| That whole "six minute flight" thing is a bit misleading. It's only a
| six-minute flight if you run at a continuous 10C draw from start to
Of course. But when you get a 10C rated pack, that generally means
-- you can go higher for short periods of time.
But if you push it at 10C *continuous*
, that's a six minute flight.
| The 20C bashers also say, "Well it only gives you a 3-minute
I've never heard of `20C bashers'. In any event, 20C packs generally
have lower internal resistances, so they tend to perform better than
10C packs, even at lower currents. (But often that lower internal
resistance comes at the cost of reduced capacity or more weight and
usually at higher cost, so it's all a trade-off.)
| Well, okay, IF full throttle current is equal to the 20C rating of the
| pack, AND IF you fly full throttle for the entire flight.
Yes. That's one possible meaning.
It could also mean a full throttle current of 30C (which the pack
might tolerate for 15 seconds) and 20C being throttled back a bit.
Either way, my point is that if you take a pack rated at whateverC,
and you run it at whateverC for the entire flight, it's not likely to
last long. Unless you're doing a pylon race or something, I'd instead
suggest going for (whatever/2)C -- your pack will last a lot longer.
| Reality is that the left stick does go up and down, and most people
| already know how to use it, or will quickly learn when their flights
| only last 3 minutes.
Reality is that if you really do push your 20C pack at 20C (or more!)
for the entire flight, you'll be replacing it soon. This could be a
result of never throttling back, *or*
of just not putting a big enough
pack in your plane.
| The truth of the matter is, that it is perfectly safe to match your
| full-throttle current to the pack's rated capacity, provided that you
| actually use the throttle!
Yes, that's reasonable. It's also safe to put your full-throttle
current well above your pack's rated maximum continuous capacity --
but you'd better make *sure*
you use that throttle appropriately.
(Also, note that the prop will unload in the air, so unless you
actually measure the current draw in flight and instead only look at
on-ground current draws, you might have over-estimated it.
Fortunately, the Eagle Tree logger isn't very expensive, and neither
are tools like Motocalc.)
| Planes should be set up so that cruise power is around half-stick,
| give or take. If you're going to go roaring around at full throttle
| all the time, then yes, I would agree that cutting the packs'
| ratings in half is a prudent move.
I don't care what your throttle is set at -- I'm talking about the
current you actually use, no matter what throttle setting is needed to
achieve that current.
Your pack may be rated at 10C or 20C continuous, but if you actually
use 10C or 20C continuous, your pack won't last long. Get a bigger
pack, or another pack, or throttle back, or a smaller prop -- or just
get used to the idea that your packs won't last long.
| > | LIPOS are in every laptop and mobile phone, and they do not
| > | spontaneously combust.
| > Actually, they do. But it's rare. And when it happens, it tends to
| > make the news, so we hear about it.
| No, they don't spontaneously combust. Some prior damage or abuse has to
| be present for a pack to combust. An undamaged, properly-built pack
| will not burst into flames just sitting on the shelf.
Ok, fine, there's a reason they combust -- it's not spontaneous. But
my point is that even laptop and cell phone batteries DO occasionally
combust, either due to abuse, or accidents or whatever else. Just
like R/C batteries.
| Drive a nail through it, okay. Set the charger for one cell more
| than the pack has, okay. Set the charger for more than 1C,
| okay. Just not sitting on a shelf doing nothing.
Not very useful sitting on a shelf.
| The "exploding" packs that made the news were caused by defective
| construction. Remember the cell phone battery scare a while back?
| Shoddy workmanship created a situation where the packs were easily
| damaged or overcharged. Same thing with the Dell batteries of late.
Yes, I recall the cell phone companies saying that. It was an OEM
pack -- our genuine packs would never do that! (Of course, all the
evidence was burned up, so we never got to really *prove*
battery came from.)
Either way, cell phone and laptop batteries sometimes burn, just like
R/C batteries do. But not very often, just like R/C batteries. The
only reason you hear about it so often is that it's considered
Doug McLaren, firstname.lastname@example.org
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