390mg Plane - Video - RC Groups
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Jul 11, 2008, 03:22 PM
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Angry_Monk's Avatar

390mg Plane - Video

FINALLY, i would like to share my latest creation: my new 390mg plane.

i spend a long time working on this, and although i knew it would be a struggle i didn't expect almost EVERY aspect of this plane to fight me every step of the way. but now it finally flies, very marginally, but flies none the less.

the only two parts on this plane that gave me a lot trouble were the RX and motor/prop (basically the only two important parts). i originally tried to make a RX like Lads but i had range issues with it. i eventually came to the conclusion that my glue was dissolving part of the IR sensor, thus decreasing my range. so i had to abandon the nice compact look of that style RX in favor of a very messy version.

the motor was by far the hardest part. i made 4 different motors for this plane and 7 props trying to find the best match. and even then i didn't get the excess of power i wanted. i still want to experiment more with different props and especially with geared BL motors. after seeing the motor Lad built for his plane i think that is the real way to go. the trouble will be making one and still keeping it at the same weight as the current motor on the plane.

the motor i have on the plane now is a beast, of sorts. it spins my custom milled version of Martin's M12 prop for the shicoh at a whopping 36K RPMs! the prop is scaled down by different percentages in each direction, giving me a custom pitch, cord, and diameter. static thrust was about 185mg at 65mA at 3.7v. but the prop used in static tests did not preform that well in the air, so i switch to one that was exactly the same but had a slightly lower pitch.

flight time on the model is only about 2 minutes or so. i'll try for a video later today or tomorrow. i'll also try some more props to see if i can get some more power out of it.

I would like to thank Helmut, Robert, Martin, and Lad for their help on this model. i talked with each of them about various aspects of this model and they provided great help (and sometimes materials).

WS: 3.125"
Length: 3.5"
Act: 130ohms, ID 1.8mm, OD 2.2mm
BL Motor: 9 ohm/ft wire, 45 ohms. Magnet: 1mm length of the shicoh magnet (1.83mm OD, 1mm ID). 0.25mm steel axle.
Prop: 0.615" diameter, max cord: 0.092"

Weight Breakdown:
Airframe + Act: 37mg
8.5mAh Lipo + on/off switch: 290mg
IR RX: 25mg
BL Motor: 30mg
Prop: 5mg
Landing skids: 3mg

AUW: 390mg

Video: https://www.rcgroups.com/forums/showthread.php?t=893896

comments or questions are always welcome.
Last edited by Angry_Monk; Jul 14, 2008 at 11:50 PM. Reason: added video
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Jul 11, 2008, 03:35 PM
OpenGL C/C++ programer
axelen's Avatar
Awsome !!!
looks like sooooo much work
Jul 11, 2008, 03:38 PM
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glenn2626's Avatar


There aren't enough superlatives to describe this.

Amazing work, you're a true pioneer.
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Jul 11, 2008, 04:17 PM
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Torx's Avatar
that second picture just about blew my mind... after scrolling down from what would look like a 6 inch plane, to a 3.5.. wow.
Jul 11, 2008, 05:33 PM
Registered User
Hello Brian,

congratulation to the new record!! I know how time consuming such a goal is. But you finally succeeded. I am happy that I could sometimes provide a little help.
Enjoy your model! I am eagerly waiting for the video.
I am sure that you will improve the flight time significantly with a geared drive. But I think you will need a little more mass.
Keep on working on your little jewels. I think together we will find ways in the future to come to even lower weight and new records.

Jul 12, 2008, 03:02 AM
Veteran's Avatar
Awesome Monk!

That motor would of been a nightmare to make.

If you add a geared motor you will obviously add more weight, so is in this case is it worth adding a geared motor or a 10mah Lipo for longer flight time.

O, btw where did you get that 8.5mg lipo from?
Jul 12, 2008, 10:04 AM
Registered User

against my former statement in the BL motor thread I have to say a geared motor gains threefold.
The motor can run at its best efficiency. This means the heat in the coil is significantly reduced which in turn means a further gain in efficiency. In addition we can use a larger prop with better induced efficiency.
The motor needs to have a higher resistance, i.e. you have to use thinner wire. The weight is about the same. With m=0.1mm gear module you can make a 5:1 gear with some 12mg! The prop is larger. The thrust loading is lower. So you can use other material then carbon to minimize weight.
I estimate that you can fly your model with half the current needed for you present plane. Since voltage drop in battery and chip decreases as well the flight time will be significantly longer.
As soon as you recover from your present work I can simulate for you a geared design.

Jul 12, 2008, 11:12 AM
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Martin SJ's Avatar
Spectacular, Brian! Congratulations! I fully understand the frustrations and difficulties of achieving this, but isn't it sweet when it flies.
Great work!
Jul 12, 2008, 11:27 AM
Registered User
Martin SJ's Avatar
On second thoughts I realize I don't fully appreciate the frustrations and difficulties of achieving this - you have halved the weight of all the components, except the battery, when compared to my 1/2 gram planes. That's really amazing!
Last edited by Martin SJ; Jul 12, 2008 at 11:28 AM. Reason: typo
Jul 12, 2008, 01:35 PM
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micro_builder's Avatar
i'd ask for some video, but that would probably be like trying to video tape a fly
amazing accomplishment, congrats!

Jul 12, 2008, 01:51 PM
derk's Avatar
Hey, Brian, i bet you could save 1/2 mg by shortening that rear wing post :P
all kidding aside, that is an amazing achievment you have done. i think a vid of just running the motor and moving the rudder would be cool enough for me

so whos going to be the first to make a single phase powered heli?
Jul 12, 2008, 01:58 PM
Your ruler, in part...
Angry_Monk's Avatar
thanks for the comments everyone. i am really glad i got the plane flying, at least once

i went to fly it last night and it didn't have nearly the same power it had earlier... and when i went back to fly it today i found the wire soldered to the aluminum battery tab had come off... now i have to cut off the battery (again) and solder the wire back onto the tab. at least the plane is back to its former self, defiant as hell.

i fixed the 8.5mg typo, i guess that was just my subconscious getting excited about future lipo improvements!

and a geared motor would be a great improvement over my current DD version. you would only add 10-15mg MAX and halve your current draw while increasing thrust. so your flight time would double. but hope to only add 5mg or so by really watching my weight. add a 10mah cell would add 50mg or more and only give you another minute or so i would think.

once i fix the plane and figure out why it doesn't like me i'll get a vid. i want one just as much as you guys do. hopefully the plane will cooperate.

in the mean time here is this vid i shot of my BL motor running before it went on my plane, just for fun:
Micro Brushless Motor (1 min 9 sec)
Jul 12, 2008, 06:56 PM
Registered User
RNAF's Avatar
I'm truly stunned.

Man for a year ago I honestly thought one gram for a flying model would be getting close to the limit of being the "lighest".. That rpm is unbelieveable too!

Great job, would love to see it fly!
Jul 12, 2008, 07:51 PM
Your ruler, in part...
Angry_Monk's Avatar
yeah, i still can't believe the RPM, but the prop works and i get good thrust from it.

an interesting note about the lightest possible plane:
i am willing to bet that the lightest possible indoor model would be about 100mg. my plane without battery is only 104mg! so assuming a new battery, and advances in other areas which would bring down the AF and RX weight i think 100mg is probably close to the absolute minimum a hobbyist can build. it would be VERY hard but i think its possible.

a little update, the battery is off, the wire is re soldered after about an hour of trying (i can't seem to get the hang of this aluminum soldering). i'll put the plane back together tomorrow and see how it works.
Jul 12, 2008, 08:13 PM
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glenn2626's Avatar
Originally Posted by Angry_Monk
i can't seem to get the hang of this aluminum soldering
Hey, something useful I can contribute to this thread!

Monk - Have you tried Solder-It Aluminum Soldering Paste?


Does the trick for me - absolutely no problem now, and no other funky tricks are necessary to solder onto those lipo tabs.

I've even got a brand new unopened tube I'll send you free, as a thank you for sharing here. (PM me)

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