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Electric Northstar ?

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Old 11-26-2011, 08:26 PM
  #1
plasticjoe
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Default Electric Northstar ?

Anyone converted a Balsa USA Northstar kit over to electric ? I have the baby brother to the Northstar... the Polaris and LOVE the way it flies. Just wanting something a little more durable and thought ... what the heck !!
I have a bunch of 4s 4000's Lipos that I run in other planes... was thinking about an 8s setup ... since it seems it needs alotta weight up front.. might as well make it usable weight vs. dead weight.
Anyone had any experiences with one electrically ?

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Old 11-27-2011, 12:38 PM
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Default RE: Electric Northstar ?

I have done a new design, based on the Northstar.
I changed the wing profile and span, the fuselage shape and construction (with a proper cockpit), I made the nose longer and added a foreplane, and I changed the construction of the tail.
I changed so much that I gave it a new name, "Lochstar". you can still see that it is based on the Northstar.
The first one was powered by an Irvine 53 turning a Master 10x7 at about 12300, and it was great!!

Then I made an electric version, using a brushless outrunner (Kv 1000)and 5S lipos tuning an APC-E 10x5 at unrecorded RPM (about 13000?)
On a freshly charged 5000 mAh 5S 20Clipo it pulled 53 amps (about 875 watts) which is a bit over over the motor's max rating of 45 amps/600 watts, but that will drop as soon as the model is moving, and as the battery discharges. I limitflights to about 6 minutes to avoid flattening the batteries completely. I cannot fit a prop with more pitch without blowing the electics.
My models weigh about 7 lb 4 oz (both of them) and the electric one has less top speed than the i.c. one, but still a sparkling performance especially on takeoff.
I am considering changing to a motor with a lower Kv (670) so that I can fit a 10x7 prop for more pitch speed with a 6S lipo and the same or lower Amps.

That should give some idea of how to electrify a Northstar?
On the first photo you can see the hatch behind the cockpit where I load the flight batteries. The separate Rx battery is under the tailplane.
The ESC is on the fuselage sidenear the flight batteries, with a small ex-computer fan blowing air over its heatsink for cooling (the fan plugs in to the rx to draw a few mA at 6 volts). Water has never been a problem there, even when the whole canopy with foreplane detached once in flight.
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Old 11-27-2011, 07:41 PM
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Default RE: Electric Northstar ?

Even Laddie M., the designer of the Northstar has converted one of his fleet to electric. Described in one of the Northstar threads, he used an AXI 4120-18 (510 KV) with a 6s battery. I am planning to build my Northstar based on a Hyperion 3026-08 motor (970KV) and a 4s battery. Given the weight advantage of the electric motor vs. a .46 glow, the need for ballast is eliminated and the appropriate balance point can be achieved with the motor battery. My own bias is towards lower voltage systems for water flying; there is less likelyhood of blowing the esc if it gets wet.

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Old 11-28-2011, 02:14 AM
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Default RE: Electric Northstar ?

Bob,
Did Laddie say how many watts he is pulling, and what size prop he is turning at what RPM? What wattage are you planning?

Even though my electic model has no noseweight it is just as heavy as the i.c. one. I didn't lighten the structure just in case I reverted to an engine later.

I find that a damp ESC will let its smoke out even at 3S, so low voltage is no protection. However I have heard that coating all the ESC components with "CorrosionX" (TM) does protect against water. It is said that a treated ESC will run under water, but I would not chance it anyway.
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Old 11-28-2011, 05:10 PM
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Default RE: Electric Northstar ?

Yea I've got some CorrosionX... I tested it with a battery powered pocket headphone radio. Dropped it in some water... let it run until it stopped working. Then took it out... took it apart... soaked it with the CorrosionX and a day later it worked fine.

So far everything sounds cool. I'm soaking it all up and going to make my own decisions....

Alasdair's variations look pretty cool !
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Old 11-29-2011, 03:05 PM
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Default RE: Electric Northstar ?


[quote]ORIGINAL: alasdair

Bob,
Did Laddie say how many watts he is pulling, and what size prop he is turning at what RPM? What wattage are you planning?

I can not tell you exact numbers. I never been too interested in the numbers. Usually I use what I have on hand. Usually on my AXI 4120/18 I use 12-6 or 12-8 prop and 6S 5000mA Lips. Right now I do not have electric NS. The model was destroyed when my radio lost the contact with the model. I am enclosing the web site where I am writing about my E-NS.
http://www.rcgroups.com/forums/showp...78&postcount=6
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Old 12-01-2011, 01:47 PM
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Default RE: Electric Northstar ?

Ladislav,
You must have raised the engine mount quite a bit to use a 13" prop.
I didn't, so I am stuck with a 10" but it's no problem.
Any idea what rpm your 12x6 or 12x8 is turning?

plasticjoe
One limitation of electrics is that I have only one 5000 battery and two 3200 batteries, so I get one six minute flight and two of 4 minutes. I could get more if I invest in an epensive fast charger and a huge 12v source battery, but I make do with 3 or 4flights a day.
The i.c. version would do 6 or 8 ten minutes flights before the battery needed topped up.

P.S. I should mention that the foreplane angle in photos 2 and 4 above is a switched airbrake function, not full up elevator. very effective too.
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Old 12-01-2011, 06:53 PM
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Default RE: Electric Northstar ?

Alistair... I am OK with the batteries and charging situation. I have plenty of 4s 4000Mah batteries ... and where we will be flying it.. we would be very close to a dock with electric

I was thinking about using a high pitch 3 blade prop to crank up the thrust. I've had success with that solution with another electric where I had clearance issues
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Old 12-02-2011, 04:19 AM
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Default RE: Electric Northstar ?

Alasdair
I did not check the RPMs. The 10” prop might be not give you enough thrust. The 10-8 three blade prop might work, but you might need to have the motor with the higher RPM / V then 515 RPM / V that the AXI 4120/18 has. I know it is a pain, but to get enough clearance, best would be to remove the nacelle and splice the extension to the bottom of the fin as shown on the drawing in previous post.
Laddie.
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Old 12-02-2011, 12:04 PM
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Default RE: Electric Northstar ?

There are a few high kv (high rpm), high power outrunners on the market, including scorpion and hyperion to name a few, that can turn a 10" prop fast enough to fly the unmodified Northstar. I am planning to use a Hyperion 3026-08 (970KV wind) on four or five cells.

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Old 12-04-2011, 05:48 AM
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Default RE: Electric Northstar ?

This is my Mikulasko "E" Arrow, which is very similar in size and weight to the Northstar. I'm using a Rimfire 32, and will have a 5S 3300 pack in it.

Specs on this motor @5S are:
10x5E prop
13,080 RPM
40.2A
65mph and close to 6# static thrust

I've found that the Great Planes performance numbers are somewhat conservative, so I'm going to start out with a 10x5 MAS 3 blade.

I made a battery box down low in the hull that runs back to the step. I checked the CG last night with the wings on, and using 20 oz of lead to simulate the pack. It's right where it should be, and I shouldn't have to add any ballast. This should keep the weight to right around 6 lbs RTF.
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Old 12-04-2011, 11:36 AM
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Default RE: Electric Northstar ?

Laddie:

I really like your electric Northstar. Did the motor and ESC hold up OK?

I found out last year that long wires between the battery and ESC can cause damage to the large input capacitors in the ESC. The available information is not real clear, but I think I ruined two good ESCs that way. Something to do with large voltage spikes during throttle changes.

I'm locating the ESC close to the pack in my E Arrow, and running long wires from it to the motor.
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