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Feb 09, 2004, 03:04 PM
Thread OP

Power system for 7 foot Ford Trimotor


I have had this question on my building thread, but have gotten no answers. I have to make decisions about the power system for the Trimotor (7 foot ws, auw 7 pounds). I have read several relevant threads, and here is what I guess will be a scale-like system with 10 minute flight times.

3 “Fully” long can speed 400 motors (aka Jamara 480) wired parallel
10 cells, GP3300 NIMH
3:1 gearboxes
10x5 props
Jeti 50 amp esc with BEC

Using P-Calc, this shows a draw of 15 amps/motor. I understand that there are some inefficiencies in taking these single motor apps to multimotor, so that is why the prop size is at the high end.

I priced this out from the HL website and each motor/gb/prop/adaptor setup will be about $55.

Alternatively, E-Flite sells a 480 motor, 2:1 gear box, 9x5 prop+nut combo for $37. It is at:

http://horizon.hobbyshopnow.com/prod...p?prod=EFLM102

At this price, it seems like a great deal. Think it could handle 10 cells and parellel wiring? Picture below.

Any opinions?

Warren
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Feb 09, 2004, 03:13 PM
Just an average RC'er
Jim McPherson's Avatar
How are your motors mounted in the model? That will affect what motors you can use.

-Jim
Feb 09, 2004, 04:42 PM
Thread OP
The design is flexible. Could bolt to a standard forward facing bulkhead/motor mount, or use mounting rails.
Feb 10, 2004, 08:29 AM
Registered User
Andy W's Avatar
Sounds like a good combination to me. Is this going to be a scale-sized prop? You'll find you'll be able to fly on reduced power once you're off the ground, which should give you the duration you need.
..a
Feb 10, 2004, 09:22 AM
Thread OP
Yes, a nine inch prop is scale.

Yesterday I ordered 3 dummy radial engines (3.75" size, smallest available) from Bob Dively. The nacelles on the plans have a 2 7/8" outer diameter.

Hope everything fits!
Feb 10, 2004, 09:31 AM
Registered User
Andy W's Avatar
The motor is external on the trimotor.. it might be OK..
..a
Feb 10, 2004, 09:35 AM
Balsa Flies Better!
Man, for that kind of money for a geared setup, I'd kick around brushless- maybe a baby Axi. They're a bit more money- but the lack of noise might be worth it. It sounds like you're going the lightweight stick and tissue approach- which means that you don't need many watts- maybe 300-350 total.

A cheap alternative is the Turbo 450 motor- direct drive, will swing an 8" prop on 7V, and do so reliably for a long time if kept under 20A draws. If you decide to to go to li-poly, I'd use 2 cells. Each motor weighs about 4.5 oz- which should give you some weight in the snoot, something which you'll probably need.
Feb 10, 2004, 09:47 AM
Visitor from Reality
Hi Warren
The snag with cheap-O motors is that once you've burned out a few, you shouldn't add up the cost just in case it comes to more than buying good ones straight off!

But to look on the positive side, you're on the right track. Years back, I converted a Lazy Bee from single glow to triple electric power. First off was a geared 400 in the nose, with two much smaller geared 280-ish motors on the wing.

The wing motors mostly made noise and sucked electricity - they didn't really contribute to progress at all. She ended up flying great with 3 DD 400's feeding off one pack of 1700s - SCRC 1700s at that.

The real cheap cheat would be a geared MM or Endo running ten jugs on the nose, and freewheelers on the nacelles, but you're made of sterner stuff so I won't seriously suggest that

Megocoupe's idea sounds attractive - DD is always much less fuss, and cheap gearboxes can be another route to frustration (pop-off pinions) and expense. If you want a system with longer legs, consider using one pack and ESC on the middle motor, with another pack / ESC to parallel feed the wing motors - if you're using brushed motors and nimh, the cost is somewhat more manageable than BL and lipo comes to

Might not be a bad idea to test fly on the quiet without the dummy radials. Lot of drag there, not to mention risking the work you'd put into making them, and if it turns out to be marginal, you might be glad you'd left them off.

Regards

Dereck


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