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Old Mar 12, 2005, 02:16 AM
Registered User
Wichita, KS
Joined Feb 2004
38 Posts
Question
Need help with a scratch built foamie

Howdy,

I'm working on my first scratch designed airplane, loosly based on the "Sea Duck" from the cartoon "Tale Spin"

It is a twin boom, twin engine flying boat made almost completely from foam parts from Nasty Toes Aviation. It will be around 60" - 65" WS and an airframe weight of approximatly 15 - 16 ounces. I have no idea what the actual AUW will be since I'm not sure what motors and batteries to use.

I want to try brushless and Li-Polys, but that may be a bit price prohibative. My question is what kind of motors and batts should I use on this? Since it's a seaplane, I can't spin large props. I originally planned on using 2 DD Speed 400s, but I'm not sure what props would be best to use with that. I think about 4 inches is all the clearence I'll have to the fuselage. I think I'll have even less clearence over the water, so I would like to keep the props to no larger than 6 - 7 inches if possible.

If anyone could post some suggestions for both brushless and non-brushless setups, I would appreciate it. I think I'll use Li-Polys either way, but I'm not sure what Li-Polys to use, so please help me here to.

Remember, I want ideas for BOTH brushless & NON-brushless setups. Thanks.

One more question. Should I use 1 ESC or 2? If I use 1, then how do I know what size ESC to use? The motors I'm looking at now have a current draw of 8.9 amps. Should I add that together to detirmine what size ESC to use (20 amp or higher), or do both motors still use only 8.9 amps?

Please help me here. I can possibly post some pics of the basic design if that would help any.

Thanks,
Cory
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Old Aug 10, 2005, 09:50 PM
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iflyatcae's Avatar
United States, NC, Charlotte
Joined Jan 2005
23 Posts
Im still somewhat a begginer, but I still know quite a bit. It doesnt matter, to my knowledge, how many esc's you use, just make sure that if you use one, that it can sustain the draw of both motors combined. Same goes with the battery. If you use one total, it has to be able to give out the sum of the two, in your case, about a 20amp discharge. You could also do two smaller bats, one on each esc, if you have two of those, and just y-harness the escs to the rx. This is all for brushed, Im not sure if you can do this with brushless, the whole one esc thing. O yea, you also have to figure out if you want to do series or parallel. You'll have to search that one, I cant tell you about that off the top of my head.

If you find out that you can do two escs on the brushless, may I suggest aero-nuts.com. they have the bp-21 and 17 amp esc combo for 40 bucks shipped. Maybe get two of those and a y harness, and be set. or get two of the motors, at 13 bucks each, and a bigger esc, maybe 20 or so. I donno, your choice.

Good luck, post results, Im interested in doing the same thing.
ryan
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Old Aug 10, 2005, 11:14 PM
Registered User
Wichita, KS
Joined Feb 2004
38 Posts
Thanks for the reply. I figured after the first week that this post would never see any attention.

I'll look into your suggestions, but unfortunatly, this project has been shelved, has have all my other RC projects. I just can't afford to fund them right now. Hopefully, I'll have a job in the near future and I'll be able to get back on this during the winter.

BTW, if you want to try it out, I could post the pics of the basic design. You could see if you can make it work. I just recently aquired a new computer (wealthy relative), so I'd have to do some looking for the model on the old system, but I think I know where it is. Let me know.

Thanks,
Cory
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Old Aug 10, 2005, 11:33 PM
Our Daddy and Heli Junkie
Fred Bronk's Avatar
In Heli Wonderland
Joined Aug 1999
22,796 Posts
Something you may want to play with is Motocalc.

It is free for 30 days and you can put any airframe in it you like and it will throw motors back out at you.

With brushed motors you can get away with one ESC, but your voltage or amperage will be double that on a single ESC setup.

With BL motors will need 2 ESC's for solid performance.
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Old Aug 10, 2005, 11:54 PM
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Wichita, KS
Joined Feb 2004
38 Posts
Quote:
Originally Posted by Fred Bronk
Something you may want to play with is Motocalc.

Yea, I already had Motocalc, but my trial expired several months ago. If memory serves, that's where I got the idea for twin 400 DDs.

Cory
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