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Old Dec 17, 2002, 07:38 AM
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Joni Piililä's Avatar
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Mini-Graphite part 3

My long waited Mini Graphite finally arrived! (16 weeks). I have Torcman 350/28 14 wind 14 pol motor to use with this plane. Now I'm making a choice which batteries to use and how to fit them inside. I noticed that fuselage is pretty narrow and because of my motor winding number I have to use 14 – 18 cells. I am going to use CP 1700 cells. What do you think if I put battery pack, which is in triangular formation, like in this picture?

Will it cause problems to have one battery lead quite long? This triangular formation causes battery leads coming from other ends of pack.

For those wondering how motor with 42 mm diamerter will fit to that nose, Torcman has a extension (like a gearbox) of 25 mm. That makes fitting it possible without major modifications to nose. Altough I am making an new nose which has bit larger diameter in front to fit any LRK motor.

How has your MG:s been flying? and would you now do something differently with this bird setup?

Joni
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Old Dec 17, 2002, 07:43 AM
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and the picture
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Old Dec 17, 2002, 12:54 PM
Foamie Hater
Joined Jul 2001
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Now when you say 14weeks was that from the time of order or when they shipped it. I too have been waiting for my MG to show up since I sent the check back in late October.
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Old Dec 17, 2002, 03:11 PM
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Joined Mar 2001
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Joni - I think that you may run into CG problems if you try to fit as many as 14 or 18 cells. I haven't yet 'built' my M-G, but from my experience with my Organic (same fuselage) and that of others, you need to get the CG of the pack more or less aligned with the intended CG of the model and have space to move it back or forward a little for adjustment. Your motor is probably heavier than something like a Hacker, so that will also compound the problem. You may be able to get away with it IF you are able to get the pack back far enough, but then where will you put the receiver and its battery pack?
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Old Dec 17, 2002, 04:48 PM
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How are you going to mount the torqman motor on the nose of the MG? I don't think you can fit 3 sticks of battery in the fuse. I saw the 2 sticks side by side is pretty tight. I think if you can fit the motor in and you will have to use the CP-1300 in a 2-stick form. May be you can use the 1700 4/5AUP nimh, good upto 30 amp.

You con't really want to run a long extention shaft without support in a glider, the landing might bend the shaft, if not supported.

Brian, an EAJ
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Old Dec 17, 2002, 05:53 PM
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Flyerman – it was 16 weeks from the order and money transfer.

Gordon – putting 18 batteries into triangular setup it will be 6 cells in row, so that will allow me to move the battery pack back and forward in fuselage.

Bhchan – Torcman is going to fit there even without cutting the nose, trick is to use their “Einbauadapter 350 / 25 mm Baulänge” here is picture of it. As for those 3 sticks of battery I can say that they will fit too I just measured it. My concern was the one battery lead which will become much longer than the another. Maybe it is not a problem. The Torcman extension has ballbearing in front of it, so it does not increase the risk of bending the shaft.
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Old Dec 18, 2002, 08:51 AM
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Joni - If you think you can fit all that gear in the fuselage, then good luck to you! Before you cut or fix anything permanently, I strongly suggest you assemble the model with all the equipment in roughly the right place in order to check that you can achieve the correct CG. I have a feeling that it is going to be nose-heavy.
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Old Dec 18, 2002, 09:51 AM
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The one longer battery lead will of course increase resistance, and hence cause you to lose some power to the motor. That being said, there's no reason it can't be done, and if you're willing to accept the (slightly) lower voltage to the motor, I would say go for it. Also, if you keep the lead at the forward end of the plane nice and short, the total resistance won't be much more than 2 "normal" length leads coming out of one end of the battery.

If you were competing, I'd argue this setup isn't acceptable, but if you're just sport flying, go with it.

Come to think of it, my brother has a 9 cell pack in his R/C speedboat (pulling 50A) and he has the single long lead setup too. Having seen his boat run, I don't think the long lead affects performance too much...it's still a darn fast boat.

Good luck. Hope that helped.
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Old Dec 19, 2002, 04:00 AM
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Eisenschmitt, Germany
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Joni,

I am 99% sure it will work. I just checked and the third battery stick fits like a glove in the fuselage. There is also quite a bit of room to move the pack.

Just be careful about where you put the switch, controller etc so they do no get in the way of the battery pack when you slide the nose on. I put my receiver pack (4 cell stick) way back in the fuselage and the receiver sits in front of that but it is still well aft.

With my Pletti/Schulze set up the controller is in the way of a third stick. The controller is almost hard wired to the motor. Has good and bad points.

I am flying my M-G with 8 RC2400's and 10 CP1700's (4/5 RC) with either a 14 X 9.5 or a 13 X 8 cam.

Keep us up to date with your test hops!

Gary
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Old Dec 19, 2002, 04:43 AM
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Joni Piililä's Avatar
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Thanks Gary!

That "I am 99% sure it will work" made me feel very good. Yesterday evening I did my first testbench runs with motor and Master - 77-3p controller. I do not have my cells for MG yet, so I used what I had. Results were amazing, 20 cells 15 x 10 it had 3400 g static thrust! and MG will propably weight something 2000g. Altough 18 cells is what I'm going to use in MG.

Torcman fits perfectly to nose without shortening it. Only problem is wiring from motor. Wires are the only reason to make hole to nose cone

Power system is almost ready, now begins the servo selection. Any servo suggestion?

Joni
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Old Dec 19, 2002, 04:53 AM
I "plant" trees (balsa)
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Eisenschmitt, Germany
Joined Jan 2002
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I used Dymond D200's in the wings and Dymond D60's in the tail. So far I am happy with them. Those tail servos need to be VERY thin and still powerful enough.

My M-G is right at 1900 grams and the climb is "adequate".
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Old Dec 19, 2002, 12:16 PM
I "plant" trees (balsa)
Gary Retterbush's Avatar
Eisenschmitt, Germany
Joined Jan 2002
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Joni,

In spite of it being possible (I think), I do not recommend the 18 CP1700 cells. I have once again looked it over and I have trouble finding a place for the ESC without having some l-o-n-g wires. Of course I do not have the motor you are going to use but I don't think the overall length is greatly different than my geared Pletti. That could be a very poor assumption. Also, the weight is going to be well over 2.2 kilos. You will have a speed demon for sure.

I would suggest swapping the motor for a different wind or just using 15 cells with what you have. However, if you press on I certainly want to hear about the results!

Gary

PS:
Gordon, I think you are right after all!
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Old Dec 19, 2002, 12:37 PM
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Quote:
Originally posted by Gary Retterbush

SNIP

Gordon, I think you are right after all! [/B]
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Old Dec 19, 2002, 12:49 PM
I "plant" trees (balsa)
Gary Retterbush's Avatar
Eisenschmitt, Germany
Joined Jan 2002
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Quote:
Originally posted by GordonTarling
Go ahead, rub it in!
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Old Dec 20, 2002, 05:26 AM
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Joni Piililä's Avatar
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I read previous MG threads and people were using 10 x 2400 cells. I don't see big difference between 18 x 1700 vs. 10 x 2400,
weight is equal and lenght of 18 X 1700 is bit shorter than 10 x 2400 (when cells are in triangular shape). Yes, there is still a problem with that long wire and bit heavier motor.

About tail servos, is Graupner 261 really enough for this plane?
I' been using them a lot in Pylon speed 400 Stinger and it is hard to beliewe that they could handle the loads... Stiger has teached me and others to put hardware to almost impossible places.

Weekend is starting, so empirical studies about fitting the gear and placing CG should be done soon.

Thank you for your help and opinions! please keep posting.
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