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Old Nov 17, 2006, 08:37 AM
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v22chap's Avatar
United States, IN, Granger
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Need help with running two motors ,one battery

O.K. you battery /motor guru's ...... I have searched for this answer ,but didn't find any thing ,,,or maybe should say didn't find what I wanted
I am an electric" newb" and am wanting to run two 1100 KV ( hacker A30 -8XL heli ) motors on one TP lite 4S 2P 4000 MAH battery ,, two ESC's ,, motors 50 " apart with wiring from the 1 centerally located battery to each ESC at the motor location.

#1--Now one motor runs fine on this setup getting about 7 mins of flight time and pulling it down about 80 % ,,but what will happen when I "Y" in the other motor and extend the battery leads out to ESC by 25 " ???

#2--Do I have to double the cells to keep the amps and volts to both motors ,,or just triple ,quadruple the MAH to get the same amount of run time out of the two motors " "Yed together on the same amount of cells?
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Old Nov 17, 2006, 09:19 AM
Frankenstein recycled packs
rampman's Avatar
USA, AZ, Gilbert
Joined Jan 2006
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Keep your ESC battery supply wire AWG large enough to handle the amps without a drop in voltage (much drop).
You will need to double your battery size or run two of the same size you presently use (one to each ESC) if I am reading this right as in your pack is down to a 20% charge after a 7 min flight, which is as low as you want to go without damaging your pack.
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Old Nov 17, 2006, 09:30 AM
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Letchworth, Great Britain (UK)
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First thing to consider is that the two motors will be drawing twice the current, so can the battery supply it without the voltage sagging too much? If that's a problem, you can run two batteries in parallel, or use a separate battery for each ESC/motor combo (in parallel is recommended).

Using the same battery, your flight time will be halved. If your plane can fly with both motors on reduced power, you could put smaller props on to reduce the amps, and that will increase your flight time a bit. Two batteries, obviously, will give you the same flight time as before.

The usual recommendation is to increase the motor leads length, rather than the battery leads; though the jury seems to be out on that one. Using two separate batteries would allow you to keep the lead lengths shorter, but the disadvantage of that is that one battery might expire before the other and get you into trouble. But if you fly against the clock, rather than waiting for lvc to kick in, you can reduce this risk.
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Old Nov 17, 2006, 10:00 AM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
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If you extend the battery leads to the ESC(s) you would be well advised to check with the ESC manufature for extra Cap. recomendations.
Most ESCs require that only the BEC of one be used in a multi setup ,I believe CC Phoenix are the exception.

Leads

http://www.rcgroups.com/forums/showp...2&postcount=32

Charles
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Old Nov 17, 2006, 10:56 AM
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United States, IN, Granger
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check with the ESC manufature for extra Cap. recomendations.
Charles ,,,that is an idea that I hadn't read or thought of yet.
And thanks for the link to the wire length problem .. Wires from ESC's to motors lengthened not the battery wires to ESC's.


abenn
I guess I should have clarified this a little more ,, I am using CC 60's and it is a VTOL ,,so smaller props to reduce amps is out as it needs really large props and lots of amps to hover and this was what I was afraid of ,,,I need to go more cells to up the amps ,,,right .... say 8 S instead of 4 S????
Or as was mentioned wire up what I have in parallel which gives me the 8 S 2 P that I need to do it with one battery ( no that would be series that way the parallel would just give me more MAH right ??? ).

I need to go take electrical 101 I guess before going any further and blowing the house up.

Code:
disadvantage of that is that one battery might expire before the other
I also am afraid of this as VTOL's don't seem to glide well or autorotate.


rampman
Yep you are reading it right ,,I am as low as I want to go on the discharge
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Old Nov 17, 2006, 12:42 PM
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Letchworth, Great Britain (UK)
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Quote:
Originally Posted by v22chap
[CODE]abenn
I guess I should have clarified this a little more ,, I am using CC 60's and it is a VTOL ,,so smaller props to reduce amps is out as it needs really large props and lots of amps to hover and this was what I was afraid of ,,,I need to go more cells to up the amps ,,,right .... say 8 S instead of 4 S????
Or as was mentioned wire up what I have in parallel which gives me the 8 S 2 P that I need to do it with one battery ( no that would be series that way the parallel would just give me more MAH right ??? ).
If 4S2P is the right spec for one motor, you don't go to 8S. What you do, if the two motors are going to demand more amps than one 4S2P pack can deliver, is put two 4S packs in parallel (red to red, black to black). If they're already 4S2P, that will give you 4S4P. The volts will stay the same, but the combination will be able to deliver double the amps, and it will have twice the mAh capacity.
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Old Nov 17, 2006, 06:07 PM
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United States, IN, Granger
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abenn
That was what I suspected ,,The volts I understood ,,but the amps had me guessing and I guess I had to hear someone else say it before I was going to be sure enough to go ahead and try it.
Thanks for all the help guys
Larry
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Old Nov 17, 2006, 07:01 PM
MINUS (-)
jsfrench's Avatar
United States, WA, Olympia
Joined Nov 2002
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v22chap:
since you are using Castle ESC's check their website for a discussion of other factors in multi-motor setups:
http://www.castlecreations.com/media...03-Mar2006.pdf
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Old Nov 17, 2006, 08:44 PM
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jsfrench
Hey thanks ,, that is a very good link , lots of good reading that needs to be reread and reread to absorb all of it .To bad I didn't find that in my searches ,,I wouldn't be having this conversation with all you great guys.
I"ll try to remember and let you all know how it turns out as it is a little different than multi motor airplanes ,,but the basics are the same .
Larry
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Old Nov 17, 2006, 08:50 PM
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Frisco, TX, USA
Joined Sep 2001
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And just curious... given already thay two motors, two escs, and the need to go to pack(s) with more amps... and the suggestions to "parallel" two packs... Why not two setups of pack-esc-motor with the throttle cables "Y" connected to the reciever?

Just curious.
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Old Nov 18, 2006, 03:21 AM
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Quote:
Originally Posted by Danal Estes
And just curious... given already thay two motors, two escs, and the need to go to pack(s) with more amps... and the suggestions to "parallel" two packs... Why not two setups of pack-esc-motor with the throttle cables "Y" connected to the reciever?

Just curious.
Yes, that's perfectly feasible and it will reduce cable lengths in some setups. The reason it's not quite so good as both motors supplied from the same "big" pack is that one battery could run down quicker than the other (or have less charge than the other) and the ESC/motor on that one would then hit lvc before the other one. The assymetric thrust of one motor only might cause your model to crash if you're not prepared for it or you're doing a low pass when it happens.

With both motors on the same pack, the only variable you've got is that the lvc settings of the two ESCs might not be quite the same. But there's debate about that because, if one hits lvc a split second before the other it might cause the battery volts to go up again (due to less amps) so that the other one doesn't hit lvc Same result.

Best thing, with multis at least, is always to fly against a clock, and never go to lvc Though there is also some kind of lipo saver that will monitor all cells in multiple packs, override the lvc in the two ESCs, and shut down the throttle if any one cell hits lvc -- if you y-lead the two ESCs into the Rx, that means that both motors will shut down if one cell hits lvc
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