450X Vibrations

[Burc]

Hey folks,

I am having some random vibrations on the 450X. It happens at IDLE2 where I have %100 TC and when the heli starts to vibrate the BX seams to amplify the vibration making it uncontrollable. If I drop it down to IDLE1 at %70 TC, then it is vastly diminished however still there.

The funny thing is that it does not always do it. In hopes that it was mechanical, I changed out the main grips but that was not it. I have played around with various blade tightness and I coul not see a relation. Also I make sure to initialize the BX perfectly still and the BX settings are the factory ones. the fact that it does not always do it is driving me crazy. Sometimes I can spool up and get it perfectly steady and vibration free but other times, even on the same flight after landing and taking off again, the heli wants to shake it self to pieces...

My next experiment will be to change out the dampeners but I am running out of ideas.

Has anyone had any similar issues? Any help would be greatly appreciated...

[RocketDog]

I assume you have balanced your blades?

Dampers would be good to check if you have a lot of time on the heli.

Check the main shaft bearings for play by trying to "wiggle" the main shaft.

If the vibrations result in a pitching motion, it could be coming from your tail. So check the belt tension, tailblade grips, bearings etc.

Did it start this after a crash/rebuild?

[ahahn]

These things are rpm sensitive.

Since you fly at a 100% constant throttle, your rpm will drop over a flight. Your rpm will vary even over a maneuver as you load the motor up. When you hit the magic rpm, then you get the "wobbles".

Slop in a heli will be taken out under positive or negative loads, but when the load begins to drop, the setup will be a bit sloppier, and under these conditions, and at particular rpms, you can get into a negative feedback situation in which the BEastX corrections are almost exactly out of phase with what is needed.

Trying to tighten things up, or to change the rpms (difficult to do without a governor to try and hold a particular rpm throughout the flight) are typical solutions.

Reducing some of the cyclic gain on the BeastX might help a little.

[Burc]

So the only slop that I have is in the main grips. When I removed and inspected the feathering shaft, there seems to be a very slight gap that allows the main thrust bearings to move back and forth but it is less than 1mm or the size of a very small spacer. This translates to some play in the main grips. Not sure if this one was a fluke but I will try out another feathering shaft as well. Anyone have excessive play on their main grips as described?

[Talesin]

Obvious question; did you put the brass step-washers back on between the grips and head when you put the new ones in, and in the right orientation? Seems like both of those would add up to around the same gap you're talking about. Manual also talks about a pair of silver washers there as well, but I didn't have any on mine.

[Burc]

Yup, the order is, brass washer, two main bearings, a small large OD and large ID silver washer, the thrust bearing and the washer and bolt that holds it in... So you guys dont have any play in the main grips? I was not sure if this was supposed to be there in this design.

[Talesin]

None at all here. Lifting it by the blades, the grips will shift up/down slightly, but there's no ability at all to slide the grips along the feathering shaft. Sure both screws at the ends are screwed in fully/not cross-threaded?

[Burc]

My grips have plenty of play up and down, left and right and if I force it in and out. I can see the blades go in and out of tracking as I fly with this much slop. Funny thing is when it starts to vibrate as I described, I can eliminate it for a short while if I pump the pitch.

I have had this behavior out of the box and have upgraded the heli part by part to the alm components but none have seemed to be the cause. Belt is ok, bearings are ok, the only thing is the slop in the head which I suspect is the cause.

Anyway, I will change the f.shaft, t.bearings, dampeners and try it again. I am aiming for zero slop in the head which I assume you all have out of the box.

[meatwad99si]

Can you take a video of you moving it?

[KnoxVille450]

I have the same issue and can't get rid of it. I've tried everything and don't have much play in the grips or the head at all. This problem only happens in idle 1 or 2. I love flying this heli and but I'm afraid she's gunna blow.

[Burc]

I found that out of the 4 thrust bearing holders, one is very loose on the spindle. The ID of the bearing is not identical to the other three. I have new bearings on order to get rid of the slop in hopes that it will reduce the mechanical issue and I can tame it down any further shakes from the cyclic gain on the BX.

[mtuccio]

Try turning down Pot-1 a bit. If the problem goes away then the gains were a bit high or your heli has some vibes in it. Once this is done you mihgt need to turn Pot-2 up a bit to get the cyclic response back to the way that it was.

Hope this helps....

[Talesin]

Originally Posted by Burc

I found that out of the 4 thrust bearing holders, one is very loose on the spindle. The ID of the bearing is not identical to the other three. I have new bearings on order to get rid of the slop in hopes that it will reduce the mechanical issue and I can tame it down any further shakes from the cyclic gain on the BX.

If you watch the feathering shaft replacement video, you'll note that two of the blade grip thrust bearing races have almost-imperceptibly smaller IDs (the outer races). If you put the outer race on the inside, it would not seat on the feathering shaft fully (as the race-seat has a matching slight bevel), likely leading to the slop you describe (and possibly throwing a grip!). The inner race should *easily* slide all the way down the 'step' on the end of the feathering shaft and butt up against the 'shoulder'.

Actually, what I did when replacing my feathering shaft was this: assemble one thrust bearing complete on the feathering shaft, put the screw in as tight as I could get it just with a driver and my fingers on the shaft, then slide it through that grip. Then assemble the other thrust bearing/grip as described in the video, making sure the race with the larger ID through-hole went on first, and cinch the whole thing down.

[mtuccio]

Originally Posted by Burc

I found that out of the 4 thrust bearing holders, one is very loose on the spindle. The ID of the bearing is not identical to the other three. I have new bearings on order to get rid of the slop in hopes that it will reduce the mechanical issue and I can tame it down any further shakes from the cyclic gain on the BX.

The Thrust bearing diameters are differnt from inner to outer race. For each side the large inner diameter should go in the grip first, the race with balls should go in next with the flat side facing out, and the small inner diameter race should go in last. You can figure out which one is large and which one is small by rocking them on the feathering shaft.

Hope this helps....

[Burc]

An update on my situation. I found that out of the four TB races I only had one large ID race on my thrust bearings as opposed to having one on each side. After changing out to a new set of thrust bearings and going back to the plastic grips which seem to have less play in them, my vibration issues have been eliminated. Now I can go back to enjoying the 450X...

[KnoxVille450]

Beautiful. That's what I'll do then, are the thrust bearings compatible with the 450 3d? Otherwise I'll have to order some in as the hobby shop does not stock 450x parts

Edit: Forget that question I realize what I have said. Lol thrust bearings on order

[Burc]

Yes I think they are identical, part number BLH1620