flight time and power - RC Groups
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Jan 17, 2013, 01:06 PM
Registered User

flight time and power

Hello,i have buid a new small airplane(aero-soarer design) around a 20mah lipo and 4mm motor with gearbox.The model fly very well for 12 minutes.I use a 60mm prop with 4:5:1 gear ratio.How i can calculate the Ampere that take my motor setup?Thanks
I thing around 90ma it is right?
Can i use a 10mah lipo?
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Jan 17, 2013, 02:08 PM
XXXmags's Avatar
20ma.h is your battery capacity. Covert that over to milliamps per minute and divide it by the flight time.

(20ma.h)*(60min/h) = 1200 ma.min

Since lipos don't get fully discharged, and say 80% of total capacity was used, this decreases the usable size of the battery to:

1200 ma.min*0.8 = 960 a.min

The flight time was 12 minutes so:

(960 a.min)/12min = 80 ma

And that's the average current consumption of your motor. An equation to find the current consumption of any motor based on battery capacity and flight time would be:

Note: 60*0.8 = 48

(C*48)/T = A


C = Battery capacity in ma.h
T = Flight time in minutes
A = Motor current in milliamps

Google search works as a good calculator. Stick in the Equation defining A and substitute the variables in the search menu and it will give you the result.

Hope that helped!
Jan 17, 2013, 02:14 PM
Registered User
Jan 17, 2013, 07:41 PM
derk's Avatar
i always use the mah as equal to 60 minutes, then divide by your flight time. multiply the mah by the result of your first number. 60/12=5 so you used your battery at 5C or 100ma current draw. however, your cell likely had some mah remaining when your LVC kicked in so its likely a small % less than 100 ma.

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