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« on: August 03, 2018, 04:41:32 PM »
aaindthu
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Hi everyone ! !  Smiley I am new to this forum and i have a doubt regarding setting up twin engine brushless motor for models requiring
twin engines.

i have searched the net and found out the basic connections to make and all that is fine.  My doubt is whether the lipo battery will drain
faster with twin engines or last as long as when used with single brushless motor??? 

i have attached the basic connections required to setup twin engine brushless motor.

Will the lipo drain quicker or last long???

ab.jpg
doubt regarding setting up a twin engine brushless motors
* ab.jpg (56.12 KB, 700x614 - viewed 98 times.)
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« Reply #1 on: August 03, 2018, 07:14:53 PM »
tictoc21
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With two motors it will draw large current if you are using it at full strength.
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« Reply #2 on: August 03, 2018, 07:20:41 PM »
K K Iyer
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@aaindthu,
Welcome to the forum.

Hope you wonít mind this analogy to your problem:
ď2 horses will eat twice as much as 1 horse,
But 2 goats may eat only as much as 1 horse.Ē

So it depends on the motor power/kv/prop combination proposed for the single vs twin.

If this is your first model, youíll have face and tackle many issues even with a single motor.
A twin will double the problems!

Please share a pic of your model, or at least the plan if construction not yet started.
Iím sure youíll get a lot of helpful responses.
Regards

BTW, duplicate threads are best avoided, as youíll get some responses on one, some on the other, creating unnecessary confusion...
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« Reply #3 on: August 03, 2018, 08:59:15 PM »
swapnilnimbalkar
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Interesting question!

I always wondered about this, this is what I think.

Please go through this thread https://www.rcgroups.com/forums/showthread.php?2889965-XXD-A2212-1000kv-3S-Thrust-Test

It shows thrust data for XXD 2212 1000kv motor with 3S battery & 1045 prop

Let us assume that we need 740 grams of thrust for a plane to stay in air,

now have a look at the table give in the thread above,

Single motor : @ 12.53 A gives you 750 grams of thrust (row no. eight)

With two motors we will need 740/2 = 370 grams of thrust from each motor

see the table again, row no.4 says that, @ 4.39 A this motor give you 360grams of thrust

Two motors: we will get 360 X 2 = 720 grams of thrust (not exactly 740 but close)

and we are pulling 4.39A X 2 = 8.78A which is less than 12.53A (with single motor for about same amount of thrust)

So twin motor setup will be more efficient but heavy and will increase the cost

This might not be true, experts may shed some light on this topic.

Thank you.

« Last Edit: August 03, 2018, 09:13:04 PM by swapnilnimbalkar » Logged
 

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« Reply #4 on: August 03, 2018, 10:07:31 PM »
K K Iyer
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Good point.

Two scenarios:
1. Two motors same as the single motor
2. Two motors smaller than the single motor

There are many variables to consider/examine

In case 1, twin motors will need to run much slower than the single.
In general, the motor efficiency will be better at lower amp draw. (E.g, See 2212 efficiency chart)
But to maintain the desired airspeed, prop pitch has to be significantly higher, (and maybe smaller diameter too), bringing up questions of prop efficiency, (despite possible gains due to lower rpm).
Then there is additional power consumption for the weight of the second motor and ESC.

So we need to compare the power consumption not for static thrust, but for maintaining the same airspeed. In cruise, when thrust=drag, the power required will be more due to the typically higher drag of a twin. In climb, the power required will be more due to the added weight.

Static thrust / power consumption can be easily compared experimentally between the twin and single setups.
But for an airplane,
My guess is that twin motors of the same size as the single will consume more power to fly at the same airspeed

Case 2 Iím leaving to others, as I havenít given it enough thought yet  Grin


DE1B2451-0252-4A7F-A56F-014DDE754C3D.jpg
Re: doubt regarding setting up a twin engine brushless motors
* DE1B2451-0252-4A7F-A56F-014DDE754C3D.jpg (29.31 KB, 800x424 - viewed 90 times.)
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« Reply #5 on: August 03, 2018, 10:17:27 PM »
swapnilnimbalkar
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Yes sir, I was confused about the airspeed.
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« Reply #6 on: August 04, 2018, 08:36:55 PM »
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@aaindthu,
Share what you are doing.
Not just theoretical enquiries, I hope...
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« Reply #7 on: August 06, 2018, 09:30:07 AM »
aaindthu
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so sorry for late reply.... i am not building my first model...  i have built many and crashed them all....  I am a noob at flying planes but i have built many planes...

Now I am building single engine trainer plane....  out of foam..  This time around I trained on a PC simulator and hopefully both fly and land my plane...  the real one..

I will definitely add pics later in a different thread..  okay??

And Thank you all for your replies..    after i fly this plane  I will make Grumman Goose model (seaplane) twin engine out of foam.....  Just thinking about it.....
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« Reply #8 on: August 06, 2018, 09:37:30 AM »
aaindthu
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Case 2 is also a great idea which never occured to me Huh?

I still have choice since i am yet to buy the motors.. I will see if i can get smaller motors..  thanks
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« Reply #9 on: August 06, 2018, 09:40:31 AM »
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Don't wake a Tiger until you've factored the teeth



Use 2 ESCs, identical in every respect. One contr-rotating prop. And toe-in

http://www.rcindia.org/electric-planes/'2016-sweepstakes'-electric-challenge-twin/
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« Reply #10 on: August 06, 2018, 09:55:36 AM »
aaindthu
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hi sanjay !!  I think you meant counter rotating motors.

fyi most of the twin engine airplanes are not counter rotating..  they rotate in same direction...
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« Reply #11 on: August 06, 2018, 10:10:28 AM »
sanjayrai55
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Don't wake a Tiger until you've factored the teeth



i have a doubt regarding setting up twin engine brushless motor for models requiring
twin engines.


You had a doubt. I built, successfully flew, and it's still flying regularly
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« Reply #12 on: August 06, 2018, 10:14:44 AM »
aaindthu
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great !!  thanx Bow
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