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🏠Home🏠RC Main Discussion › What battery?
02-15-2021 04:55 PM  8 months ago
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Peter Wales

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What battery?
I am building a 3 blade Kraken. My ESC does not have a BEC so I want to use a 2s battery. The problem is that SAB have provided a very small plate to use if I want to use a battery so I need a small battery.

I have found some small 2000maH batteries which will fit but am concerned about voltage drop. I got low battery warnings while just cruising around the other day.

Worse was when I landed, I had adjusted the bottom stick pitch up slightly and not the off pitch so when I turned the switch from flight to shut down the blades went from slightly negative to more negative, then the blades went to full negative as the battery did not power the servos enough to stop it. A second or two later it went back to normal operation as the motor slowed down.

I am concerned about this happening if I went from positive to negative pitch in something as simple as a loop.
Peter Wales
http://scalehelicopters.org
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02-15-2021 05:21 PM  8 months ago
helitom

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Let me start by noting that I have never seen the set up to which you refer. If the battery mount plate is small, is there room to stack upward? If so, you could stack two 2000''s and wire them up in parallel to make a 4000 pack.The older I get, the fewer things seem worth waiting in line for.
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02-15-2021 06:00 PM  8 months ago
youngbuck

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Have u looked into that scorpion back up battery thingy? I’m not a very experienced heli guy but from the info I’ve gathered, it may work?
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02-15-2021 08:42 PM  8 months ago
Rojoalfa

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A single 2500 mAH, 7.4 volts, 10C should be enough for electronic, if you are running HV servos.

If you think this is not enough, run a 15 amps BEC!

There is no difference in term of requeriment of power between that kraken and a raptor 90.

It is a old design in a new box and pretty face.

/
Saludos cordiales,
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02-16-2021 02:45 AM  8 months ago
Peter Wales

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I am still nervous of those batteries. I dont care how many c's it says on them, they are probably lying. The cells inside the batteries are round so they are probably 18650 cells which should be good for 20 amps surge. The plate to put them on only supports half of the length of one battery.

I haven't looked the the scorpion battery back up. I imagine it is a very large capacitor or capacitors and I have some Castle ones and some from the ESC I am using. I'll look into it, thanks for the tip
Peter Wales
http://scalehelicopters.org
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02-16-2021 02:25 PM  8 months ago
v22chap

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Peter .. check that your power is going directly to the FC . Most tell you to go direct to it and not thru the RX first . I have had trouble with this very item and it sounds just like what you discribe .Once I found that in the manual and did it .. my little 2000 mah 15 C battery flies for 4 or 5 flights with no problems .Larry C ----------Bergen R/C helicopters
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02-16-2021 08:48 PM  8 months ago
Rojoalfa

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That is correct.

Let's do an absurd calculation...

You are going to fly an electric helicopter with 8 HV servos, each one is going to take 4 amps.

So, 8 x 4 = 32 amps peak.

With a lipo of 2500, 30C, it is going to give 2.5x30, 75 amps but... Sorry... I don't believe that... Ok! Take a half... 75/2, 37.5 amps... Good.

This lipo is going to handle that 37.5 amps peak without problem in our hypothetical helicopter.

So, for our helicopter with 8 hungry servos consuming 32 amps peak, a lipo pack 7.4 volts, 2500 mAH, 30C is going to work without problems.

Now, for our little "kraken" that only have 4 servos, you only need half of the calculation of our hypothetical helicopter... Instead of a 30C, you may have 10C... You know... A safety factor...

So, a 7.4 volts, 2500 mAH, 10C is going to give you 5 flights between charges.

/
Saludos cordiales,
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02-16-2021 09:08 PM  8 months ago
Peter Wales

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Thanks Larry, it did occur to me last night that I was feeding all the power through one single UDI line to the Axon.
Then this morning I forgot all about it. I guess my little 2000maH battery could do the job after all.
The biggest problem is the wires dont reach so now I have to figure something else. I am using a switch with a Deans connector on one end and two servo style wires on the other end. Moving it is something I don't want to do. Some thinking is required here.
Peter Wales
http://scalehelicopters.org
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02-16-2021 09:11 PM  8 months ago
v22chap

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Yep ,, there is always something right

Good luck on the relocation
Larry C ----------Bergen R/C helicopters
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02-25-2021 12:05 AM  8 months ago
EEngineer

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TX

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A battery with dual leads is better, since only 1 lead limits the current to your avionics by a factor of 2. A Y-connector will not help. Tap from the battery itself.Logo 600SXs, 800XX, TDR IIs
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02-25-2021 02:37 PM  8 months ago
Peter Wales

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The problem was solved with a heavy duty switch which had a Deans connector for the battery in and two heavy duty servo wires out which both went into the Axon.
I flew the heli yesterday and it scared the poop out of me but I got no low battery warnings, but did need a clean pair of shorts.
Peter Wales
http://scalehelicopters.org
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02-25-2021 02:39 PM  8 months ago
v22chap

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Glad it is sorted out Peter !!!
FYI : I will not use Deans any more !! I had a bad crash at IRCHA in 2019 with my Rotormast V-22 because of them . It runs with two 4S 2200 mah batteries hooked up parallel and sharing the power between the two motors .So in theory one battery can power up the unit and even fly it until two motors using what two batteries should supply makes the one battery get low way to quickly . Which is what my first flight did .. one batteries deans plug was not making contact and I was on one battery which did let me hover around for a few simple moves ,, go into forward flight and do a conversion but when I went to turn around and convert back to hover it was to much for the one battery and the FC's voltage dropped to low and it reset in flight and was headed back towards the scale tent . The TX's fail safe couldn't even work and it just hung in fast forward flight in partical airplane mode waiting for the FC to finish reset ,, but couldn't as there was still no power for it !It did clear the tent and people and then ran completely out of power and air space , further away from the tent .
I didn't find this until during the rebuilding of it and was using one battery to set it all up ... and one would not power anything up at all unless I held sideways pressure on the connector !!!! I will admit that the plug in question was 4 yrs old and had a lot of connection under its belt . Lesson learned ... do preventive replacement of parts every now and then
Larry C ----------Bergen R/C helicopters
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02-25-2021 03:50 PM  8 months ago
Peter Wales

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Hi Larry,
Thanks for the heads up. The Deans connectors are new, one came on the battery and the other came out of the packet. I guess they are both chinese but they are very tight to insert so I think they will be ok. I dont think it will be the deans connector and battery failing which causes me to plant this thing
Peter Wales
http://scalehelicopters.org
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02-25-2021 04:39 PM  8 months ago
v22chap

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Understand all to well !Larry C ----------Bergen R/C helicopters
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03-02-2021 11:42 AM  7 months ago
wjvail

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Meridian, Mississippi

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Peter... It sounds like you've made progress on solving your original question. Still, possibly you will find something you can use in the below thread. I 1st weigh in on the topic in post #35 (I'm the same person over there as here). I personally will never use LiPo batteries for flight packs again. LiIon batteries are now capable of supplying up to 35 amps continuous and and don't seem to mind being stored charged. Packs built from 21700 cells will be 4,000 mAh and quite a bit smaller and lighter than similar size Lipo packs.

Maybe there is something useful in this thread:
https://www.helifreak.com/showthrea...highlight=21700
"Well, nothing bad can happen now."
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03-04-2021 02:18 PM  7 months ago
doorman

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One Question..
Peter,
WHAT THE HELL ARE YOU DOING WITH A KRAKEN????

Stan
AMA 2918-Team Spin Blades,,Castle Creations, Unique Aircraft
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03-04-2021 04:09 PM  7 months ago
v22chap

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I wonder the same ,,but didn't want to talk about the elephant in the room !!!! Larry C ----------Bergen R/C helicopters
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03-04-2021 05:42 PM  7 months ago
Peter Wales

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Orlando Fl

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I was waiting for that one guys

Due to severe arthritis in my shoulders I cannot pick up a scale heli except a very small one. The problem with 500 and 600 size helis is that I have trouble seeing them at any distance so I needed something bigger. Old age is a bitch.

So I went back to my early days of flying when I used to fly OS 60 powered xcells at 1500 rpm, thinking that if I ran the head speeed low I would be able to do a loop and a roll or two and enjoy my flying. I could get my jollies watching Marcus flying his scale helis. It turned out, he liked watching me trying to crash the Kraken, which I can only tell which way it's going in bright sunlight. Fortunately we get a lot of that in Florida.

The headspeed I am running is 1300 on the 3 blade head and I can do most of the stuff I was doing 25 years ago, but its not 3D by any means and I am having fun again.
Peter Wales
http://scalehelicopters.org
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03-04-2021 06:08 PM  7 months ago
v22chap

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Granger, Indiana

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Peter Wales Old age is a bitch.
Peter Wales I am having fun again.
Peter ,, I can relate well to both those statements of yours !!
Larry C ----------Bergen R/C helicopters
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03-04-2021 07:32 PM  7 months ago
Rojoalfa

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what battery?

Ok... my rule of Rojoalfa...

Helicopter size... 500-600, load per flight, 250 mAH/fl.
So, If I want to get 4 flights without recharging, then:

250 mAH/fl x 4 fl = 1000 mAH.

If I want a LIPO for the job, multiple by 2. LiPo battery give no more than half the total energy capacity.

1000 mAH x 2 = 2000 mAH.

So, you need a LIPO with at least 2000 mAH energy capacity.

Ok, I have 5 servos, each will get 2 A at full load.

5 x 2 A = 10 A peak

Then, 10 A x 1000 mAH/A , divide by 2000 mAH = 5

I need a battery with at least, 5C of discharge capacity.

Looking on the market... 2S LIPO 2500 mAH, 20C works very good.

On a busy day, 4 flights without recharging...nice.

PD:

For a 700 size, average load 350 mAH per fl.
Repeat the calculation and you will get a proper LIPO for the job.

/
Saludos cordiales,
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