I have an old BNB Digital Power recorder so I wanted to have a look at the hovering power requirements of my quad. The weight of the quad with either battery is very similar.
Quad specs:
APM2
KDA20-22L motors from Hobbyking
2 x Super Simple 25-30A ESC's from Hobbyking
2 x Hexfet 25A ESC's from Hobbyking (2 of 4 were DOA)
10 x 4.5 props from Goodluckbuy.com
Batteries: 4S 2200mAh Nanotech 25C
3S 3000mAh Turnigy 25C
X525 frame
3S TEST: *taken from level portion of graph excluding full power climb | 4S TEST: *taken from level portion of graph excluding full power climb |
Current Max: 17.58 A Full power climb: 41.99A, 464W Weight: 1263g | Current Max: 14.89 A Full power climb: 41.50A, 552W! Weight: 1268g |
Full Graph | Full Graph |
Comments
Voltage of the 4S graph at the end of the flight (but still flying) was 3.6V per cell, so yes, very close.
The voltage of a fully charged cell (4.2) will drop like a rock and stabilize and stay more or less linear around the nominal voltage (3.7v) under load. After you remove the load the cell voltage may rise again to a higher if there is enough energy left in the cell.
Yup, the 4S pack's max voltage seems a little low but once hovering/discharging the voltage of a LiPo doesn't vary considerably except the very beginning and the very end of a discharge, so this is fairly indicative of what's happens. It's also not intended to be scientifically accurate at all, this was just for interests sake. I may do another with the 4S pack starting at 16.8V but I doubt the numbers will vary that much. As for other loggers or prop matching, sorry, I'm not really worried :)
I don't believe that the starting voltage of these batteries is indicative that they were charged to capacity. Maybe I'm reading your stuff wrong. You also need to adjust for mass of the battery to get a good comparison between the two setups. You should really buy one of those Eagletree loggers, calibrate it, and then you could provide the graphs in a much easier fashion and show one of those mAh vs. time plots. There are also quite significant differences between battery vendors .... I also totally agree with @John that prop matching would help.
3S should start at ~12.60 V if properly charged
4S should start at ~16.80 V if properly charged
Don't think of this is you did something wrong. Just think of it as the start of a long an interesting project.
At 4S the motor/prop size is probably mismatched. As a general rule of thumb it is more efficient to raise the voltage then to raise the current in electrical application. A lower kv motor would give better 4S results.
Yes, although the average current with the 4S pack is lower, the 3S 3000mAh pack will fly longer. It would be interesting to know how a 4S 3000mAh pack with it's increase in weight would affect flight time.
Not sure how that was calculated. Back of the envelope I get 3s = 11.88 min, 4S = 9.90 min. 4S has more lift power, 3S has longer flight time at that weight, but as weight increases this will have a crossover and the 4S will get longer flight times at some point on the curve.
The 4s was 2200mah. If you upped it to 3000mah, the weight would increase and thus the hover amps. If you could find a 4s 3000 that weight the same as the 3s 3000 post a link! :)
Hi,
it looks to me like 4s will deliver longer flight times. Averange amps is 1.81 amps less.
At 3000mAh:
3s flight time with avg 15.14 is about 12 minutes.
4s flight time with avg 13.33 is about 13 minutes 50 seconds.
Very cool! So it looks like you are getting longer flights with the 3s. I wonder how a lower kV motor would perform. I have an eagle tree and have been doing similar analysis. Haven't tried a 4s though