Electric Stunt > Gettin all AMP'ed up!

Battery capacity vs. voltage

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Alan Hahn:
Jeffrey,
I don't think the calculation is exactly easy. But here are some general things.

If I remember correctly, the power needed depends on the square of the airspeed. So if you want to slow your flight down from 5 s to 6 s a lap (on 35 ft. lines this sounds too slow to me), you need to decrease the power by 5/6 squared or 70% of where you are currently flying. But power isn't linear in throttle either and my guess is that the needed throttle will actually be less than 70% of what you currently have.

To be honest, a lot of flying settings are trial and error, initially based on what we are use to having with normal glow flying. As we fly a plane more, then we adjust the settings to put the lap speed etc. where we like to have it.

Anyway I can't tell if you are happy the way it is flying or not. For example, on my 1/2A setup, I am also using "only"~35% of the battery capacity. However I need about 9A or so for the 2 minute beginner pattern. My battery pack can only run at 12C (it is a 2s Thunderpower Prolite 730mAHr pack which can only supply about 9A. I start off with less than full throttle (to give me the flight speed I want), and then let the timer/throttle slowing increase the throttle as the pack voltage drops--trying to keep the power in (watts) nominally constant. Actually my timer/throttle actually is increasing the throttle too fast, so I need to adjust the final flight throttle accordingly (trial and error again). If I had a governor on this particular ESC, I could simply set a desired rpm and let the ESC figure it out, but this ESC doesn't have a governor (Castle Creation Thunderbird 9A). So I play with it.

john dillon:
Hi Motorman,
   Your number for Amps, 82.5 is the maximum amps possible to pull from your 25c battery.
You should use the actual current you are using to work out duration.
Or if you don't have the kit to measure current use your duration and the amount of charge
you have to put back into battery to work out your actual average current for the flight.

John

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