Atom 500 FBL & Skookum 720 Vibration Problem

[TallPaul]

I didn't have any issues with my 720 and the 500 initially. Vibration levels were always low, well, until I crashed it I've fixed it and upgraded the Skookum to version 3.02. Now I can't get my vibration levels down.

I've taken off the tail and head and I still have the vibration.

At 324hz, 19260 rpm, I get a 34x vibration (10x max desired)\

At 403hz, 24180 rpm, I get 35x vibration

The good people on the Skookum board suggest I have something wrong with the bearing in my head or motor. Do these RPMs tell you a different area to review?

When I feel the bearings in the head block - they seem ok, but remember I'm fairly new. What should I be looking for?

I'm not sure about the motor. I don't feel any side-to-side movement. Obviously, when you spin the motor, its not smooth because of the magnets in the motor. How would I tell if the motor bearings have issues?

I'm very frustated with the process at this point.

[Jimmy!]

I would rebuild up one step at a time, checking for vibes on each step.

1. Run the motor by itself; no maingear, mainshaft, or tail. Vibes here indicate bad bearings or a tweaked motor shaft.
2. Add the maingear with mainshaft. Vibes here indicate either bad bearings, an out-of-round maingear, or bent mainshaft.
3. Add the headblock ONLY. Vibes here indicate a bent head block.
4. Add the rest of the head assembly, from swash to blade grips. Vibes here may indicate a bent spindle, imbalanced blage grip assemblies.
5. Add tail section with a BARE tail shaft; no hub, grips or blades. Vibes here indicate a bent tail shaft or bad bearings.
6. Check the tail hub for any bends. (both the tail shaft and hub bend easily in a crash)
7. Add tail hub and grips. Vibes here may indicate imbalanced tail grip assemblies.
8. Add tail blades. Vibes here indicate imbalanced tail blades.

In general, high frequency vibes come from the motor and tail. Low frequency vibes come from the head and driveline. Bearings should have very minimal play. It only takes 1 part being slightly out of true to vibrate the heli pretty well.

[TheBum]

It sounds like motor bearings or a bent motor shaft at those frequencies. I was able to get rid of a similar vibration in my 6HV motor by replacing the bottom bearing, which was noticeably rough when I took it out. I had a triple peak around the motor frequency on the VBar spectrum analyzer.

[TallPaul]

Jimmy - what a great list - THANK-YOU

Alan - My Skookum graph is showing a triple peak also - I will check that.

[TallPaul]

Originally Posted by TheBum

It sounds like motor bearings or a bent motor shaft at those frequencies. I was able to get rid of a similar vibration in my 6HV motor by replacing the bottom bearing, which was noticeably rough when I took it out. I had a triple peak around the motor frequency on the VBar spectrum analyzer.

Alan, where do you get the shaft and bearings?

[TheBum]

Originally Posted by TallPaul

Alan, where do you get the shaft and bearings?

Don't know about the shaft. I get the bearings from RC-Bearings. The sizes you need are 6x15x5 and 6x12x4.

The only tricky thing about changing the bearings is getting the snap ring off the shaft without damaging it. It requires a very small set of snap ring pliers, smaller than what I have. I bought a bunch of 6mm snap rings from Grainger that work with my pliers and it's a good idea to put a new snap ring on every time anyway.

[TallPaul]

Originally Posted by TheBum

...The only tricky thing about changing the bearings is getting the snap ring off the shaft without damaging it. It requires a very small set of snap ring pliers..

The good news is I have experience with this snap ring since my motor shipped without one originally (luckily, this was caught before its first flight).

Lucien Miller - distributor for Scorpion motors - did a nice video about changing a shaft and bearings for his motors and I assume it will be similar on the Atom. He showed some small snap ring pliers he got from Harbor Freight - which I can now vouch that they still have!

If my shaft is bent - where would I get it?

[TallPaul]

Originally Posted by Jimmy!

1. Run the motor by itself; no maingear, mainshaft, or tail. Vibes here indicate bad bearings or a tweaked motor shaft.
.

Well, it didn't take me too long to find the main cause. The motor all by itself creates significant vibration.

To get the pinion off, do you normally have to simply heat it up?

[Jimmy!]

You shouldn't have to heat the pinion up unless you're melting threadlock on the grub screw. I would recommend taking a flat-head screwdriver and prying it off. That usually does the trick. If you just can't yank it off, then try heating it up w/ a lighter, soldering iron, or heat gun (preferably). There may have been an excess of loctite that stuck the pinion to the shaft.

[TallPaul]

Thanks Jimmy. I ended up heating it with a soldering Iron (only thing I had) and then prying on it with a screw driver. A bunch of gunk on the shaft, not sure what - but it finally came off.

The bearings didn't feel notchy, but decided to take them out. One came out easily but the other was harder and came apart (probably my error). So new bearings should be here in a few days (are there normal places to get bearings besides the internet?).

Portland Oregon or Maine?

[Jimmy!]

I'm in Oregon
I usually just get bearings online, but if you really want local, you could try McGuire Bearing of Portland: http://www.mcguirebearing.com/?page_id=67

Online, at Boca Bearings, you have a wide selection of bearing quality to suit your needs, but Compass usually sells their own replacement (all of the same type & quality) for cheaper. I would recommend steel-ceramic hybrid bearings from Boca if you go that route--they handle higher speeds and are "supposed" to last longer and run smoother.

[TallPaul]

SOLVED

Started with Jimmy's check list and sure enough, as Alan suggested, it was the motor. I ordered another one as I try to figure out how to replace the shaft/bearings. The new motor came in today and with the motor only - vibrations went from 35.0x to .3x - WAHOO!

Thanks guys.

[Inverse]

The fact the bearing fell apart indicated that's the bearing that failed, not ham fistedness on your part.
Broken bearings collapse.

[TallPaul]

I've been flying with my new motor, having never fixed the bearings on my old motor. Now I want to do that.

To replace the bearings on the bottom of the can, do you have to removed the shaft?

[TallPaul]

Well, I went ahead and took out the shaft, but I'm left with the puzzel on how to remove the bearing - Help please.

[TheBum]

There is no bearing in the can. The bearings are both in the stator.

[sly the dogman]

Hey TallPaul, you should record your work step by step
and maybe it can be made into a sticky for others to learn from.

Probably me, with the crash I had, nose in. Just hope the motor's
in good shape. I have nothing to analyse with if there's any vibrations.
Guess I'll find out upon the first flight.

And the canopy is a gonner T.P. , its torn near the Booya clip-ons.

[TallPaul]

Originally Posted by TheBum

There is no bearing in the can. The bearings are both in the stator.

You know, I dont know whether to laugh or cry. WOW - what would I do without you guys!!!!

I assume you can try to gently move the wires to get at the bearing?

I did also confirm with Mike that Nankin does NOT have just the shaft.

[TallPaul]

Originally Posted by sly the dogman

Hey TallPaul, you should record your work step by step and maybe it can be made into a sticky for others to learn from..

I'm just thankful for the great guys on this board, because I'm sure I'm making every error that is possible!

And the canopy is a gonner T.P. , its torn near the Booya clip-ons

I have 2 other canopies that look very similar. I'm afraid to put the new one on.

[sly the dogman]

Record everything,

what not to do and more