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Helicopter
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Other › My T-Rex can fly 40 minute
04-01-2005 06:46 PM  13 years agoPost 1
patti

rrNovice

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Hi I'm from Thailand so my english will be bad for your. I just want to show some of mine idea about how to extend fly time. I use 2 battery pack first "Li-Poly 2200 mah 15C 11.1V (place at rear)" and "Li-Poly 1900 mah 10C 11.1V (place at front)" so I have total 4100 mah at 11.1V and my t-rex use Align 400L (13T) motor, speed 25A Align main blade was Align CF 325 mm. total weight is 850 g. so I can fly 40 min. and my t-rex have more stable (can compare to .30 glow engine heli) because now it have a perfect CG at main gear. but if you want to setup for 3D by use this battery system please change speed and motor to 40A you will get more power but fly time will only 20 min.

P.S. this battery system must charge seperate because mah was difference

[IMG]http://www.mea.emodeler.net/board/getfile.php?key=1112182910&att_id=18735&site=mea&bn=mea_heli[/IMG]

[IMG]http://www.mea.emodeler.net/board/getfile.php?key=1112182910&att_id=18736&site=mea&bn=mea_heli[/IMG]

http://www.mea.emodeler.net/board/g...mea&bn=mea_heli

[IMG]http://www.mea.emodeler.net/board/getfile.php?key=1112183134&att_id=18740&site=mea&bn=mea_heli[/IMG]

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04-01-2005 07:07 PM  13 years agoPost 2
raytor

rrApprentice

Southern US

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Interesting pictures patti - that is quite a load you are carrying. I would be a little concerned about that 1900mah pack reaching critically low voltages before the other pack but then at 800+ grams you may have to set her down before either gets there.
What motor are you running that can go full out for 40 minutes w/o overheating?
(then too this IS April 1st)

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04-01-2005 07:53 PM  13 years agoPost 3
jensenflemming

rrNovice

Aarhus, Denmark

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If you connect the two pack in paralel they will share the same voltage but the current draw will be different between the two packs.

Meaning the highest capacity pack will carry the more load.

So as I see it there is no problem in discharging the batteries like this.

But 40 minutes! I can't figure that one out!

My simple calculations says the following asuming you can fly 10 mins with the 2200mAh pack total weight 700g.

Weight of 2200mAh pack: 155g
Weight of 1900mAh pack: 134g

Amp draw with the 2200mAh pack: 2,2 * 6 = 13,2 A
Trying to calc increased amp draw: (700+134) / 700 * 13,2 = 15,7 A
How long does it take to discharge: 4,1 / 15,7 * 60 = 15,7 mins

Can it be calculated like this?


T-Rex 450XL CDE & 450X V1

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04-01-2005 09:06 PM  13 years agoPost 4
Heliramos

rrNovice

south of the Caribbean

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It is possible in hover the 400s pulls 6 to 7 amps.
you can use 4100 mah 1 hour if you motor is pulling 4,1amps.

so if your motor uses 4,1amps it can run 1hour
'' " 8,2 amps it can run 30 min
" " 12,3 amps it can run15min

This is theoretical of course.

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04-01-2005 09:22 PM  13 years agoPost 5
RC_Hobbies

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Canada

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40 MINUTES FLYING TIME!!! THIS IS IMPPOSSIBLE.

My TP2100 gives me 14 minuites flying time. Doubling the pack gives 4200mAh and assuming no increase in weight, you will get 28 minutes flying time max. If you also consider the added weight, I will say 23 - 24 minutes max.

40 minutes, NO WAY!!!!

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04-01-2005 09:55 PM  13 years agoPost 6
Heliramos

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south of the Caribbean

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well my poly quest 1800 gives me 14min fly time and i'am using 300mah less than the tp2100.

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04-01-2005 10:22 PM  13 years agoPost 7
Lowell Foo

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Vancouver, BC, Canada

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Maybe on a windy hillside?

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04-01-2005 10:37 PM  13 years agoPost 8
thunder21

rrApprentice

College Park, MD

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Altitude and wind conditions do vary the amount of collective needed to stay aloft.

But even after 14 minutes on my TP2100 pack I'm frazzled. I wait a few minutes between packs to let ME cool off. My motor (Mega 16/15/3) would be fine running for 40 minutes non-stop doing circuits, not 3D, etc.

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04-01-2005 10:51 PM  13 years agoPost 9
Calvin-L

rrNovice

Hong Kong

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I think even you can fly so long but your motor be not capable for this. I also use this motor "400L" with 13T and heat sink, after 10 min fly, it becomes very very hot!

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04-01-2005 11:48 PM  13 years agoPost 10
LTEDT

rrApprentice

Westminster MD

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I think you all been had!
April Fools Prank...I would guess!!!

I thought we all were ready for soemthing like this today guys...I guess not!!!!!!!!!!!!!!!

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04-02-2005 12:25 AM  13 years agoPost 11
dkshema

rrMaster

Cedar Rapids, IA

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If you connect the two pack in paralel they will share the same voltage but the current draw will be different between the two packs.
I think NOT. Same voltage by virtue of being connected in parallel. Different current delivered out of each pack to a common load? Not on your life.

Current = voltage / resistance, thanks to Mr. Ohm and his law.

There is nothing in that equation that discerns or recognizes battery capacity.

The smaller mah battery pack WILL run out of steam before the larger one does. That is why battery manufacturers of ANY type of battery tell you not to mix different capacity batteries in the mix your using with a particular load.

As the smaller mah pack is exhausted, it's terminal voltage will drop. In the case of LiPos, that can be deadly to the battery should it drop below the 3V/Cell limit. Further, the larger battery that still has juice left in it, will try to charge the lower potential voltage, discharged pack.

VERY bad idea to mix different mah rated packs in anything.

Dave

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04-02-2005 01:03 AM  13 years agoPost 12
raytor

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Southern US

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VERY bad idea to mix different mah rated packs in anything.
Exactly as I said dkshema - thanks for backing me up.
When you couple 40 min flying in an 850g Trex with that battery hookup and that motor, this has got to be 04/01 B.S. - but then do they even know about that day in Thailand (if it was indeed sent from there)?

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04-02-2005 03:00 AM  13 years agoPost 13
epkoncept

rrNovice

San Diego County

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ohms law but
The load impedance seen by each pack may be the same, but the internal resistance of each pack is different. If the packs are of the same construction but differ in capacity, impedance of the pack will be inverse to capacity, but not always. Hence the large pack typically has a lower internal impedance and thus will deliver more current to a given load than the pack that has a higher internal resistance.

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04-02-2005 03:16 AM  13 years agoPost 14
TonyTypeS

rrElite Veteran

New Orleans, LA & El Monte, CA

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Maybe he ment he got 40 minutes of flight time hovering a lil and landing to let cool then fly again. I got 15mins from my rex using an etec 1700hp batts and align 400sf. I program my remote so the pitch is fixed and flew just like a FP micro heli. I didn't measure the pitch but i had enought to fly with only 50% throttle.

But can you really have 2 different mah packs running together? Wouldn't one get underdischared sooner then the other one? I been told that you can't do that.

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04-02-2005 03:52 AM  13 years agoPost 15
dkshema

rrMaster

Cedar Rapids, IA

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The internal impedance of the battery packs is going to vary by a few milliohms...not enough to make a difference.

You just don't mix different capacity packs unless you want trouble down the road. The battery manufacturers really do know what they are talking about when they tell you not to mix different capacity batteries....

Dave

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04-02-2005 06:25 AM  13 years agoPost 16
RC_Hobbies

rrNovice

Canada

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What the battery manufacturer means by not mixing different battery is NOT to mix them in SERIAL connection. You can mix batteries in PARALLEL, and there is no problem. When connecting two different packs (of the same voltage of course) in parallel, the larger pack will pull out more charges/current than the smaller pack. However the voltage across the 2 packs will always be the same. The 2 packs will die down at the same rate, and there is no worry about over discharged.

Another way to look at this is to fill up 2 water tanks of different size and connect them together at the bottom. The height of the water level represents the voltage. The water level will always be the same in both tank (they will balance themselves automatically). Cut a hole along the connection pipe and let the water drains. Keep an eye on the water level at both tanks. They will be dropping at the same rate. The bigger tank will drain out more water than the smaller tank, but the water level in both tanks will be dropping at the same rate (i.e. their voltage is dropping at the same rate.)

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04-02-2005 09:31 AM  13 years agoPost 17
daz59

rrApprentice

Tokoroa, New Zealand

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The packs will both go flat at the same time, the bigger pack will tend to charge the smaller pack “if” the volts on the smaller pack dropped lower than the bigger pack.

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04-02-2005 09:39 AM  13 years agoPost 18
daz59

rrApprentice

Tokoroa, New Zealand

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RC_Hobbies.....Good analogy, that’s exactly how it works.

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04-02-2005 03:41 PM  13 years agoPost 19
NewRCHeliPilot

rrApprentice

Panama City, Fl.

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Now where did Nikola Tesla go, I can never find him when I need him.

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04-02-2005 04:09 PM  13 years agoPost 20
Sparkhead

rrKey Veteran

Melbourne Australia

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Doesn't sound like good Lipo practice to me!!!!!!!!!!

I think you're asking for trouble mixing packs like that.;

I've been using Lipos for about 2 years and the way you are going about things is totally wrong.

Anyway I wish you all the luck in the world, but will be waiting for your thread on Lipos going wrong.


Mick.

Robbe & Futaba.

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