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Helicopter
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Electric General Discussion
› Wild oscillations on Dragonfly 4
04-02-2005 10:04 AM  13 years agoPost 1
Quaxo

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Italy

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Hello,
I just received a Walkera Dragionfly #4, and it's my first helicopter.
I've never flown a heli before, but I practiced a lot on simulators, and I'm able to hover in all orientations and to make "not too fast" circuits and eights.
I reviewed the assembly and setup of the heli, and corrected a few "gross errors" in assembling, and then test flew the heli in a big theater. But I have a weird (and very serious) problem.
Basically, after a few seconds of flight (sometimes after 1 second, sometimes after 20 seconds... unpredictable) I get a very hard, diverging oscillation of the whole helicopter, around both the pitch and roll axes. The yaw axis seems unaffected. The oscillations quickly grow harder and harder, when that happens the heli becomes totally uncontrollable and I can just lower the throttle and hope for the best. The oscillations have a frequency of about 2-3 per second, so it's not a high-speed vibration.
In one of my last flights, I had a nice hovering for about 20 seconds (at 2-3 feet) then I mistakenly touched the ground, very gently, with the landing gear. It was a very gentle touch, and the heli just bounced back in the air, but after that, the oscillation began immediately.
It doesn't look like a radio/servo problem, as the servos don't seem to be moving during the oscillations.
Does anyone know what might be causing this?

Thanks,
Cristian

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04-02-2005 07:34 PM  13 years agoPost 2
Tim B

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Pasco, Washington

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I had this problem on a piccolo once. It developed a such a wobble that the heli would literally wreck itself in midair. I had a hard time tracking down the source though. After tinkering with it for about a week, I ended up just taking the heli with me to my LHS and began replacing parts starting with what we all thought to be the most likely culprit. By deduction (about $50 later and being the only part left to replace) it turned out to be the main gear causing the trouble. None of us could see anything wrong with the main gear, but replacing it did cure the horrible wobble.

Hope you have better luck on your hunt.

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04-03-2005 03:16 AM  13 years agoPost 3
Quaxo

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Italy

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Tim, thanks for the reply... I didn't think about the main gear. I was thinking about something moving with a wider "radius" - the blades, paddles, and flybar weights... But as I have a spare main gear, I might as well replace it, just to see what happens!

Cristian

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04-03-2005 05:42 AM  13 years agoPost 4
jknoell

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I have the same heli (Walkera Dragonfly #4), and had that same problem myself - AFTER tinkering with the landing gear. It turned out in my case that I hit a harmonic frequency. Adding a little weight (a gram or so) fixed the issue.

You didn't mention if you use a training gear...? If so, some people reported similiar problems on other helis with the training gear on.

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04-03-2005 11:06 AM  13 years agoPost 5
mike5334

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traveling to North Carolina via MI and FL

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The oscillations result from the blades being too loose on the head. Tighten the blade bolts snugly and the oscillations will go away. Make sure that the blades are straight, i.e. one blade is not turned forward more than the other one.

Keeping the blades lined up and the blade bolts tight is critical in making the dragonfly fly.

Mike M

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04-03-2005 03:33 PM  13 years agoPost 6
Quaxo

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Italy

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jknoell,

I have tweaked the landing gear too, I had to shorten the two front rods to make the heli sit straight while on the ground. I don't know if it oscillated before - I never dared to lift it off the first times!
And, it oscillates both with and without the training kit. Might I try putting a tight rubber band around all 4 legs, to make it more stiff? Would that help?

Mike,

I thought about that... I read here in the forum that the blades should be just so tight that they don't fall under their own weight, and that's how I set them up. If I tighten them, how can I be sure that they're *really* aligned? If one is slightly more advanced, I'll get head vibrations...
Also, tight blades will not fold as easily in a crash, right? Isn't that dangerous for the head?

Cristian

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04-04-2005 10:47 AM  13 years agoPost 7
mike5334

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traveling to North Carolina via MI and FL

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Mine are tighter than that. You have to give them a wack to move the blades ... which normally happens when I bump something while flying. I've even roughed up the blade root and the blade holder with sandpaper to give more movement resistance.

I've been able to eyeball the blades straight enough to stop the oscillations. If the heli shook, then I just stopped and readjusted the blade lagging behind. It's not supercritical, just critical.

I have not broken a head yet, and I've done everything from crashing into a refridgerator to dropping the heli to the ground from 30' up. The dragonfly is a very light heli, and most of the time it bounces instead of breaking. Cutting the throttle right before it hits something helps save the blades too.

Mike M

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04-04-2005 11:41 PM  13 years agoPost 8
Quaxo

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Italy

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Problem solved!!! It was the blades... I tightened them, tested the heli in the theater again, and now it flies like a dream! Thank you so much!
I was starting to think that my heli would never fly, and that I had wasted my money... Luckily I was wrong!
It's "peculiar" to fly - it doesn't react like the helis of the simulator, because they are all CP helis. But it's easy anyway... IF I keep it tail in! If I put it nose in or sideways I have problems to hover, it starts moving all around. In the sim it was easier!
And if I go into FF, some slight wobble comes back... I'll have to experiment some more. But anyway, it is flying now, and flying quite well!

One last question... I know the dragonfly isn't meant to be flown in wind. But exactly, how much wind is too much? Could I fly it in a calm day, when only some leaves are moving on the trees... or does the air have to be REALLY still to fly it outside?

Thanks again,
Cristian

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04-05-2005 12:45 AM  13 years agoPost 9
Tim B

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Pasco, Washington

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I believe that most all fixed pitch micros helis are pretty much the same so I will chime in with my piccolo experience to say that it did not like even the slightest breeze. It actually behaved like a feather in the wind and would get swept away and usually crashed in any breeze. A gymnasium environment will give you the most enjoyment with fixed pitch micros as they really aren't capable of forward flight either. They seem fun for awhile, then they become quite aggravating I'm sorry to say. If you keep an interest in helis you'll be moving on to collective pitch models very soon.

But until then, here are some fun videos to inspire your fixed pitch adventures: http://www.heliholics.dk/video.htm

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04-05-2005 02:06 AM  13 years agoPost 10
jknoell

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In my experience it's possible to fly in a very slight breeze (really just the leaves wiggling). Anything harder than that and the heli will drift off quite quickly. I think the maximum where I have flown it without crashing is like 3-5mph.

Edit: Just saw some of the movies... HOLY CRAP! These piccolos really are pieces of crap. I've slammed my cheap clone heli into concrete walls, wire fences, furniture, metal posts, and once more or less dropped it from about 30' up onto asphalt - the only things I ever broke were tail rotor and landing skids, plus one burned out tail motor and a fried 4-in-1 board.

Boy am I glad I bought a cheap bird. Seems more durable than the more expensive ones.

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04-05-2005 03:19 AM  13 years agoPost 11
Tim B

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Pasco, Washington

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Well in somewhat defense for the piccolo, the head is designed to pop off easily so that damage would be less likely, so when you see the heads fly off don't worry they snap right back on. But they do wear out and begin popping off at odd times. I would prefer they didn't pop off myself. But I'm done with those silly things now anyways.

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04-05-2005 07:15 PM  13 years agoPost 12
Quaxo

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Italy

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Tim, those videos are really fun! And I like how they were done, how the music matches the video...

I know I'll outgrow this small heli... But for now I like it. And in my present situation, it was the dragonfly or nothing... I chose the dragonfly and I'm happy with it!

I have another question now. As the wobble is fixed now, I decided that it was time to learn how to hover... and I started flying in my living room. I had several "small" crashes, without consequences, but once I hit my piano with full throttle. And I made a "nice" crack on the main blade (a longitudinal crack, the heli still flies but I'm scared with that blade). So I installed two new blades I had bought with the heli, but they seem to generate no lift!! Even at full throttle, the heli barely "bounces off" the ground. And I can hear that the head speed is much higher than it used to be with the old blades.
What can I do to restore proper lift to my heli? Do I just have to throw the new blades away and buy some others?

Thanks,
Cristian

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04-05-2005 07:34 PM  13 years agoPost 13
Arky

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Corfe Mullen, Dorset, UK

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no m8y read the instruction it tells u how to twist the blade to increase the lift they generate.

hope this helps

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04-05-2005 07:47 PM  13 years agoPost 14
Quaxo

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Italy

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The instructions? You mean the manual that came with the heli? Mine is in Chinese! Not much use for me!
So should I twist the blades? Isn't this a little "rough"? How can I be sure that I have bent both blades of the same amount?
Do I have to heat the blades before twisting them?

Cristian

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04-05-2005 08:55 PM  13 years agoPost 15
Tim B

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Pasco, Washington

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I'm not familiar with your particular heli so I don't know if it has an adjustable pitch or not. Afriad I don't have advice to offer here.

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04-05-2005 10:11 PM  13 years agoPost 16
Arky

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Corfe Mullen, Dorset, UK

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if its the same as hummingbird which i think it is, all u need to do is twist the blade untill u get the life u need do both and fly check tracking etc.

hold the blade grip and twist the end of the blade, do it a few times and it will have a small afect on the pitch of the blade do the same amopunt on the other side.

no heat neaded!!!

Arky

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04-06-2005 11:57 AM  13 years agoPost 17
Quaxo

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Italy

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OK... I bent the main blades... That worked. But I had to heat them a little before, otherwise they would return to the original shape after a few minutes.
I found out that the pitch is critical... Too little pitch and the heli won't lift, too much pitch and it will be uncontrollable - not enough tail authority and sloppy cyclic response... just a matter of trial and error!

Cristian

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04-26-2005 12:02 PM  12 years agoPost 18
Bogomir67

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sloppy manual...
There is a german version of the manual, I don't know if this would be of any help. There is also a report from a guy here in germany, giving some tips on basic setup, wobble and vibration.

I followed his instructions on adjusting the motor to the main gear (minimum distance between the gears all around etc.) and the balancing of the blades (using just adhesive tape).
It worked fine with my DF#4, I am glad I did all that, rather than fly the thing right out of the box. No wobble other than the tail being too flexible.

Did any of you guys experience a burnout of the tail motor? I had that happen to me twice - the store where I bought it gave me a replacement for free both times. Both times the brushes where burnt off completely. I am wondering if this is a general problem.

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04-27-2005 03:32 AM  12 years agoPost 19
mike5334

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traveling to North Carolina via MI and FL

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Burned out tail motors are a common problem with all of the Dragonfly clones. The stock motor cannot handle the current because of very flimsy brushes inside.

There are a few options to fix the problem. One is to go with a dual tail motor setup, which splits the current between two motors. The two motor setup will require an aftermarket mount. The other option is to buy a GWS IPS motor like the one they use in thier EDF40 ducted fan units. The motor is a little longer and has way better brushes to handle the current.

Mike M

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06-14-2005 09:06 AM  12 years agoPost 20
libertycat

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FRANCE

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› Wild oscillations on Dragonfly 4
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