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Mikado Logo Helicopters Mikado Logo Helicopters Discussion


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Old 11-16-2019, 05:50 AM   #1 (permalink)
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Default Trembling 690

I have an almost new Logo 690 , it’s been flying great since I’ve owned it and now. 15 flights in, This past couple of flights though it’s developed a fast tremble that’s most noticeable in the skids.

Initially the heli lifts and all appears ok I do a small circuit and hover and that’s when you see it and it slowly gets worse and worse. I’ve checked the vibe graph on my vbar touch but nothing seems out of the ordinary.

I’ve had the head apart , greased the orings, balanced the blades, etc.

I’m out of ideas now, could it be programming of the vbar control? It has flown fine with no setting changes though.......

Any help or suggestions greatly appreciated

Andy

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Old 11-16-2019, 07:08 AM   #2 (permalink)
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Check if your main shaft is bent.
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Old 11-16-2019, 09:11 AM   #3 (permalink)
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lower your gain or add some head seed ?
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Old 11-16-2019, 09:56 PM   #4 (permalink)
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Just as mentioned above, try raising or lowering your headspeed even 50 rpm to see if it changes the shake. I have had this on several helis and often it goes partially or fully away with some more time on the dampers or a slight speed change. My one you could lift off in a hover and all was fine then take off and come back in and it would be shaking. Bumped the speed up or down and it was gone.
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Old 11-17-2019, 04:52 AM   #5 (permalink)
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I had a 690 with the same thing, it was a wobble that would develop after some circuits.

I took apart the head, changed the main shaft and spindle, main shaft bearings, new auto hub, swash plate, headblock, main blade grips, tail shaft, belt, and some more things too.

The only thing that helped was changing to a new frame. My theory was the plastic that served as the bearing blocks had elongated or something, it kinda seemed like there was some play that had developed there and the bearing didn't go in as snug as the new frame.

I also epoxied the bearings into the frame to try and give some extra strength. It kinda had looked like one of the bearings had spun in the plastic bearing blocks a little on the old frame.
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Last edited by RappyTappy; 11-17-2019 at 07:46 AM..
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Old 11-18-2019, 09:21 AM   #6 (permalink)
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Hi

Thanks for all the replies, I've moved the head speeds up and down (3 banks) and changed the gains both up and down. No real change I'm afraid, initially it lifts off and its smooth and then the tremble/oscillation slowly builds and gets worse .

I've noticed there is quite a lot of play in the tail rotor grips in all axis despite the screw being done up tight.

Could that cause the wobble? Well its one place to start i guess, these hard to find issues are the only downside to this hobby!

Andy
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Old 11-18-2019, 10:55 AM   #7 (permalink)
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I remember having this on old 600SE, ended up being damping.
Put more flights on it it will loosen up. Also be sure dampers are greased inside and out.
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Old 11-18-2019, 12:04 PM   #8 (permalink)
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Did you check the main shaft bearings in the frames? They should go in snuggly and kind of *click* into place when they bottom out while pushing them in. The frames should not be fully tightened when checking this. Once installed and the frame bolts are fully tightened they should lock into place and not move or be easy to take out. I do not believe these plastic frames were ever designed to handle 700 size blades. Thats my main issue with the 690, it is a helicopter full of compromises for a airframe that is stretched beyond what it was originally designed for.
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Last edited by RappyTappy; 11-19-2019 at 03:19 AM..
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Old 11-22-2019, 10:52 AM   #9 (permalink)
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Well still not solved it, new head bearings, thrust races, spindle, the main shaft bearings are free and secure,

the shakes happen about a minute in to a flight, could this be more of a vbar neo issue?

They start off very light and then increase over a period of 30 seconds or so to the point I put the heli down , I can then lift off again and it’s smooth for 15 odd seconds then the shakes occur again.

Andy
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Old 11-23-2019, 01:43 AM   #10 (permalink)
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what tape are you using for the neo ?
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Old 11-23-2019, 05:39 AM   #11 (permalink)
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Well this mornings test flight seemed ok, now that the new bearings are seated, along with the oring dampeners and a higher head speed 1830rpm bank 1 2050 bank 3.

I did read somewhere that the max headspeed for a 690 was 1800. So I am hoping to lower these Rpms once it’s more run in.

I’ll look back through the forum to see what rpms are the average. I’m not a 3D flier so don’t need it to be mad.

The hardest bit about taking the head apart and putting back together again. was getting all the orings to seat correctly without any sticking out of either end of the hub. Anybody have any cheats to get this perfect ?

Thanks for all your help and suggestions.

Andy
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Old 11-23-2019, 07:28 AM   #12 (permalink)
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As I suspected, Dampers just nee run in.
L690 is rated to 2k rpm but plenty fun bellow that. As long as you built it to spec 16-1700 is good starting point.


As for building head, grease Dampers inside and out as well as Spindle lightly. I have 10mm hole in my bench i put the Head over then push Spindle through letting it run through Head into bench. This gives the Dampers something to rest against and not push out of head block.
Then just bolt up grips and give Spindle a few turns and it will self center.
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