mCPX Owners: Got vibrations? Check your main gear! - RC Groups
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Mar 24, 2011, 11:56 AM
If it ain't broke, fix it.
Hasher66's Avatar

mCPX Owners: Got vibrations? Check your main gear!

Hey Folks,

I've seen a rash of requests for help in sorting out vibrations in the mCPX over the last few days, so I thought that I would post this little thread about what I have been seeing as the most common source: Misaligned or slipped main gear.

A main gear slip can happen for several reasons, but the most likely one is a crash, (although several members have reported them being this way right out of the box). And after multiple slips, it can even occur mid-flight under heavy loads...which means it's probably time for a new main gear

So for those of you who haven't experienced this yet, (and don't know what to look for), here is what a properly aligned and seated main gear should look like:

See how the flat part of the main shaft is nicely aligned with the notch in "D" shaped hole in the main gear? In addition, the bottom of the main shaft should protrude a millimeter or so out from the from the collar at the bottom of the main gear. The main shaft should have no up or down play whatsoever when the main gear has been properly 'clicked' into place.

Now here is one that is misaligned with the flat part of the shaft:

The flat part of the main shaft is no longer aligned with the notch in the main gear, and it has slipped down the shaft to the point where the collar is almost flush with the bottom of the shaft.

In addition, you can have your main gear notch aligned with the flat part of the shaft, but still have it slipped down the shaft a bit:

This also needs to have the main gear clicked back into place, where there is no up or down play in the shaft. So check both the alignment of the notch, and whether the bottom of the shaft is sticking out from the collar.

Now what can happen from a minor main gear slip? This video is a good example of where the vibrations show up only at mid stick right before lift off, then disappear when the throttle is moved higher:

And what can happen from a major main gear slip? This video shows us what possibly can occur:

MCP X Blade/Rotor Blowing Apart (2 min 45 sec)

As is shown in the video above, it is not recommended that you continue to try and fly your mCPX when this type of problem has occurred. When the main gear slips down that much, it becomes almost impossible to take off since the main shaft pulls up due to the lift generated by the rotor, and the collective goes way too positive and the blades are most likely in a stalled angle of attack.

Now there are other sources of vibration that can be hard to trace, like a bent feathering shaft, (pull it out and roll it on a flat surface to check it--if it wobbles while it's rolling, it's bent), or jittery servos which may have gone bad, but this post is not really meant to address those other sources.

At any rate, please remember that the mCPX is NOT a toy. It is a full FBL CP heli with a high rotor headspeed and should not be flown indoors without eye protection...and please take care when flying around other people, especially small children. And also take appropriate precautions when flying this heli outdoors as well.

Remember, CP helis take more care and maintenance than other micros in this weight class, so you should always check the lateral play in your blade grips and where your main gear is before each flight...even if you haven't crashed it in a while.

Cheers and safe flying!


UPDATE: Please see the safety bulletin issued today from Horizon Hobby on the new blade grips:

This should help prevent a repeat of the destruction shown in the last video if you are unwise enough to keep trying to fly the mCPX in a massively vibrating condition.
Last edited by Hasher66; Mar 25, 2011 at 12:18 AM. Reason: Update
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Mar 24, 2011, 05:23 PM
Registered User
destinbeachman's Avatar
Originally Posted by Oenta
for all the people who are experiencing major wobbles and shakes... check this post on helifreak...

wobble problem solved!

SHAZAM!!! That crap works!

Mine has been shaking for over 100 flights now-I tried everything and nothing would help except to keep it moving as it would stop as long as cyclic was being applied,but it doesn't shake at all with a rubber band across the grips.Who woulda thought? Wow
Mar 25, 2011, 12:09 AM
Registered User
Check out my vibration fix - turns out it was the main shaft diameter being too thin and there was slop between the shaft and the main-shaft bearings. *Careful* application of thin-CA fixed it:
Mar 25, 2011, 12:12 AM
If it ain't broke, fix it.
Hasher66's Avatar
Originally Posted by clintfisher
Check out my vibration fix - turns out it was the main shaft diameter being too thin and there was slop between the shaft and the main-shaft bearings. *Careful* application of thin-CA fixed it:
Cool! Thanks for posting that.

This is the first time that I've heard of sideway play between the main bearing and the I now I'll know to check that as well.
Jul 01, 2011, 04:37 PM
Registered User

Battery issue?

I can't explain this but I have been having a really bad vibration problem with my MCPX. I have changed the main bearings, feathering shaft, swash plate, blade grips, blades, tailboom and main drive, oh! and the motor!

It seemed to run fine for a flight and then started on the next battery with the same really bad wobble. It seemed to be induced by right cyclic but not always!

Anyway as I could not get a new main shaft or servo as they seem as easy to get as Hens teeth I bought a new MCPX. Fitted a battery, bound the new MCPX to my transmitter and it flew as smooth as silk, put another battery in and could not believe it, same problem! I now started to suspect my transmitter had a problem. Sounded like a good excuse to change my DX7 for a DX8! However, as I can't afford a divorce decided to dig further.

I charged all my batteries and one by one flew the helicopter for three minutes on each battery. It appears I have two duff batteries, one stock battery and one overland 260 mAh. So my question is can a battery cause vibration? It certainly appears so from the evidence!

Anyone else had a similar problem?
Jul 01, 2011, 07:38 PM
Registered User

shaking fixed

My new McpX has been shaking after about 3 minutes. This is on a new heli with only 5 flights on it. I put in the ball connect grommets and verified all connections and gear was tight as described here. still had the shakes. Then I noticed that there was some looseness in the swashplate. The small inner plate was moving up and down more than I thought it should. I replaced it with a new stock swashplate and no more shakes even at the end of the battery run. Flys nice when it isn't shaking....
Jul 01, 2011, 11:20 PM
Registered User
sirs69's Avatar
Both, a metal swash would help this. It did in my case. I replaced my plastic with this because the swash bearing kept coming out.

Otherwise, ensure the blades aren't too loose, this could cause vibration too.

Another poster/thread mentioned battery power plays a part since the head speed lowers after time, especially with the stock batts.

Since replacing my stock swash though, most of my problems went away. I didn't even do the grommet mod.

I ordered a couple of the new Hyperion "MCP" batteries so I can't comment yet on the battery dealy
Jul 04, 2011, 08:01 PM
Registered User
This may have already been discussed. But cleaning the contacts behind the servo motors always stops the wobbles in my mcpx.
Jul 09, 2011, 03:32 PM
Registered User

Fixed my bad vibrations

Thanks Hasher66, that did the trick for me!
Jul 10, 2011, 04:21 PM
Mike's Ma Maaaaaaaaan
PaulB's Avatar
My wobbles ('bout 10-15 cases in over 100 flights) have always been due to a bent feathering shaft or in 2 cases a split main shaft.
Jan 05, 2012, 11:31 PM
Registered User

Thank You!

I am brand new to CP helis; the mCPX is my first. I started out in my kitchen, hovering it around a little (I have lots of G5.5 sim time - but this is definitely harder! LOL). About 1/2 way through 2nd battery, of course I crashed it pretty good into a cabinet. Big vibration after that, it came on hard and from "nowhere" along along 1/2 throttle/pitch; symptoms exactly as you described; very little lift; lots of vibration. And it would sometimes stop at full throttle. I had looked and looked, but didn't know what to look for (nothing looked bent or broken). I did notice the vertical play in the shaft, and because it moved the blade pitch, I was thinking that wasn't right - but had no idea, to be sure. A simple google search put me on this article. Upon close inspection, I found my main gear flush with end of shaft at best, shaft might have been recessed a little (not much). I carefully pressed in back on as deep as it would go, and I am back in business. Putting it away now until I can continue to learn to fly it somewhere with allot more space (duh!). It's a twitchy little bast**d... LOL Thanks for your excellent article, here.
Oct 05, 2013, 05:42 PM
Registered User
Amazing the power of an older thread bringing the life back into the like-new McpX I purchased last year -- this was exactly my McpX's vibrating issue.

No one I ever spoke with ever mentioned anything about the alignment, or rather mis-alignment, of the "D" shaped notch. I'd actually all but given up on CP-flying and just kept going back to flying my 120SR, which is where I learned FF and FFF so all was not lost in my McpX sitting idle in it's case for many months.

This thread is worth bringing back to life!
Oct 20, 2013, 05:22 AM
Venting Invent
Definitely helpful hasher! Thanks
Jan 17, 2014, 06:34 AM
Big Ski
This so helpful.

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