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Old Mar 28, 2012, 08:23 AM
Crash proof pilot
FlyDave's Avatar
Svizzera, TI, Bellinzona
Joined Oct 2005
380 Posts
Question
3 motors + 3 ESC and 1 battery, feasible ?

Hi all !

I'm repairing an old JU-52 made by Graupner, this mean... 3 motors.
The original kit used 3 brushed motors, and i want to use brushless motors instead.

I never done multiple engines aircraft, so i need to ask to you experts if my scheme (see below) is correct, as i want to use only 1 single LiPo battery to power up this system.

If each motor draw 30A (just as example value), it is correct to think that the battery should be able to draw 90A ?
if it is correct, i plan to use a LiPo 3S / 3300mA / 35C to feed the whole setup. (115A costant)

The drawing doesn't show the RX cable, i plan to join the three ESC's cables to 1 channel of the RX, if this work.

Thank you for suggestions and/or constructive critics
Dave
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Old Mar 28, 2012, 08:50 AM
Crash proof pilot
FlyDave's Avatar
Svizzera, TI, Bellinzona
Joined Oct 2005
380 Posts
I forgot : for the same setup... it's right to think that the thrust is the sum of the 3 motors ?

So if each motor pull 500gr the total thrust (without losses) is 1500gr ?
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Old Mar 28, 2012, 09:03 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
10,686 Posts
Seperate batteries will give you extra safety.
Your 3x30A is correct, but keep in mind ... starting at 'for everyone else':
About de-rating!! controllers and motors - RCGs

One single battery may lead to long battery wires, not a good idea. Too long battery wires will kill ESC over time:
http://www.rcgroups.com/forums/showthread.php?t=952523
Contents
  • Expert/manufacturer opinions
  • Problem
  • Solution
  • Rule of thumb
  • Capacitor type
  • Capacitor polarity!
  • How to add extra capacitors
  • Rules of thumb, installation
  • Explanation/theory
  • Measurements
  • DIY pictures
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Old Mar 28, 2012, 09:07 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,185 Posts
Three motor, one battery is no problem.

Thrust measurement is 'static thrust', so what happens in the air is still down to using the right propellers.

I'm not sure of the Graupners size or weight, but you shouldn't need anything like 30A per motor. My Sunderland, 90" span, is taking off grass or water on 12A per motor.

If you are going to use a ESC BEC, disable the other two, (only use one on a multi ESC, or a separate BEC).

I noticed this one on Youtube -

Graupner JU-52 (4 min 41 sec)
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Old Mar 28, 2012, 09:09 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
10,686 Posts
Quote:
Originally Posted by FlyDave View Post
... If each motor draw 30A (just as example value), it is correct to think that the battery should be able to draw 90A ? ....
Total current is 90A. But I would go for batteries with higer C-rating for longer battery life. Also keep in mind ... starting at 'for everyone else':
About de-rating!! controllers and motors - RCGs

Quote:
Originally Posted by FlyDave View Post
...it's right to think that the thrust is the sum of the 3 motors ?
So if each motor pull 500gr the total thrust (without losses) is 1500gr ?
Correct.

www.baronerosso.it -> forum

Seperate batteries will give you extra safety.
One single battery may lead to long battery wires, not a good idea. Too long battery wires will kill ESC over time:
http://www.rcgroups.com/forums/showthread.php?t=952523
Contents
  • Expert/manufacturer opinions
  • Problem
  • Solution
  • Rule of thumb
  • Capacitor type
  • Capacitor polarity!
  • How to add extra capacitors
  • Rules of thumb, installation
  • Explanation/theory
  • Measurements
  • DIY pictures


Vriendelijke groeten Ron
diy motor tipsDrive Calculator
diy motor groupCumulus MFC
• Get a life ... get a Watt-meter!!! •
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Last edited by Ron van Sommeren; Mar 31, 2012 at 07:22 AM.
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Old Mar 28, 2012, 09:21 AM
Registered User
Letchworth, Great Britain (UK)
Joined Jul 2004
11,541 Posts
The advantage of a single battery is that it ensures that all motors get exactly the same voltage, and so turn at the same rpm as each other throughout the flight. It's also generally more convenient when it comes to arming the system and changing the pack.

Don't forget that on a 3-motor model the three motors don't have to be the same power; outboard ones must the be the same, but the centre one can be different. You could have most of the power delivered by the centre one, if that makes things easier.

As Ron van Sommeren has pointed out, long battery leads to the ESCs can cause problems, but in the links he's given there's simple solutions to that.
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Last edited by abenn; Mar 28, 2012 at 09:28 AM.
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Old Mar 28, 2012, 04:04 PM
Crash proof pilot
FlyDave's Avatar
Svizzera, TI, Bellinzona
Joined Oct 2005
380 Posts
Quote:
Originally Posted by eflightray View Post
I noticed this one on Youtube -
Yes this is the same size and model as mine !

I'm doing a semi-total rebuilding because it was damaged from the previous owner, only the fuselage is still in good shape and i have only to re-cover it

You're right, i don't think i will need 30A on each motor, it was only an example value to simplify the calculations.

The reason for a single battery, it's because there is not much space inside the fuselage for additional batteries.
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Old Mar 29, 2012, 01:20 AM
Crash proof pilot
FlyDave's Avatar
Svizzera, TI, Bellinzona
Joined Oct 2005
380 Posts
Thank you Ron for the info's and links !

I've understood now that is better to put the esc's near the battery, and use longer motor wires, twisted.
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Old Mar 30, 2012, 07:23 AM
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peterangus's Avatar
Blackpool, Great Britain (UK)
Joined Dec 2003
1,342 Posts
Dave

This might help'
http://peterangus.pwp.blueyonder.co....0multi%20b.htm
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