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Jul 02, 2009, 06:50 PM
Your ruler, in part...
Angry_Monk's Avatar
Discussion

920mg Sub Gram Ornithopter - With Video


I'd like to share with you all my latest creation on my way to making an r/c bug: my 920mg ornithopter.

Only recently did I start getting into flapping winged vehicles, so its only natural that I would eventually take one into the sub gram field. I wanted something that really looked like a bug. I think I'm getting closer with this orni. Its a little bigger than I wanted, but I think it fits the bill well.

I didn't take extra ordinary steps to lighten every component on this orni, which is probably why it came out over my weight predictions. I planned it to be an 850mg orni, with a 2" span, which it was until I flew it and realized it didn't have enough power. So I increased the span to 2.5" and made a more powerful motor to compensate, and that did the trick. Flight speeds are actually surprising slow, on the order of 2-3ft/s. I'm not yet sure on flight times but I am hoping for 3 minutes or more. The motor draws a good amount of current which is the main limiting factor. This orni needs a good deal of power to fly, which I find odd. There is a chance my wings are not optimized so I will have to look into that at some point. Controllability is also very good, I could probably fly this in my house with ease, but I have a cat so that isn't a wise idea...

Specs:
Battery: 8.5mAh Li-Po, 310mg
RX: IR by Koichi, 43mg
Motor: BL, 3x2 Magnet, 41AWG wire @ ~20ohms, 270mg
Wings: 2.5" WS, Quad wing setup, 30mg
AF+Act+Gears+Misc: 267mg, Act = 150ohms of 50 AWG wire w/ 2 1mmx0.5mm magnets
Gearbox: 10:1 using mod 0.2 Didel 60t gear and 6t pinion from Koichi

AUW: 920mg

Videos:
2.5" Wing Span 920mg R/C Ornithopter (1 min 47 sec)

Flight Vid 2 - Micro 2.5" Span 920mg Ornithopter (1 min 12 sec)


While I am happy with this orni I feel like an even smaller, lighten one is possible. I would very much like to attempt a 700mg or less version with a 1.5-2" span. I have no idea when I might attempt another one, but its definitely something I want to shoot for.

Comments are welcome.
Last edited by Angry_Monk; Jul 09, 2009 at 06:13 PM.
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Jul 02, 2009, 07:18 PM
Beware the Axis of Weasel.
thewildweasel's Avatar
That is another real acheivement you've got there. You never fail to amaze me with what you build and the skill you obviously have got to be able to do so. Well done!
Jul 02, 2009, 10:18 PM
Registered User
wrcsti's Avatar
Thats an cute little motor you got there!
Jul 03, 2009, 12:26 AM
Registered User
Martin SJ's Avatar
Beautiful job, Brian! And well under a gram!

I know very little about ornithopters, but you seem to have a large wing sweep angle - about 60 degrees. Have you tried configurations where both wings stay closer to horizontal?

Try locking the cat in the bathroom.
--Martin
Jul 03, 2009, 01:05 AM
TheyreComingToTakeMeAway!
derk's Avatar
Martin, i think he has them so high so that the 2 upper wings clap together as well as both sides. that would give it one more thrust "push" per cycle.

It is another amazing feat though! i would love to see a vid of it flying (if you could get one lol)
Jul 03, 2009, 02:08 AM
Your ruler, in part...
Angry_Monk's Avatar
Thanks for the comments.

Martin,
derk is right, I was talking to the guy who leads the Delfly research at this past NEAT fair and he explained to me how if you let the wings meet on the "up" stroke they generate extra thrust. I don't have any concrete numbers to back that up, but I've tried the design and it works.

The thing that gets me is if the drag on the wings created by traveling all that extra distance just to make the two upper wings meet is actually worth the added thrust. It would be very interesting to see some kind of quantitative analysis.

I still have the old set of 2" span wings for this orni. It looks so much smaller with that set on! I will have to put that set back on and test it in flight to see if it can still manage.
Jul 03, 2009, 03:22 AM
Registered User
Uwe Steller's Avatar
Great, Brian!
So much additional technique and the same weight as my lightest plane. For me it looks definitely small enough.
What current does the motor pull ? 20 Ohms seems a quite hot wind, any additional data ? May be, I could use something similar for more power in my Piper.
Uwe
Jul 03, 2009, 04:28 AM
Mc-Fly
Veteran's Avatar
Well done monk, that's a real achievement and i believe it just might be the lightest RC orni so far... I don't believe ive come accross any lighter than this to date

I'm always surprised how the sub 3g ornis can get away with only two gears, if you put a middle gear in she would be like driving a Lamborghini and you could afford to use a much smaller motor


Love the little pull switch
Jul 03, 2009, 06:57 AM
A.K.A sir Crashalot
methuso's Avatar
Thats a fantastic peace of artwork.

A question/suggestion.
Does the pianowire weigh much? those between the gear and wings. In the F3P thread people have "bend" carbon rods for landinggear by touching the rod with a soldering iron, "melting" the epoxy in the carbon, bending it and then adding ca to stiffening the bend again. Might even put a crossbrace betwee nthe bends to stiffen it a bit and then the flapping would not flex the bends much so You could use eve nthinner carbon.
Might this reduce the over all weight for You ?

/Ulf
Jul 03, 2009, 07:10 AM
Registered User
Monk

Congratulations on another fantastic achievement.

I recently bought a RC Orni 'toy' for 8 ($5) and tried to sneak it past the wife but the kids 'grassed' me up! Oh well I am getting used to sleeping in the shed ;-)

On a more serious note do you have any problems with the BLM starting ? I assume it needs quite a lot of torque to flap all that area ?

Also is there any benefit in getting the wings to clap at the bottom as well ? (I have just looked back at your pictures, I guess there is some stuff in the way for that to happen. Doh)

Well done.

Rob
Jul 03, 2009, 07:36 AM
Registered User
rguillot's Avatar
Fantastic effort, Brian. I imagine it DOES looks very insect-like in flight, owing to it's small size. Can't wait to see the video. I hope you will be demonstrating this at KEIF this year!? No telling WHAT you'll have built by then though?

Your craftsmanship is superb, as always. Keep up the good work and I'm looking forward to that video!!

Robert
Jul 03, 2009, 08:00 AM
foamanologist
customminatures's Avatar
ROBERT!!!! Where have you been? I have missed your planes on here very much!!!

Brian...........Awesome work on the Orni!!! I to cant wait to see a video! Maybe some cat play?!!!
Jul 03, 2009, 12:17 PM
Your ruler, in part...
Angry_Monk's Avatar
Uwe,
The motor is very hot, and draws about 95 mA at 3.7v with one of Robert's 1" props. That's all the data I took before I put the motor on the orni. Its more powerful than I wanted but this orni seems to need it. With it I will probably end up with about 3 minutes of flight...

Vet,
To the best of my knowledge this is the lightest. Petter's Hummer is 1.1g 100cm span orni is the closest orni in weight to this one, but it only has throttle control, so its sort of free flight. There is also a 60mm span orni here: http://translate.google.com/translat...p/flappingwing (second page) which is around 1.5g.

I know what you mean about the gears. I tried to save weight here as much as possible w/o going overboard so I used one spur gear and the smallest pinion gear I could find. It works but I think its too little reduction. On my next orni I will use even smaller gears and get a reduction closer to 20:1.

methuso,
The wire does add a bit of weight, but its important to have the strength for the crank shaft due to the stress its under. You have an interesting idea for 'heat bending' carbon fiber rod for the crank... The only issue I would want to avoid is the carbon rod wearing down inside my bushing. But its a interesting idea, so thanks for that. I will have to incorporate it into my next orni someone to save weight.

Rob,
Next time, buy two r/c toys! Hide them in different places. When they find one, they think they found it all, because when do people usually have more than one thing to hide at once??

But to answer your question, there is a lot of starting torque required to flap the wings. I frequently have to give the motor a 'kick' to get it moving. If I had a larger gear reduction I don't think I would have this issue though. And if you did manage to get the wings to come together on the bottom it would have the same effect as they coming together on the sides or top, but like you said there is a lot in the way...

Robert,
Nice to see you back! I'm glad my orni seems bug like to others as well. I'll have to bring this to KEIF, it seems like the big thing instead of NEAT now (but I'll probably go to NEAT as well). I look forward to seeing you there, and everyone else.

Video is coming soon...
Jul 03, 2009, 02:44 PM
No more nicotine for me!
micro_builder's Avatar
That is quite excellent, must be giving the MIT and other university guys a run for their money (or at least a headache!). Nice work on that motor too, very cool to see one of those being used in an ornithopter.

Nick
Jul 03, 2009, 07:39 PM
Mc-Fly
Veteran's Avatar
I just finished making a 0.5g rubber powered Orni for experimenting with electric power and all went well with the tests so time to try it out with electric.


Here are the other similar Ornis that Monk is referring too.

https://www.rcgroups.com/forums/showthread.php?t=867959

https://www.rcgroups.com/forums/showthread.php?t=948333


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