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Old Feb 11, 2005, 02:49 PM
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Pierre_de’ Loop's Avatar
United States, MD, Bethesda
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Lil' Poke

I'm going to post a few pictures and comments about my Great Planes Lil' Poke for folks thinking about building one of their own. The airplane has been around for some time, so the small number of threads discussing it surprises me. Moreover, what posts I do see all say the same thing, "it needs a speed 400 motor."

I built mine stock with the Electrifly components; MPJet 4:1 gearbox, Great Planes C-10 ESC, and Electrifly 7.2V speed 280 motor. Indeed my initial flight with an Electrifly 7.2V, 650 mah NiMH battery was disappointing due to the lack of power this set-up provides. I don't recall the exact weight of the airplane, but I believe it was 12 oz. ready to fly (w/ 2.73 ounces of battery).

("Lack of power" is an ambiguous term. Let say that my expectations for the airplane are modest. I want something to float around a small park in the middle of Washington, DC. When I say "lack of power" I mean anything less than full throttle and it will sink quickly - not drop, but sink).

The issue looked to me to be the 7.2V motor. In short, I needed to put more into the motor. So my next flights were flow with an Electrifly 8.4V, 1200 mah, NiMH battery. Success! This provided enough power to fly, but it was a heavy airplane with 5.8 ounces of battery pack tucked into it.

Once more, the issue was the 7.2V motor, which prevented me from putting my 2S 1500 mah Kokam lipo in it. This would have put a mere 0.2V more into it.

I tinkered with the idea of a 3S lipo pack, but I'm only set up to charge 2 cells. I don't see needing 11.1V batteries for my Bristol Scout D or Eastbourne monoplane, so the charger upgrade seemed wasteful. The cheaper solution - I hope - will be a Graupner 6V speed 280 motor and a new GWS, 7.4V, 1300 mah lipo battery pack.

I'll post my experience with the new motor and battery as soon as the wind calms down. In the meantime I'd like to hear from other Polk owners.

If you are building a Lil' Poke and fishing for a pilot figure let me modestly suggest a pig for the Poke.

Thanks.
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Old Feb 11, 2005, 03:00 PM
Faster!
Joshua Wesley's Avatar
United States, NV, Sparks
Joined Oct 2004
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Looks good Andrew, I hope to have mine flying soon. I'm going to power mine with a stock CDRom from GOBrushless.com 9x5 gws DD, 3s 450 or 600 lipo, about 4 amps. If yours was aound 12 oz AUW, mine should come in around 9.5 to 10oz on about 40 watts of power. Do you have an idea of the amp draw with the 8.4v battery? Do you have ailerons?

-Joshua
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Old Feb 11, 2005, 03:15 PM
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Hi Joshua,

No, I'm sorry I do not know the amp draw with the 8.4V battery. I opted for R&E alone because I wanted something simple for the park.

I'm anxious to see a brushless motor in a Poke. A few folks have used speed 400 motors with success, but I don't recall anyone using a brushless motor in one. Let me know how it goes.
Thanks!
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Old Feb 11, 2005, 07:24 PM
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In my Blu heaven! near Lincoln NE
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I have always admired the looks of this plane and thought one day to have one yet when I did a search here and elsewhere and found the same thing. Most were under impressed and found it very lacking in the umph department. I too was wondering about the lack of using inexpensive brushless for this and no one seems to have done so.

I will be watching this thread hoping to see something good to come of it.

Robert
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Old Feb 14, 2005, 09:10 AM
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This weekend's weather gave me a chance to try some new things in the Poke:

(1) Graupner 6V motor;
(2) GWS 1300 mah lipo battery
(3) Batteries America 1200 mah lipo battery
(4) Maxx Products International 15 amp, ESC for 2S lipo batteries; and
(5) APC 9X6 propeller.

In short, the 6V motor is an enormous improvement over the recommended 7.2V motor. No surprise there. The 9X6 propeller too is a vast improvement over the recommended 10X4.7. Notice I am slowly dismantling the recommended power package. Moreover, the lipo batteries drop the weight of the airplane without upsetting the center of gravity; thus improving performance. (Sorry, no scale handy so I can't say for sure what the all up weight is with them, but I can say that the batteries weight 1.9 and 1.7 ounces respectively; down from 5.8 for the NiMH). I can throttle back and float around without much worry.

(Robert, IMHO the 6V motor and 9X6 propeller make this a comfortable airplane to fly in terms of power.)

However, I'm still plagued with what I believe to be a radio, ESC, and/or motor issue. When I first flew the airplane with the 1200 mah battery I had to fly at full throttle. Often my motor would stop for a split second and then start again. I attributed this 'glitch' to the BEC. I was after all, always flying at full throttle.

I expected to solve the problem when I replaced the 7.2V motor with the 6V motor. My thinking was that I would feed less power to the motor and avoid tripping the BEC. Indeed, the 6V motor and lipo battery combination allows me to fly around at about 2/3rds throttle. But the problem persists.

Imagining the problem to be the Electrifly C-10 ESC, I soldered JST connectors on a Maxx Products International ESC (the ESC is item number MX9217 on the MPI website). The airplane took off, climbed nicely and made a turn before the motor stopped. Once the motor has stopped the MPI ESC does not allow you to start it again. Consequently, I observed a dead-stick landing (no trouble, but not much fun). Needless to say I have put the C-10 ESC back in.

Sunday night I made an effort to pay attention to when exactly the motor cuts out. This is what I found. Left turns, even at a low throttle setting, will cause a "glitch" and stop the motor for a split second. I also saw an 'up' elevator glitch, which is to say the elevator jumps up for a split second without any input from me (uh, oh).

My first thought regarding the motor 'glitch' was this. The BEC is always about to kick in and does so when the radio needs to power a servo. However, this does not explain why it occurs with a left turn, but not a right. Moreover, a modest throttle setting should not exhaust the battery to this point. I have also nixed interference from the surrounding area as a possible explanation. I have been flying in this park without incident for more than a year with the same transmitter, receiver, and servos. Plus, the initial motor 'glitch' I saw with NiMH battery occurred at another site far from anything that might cause inference.

The only other explanation I have come up with is "noise" from the motor itself. This may well account for the newly developed elevator 'glitch' too. I soldered the capacitors that came with the Electrifly C-10 to the new motor as instructed (opting to use these capacitors rather than the capacitors that came with the motor after reading the words, "may not be suitable for R/C" in the Graupner directions). All I can I think to do is pull the motor out tonight and inspect the solder for weak points.

Other suggestions are most welcome!
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Old Feb 14, 2005, 10:14 AM
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Hey Andrew,
You might check your controls. If it binds even a little when your servo directs a left turn, that could cause it. Or, the servo could be bad(rough gears in the left position), if you have another try swapping it. If this phenomena occurs only in left turns I doubt its bad caps or loose connections.

I also have a lil' poke, though my experiance is slightly different than yours. I fly it with the 7.2v 280 4.1:1, 10x4.7 and Electrifly 2s 1200 or 1500 lipos. It is by no means a screamer, but I have no problem keeping it in the air, it floats beautifully. I must say, (although I'm sure you are on the same page) the last thing this plane needs is 400. Light, light, light, is the key to this plane. If you were really hankering for power you could put in a 300, but for how it was designed to be flown, that seems kinda pointless. What material did you cover your LP with?

Sam
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Old Feb 14, 2005, 10:58 AM
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Hi Sam,

Yes, I am on the same page regarding the need for a speed 400 motor in the Poke. The 6V motor and 9X6 propeller is plenty for this little airplane.

I used white Coverlite and Sig Stix-it on my Poke.

Your advice regarding the servo makes a world of sense due to the left only rudder issue. However, the elevator glitch I encountered is nudging me in the direction of isolating motor noise as the problem. Nevertheless, I will check for binding before I do anything else.

I have seen where other folks experiencing the same trouble with a C-10 have soldered a third capacitor between the motor terminals (!) and cut the leads from the motor down as much as possible to minimize noise. Do you have opinion on this?

Thanks!
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Old Feb 14, 2005, 11:33 AM
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I just received a message from a fellow who experienced the same problems with his Great Planes Tutor. In short, the aluminum pushrods used in the Tutor and Li'l Poke produced noise and thus 'glitches' when they touch each other (as I'm sure mine do). I'll replace the aluminum rods with conventional music wire and plastic sleeve style pushrods before I do anything else. Thanks Marc!

Sam, you were mighty close when you had me look for binding, eh?

Thanks.
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Old Feb 14, 2005, 06:14 PM
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Cool, glad you got figured out, and that makes perfect sense. I use a berg with mine, so whether or not the pushrods touch(I don't remember if mine do or not) it doesn't really matter. I have a C-10, which I have not modified at all. I have flown it with single conv. RXs and have not had any great trouble. Any glitching I have experianced I have always contributed to the RX (wether it always is or not is hard to say, its never been bad enough to worry about).

Sam
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Old Feb 15, 2005, 09:19 AM
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I had to temper my enthusiasm for this seemingly exhaustive explanation when I failed to get the pushrods to touch. I put every conceivable command combination into my rudder and elevator and never once did they meet. Nuts!

Aware that things change in-flight I replaced my rudder pushrod with one made from music wire and a plastic sleeve. I'll plug a third capacitor between the motor terminals too. If all else fails I'll see about routing my antennae away from the servos (noise from the servo motors, perhaps?).

Sam, any pictures of your Poke?

Thanks.
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Old Feb 15, 2005, 09:50 AM
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Ah, that is discouraging. Where is antenna routed currently? I do not currently have any pics, I'll try to get a few soon though.

Sam
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Old Feb 17, 2005, 02:11 PM
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Prevailing winds are too much for the Poke. Nevertheless, I'm optimistic that the 1-2-3 combination of a new pushrod, third capacitor, and new antenna path will resolve the glitch issue.

We wait and see…
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Old Mar 15, 2005, 01:53 PM
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I did want to mention that the Lil' Poke is flying very well these days. The weight of the airplane - without the battery - is 8 ounces. I have replaced my 1/2" Sullivan tail wheel with a Du-Bro micro-tailskid to make landing at the local park less like landing on a carrier.
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Old Mar 15, 2005, 05:24 PM
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Great! I need to recover a small section of the fuse and mine will be in business as well.

Sam
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Old Mar 16, 2005, 03:50 PM
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Great! Any pictures yet?
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