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Old Nov 24, 2008, 08:24 AM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
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Need help with 257" B-36

All,
I need some help. I have read about 10 seprate threads on how long my wires can be and there seems to be zero 110% sure answers. I will be using 6 AXI 5320/34 with 8 cell lipo's. The planes CG can be met if I have the packs in the fuse and leading edge of the wing. I would like to have 16" battery to ESC leads and 30" ESC to motor. I posted this question on my thread, but then was told to ask this here. i need the batteries up front as much as I can to hit 55 pounds.

My thread:

http://www.rcgroups.com/forums/showthread.php?t=933242

Thanks all,

DAG
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Old Nov 24, 2008, 10:12 AM
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Xpress..'s Avatar
Joined Oct 2007
20,934 Posts
^I think you would get better answers in the "Electric Motor Design and Construction" forum.

But I think you should be fine with wires that long, as long as you aren't looking for stellar performance, with vertical climbs.
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Old Nov 24, 2008, 10:49 AM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
5,882 Posts
Quote:
Originally Posted by Xpress..
^I think you would get better answers in the "Electric Motor Design and Construction" forum.

But I think you should be fine with wires that long, as long as you aren't looking for stellar performance, with vertical climbs.
Thanks, didn't even think of that place.

DAG
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Old Nov 24, 2008, 12:24 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,029 Posts
Might be worth having a read of this thread, if you haven't already -

Long battery leads will kill esc
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Old Nov 24, 2008, 01:41 PM
AndyKunz's Avatar
Illinois
Joined Sep 2001
23,005 Posts
I think I would look at my construction of the airframe. The motors are behind the CG, but not by much. The CG looks pretty close to mid-fuselage. Can you put a lifting tail on your model? That will allow the CG to move back some more (old FF trick). Will your cells physically fit within the nacelle area of the wing? They would come pretty close to offsetting the motors.

Another thing you could do is put a longer driveshaft on the motor, moving the motor body up toward the CG. The bearings you need are easily available from Boca, and the couplers for motor-to-driveshaft should be pretty easy to obtain in the model boat market. If you're below 350W per motor, you can use a Graupner flex coupler which would allow you a little alignment error and still have a very good power transfer. Need to watch the prop rotation though to keep from unwinding the coupler.

Just a few ideas.

Andy
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Old Nov 24, 2008, 01:45 PM
It only takes one good idea
dag214's Avatar
Fishers, Indiana
Joined Oct 2004
5,882 Posts
Quote:
Originally Posted by AndyKunz
I think I would look at my construction of the airframe. The motors are behind the CG, but not by much. The CG looks pretty close to mid-fuselage. Can you put a lifting tail on your model? That will allow the CG to move back some more (old FF trick). Will your cells physically fit within the nacelle area of the wing? They would come pretty close to offsetting the motors.

Another thing you could do is put a longer driveshaft on the motor, moving the motor body up toward the CG. The bearings you need are easily available from Boca, and the couplers for motor-to-driveshaft should be pretty easy to obtain in the model boat market. If you're below 350W per motor, you can use a Graupner flex coupler which would allow you a little alignment error and still have a very good power transfer. Need to watch the prop rotation though to keep from unwinding the coupler.

Just a few ideas.

Andy
Thanks Andy,
Look at my renderings my motors are ahead of the CG and they are all driven on .5" shafts held in bearings.

Thanks,

DAG
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Old Nov 24, 2008, 02:47 PM
BEC
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Auburn, Washington USA
Joined Jan 2001
12,937 Posts
I think the lengths you're suggesting are reasonable with one caveat: make sure the ESCs (and therefore their input capacitors) are rated for at least a few volts more than the batteries you are going to use. Using good quality ESCs (comparable to the motors) is also a good thing.

I've always wanted to do a B-36, but not one quite that big!
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