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Doubling up rubbish motors.

Old 04-10-2015, 06:50 PM
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solentlife
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Default Doubling up rubbish motors.

I have a number of 1550kv Donkey motors for 3s and ~7" props. Despite claims they don't pull skin of a pudding let alone fly a model .... so I keep looking at them and wondering about doubling them up on a twin jobbie, say an 800mm span, 800gr high winger.

So now just looking for a simple setup high wing job that can have engine nacelles glued on either side of fuselage to wing ....

My ideas being 800mm span, 720mm length, wing semi symet of about 140mm chord. Flat top fuselage with angled up lower section to tail and nose. Square box fuselage to make easy to build / install gear.
3S lipo centrally mounted and esc's out in nacelles.

Let's see what comes out of the woodwork !

Nigel
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Old 04-10-2015, 09:55 PM
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Wrongway-Feldman
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Flite test has their mighty mini cruiser. Meets most of your needs. Free plans on their site.
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Old 04-10-2015, 11:34 PM
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Originally Posted by Wrongway-Feldman View Post
Flite test has their mighty mini cruiser. Meets most of your needs. Free plans on their site.
Forgot about that .... cheers, you've reminded me - I should have that somewhere in my download archive !

Nigel
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Old 04-10-2015, 11:44 PM
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Originally Posted by solentlife View Post
Forgot about that .... cheers, you've reminded me - I should have that somewhere in my download archive !

Nigel
Glad to help. Let us know how she turns out. Thinking about building one myself.
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Old 04-11-2015, 12:09 AM
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Just found the latest plan added there ---- Lancaster !

Nigel
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Old 04-11-2015, 03:04 AM
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They have a few plans I've been interested in building and modifying. I have this idea in my head of building another pusher puller biplane and trying to mid mount the motors for less pitch change under throttle.

Interesting things happen when the motors are infront of each other. My slowstick bipe had a 480 pushing 350 watts and a 450 pushing 240 watts. Stacked together, they pulled 540 watts together. The front motor had 11x5 and the rear had an 11x8, both of which were a bit large for the motors. When both ran, it stayed well below the limits and the rear motor produced most of the thrust. It had about 96 oz of thrust on a 40oz air frame.
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Old 04-11-2015, 12:05 PM
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Larry3215
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How many motors do you have? Nine maybe
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Old 04-11-2015, 12:09 PM
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Kidding aside, a really fun and different "twin" is the Jinx. Wingerons are cool. Can you say 'insane roll rate' three times fast?

Here is my variation on that theme.

By the way, I think the original plans are still out there somewhere.
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Old 04-11-2015, 12:59 PM
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"Donkey motors won't pull the skin of a rice pudding"
I could say don't build a "rice pudding"!

Light and aerodynamically 'slippery' this uses a motor very similar to the 1500kV donkey and it does very well with just one of them!
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A 1500mAh 3s gives a substantial duration as with a 7x6 prop it is only drawing 12A (or just 8C) from the battery at full power but still has a near vertical climb.
Finally being 'slippery' it handles wind much better than its size (40" span) and modest weight (12oz) might suggest.
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Old 04-11-2015, 01:08 PM
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Originally Posted by quorneng View Post
"Donkey motors won't pull the skin of a rice pudding"
I could say don't build a "rice pudding"!

Light and aerodynamically 'slippery' this uses a motor very similar to the 1500kV donkey and it does very well with just one of them!
Attachment 180126
A 1500mAh 3s gives a substantial duration as with a 7x6 prop it is only drawing 12A (or just 8C) from the battery at full power but still has a near vertical climb.
Finally being 'slippery' it handles wind much better than its size (40" span) and modest weight (12oz) might suggest.
I will always bow to your skills Q. Said it before, if I could build half as well as you - I'd be happy.

I am always amazed at the low power setups you install in models. And you succeed !

Cheers
Nigel
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Old 04-12-2015, 02:25 PM
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OK - I've been sketching and coming up with simple 'bomber style' twin.

See attached.

Idea has evolved into a Fun Fly high wing job that can carry a few sweets / maybe a Parachutist. So needs a 'bomb-bay' and that requires a slab centre form.
I've kept size down to 800mm so the Donkey motors have a chance. Simple low aspect wing allowing addition of woodwork to take motor / ESC weights.

If anyone wants to use my plan as basis of their own modifications / design - feel free. Please if you do, can you post the modified plans up here so we all get a look ?

I elected for trike U/C but that's of course optional until I get to see how she fairs in real life.

Sort of Mitchell / Liberator look to her I think ... will lend itself to military markings I reckon.

Nigel
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Old 04-12-2015, 03:52 PM
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The name 'Donkey' should have been a give away as to their performance! The second and bigger clue to their quality would have been their use of plain bushings to run on rather than ball race bearings

Anyway, personally for a motor costing $6 and running on plain bushes I'd not throw any more good money after bad. Just put it down to experience and drop it in the trash.
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Old 04-12-2015, 03:56 PM
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Originally Posted by JetPlaneFlyer View Post
The name 'Donkey' should have been a give away as to their performance! The second and bigger clue to their quality would have been their use of plain bushings to run on rather than ball race bearings

Anyway, personally for a motor costing $6 and running on plain bushes I'd not throw any more good money after bad. Just put it down to experience and drop it in the trash.

I bought 4 of them when I was putting together parts for the Lancaster ... a model that I will get back to sometime !

If they turn out as unsuitable on this twin - no problem as they will just get swapped out.

Nigel
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Old 04-18-2015, 08:07 PM
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Donkey Twin is on board being built now. Wings made ... just sorting nacelles and starting on Fuselage.
Simple cosmetics - packing tape ! I have RED, BLUE, BLACK, GREEN, ORANGE and YELLOW.
Wing has been changed to two sheets of 6mm separated by 3mm pine dowel glued inside. Sheets then pulled together at edges and taped up. Will mean fashioning a bridge piece over top of wing to fair to fuselage. But the wing is much easier to build.

Nigel
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Old 04-19-2015, 02:14 PM
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Decided to change motors to Emax 2S jobbies ....



Here's the model coming on ...







Side on - it has a sort of Bomber look ... actually quite pleased with the lines ... simple but seems to go together well.



Nigel
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Old 04-19-2015, 02:19 PM
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Couple of wifes Hairspray caps as engine cowls ...

5x5 props .....

Ailerons with 6gr servos, Flaps single 9gr, elevator 9gr, rudder 9gr ... she's going to get tail-dragger form U/C ... I was going for trike - but can't find my spare Stinger nose steering job.

Nigel
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Old 04-19-2015, 03:02 PM
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Forgot to show !!



Changed to 6x4 props ... 5x5 was a bit small against the cowl frontal area ...

COG is spot on NOW !! without any gear. That's good ... I will put the LiPo's and ESC's at CoG under wing ... The Tail servos at tail ... instead of running control rods .. Rx will go in the nose ...
Once the alloy wheel job is fitted - that will offset the rear servos.

I'm hoping for more than 1:1 power to weight ...

Idea is to create a fun twin that I can adapt to possible 'bomb drop' ....

Nigel
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Old 04-19-2015, 03:55 PM
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I like Bomb drops! E-max for sure will fly this. Donkey? Well, I often wonder who they are calling a donkey.
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Old 04-19-2015, 09:11 PM
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quorneng
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Do you know the kV of the Emax 2805s?
They do two versions 1500 and 2800.
A 6x4 could be a bit much for a 2800 even on a 2s.
I use a 5x3 3 blade on my 2800 with a 2s and they get quite warm if run at full power for long.
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Old 04-19-2015, 11:15 PM
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Originally Posted by quorneng View Post
Do you know the kV of the Emax 2805s?
They do two versions 1500 and 2800.
A 6x4 could be a bit much for a 2800 even on a 2s.
I use a 5x3 3 blade on my 2800 with a 2s and they get quite warm if run at full power for long.
Oops ! I think they are 2800's......

Will check out a test run. The motors don't say what kV unfortunately.

Nigel
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Old 04-20-2015, 10:37 PM
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Just waiting ESC's ad fit U/C .....







Turns out that LiPo's are now right up front ... ESC's will be under wing ... Rx is set under wing also.

I decided to do without flaps, but so I can fit later if decided - I pinned them in place and taped up. Just means slice tape ... pull out and hinge.

Quite pleased for a quick sketch .. cut and build !

Nigel
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Old 04-21-2015, 12:26 AM
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quorneng
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Looks very nice
But if it were me.......
I would double the size of the fin (4 times the area) and probably 1.4 times (double the area) the tailplane too!
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Old 04-21-2015, 08:33 AM
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Originally Posted by quorneng View Post
Looks very nice
But if it were me.......
I would double the size of the fin (4 times the area) and probably 1.4 times (double the area) the tailplane too!
Its funny .... I used another plan for the foundation ... ie ratios of parts.

I agree that the tail parts look small in the photos, in actual they are not so bad.

Weathers crap at moment so no chance to trial ...

Nigel
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Old 04-21-2015, 03:04 PM
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OK - She's already to go ....







Tested the motors on 2S and 6x4 props .... WOW ! ..... and I kept them going for reasonable run .... no sign of overheating or hot at all.

She has easily more than enough for vertical ... on storage charge LiPo's ... she was trying to leave my hand !

Q ... now view from rear shows the tail is not as small as first appears ... but I do agree with you - it could do with a touch more ...

Nigel
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Old 04-21-2015, 04:43 PM
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quorneng
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Nigel
What capacity LiPo will it use?
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Quick Reply: Doubling up rubbish motors.


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