Vibrations vibrations

[cjm180]

Hey

After between 200 and 250 crash free flights on the 600l yesterday / today its developed its first mechanical issue. You remember when u had those crappy training legs / balls on your copter, then after a while in the hover it would slowly start to oscilate about the head and slowly get worse, i am seeing that same thing with no legs on lol.

its been flying fine. The last work i did on it was about 10 flights ago. I had the one way bearing seize. I had used a bit of silicone grease in it which i now know was a mistake. I took it to bits, but had to hammer it apart as it was solid. When it came to bits i saw 3 scratches in the sleeve from the tight rollers. I cleaned it all out and re-assembled pending me ordering a new one.

I first noticed the oscillation about 5 flights ago, just a really small wobble at the skids during the hover, put perfectly flyable. Today it got so bad i landed it and packed up.

I dont immediately think the OWB is to blame, as its locked when running as we know. Unless maybe those scratches or the force i applied to seperate it has made the main gear not sit concentric, or the OWB is worn a little?

Anyways when i got home i took the blades out, slapped a pack in and ran it up. I could feel the vibrations in it, and it was noticeably worse in IU1 than normal.

The swash seems to be wobbling around a little, which is visible on the swash ball links going to the servos.

i removed the head and checked it. No End play in the spindle, head dampners still tight, no play in the blade grips, everything rotates nice with no notchiness.

The OWB seems ok, no visual eccentric running of the main gear at various speeds. The only thing i could find is the swash had a slight bit of up and down movement / play. I wouldnt say excessive tho. With the swash in your hands it spins freely, but u can hear it. Not notchy but like its dry inside.

Main shaft looks straight with no obvious wear, and with the shaft in the main bearings it feels good, with no movement, play or notchiness.

I have ordered a new swash and a new OWB, hope it fixes it. After that it will be main gear and main bearings. Any other ideas?

Kr
Craig

[helinut]

After that many flights and no incidents, I would definitely be thinking bearings. Are you sure play in the mainsheet bearings or their holders hasn't developed?

[Mike Sanders]

I too have had a OWB problem with my 600. It didn't cause any oscillations but just the odd twitch when I think, the OWB locked up. I changed the OWB for another (second hand one). It seized after one flight. So I changed it for a brand new bearing. That too seized on the first flight!

My friend Mike365 loaned me a good second hand assembly including the OWB shaft. That worked perfectly. So I have come to the conclusion that the locking up is caused by wear on the shaft. I have ordered a new one which will be delivered tomorrow.

I will let you know how I get on.

[myxiplx]

I too have had a OWB problem with my 600. It didn't cause any oscillations but just the odd twitch when I think, the OWB locked up. I changed the OWB for another (second hand one). It seized after one flight. So I changed it for a brand new bearing. That too seized on the first flight!

My friend Mike365 loaned me a good second hand assembly including the OWB shaft. That worked perfectly. So I have come to the conclusion that the locking up is caused by wear on the shaft. I have ordered a new one which will be delivered tomorrow.

I will let you know how I get on.

Repeated problems with the OWB on a Trex 600 is often down to over-tightening the lower jesus bolt. You need to just nip it tight and let the locking nut hold it.

If you tighten it, the pressure will deform the housing slightly, and cause OWB failures.

[cjm180]

Hey guys,

Just an update, i have replaced the swash, and while on the bench it feels not much better, the oscilations about the head have gone in flight, or at least on the 3 minute flight i had yesterday.

I have a new OWB but didnt fit it for this test. I have also ordered up a full bearing kit for the head and mains, as well as a new shaft. So if it comes back i am prepared to give it an overhaul.

Thanks for your replies

[atomiccomp]

I would also check the motor isn' the source of some vibration by removing the main gear and running up. I had a Compass 6HV with a bad motor, in fact so bad you could feel the vibes through the floor.

[coolice]

Hey buddy.

How's your torque tube drive to the tail, is it straight and able to float a little between both couplers? Also if after a crash you changed this, did you offset the support bearing?

This drive shaft can give some funny vibes which are then picked up by the FBL controller.

The auto hub has been a problem for some time, to stop it locking up I smear a good amount of thr Align kit supplied grease inside the race before assembly and it doesn't lock up.

Ian

[scallybert]

Do you have any [measured] evidence that there is significant vibration ?

Secondly, does vibration [as in motors, bearings, etc] tend to give this kind of oscillation ? [My suspicion is 'not'.]

[cjm180]

Well my optimism was short lived. Flew great today for the first 9 flights, then it comes back the same as before!

I cant think what else it could be other than bearing wear. Its flown great until recently. I don't think its a particularly strong vibration, I think its just manifesting itself so badly because its close if not on the natural frequency of the heli. Its def a resonance problem I think. It hovers fine for about 5 seconds then starts to come in. If I put in an input or move he heli some it goes, but as soon as you stop it just starts to creep back. Its exactly like having the training legs on, that exact type of oscillation and the same characteristics.

It completely disappears at 1950 and 2300 rpm. Its on visible at 2200 rpm, which is my normal flying speed.

Its a side to side vibration, not forward or backwards. Umm...

I have a full set of head and main bearings, I will change everything out. I am still thinking the vibes are just a little bit everywhere. It may not be vibrating any more than normal from a magnitude point of view, it may of just changed in amplitude and bringing it inline with the natural frequency.

Why it flew for 9 flights I don't know. After this round of stuff I will look at the motor.

I will say assembled with no head on the heli feels great to the touch. But I know vibes change with loading.

Back to the drawing board!!

[cjm180]

Do you have any [measured] evidence that there is significant vibration ?

Secondly, does vibration [as in motors, bearings, etc] tend to give this kind of oscillation ? [My suspicion is 'not'.]

Hey

I have no measured data as i am running the GPro. I think its not a high vibe its just like on the resonance frequency. I cured it with the legs when i was learning hovering by adding weight to the legs.

So i am thinking rather than trying to eliminate the vibration, as its a heli, i just need to shift it somewhere else. And the only way to do that rather than altering weight / speed is to change the bearings for new, as the old ones must be getting worn now.

[cjm180]

Hey buddy.

How's your torque tube drive to the tail, is it straight and able to float a little between both couplers? Also if after a crash you changed this, did you offset the support bearing?

This drive shaft can give some funny vibes which are then picked up by the FBL controller.

The auto hub has been a problem for some time, to stop it locking up I smear a good amount of thr Align kit supplied grease inside the race before assembly and it doesn't lock up.

Ian

Understood. I will assess the tail when i do the bearing overhaul.

[cjm180]

I would also check the motor isn' the source of some vibration by removing the main gear and running up. I had a Compass 6HV with a bad motor, in fact so bad you could feel the vibes through the floor.

So got it all stripped out and replaced all bearings for the main shaft and head, including new dampers. The only notable thing i saw was the outer thrust race in one of the grips:



While it was all out i ran it up with just the motor, and while the vibrations are slightly less, they are still there. So i am thinking a motor bearing?

I have it all back together and bench ran it, its still the same. I see you can get a spares / bearing kit for the motor. How does the motor come to bits? I see two grub screws thru the cooling holes at the top. Everywhere is out of stock for that motor.

Are there any alternative motors that will fit?

[Rich23]

Hi

You should be able to replace the bearings in it yourself. 750MX Bearings. You can use Youtube to see how its done. On my Protos MAX V2 I had bad motor vibrations so went to replace the bearings and found the motor shaft worn as well, this was after 250 flights. If you want to replace the motor you will need a 530KV motor. This Scorpion one should do it but double check the info so the shafts are the same thickness and length and the can size is similar.

Hope this helps

Rich

[Grumpy]

To get the bearings out on the 750MX you have to press the shaft out. This is easy enough if you have access to an arbour press.

The Scorpion HKIII4035 works well in the 600, that's what I have in mine. It only picks up two of the mounting screw positions. Two will be fine but I got someone to slot the hole in the mount for me so i could get all four in because I'm fussy that way.

The bad thrust bearings could easily explain the wobble, pitch movement of the grips will have been notchy.

[cjm180]

Thanks for the replies.

Always amazes me things can feel fine in your hand, but under load it must not be working well.

I am a bit of a plug and play guy, i am looking at the scorpion 4035-530 that has been quoted. I am also looking at the same motor thats in my goblin, an Xnova 4025 560kV. I dont know the significance of the 4025 bit?

So the diamensions for the 750mx is:

Can Dia = 52
can length = 61.5
shaft extension = 36.1
shaft dia = 6

the xnova is

Can Dia = 49.5
can length = 62.2
shaft extension = 38
shaft dia = 6

Does this look like it will fit?

I would sooner replace the motor to get me flying again. Then i will repair the 750mx as and when i get time, and use it as a spare for the 600l and maybe the goblin also