Unexpected cause for severe wobble

[timox72]

Hey guys,

My Nano had a severe wobble which I couldn´t trace for some time. Changed fs, main gear, blade grips and did some more checking of the usual stuff but no luck....untill today. Made a new main shaft from some 2mm cf I had laying around and it´s rock solid.
No wobbles and no vibrations anymore, love this little Nano!!

So guys with "wobbletrouble".......check your main shafts

Thanks!

Blade Nano CPX bend cf main shaft (0 min 18 sec)

[jbilliter]

How do you handle the little collar? How can you get it off the old shaft and on to the new?
Or do you do something else?

[timox72]

Originally Posted by jbilliter

How do you handle the little collar? How can you get it off the old shaft and on to the new?
Or do you do something else?

Use acetone (nail polish remover) from your gf,sister, wife or mum Just put some drops on top of the collar and let it sit there for a while, later on two pliers, one you hold the ms other the collar, you twist slowly untill you hear a crack from the old ca breaking.

Put it on the new main shaft with CA, 19.05mm measured from top of the main shaft.
Honestly I wasn´t aware that such a small piece of cf could bend, thought it would just snap in a crash

[KLR Rico]

Did this cure the transient shakes around zero pitch, or the overall vibration?

I've noticed my main shaft is slightly tweaked. It's only about 1mm off center, and causes a noticeable vibration, but doesn't seem to affect flight much.

I already have the 2mm carbon shafts that I bought for the tail boom, just wondering if it'd be worth the trouble to swap.

[jbilliter]

I think the cause of my wobbles was a cracked shaft. The old one flexed quite a bit. My first attempt at making the new shaft was woefully off (0 pitch was way off). Here's what I learned.
I used acetone but still couldn't get collar off, so I found a nut that just slid over the bottom of the shaft and supported the collar I very loosely put the bottom of shaft in a vise with the nut on the top of the jaws and then lightly hammered on the top of shaft. The shaft slid down through the nut and collar.
For the new shaft I lightly sanded (400) the top of the shaft so the swash slid OK and it goes into the head OK. Dont sand the lower half of the shaft. Also I didn't CA the collar yet, but I could move it on the shaft, using pressure. Assembled the whole heli and adjusted the collar and shaft so that I had nearly 0 pitch (like it was before I took it apart). I then applied a little CA to the top of the collar.
The first flight had no wobble.

[timox72]

Originally Posted by KLR Rico

Did this cure the transient shakes around zero pitch, or the overall vibration?

I've noticed my main shaft is slightly tweaked. It's only about 1mm off center, and causes a noticeable vibration, but doesn't seem to affect flight much.

I already have the 2mm carbon shafts that I bought for the tail boom, just wondering if it'd be worth the trouble to swap.

Fot me it was worth the trouble, for you I don´t know. one mm is quite a lot Btw it is really easy to do.

[timox72]

Originally Posted by jbilliter

I think the cause of my wobbles was a cracked shaft. The old one flexed quite a bit. My first attempt at making the new shaft was woefully off (0 pitch was way off). Here's what I learned.
I used acetone but still couldn't get collar off, so I found a nut that just slid over the bottom of the shaft and supported the collar I very loosely put the bottom of shaft in a vise with the nut on the top of the jaws and then lightly hammered on the top of shaft. The shaft slid down through the nut and collar.
For the new shaft I lightly sanded (400) the top of the shaft so the swash slid OK and it goes into the head OK. Dont sand the lower half of the shaft. Also I didn't CA the collar yet, but I could move it on the shaft, using pressure. Assembled the whole heli and adjusted the collar and shaft so that I had nearly 0 pitch (like it was before I took it apart). I then applied a little CA to the top of the collar.
The first flight had no wobble.

Perfect I have to admit I combined the swap of the main shaft together with putting other grommets, and doubled some, on the whole set up. Whatever I do to the Nano, it will not wobble or vibrate at all.
For me worked extremely well the grommets from the FS, I have a few bend ones so I used those grommets. Hardly any play in the swash anymore
Here´s a pic:

[KLR Rico]

Originally Posted by timox72

Fot me it was worth the trouble, for you I don´t know. one mm is quite a lot Btw it is really easy to do.

I ended up making a new shaft. I had to lightly sand down shaft to make the swash move up/down freely, but it works like a champ now. Much smoother in flight.

[Rustynailz]

I've twice had the wobbles on this heli because of a warped main shaft.

One question: did you have any special technique for filing down the flat parts on the shaft just right?

[togy]

My main shaft vobbles. I've ordered a new one, but you guys seem to prefer making your owns? Are the blade stock shafts always bad or why?

[tchilds]

The nano cpx shaft does not need to be center hole punched or machined to get perfect balance.

Since all the shaft consists of is CF rod, 3 flat surfaces, and the collar pressed on/glued in place, they are easily manufactured at home with an exacto knife and some glue for pennies. Paying for an eflite shaft is a good idea as they're made on machines to exact tolerances, but if you're breaking a lot of them its better to learn on home made ones.

Some guys build custom shafts to lower the height of their rotor head as well since you want the tail motor and main rotor as close to parallel as possible given the material/weight restraints of the design.


The nano cpx shaft is a very good shaft. They rarely break if you use throttle hold and the stock weight/size blades. My MCPX had hollow shafts that snapped in one crash every time for $10 a pop and were nearly impossible to make correctly even on a drill press. Unbalanced shafts destroy rotating assembly parts such as bearings and rotor head parts. I completely sawed off one rotor head and destroyed a $15 metal hub on my MCPX with an unbalanced shaft.

[togy]

Thank you for your answer! My question was actually meant like "are the stock shafts often not straight?". My new nano came with a slightly bent shaft which make it unflyable..

[Ric66]

Two out of three I've purchased were bad. One came on a nano out of the box, and had the collar glued on crooked. Apparently there is enough clearance on the ID that it can be easily skewed relative to the axis of the shaft. My other nano has a near perfect shaft and collar assembly. The one that I purchased as a replacement part is worse than the OEM one with the skewed collar. The rod itself is actually not straight and it also has a skewed collar! QC is not very good in my limited sample size of three parts. I think the aftermarket could make some money on a one-piece machined part, perhaps made from hardened tool steel for durability. It wouldn't add too much weight and would probably be worth the trade off.

[togy]

Got the new shaft and vobbles went away:-)