You neglected to say how much the rest of the plane weighs. You need to match the total energy available from the pack to the plane weight -- get it wrong, and you either don't have enough battery, or you don't have enough oomph to finish a flight.
But, let's analyze.
First, let's ignore Kv:
One 3000mAh 3.7V cell will deliver (approximately, and at the very most) (3A) * (3600 seconds) * (3.7V) = 39960 Joules. Round that to 40kJ.
Four of 'em will deliver four times as much: 160kJ.
Five of 'em will deliver five times as much: 200kJ.
If you need 200kJ to fly your plane, you need 200kJ to fly your plane. Going to a 4s pack would mean you'd need to increase the battery capacity by 5/4, to 3750mAh.
How heavy is the plane going to be? A 60 ounce plane would need those 200kJ, so it'd need the extra cell. A 48 oz plane could get by with the 4s pack.
Now, let's pay attention to Kv:
That 750kV motor could be made to turn up to 10k RPM on five cells (really, you'd want it slower, but 10k max). On four cells, you would only be able to ask for about 8300 RPM. That's kinda slow: you could maybe make it work with a high-pitch prop, but speed regulation would suffer.
Now, let's pay attention to battery pack capacity:
If you need to use that motor, and if your plane isn't going to weigh 60 ounces, then don't use fewer cells: use five smaller cells. You weight will go down roughly proportionally to the cell capacity, and your motor will turn fast enough.
Topic: 4s against 5s (Read 858 times)
