How was the motor on the extra above hot?

 

[gyro]

Like I said earlier, I assumed 12s 5000 785gr x 2 that is an extra 1.75 lbs. What will flight times be on 2600 mah @ 75 amps is 2.08 min (wot and not realistic)? 5000 would be 2.5 @120a How was the motor on the extra above hot?

Flight times would be longer on the 12s setup I referenced when compared to the 6s setup due to more efficiency. I think there is an error in your calculations...
[MENTION=95]Aeroplayin[/MENTION] where are you?

 

[Dr. Gonzo]

This is interesting.

 

[AKfreak]

This is interesting.

Indeed I stated before, it took me some time to wrap my head around it. However my research proves to me that the 12s will give me much longer flight times than a 6s setup even with reduced capacity of the 12s pack. I will however test and see how the plane flys with 2 5000mah packs in it. I am mainly interested in post stall capabilities, this is why weight is at the top of the list of things to pay attention to in this build.

 

[Aeroplayin]

Flight times would be longer on the 12s setup I referenced when compared to the 6s setup due to more efficiency. I think there is an error in your calculations...
[MENTION=95]Aeroplayin[/MENTION] where are you?

I didn't have time to read through everything and I certainly like to do that so that I'm not covering the same ground twice, but what I don't see are numbers, and numbers tell the story.

Here’s a real example since I see the DM4325 mentioned:

I have an A60-7S 215Kv motor that I had set up on a 2x5S 4000 pack in my 10.7 pound 74 Edge. I was spinning a 21x10 prop to 6500 RPMs and producing 2445 Watts at 66.91A. This is the power equivalent of 2.8 HP and 18.9 pounds of thrust.

67A with a 4.0Ah capacity is a 16.75C discharge rate, or 3.6 minutes at WOT, but at a safe 70% capacity (2800mAh), that’s more like only 2.5 minutes. But if I fly at an average of 33% power, then I would calculate the flying time like this:

67 Amps x 33% power = 22.11A
4000mAh x 70% safe capacity = 2800mAh
2800mAh is 2.8Ah
22.11 Amps divided by 2.8Ah is 7.9C
60 minutes divided by 7.9C = 7.6 minutes.

I then put 2x 6S 3300mAh batteries on the plane and picked up about 60 grams, or a bit over 2 ounces in all-up weight.

I had to drop the prop size down to a 20x8 PJN, and actually saved a few grams there, but the 12S setup with the 20x8 now does 7990 RPMs, 3102 Watts, on 68.59 Amps. This setup produces 21.7 pounds of thrust and at 3.16 HP, and at virtually the same weight and Amps, produces almost 3 pounds more thrust.

To calculate the relative flight time, we can go through the same calculations:

68.6 Amps x 33% power = 22.638A
3300mAh x 70% safe capacity = 2310mAh
2310mAh is 2.31Ah
22.638 Amps divided by 2.31Ah = 9.8C
60 minutes divided by 9.8C = 6.12 minutes

But, of course, this is 6.12 minutes at a higher average power level than the 7.6 minutes because 22.638A on 44.4v is 1005W on average, and 22.11A on 37v is only 818W.

Guys flying a 6S setup on this plane are using 5300mAh batteries, which will be a lighter setup, but at 105A on 22.2v, they are also running a hot setup to only 2331W. The 8 oz you will save needs to be compared with power, so if my 10.7 pound plane is doing 3102W, that’s 290 Watts per pound at under 70A. If I drop 8 oz and generate 2331 Watts, well then that's only 229 Watts per pound at a hot 105A.

Your call, but more cells are more efficient because efficiency is all about more power on less (or the same) current.

If I flew around trying to match the same flight power, I would get more flight time with more cells and less capacity, but since we tend to enjoy the power when we have it, we tend to use it.

 

[3dNater]

Very nice. The numbers truly do tell the story.

 

[AKfreak]

Just humor me fir a sec. lets look at this as, more cells are about not more power, but more about less current draw. Look at the motors/ setups as being equal watts per pound. One draws lets say 120 amps at WOT, and the more efficient setup draws 70 amps WOT. Now imagine putting the largest packs your plane can handle and maintain the same flying weight. Which system would you want?

I am not saying the 6s and 12S systems are equal, because they are not, but just say they are. I would choose the 12s. With that said, I can swing a larger prop with the lower KV motor, and the actual wattage is higher on the 12s setup.

I am down for more power, and swinging a bigger prop for post stall. In the end, we all collect information, then we try to make the best decision we can, but it makes no difference until we put all of the theory to practice.

 

[AKfreak]

Now it's time to finish my wings tonight. And I still have to get servos, grrr

 

[Dr. Gonzo]

This is what I came up with using these figures:

12s 2600 (450g x2= 900g or 31.75oz) based on the estimated amp draw of 75 amps stated earlier.

75 Amps x 33% power =24.75
2600mAh x 70% safe capacity =1820
1820mAh is 1.82Ah
24.75 Amps divided by 1.82Ah = 13.5C
60 minutes divided by 13.5C = 3.6 minutes

Using Gyros numbers from the video above on 6s 5000 (798g or 28.14oz).

115 Amps x 33% power = 37.95A
5000mAh x 70% safe capacity = 3500mAh
3500mAh is 3.5Ah
37.95 Amps divided by 3.5Ah =10.84 C
60 minutes divided by 10.84C = 5.35 minutes

Now we have a more resonable choice
12s 3300 (550g x2=1100g or 38.8 0z) @ 75a

75 Amps x 33% power =24.75
3300mAh x 70% safe capacity =2310
2310mAh is 2.31Ah
24.75 Amps divided by 2.31Ah = 10.71C
60 minutes divided by 10.71C = 5.6 minutes


So the way I see it, running the 6s 5000 you already have wins hands down. Cost is free since you have the packs. Only one pack to mess with. Now if you had a bunch of 6s 3300 around that would be a different story. Assuming these are 30c 6s 5000 (peak 150a) or better packs 115 amps is no problem. Not really "beating" on a pack. So based on my calculations here, the weight of the 6s would lower wing loading for post stall flight. Still provide 2700 watts and 245 watts per lb. If you can make the 11lb weight. Look at the video above! So if you are drilling lightening holes to shave weight the first place to look would be pack weight. If weight is a primary concern you may give up some efficiency to get it. It is indeed a balancing act. If I made any mistakes pleas correct me, it is late and I am tired.

 

[Dr. Gonzo]

12s 5000 (798g or 28.14oz x2=56.28 oz or 3.5 lb).

75 Amps x 33% power = 24.75A
5000mAh x 70% safe capacity = 3500mAh
3500mAh is 3.5Ah
24.75 Amps divided by 3.5Ah =7.07 C
60 minutes divided by 7.07C = 8.48 minutes