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Electric Stunt => Gettin all AMP'ed up! => Topic started by: David Hoover on February 24, 2013, 04:58:15 PM

Title: Hypothetical Power System
Post by: David Hoover on February 24, 2013, 04:58:15 PM
Based on various rules of thumb that I've picked up from this forum I've worked up the following power system parameters to power a 65 oz. plane using a 770 kV motor.

Peak power required = 715 Watts
Number of cells = 5
ESC current rating = 50A
Battery capacity = 3300 mAh

Expected battery weight based on power required = 230 grams approximately

Does the above make any sense at all or is it right out to lunch?  Comments?  Anyone?  Anyone?
Title: Re: Hypothetical Power System
Post by: John Cralley on February 24, 2013, 05:17:28 PM
Yep, it makes sense although you don't state what particular motor you plan to use (just the KV).

I suggest that, if you have not yet done it, you go through the "list your setup" sticky thread at the top of this forum. You will likely fine listings for models in your ballpark. Some most likely using 4S and some using 5S batteries.
Title: Re: Hypothetical Power System
Post by: Tim Wescott on February 24, 2013, 05:29:42 PM
Unless the motor contemplated is dramatically less efficient than the usual, I don't think it matters much for the capacity calculations.

It may matter as far as motor longevity goes, though.
Title: Re: Hypothetical Power System
Post by: Dean Pappas on February 24, 2013, 05:34:21 PM
Hello David,
Yes, and a 3000 mAh pack will almost certainly do, as well.
With some experience on that airplane, you may find lighter, smaller capacity batteries that will work, so don't buy all your batts up front.
take care,
  Dean P.
Title: Re: Hypothetical Power System
Post by: Dennis Adamisin on February 24, 2013, 05:42:41 PM
Nice bit of calcuations, some other ideas:

* KV x voltage --> RPM.  you want to run around 70%-75% of the available RPM with nominal voltage.  With 770 kv you can run 4S and a 6 pitch, or 5S with a 4.5 pitch; either can work, you just need to decide where you want to go.

* Also 5Sx3300 mah is going to weigh quite a bit more than 230g.

* John C gave tood advice, go to List your set-up", I think you will find systems of comparable power range are using either 4Sx3300 or 5Sx2700
Title: Re: Hypothetical Power System
Post by: David Hoover on February 24, 2013, 05:51:36 PM
Sorry, I meant motor weight, not battery weight.  And I reread that post at least three times before posting!
Title: Re: Hypothetical Power System
Post by: Crist Rigotti on February 24, 2013, 05:59:33 PM
David,
Here is a spreadsheet and article I published in Stunt News a year ago.  It'll figure everything you'll need based on the circle ready airplne weight.  Works very well.

Title: Re: Hypothetical Power System
Post by: David Hoover on February 25, 2013, 07:59:55 AM
A big thanks to everyone who weighed in on this.  You've been immensely helpful.