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700 Class Nitro Helicopters 700 Class Nitro Helicopters manufactured by Align, Tarot, SYMA, Airhog, Chaos, HK and similar.


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Old 10-31-2008, 03:48 AM   #1
3dhelidude
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Default T-rex 700 Bad Vibrations

Guys,

I've got really bad vibrations in my T-rex 700 and need some help. It's driving me freakin' nuts.

The symptoms are:
Foaming in the tank, Tail Slider moving in idle on the ground, tail swinging in hover and forward flight, canopy now cracked around front mounting posts and you can really feel the vibrations when trying to adjust the High and mid needles. Itís like a freakin' vibrator.

I've ripped the motor out again and measured the runout and added the measurements to the attached picture. All measurements are in mm, the arrows pointing down are measurements take at 90 degrees to the flat. Are these acceptable for each component?

I think the clutch is out of balance and not running true, is this a common problem?
On a highpoint balancer attached to fan hub you can see it wobble and it has a heavy spot.

Can I modify this without compromising the integrity of the clutch or do I need to replace it?

Cheers,

Matt
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Old 10-31-2008, 02:01 PM   #2
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This looks like way too much to me. Is there some way you can adjust this?
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Old 10-31-2008, 02:29 PM   #3
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Nothing looks too out of wack except the one way bearing inside the clutch but I wouldnt trust that measurement as its nearly impossible to find a good surface to indicate on in there with the needle bearings. I had a similar issue on my 600, searched high and low, checked balance on the fan, fan mount, clutch etc. All were good.

Nearly at the end of my rope I bought a blade balancer, yep, one blade out of balance. When I realized what was causing it I nearly threw myself down the stairs... Some blades come with little holographic stickers (for orientation and tracking I assumed, it was my first heli) Well the set only came with one sticker (Again the assumption about tracking was going through my head) so I put one sticker near the tip of one blade. When I saw which was the heavy blade and pulled the sticker off... yep, blades blanced. Next flight, vibration is gone. Live and learn I guess.

By the way, even my 600 vibrates a lot when idling but once spooled up its smooth as can be.

Chris.
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Old 11-04-2008, 01:20 PM   #4
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i had some of the same problems. first fix corrected about 50% of the problem i had the torque tube shaft in too tight causing the shaft to cavitate. blade balance had to bee spot on perfect. fixed another 20%. dissassembled entire drive train balanced fan alittle and made sure clutch assembly was perfectly aligned.
now only alittle foaming i think the fan/motor collet is either out of round or just off some how but can't seem to get those at my lhs yet. after all this the heli flys great and with a fuel magnet the foaming is down to where it doesn't affect motor tuning, before it was soo bad i couldn't tell how much fuel wasin my tank midflight. but i also got one of the first production run kits in the country so perhaps some new heli inconsistancys to consider. i still love this heli alot it flys like its on rails.
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Old 11-05-2008, 02:49 AM   #5
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Hey Scooby,

Mine is also one of the first run production kits as well.

I believe my issue is coming from the motor/fan/clutch assembly as I can see the tial slider slowly moving while it's sitting on the ground. I can here the tail push rod vibrating in the guides.
My issue is there at idle and worse at idle up.

If I take the canopy off when the motor is running and put my finger on the gyro sensor it feels like a set of electric clippers running............that can't be good.

I checked the balance of the fan, I've checked the run out, added another piece of foam under the gyro sensor and it's still kicking the tail and drifting counterclockwise.
I've already moved the tail boom out a few mm to make sure the shaft is not adding to the issue when in idle up.

Iíve ordered some Zeal tape but thatís only going to mask the real issue even if it does fix the tail drift.


Anyone got any good tips for isolating this issue?
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Old 11-05-2008, 11:04 AM   #6
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I bet you're running the OS SZH, that one has a lot of vibrations.
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Old 11-05-2008, 02:32 PM   #7
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i'm running the ys91sr so its not just an os issue
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Old 07-10-2009, 10:46 AM   #8
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3Dhelidude - Did you solve the problem? I'm having the exact same issues with the same combo.
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Old 07-11-2009, 05:15 AM   #9
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Hey T-rex Pedro,

I got it sorted.................I bought an N9

The T-rex 700 is just sitting in the garage gathering dust, I couldn't for the life of me get it running anywhere near as good as the N9 runs .


Cheers,

Matt
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Old 07-12-2009, 12:39 AM   #10
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The engine crankshaft looks good. Take the fan mount and fan and balance of hi point balancer without clutch attached. You can rotate fan to 4 different positions to get best balance. Try rotating clutch 180 degrees from current position and check balance, mark hub and clutch before removing. I'd double check dampers in head and check blade balance.
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Old 07-12-2009, 03:10 AM   #11
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I haven't had that bad vibrations but I have the same engine YS91SR and it does vibrate more it the engine needle settings are off. Maybe try to play some more with the needles...?
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Old 07-13-2009, 11:42 PM   #12
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i had a really bad vibe in mine and what felt like a rough or high spot on my main gear. turned out to be a bad clutcvh. put in a quick uk and prob is all gone. good luck.
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