15 Minutes

I got a solid fifteen minutes flight time on a single battery! To achieve this, I got a bigger battery, of course, changed props, and moved from 3S to 4S power.

Actually, the prop change was the inspiration for the upgrade. I wanted to switch from the 10" props I've been using to the slightly smaller DJI 9450's. I think that I've been getting some camera vibration from the prop downwash and smaller props will be a little further away. But smaller props generate less thrust and my calculations showed me already past the 2:1 thrust to weight target. But move up from 3S to 4S LiPo's and the higher voltage lets the same motors and props generate significantly more thrust. For the EMax 2216 motors and DJI 9450 props, a 3S LiPo will give only 600 grams of thrust. Using a 4S LiPo, the same combination can generate 910 grams of thrust! This gives me the payload capacity to carry the much larger 5200 mah 4S2P battery, shown below with the the 3S1P 2700 mah battery I was using, to get to fifteen minutes of flight time.

When moving to a higher voltage battery, one must consider if each piece of gear connected to that battery can take it. The motors and ESCs are rated for 3 or 4S. The flight controller and radios all run off 5V provided by redundantly by one of the ESC's BEC and from the power module. The camera (Firefly 6S), gimbal (Storm32), and transmitter (Boscam ts832) I'm using have ratings as low as 2S and as high as 6S, but they can all do 4S. The one piece of gear on my S500 drone that both needs 12V and can't take the 16.8V that a 4S LiPo runs fully charged is the little on-screen display (OSD) unit. I've heard several stories of these things being burned out by high voltage. So I got a 7812 voltage regulator and a 100uF 25V capacitor and put them in the line that goes between the video transmitter and the OSD unit. You can see the results, installed on S500 drone, here:

Watching the OSD, I can see that the drone actually works less with the heavier battery attached. With the 3S battery, it takes around 60% throttle to hover, while with the 4S it only takes 40%. This helps explain why a doubling of capacity (2700 to 5200 mah) gives more like a tripling of flight time (5 vs 15 minutes). It also makes more sense it we look at watt hours instead of just milliamp hours. Simply multiply by the nominal voltage (I'm using 11.1 and 14.8) and we get 30 watt hours for the 3S battery and 77 watt hours for the 4S. Still not quite triple so I am assuming that the motors run more efficiently at the lower throttle setting.



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