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Old Dec 02, 2012, 09:41 AM
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Battery flight time testing

If I put a battery in a plane, run it at variable speeds, mess with the control flight surfaces (servos) a bit, and do this all inside while holding the plane still on a table until the battery is drained to the point it reaches Lipo cut off (using a watt meter), how comparable is this to actually flying the plane until Lipo cut off is reached?
Close enough for hand grenades?
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Old Dec 02, 2012, 10:18 AM
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Not very because you'll probably over heat your components and fry something due to lack of air cooling.
Do this outside in front of a huge fan and it'll be reasonably accurate.... except for the part that unless you have a GOOD ESC with a DECENT LVC you shouldn't fly to LVC.

Some ESC are SO crappy that the LVC is lipo destructive (Electrifly, Supertigre, GWS to name a few).

Read your ESC specs, know what the mean.

Get a battery volt checker, fly a measured period of time, land, measure voltage vs time, do some math, and quit when you have 3.5-3.7v/cell left. THAT's close enough for 'hand grenades'.
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Old Dec 02, 2012, 11:00 AM
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The only hand grenades here will be your components... Long-term bench testing is a good way to fry things, especially if you're running less than full throttle without giving the ESC much/any airflow.

To get an idea of minimum flight time, just measure the current draw at full throttle. From there it's all just simple math: Take your battery capacity (e.g. 1500mAh = 1500 milli-Amp hours), divide by 1000 to eliminate the "m" (1.5Ah), and then divide by the current draw (e.g. 10A) to get "h" by itself (1.5Ah/10A = 0.15h). The "h" stands for "hours", so now you just multiply one hour (60 minutes) by 0.15 and get 0.15*60 = 9 minutes. You can only use 80% of your battery's capacity before damaging it, though, so multiply by 0.8. If we tidy it up all nice and clean, you pretty much just get this equation: 0.048 x (capacity/current). Just plug in your numbers for capacity and current.

This represents the absolute minimum amount of time you'd be able to run the motor at full throttle in a static condition, assuming nothing fried. In the air, full-throttle current draw will drop by ~10-25% since the prop is unloaded, and at half throttle you'll draw about quarter of that number. Let's assume you'll draw an average of 60% of your static current on average during a flight: 0.048 x (capacity/(current*0.60) = 12 minutes of realistic flight time as a starting point.

So go out and fly for the number of minutes you've just calculated, then land, wait a few minutes, twiddle your thumbs, then check the pack's resting voltage. If it's between 11.1 and 11.4V, congratulations. Set your timer for this number in the future. If it's higher than ~11.4V, increase flight durations by 30 seconds until you hit it.
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Old Dec 02, 2012, 11:07 AM
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Thanks
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Old Dec 02, 2012, 11:15 AM
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Quote:
Does the plane use more or less battery power flying in the air at full throttle, or held in a controlled enviroment at full throttle. If so, any opinions on how major or minor the difference would be?
It will draw more current in a static condition than it will while flying. The difference can be anything from like ~5-35% at the extremes, but generally it'll be within the 10-25% range. It depends very much on the model and its power system.

A Slow Stick with a slow-n-easy power setup will usually only have a little current drop, while a super-sleek pylon plane with a small/fast prop can drop by quite a surprising amount.
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Old Dec 02, 2012, 11:19 AM
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Yup, ask the wrong question, get the wrong answer, esp. when you only have 31 posts. I made an assumption of a complete newbie that likely didn't even know what a wattmeter was, and probably didn't even have a voltage checker.

C4K10 is right on. The data you get is 'sorta useful'. Maybe as good as my method, likely no better, no worse.
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Old Dec 02, 2012, 11:21 AM
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Quote:
Originally Posted by C₄H₁₀ View Post
The only hand grenades here will be your components... Long-term bench testing is a good way to fry things, especially if you're running less than full throttle without giving the ESC much/any airflow.

To get an idea of minimum flight time, just measure the current draw at full throttle. From there it's all just simple math: Take your battery capacity (e.g. 1500mAh = 1500 milli-Amp hours), divide by 1000 to eliminate the "m" (1.5Ah), and then divide by the current draw (e.g. 10A) to get "h" by itself (1.5Ah/10A = 0.15h). The "h" stands for "hours", so now you just multiply one hour (60 minutes) by 0.15 and get 0.15*60 = 9 minutes. You can only use 80% of your battery's capacity before damaging it, though, so multiply by 0.8. If we tidy it up all nice and clean, you pretty much just get this equation: 0.048 x (capacity/current). Just plug in your numbers for capacity and current.

This represents the absolute minimum amount of time you'd be able to run the motor at full throttle in a static condition, assuming nothing fried. In the air, full-throttle current draw will drop by ~10-25% since the prop is unloaded, and at half throttle you'll draw about quarter of that number. Let's assume you'll draw an average of 60% of your static current on average during a flight: 0.048 x (capacity/(current*0.60) = 12 minutes of realistic flight time as a starting point.

So go out and fly for the number of minutes you've just calculated, then land, wait a few minutes, twiddle your thumbs, then check the pack's resting voltage. If it's between 11.1 and 11.4V, congratulations. Set your timer for this number in the future. If it's higher than ~11.4V, increase flight durations by 30 seconds until you hit it.
I appreciate all this great info....but it is still not the answer to my question.
I understand about ruining componets from excessive bench testing, and I should have left the words "hand grenades" out of my post as that gives you guys ammo (pun intended) to tell me how I am going to blow up my componets.
I have voltage checkers, watt meters, formulas, temp guns, and all kinds of cool stuff to figure this out...so lets leave this out please!

Does full throttle on the ground holding the plane coorelate to flying at full throttle in the air in regards to battery runtime?
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Old Dec 02, 2012, 11:23 AM
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Quote:
Originally Posted by flydiver View Post
Yup, ask the wrong question, get the wrong answer, esp. when you only have 31 posts. I made an assumption of a complete newbie that likely didn't even know what a wattmeter was, and probably didn't even have a voltage checker. I had a high probability of being right.
I asked the right question, you assumed to much.
I apoligize for not being "clearer".
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Old Dec 02, 2012, 11:26 AM
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Since all you want is quick, simple, cut-n-dried answers with none of that useless extraneous info, here ya go:

Quote:
Does full throttle on the ground holding the plane coorelate to flying at full throttle in the air in regards to battery runtime?
No.
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Old Dec 02, 2012, 11:29 AM
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I asked the right question, you assumed to much.
It's called being helpful, man.

Sheesh... Any half-sane person would expect, at the very least, to receive thanks for offering their own time, knowledge, and effort to help someone out with pertinent information on the topic, even if it wasn't specifically asked for. Instead we just get a slap on the wrist for not saying exactly what we were supposed to.

What?
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Old Dec 02, 2012, 11:33 AM
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Originally Posted by C₄H₁₀ View Post
Since all you want is quick, simple, cut-n-dried answers with none of that useless extraneous info, here ya go:



No.
Did I say it was useless? I did say it didn't answer my question? Did it?
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Old Dec 02, 2012, 11:40 AM
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No.
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Old Dec 02, 2012, 11:50 AM
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Thanks for.the help.
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Old Dec 02, 2012, 11:54 AM
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Quote:
Thanks for.the help.
Hah. Good one.
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Old Dec 02, 2012, 12:40 PM
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Originally Posted by C₄H₁₀ View Post
It will draw more current in a static condition than it will while flying. The difference can be anything from like ~5-35% at the extremes, but generally it'll be within the 10-25% range. It depends very much on the model and its power system.

A Slow Stick with a slow-n-easy power setup will usually only have a little current drop, while a super-sleek pylon plane with a small/fast prop can drop by quite a surprising amount.
Seriously, thanks for that. I truly appreciate the help.
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