For a UAV application weight and volume and price is a constant battle.
normally one would use commercially available lithium polymer batteries for this kind of project.
But the quest to longer flight times requires the use higher energy density batteries.
In this case it consisted of moving from a 6 cell 8000 mAh Li-Po battery weighing at 1300 grams to a 6 cell 3 parallel 8700 mAh battery pack weighing at 870 grams consisting of 18 Panasonic NCR18650PF Li-Ion batteries in a quadcopter design.
The motors and propeller size were specially selected for this new battery pack. A increase of 700 mAh and an decrease of weight by 430 grams was realized by using this newly designed battery pack.
In theory the used quadcopter would only hover for ~35 minutes and it would be empty. But because these cells allow safe discharging to 2.5V a hover time of 45 minutes was achieved using Arducopter’s position hold mode in 3-4 Beaufort wind condition. The pack even had charge to spare, at landing there was 17V in he battery pack. When discharging to 2.5V per cell this would be 15V. So additional flight time can be achieved by draining the battery completely.
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