Weird vibration issue with my X5

[zborecque]

@PassinThru: I don't think it was the tracking. I always make extra-sure that blades track perfectly. I don't even accept when the blades are going out of track only sometimes (you know, when the main rotor head is worn out - sometimes blades loose the track when you give some high input on pitch, ail or elev).

Anyway my X5 crashed badly last thursday (didn't notice that the back linkage ball was screwing out of the swashplate, and eventually it came off - as a result the heli became really unstable in the elev axis for just a second before a spectacular boomstrike). Luckily it wasn't in any fast forward flight and not much above the ground (about 1.5 m) so it simply fell down. But I lost the tail boom with torque and tail linkage, main shaft and spindle, main gear, canopy holders, main grips, and of course all blades Luckily electronics are fine

[zborecque]

Hi everyone, just thought I will update this thread with some of my lately thoughts about this.

After two MAJOR crashes of my X5, I am now pretty sure, that this vibration issue is caused by the tail vibrations (I mean the torque tube) OR the head dampers (the rubber ones that goes inside the hub).

It's because these are the only two things I changed recently, and the vibrating stopped. I also recently changed MANY other parts: almost new head, new tail, new tail boom and torque, new gears. I did have some troubles with vibrating tail, causing the fbl to got stupid, so I had to fight with that for some time. I noticed, that tail vibrations can be lowered with straightening the TT as much as you can (simply using your finger) and properly placing the TT bearing (the one that goes inside tail boom) in the right place. Right now my X5 runs with low vibrations, but very loud (new gears mixed with some old ones, I guess I can still do something to make it quieter in some time).

BUT, since I also changed the rubber dampers (from the pink ones (95) to the black ones (75) - a little softer, but newer :-) ) I can't tell for sure, that the vibes stopped because of the tail vibrations.

The vibrations I had were of very high frequency, and they stop as soon as heli touches the ground. Plus I have some experience with what happens - if the vibrations of running parts are causing the gyro to do stupid things - and they are not usually of that high frequency. That's why I think - these kind of strange vibrations may be caused with something mechanically resonating within the head (the vibrations are showing only with certain RPM ratio). So I think - switch the rubber dampers first (change their softeness as well), and then check the tail vibrations.

As a fun fact: recently my 450 (Tarot) started to roll the right. Just in the middle of the flight. It clearly looked like the FBL is faulty. Spinning it up without blades - everything is fine. Spinning it up with just tail blades - and swashplate is tilting right. Spinning it up with BRAND NEW tail blades - swashplate still tilts. WTF? Then after carefully examiming the tail - I saw, that the tail case (that metal part that hold the gears and the tail output shaft) was missing 2 screws. I guess old tail blades were a little un-balanced, and these two screws were screwed with too little locktite. When they went out - the whole thing was vibrating as hell - since the output shaft wasn't working holding it's axis. Anyway, putting the screws on place and putting new tail blades (just in case) solved the problem. But what I really mean is - it is usually possible to see the difference between the "confused-FBL" vibrations and "mechanical-resonance" vibration

[cudaboy_71]

Just thought I'd add a source of vibe I just uncovered.

I had noticed my X5 getting a worse and worse tail vibe over time. But, nothing I could track down. And, no crashes...just an increasing vibe.

Luckly, vbar vibration analysis made it pretty easy to trace down to the tail. But, where?

After tearing down the tail completely, it was left to the task of taking off a frame side and inspecting the front of the boom.

Bingo! the bearing of the vertical umbrella gear shaft was bad. Weird thing is in my hand it felt fine. In the frame it felt fine. It was only after it was in the frame with the shaft in the bearing that it exhibited some notchiness. Replaced that bearing and it's all smooth as silk again.

So, remember--check the bearings while installed and loaded.

[zborecque]

I thought I post some update from my side. I know, I know, it's been almost 5 years now But my X5 is still alive and kicking.

TLDR:
My 'almost final' solution to shaky X5:
- check if your servo arms are moving slightly when the heli is spinned up (without blades!!). The movement might be very tiny, but should be noticeable.
- if so - check if your FBL is high-freq vibrations intolerant (like my AR7200BX)
- you might have some high-freq vibrations sources, I would definitely check the tail output shaft and the torque shaft (you might want to reposition the torque holding bearing inside the boom or even add a second one, to make the shaft being supported at 4 points instead of 3)
- you might want to check the engine - my Scorpion went unbalanced a bit - but high enough to cause insane vibrations that were transported through all the frame up to the FBL
- you might also try adjusting the position of your FBL (like try different double sided pads, loosen or tighten the cables going into it,
In the end - in my case it wasn't the vibrations that caused the shakes directly - it just made the FBL move the servos a little bit causing whole heli to shake.


***

In the meantime I upgraded the kit to V2. The shakes seemed to stop for some time after the upgrade, but they did come back eventually. What I really think is with my X5 is two main sources of high-freq vibrations and AR7200BX which I guess does not like even the slightest vibrations. FBL was generating a slight shaky input to the head servos causing the whole model to shake/wobble.

Basically I was removing the rotating parts from my heli and spinning it up (no blades) to see if the servo arms are still a bit "shaky". The movement is almost not noticeable, but it's there. The first major high-freq source is the tail shaft (the one inside the boom - that drives the tail). The tail itself seemed balanced, and was not doing much difference when it was off. But when I removed whole boom - leaving just the motor, main gear, the head (no blades ) and the front gearbox - the servo arms were still moving a bit. I had to remove almost everything tho find out that the next major source was the main motor (the GAUI stock Scorpion one). I tried to balance it, but no luck. I seem to suck in balancing motors, my racers also have some vibrating motors, and I just replace them when they are too much worn off.

The third part is the AX7200BX - I am sure that this is what is causing the whole X5 to be 'shaky' at some headspeeds - because:
1) When I detach it from the frame - the servos remain still even if I put the worst parts I have and whole X5 is vibrating like hell
2) I observed that my old X5 kit, which I sold to my friend and he built a whole new X5 out of it - is not shaking at all any more. Even though there are some high-freq vibs present from the torque shaft. He left most of the mechanic parts as they were, just the electronic setup was new - and the FBL was ZYX2.

So what I ended up doing:
- replaced the Scorpion motor with different one (XLPower XL52M03 4025 1100KV to be exact). BTW I love it more than the Scorpion one - it's powerful like hell, I had to reduce my flight time to 4 minutes (from 4:30), end even with my poor 3D skills - the battery gets very hot. Anyway - the highest freq. vibrations caused by the old motor stopped, and I noticed major improvement with the shaking thing
- carefully repositioned the bearing that is holding the torque shaft inside the boom in the middle - trying to reduce the possibility of standing wave or the resonance. I replaced the tail output shaft with a new (and hopefully straightest) one - just in case Just to make sure that the vibrations from the whole tail part are as low as possible. I don't remember if I have done this in my X5, but I remember that in one of my 450s I added the second bearing (so that the torque is supported in 4 points instead of 3). In my oppinion the torques should not be trusted to be ideally straight. Usually the single bearing is enough - but in that 450 it was still wibrating inside the boom (you could tell by removing the tail rotor - leaving just the boom, and the tail case, and spin up). Finding a right position of these two bearings inside the boom might be tricky, as well as keeping them in that position while inserting them to the boom But that's the art I guess.

Right now there is only one or two very narrow range of headspeeds that the shaking occurs - and even then it's highly reduced now. I just learned what throttle inputs to set up in my TX. It's not perfect - because some batteries are worn more than others - so in addition - I added a slight (ca. 5%) mix to a throttle channel and assigned it to one of back dials in my DX9. Whenever I see the shaking - i move the mix up or down a bit to 'go out' the shaky range.

What I would still need to do is replace the AX7200BX with some other FBL system. But - except the vibration intolerance - I just love the way BeastX stabilises the heli (when it's set up right of course). I have some experience with the MSH Brain (it's OK, but still prefer the BX). I have never tried the V-Bar, and many heli pilots recommended this to me already. I might end up trying one some time - but considering that AX7200BX is also a receiver - it makes the cabling so easy and neat. It's a pleasure to just look at the cables now I remember when I had a separate BeastX box installed in my X5 and a separate Spektrum RX with two (!) satellites, and the cabling was a nightmare. ;-) Anyway I also tried to find some optimal position of the FBL - so that the vibrations are less noticeable by it. I tried some different double-sided pads, loosen the cables plugged into the FBL a little bit and on top of that I pressed the FBL to the frame using a velcro strap. It seems to be pretty good now.

Anyway - my X5 is still agile as hell, and among my fleet I think it's still the X5 that gives me the most pleasure

[SerjA6]

I got vibrations from the tail. I tried a lot of things, but only one thing helped. Installing a thicker beam from X7.