advice on electric motors needed

I bought a Wattage brand, "Pitts 400 EP ARF" a few years ago and am just now
getting around to building it. They give you a Wattage "Super 400 cobalt"
motor and a 7-4 prop. They have you use their 7 cell NiCad battery (cp1300)
which I assume is a 1300 ma. It fits but there is some room to put a longer
one in if needed by carving out some of a bulkhead in front of the bottom
wing. The guy at Hobby People told me the other day that the kit is good but
that the motor really sucks up the juice fast. He recommended that I use the
"KMS brand" motor # KMB 31/12 instead. It's a brushless. Is that good advice
and is the KMS motor as powerful? The motor and controller (18 amp) are on
sale tomorrow for $20 and $30 respectively. If this is better, what would be
a good prop for it? The plane is supposed to weigh 30 to 33 oz. and have a
wing loading of 15-17 oz / sq. ft. Thanks
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Reply to
Forrest
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OOPS ... messed up the copy and paste for the Wattage motor link. It should be
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Reply to
Forrest
If you go with the brushless and a LiPo battery you can get about twice the flying time for the same weight.
Reply to
Paul McIntosh
"Forrest" wrote in news: snipped-for-privacy@comcast.com:
I'm flying a KMS 31/12 on a sport plane at about 250 sq in and 22 oz, and it powers the plane quite nicely. Not quite unlimited vertical, but it's close. I'm usually flying it with a 3cell 1550 LiPo.
Now, for your situation - the KMS would probably outperform the 400, but it really won't be happy on a 7 cell nicad. If you can run it on 9 cells, you'll be a lot happier, and a 3 cell LiPo would be better still. The Tanic 3 cell 1550 is on sale tomorrow, too, for $50. The Tanics are kinda pricey, but they're very good packs.
So, for your plane, try the KMS 31/12 with a 3 cell 1550 pack, an APC 9x6 slow flyer prop, and a Castle Creations Thunderbird 18 speed control. I haven't tried a KMS ESC, but the TBird is from Castle Creations, and I'm a big fan of theirs. The Tbird's regular price is $35, which is only $5 more than the super-sale KMS price. Unfortunately, the Hobby People site says it's not in stock, so if you want to fly this weekend, you may have to go with something like the KMS.
That setup should pull the plane around pretty well, but you won't have huge vertical with it if you really are coming in at 30+ oz. Of course, the KMS is an ounce less than the 400 (ignore the box. The KMS 31/12 and 31/09 weigh 65 gm each) and the Kokam LiPo would be about 3 oz less than that Nicad pack.
If the plane comes with a 7" prop, better make sure you have clearance for a 9". When I tried an 8" on the KMS, the performance suffered quite a bit.
One last warning about that KMS - it doesn't come with a real radial mount. It has two (or 4?) screws that go into threaded holes in the backplate, but there's almost no practical way to mount the engine like that unles you have a radial mount that you got elsewhere. The 'standard' radial mount that comes with, say, an EssKay or Himaxx outrunner will fit just fine, and GWSExpert sold me a few radial mount sets for $5 each, but you'll need something.
Reply to
Mark Miller
KMS has a neat square stick mount for a couple of bucks. I went to the Hobby People site and ordered about $300 worth of the KMS stuff to test with my new LiPo line.
Reply to
Paul McIntosh
| The Tanic 3 cell 1550 is on sale tomorrow, too, for $50. The Tanics are | kinda pricey, but they're very good packs.
Where?
Who else is running cool R/C related sales on `Black Friday' ?
(Ok, I know Radio Shack has R/C crap^H^H^H^Htoys, but I'm talking about the good stuff :)
Reply to
Doug McLaren
Off subject, I know, but where does the term, " Black Friday" come from. I live in So. Calif. and have never heard it before. Just curious.
Reply to
Forrest
The ungeared cobalt is a complete mismatch.
Its a good motor, but not with a 7x4 stuck on it.
On 8 cells a permax 450 turbo is a far far better animal in that class.
the cobalt needs gears and a lot of amps, Then it really delivers.
Reply to
The Natural Philosopher
snipped-for-privacy@frenzy.com (Doug McLaren) wrote in news:uWxhf.14587$ snipped-for-privacy@tornado.texas.rr.com:
Hobby People. Some of the stuff is 1-day-only (today), and some prices go on through the weekend. I picked up another of the Tanic 3 cell 1550s this morning.
Hobby Lobby is running their weird hourly sale for the next few hours; you should check it out. Every hour for the next few hours.
Last, and least, GWSExpert is having a sale, but I haven't seen any wild markdowns like Hobby Lobby and Hobby People are running.
Reply to
Mark Miller
If left un-geared and given the "lots of amps", say the Tanic Li-Po 11.1v 1550 mah (3 cell), what would be a good prop for it if hauling around a 32 oz plane ?
Reply to
Forrest
Forrest. Since many businesses depend on Christmas season sales to show a profit for the year , they operate in the 'Red' until the beginning of the Christmas selling season. Friday is the official beginning of the season and this is the day they start operating in the 'black'....or hopefully so.
Ken Day
Reply to
Ken Day
=2E..
Hej Forrest
Here you have a lot of links about (DIY) Brushless DC-Motors &=20 Speedcontrollers for Model-Aircrafts:
Peters LRK Site:
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machinedesign.com: Do-it-yourself brushless:
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Citat: "...Authors report good results using 1-mm wire with a polyamide=20 lacquer coating able to take up to 250=B0C...efficiencies of around 90% o= r=20 better. Typical prop motors generally weigh less than 5 oz and those=20 built to date produce outputs ranging from 20 W to 2 kW. Some reportedly =
run at around 15,000 rpm..."
List of my Super Magnets for Motor Builders:
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DIY Controller Schematic. It is at
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but is poor quality...I have redrawn it more=20 clearly. The source is also posted at this site but you need to register =
first:
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Tornado N-Kanal:
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"... Aufgrund der Schwierigkeiten, die wir mit den verwendeten Treibern=20 (TC4427) hatten, haben wir nun einen reinen N-Kanal Steller entworfen.=20 Dieser basiert auf dem Atmel Mega8 Mikrocontroller. Als Treiber kommen=20 hier IR2102 zur Anwendung. =2E.."
brushless LRK motor:
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Simpel: Speedcontroller 2:
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Controller Speedy-2 with Microcontroller PIC16F84-04/SO:
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Speedy-BL - Drehzahlsteller f=FCr b=FCrstenlose Modell-Motoren:
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seven diy brushless ESC designs:
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?s=3D&threadid=3D157193 Brushless Motor:
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A Brushless Motor You Can Build:
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regards, Glenn
Reply to
Glenn Møller-Holst
5x5 will try and draw about 20A. As will 6x3 folder and 5.5x4.5 and a Gunther.
20A will fry the pack fairly quickly.May fry the motor too..Motocalc reckons its dumping 60W of heat at that power level. Still, its cobalt, and tehy can run a lot hotter without demagging.
Reply to
The Natural Philosopher

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