Mar 25, 2010, 09:34 AM Registered User Canada, ON, Toronto Joined Dec 2007 417 Posts Question Increasing flight time with larger battery? For a given multi-rotor craft, what's the best way to extend flight time? It seems that the average flight time for most multi-rotor guys is 10-15min. So short of loosing weight (which beyond a certain point becomes in-practical), and getting more efficient motors, what's the effect of using a larger capacity battery? Does it scale linearly? Exponentially? Any studies done on this?
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Mar 25, 2010, 09:58 AM
CNC Guitar
New York, NY
Joined Feb 2010
433 Posts
Quote:
 Originally Posted by outsider787 For a given multi-rotor craft, what's the best way to extend flight time? It seems that the average flight time for most multi-rotor guys is 10-15min. So short of loosing weight (which beyond a certain point becomes in-practical), and getting more efficient motors, what's the effect of using a larger capacity battery? Does it scale linearly? Exponentially? Any studies done on this?
Well do a search here, and on google, and you will find lots of good information on battery size vs flight time.

Basically, given a certain set of motors, and speed controllers, at a given load, and a given Prop size, they will draw a given current. Knowing this, you can then calculate the size of battery needed, given an amount of time you need to fly.

There are many well defined formulas that give you this, as well as power meters, that will help one in determining these values, with their equipment.

Everything is a trade off...since more time, requires larger capacity batteries, and those will weigh more etc etc.

 Mar 25, 2010, 10:06 AM A man with too many toys United States Joined Feb 2001 17,613 Posts When weight goes up the watts per Kg tend to stay about the same. I have found that props due make a difference. When I went from an APC 10x4.7 to 10x3.8 I got more flight time so it pays to due some experimenting. I have seen setups that hover at very low throttle level which can be below the motors maximum efficiency current. In that case a larger battery would give both a longer flight time and better efficiency. Again it pays to experiment. Every multi-rotor is different so some flight-testing is the best way to see what works best for what you want. Also some of the new batteries are very heavy for their capacity so take a close look at that before you buy a new battery. Last edited by RC Man; May 31, 2010 at 06:43 PM.
May 30, 2010, 08:09 PM
Registered User
United States, CA, Los Angeles
Joined Aug 2009
11,692 Posts
Quote:
 Originally Posted by RC Man I have found that props due make a difference. When I went from an APC 10x4.7 to 10x3.8 I got more flight time so it pays to due some experimenting.
RC Man, what size was the Bell on the motors you were using in the above example?

Thank you.
May 30, 2010, 10:13 PM
Registered User
Joined Jun 2009
291 Posts
Here's a little empirical case study for a hexrotor I'm building. It was made by measuring current in tethered flight with ballast weight.

The battery assumed in this study is a 5000 mAh 4s1p Zippy pack, weight 475 g. With a single pack it gives me up to 24 minutes of hover time, with two I should get about 35 minutes (+11 minutes), with three packs it comes down to about 42 minutes (now only +7 minutes). Beyond this point it's no longer viable to add more batteries, because the motors have to run at RPMs so high that the power requirements skyrocket. The relationship is logarithmic then.

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