Trex 450 shudder????

[Lee777]

Hi All,

I had a crash with my trex 450 and had to replace main shaft and main blades now I have fitted the new parts when I spool up it has a slight shudder but then when head speed goes up to hovering all is fine and stable but if I push forward and back fast on the cyclic ( like a fast snap forward and back) the heli has a shudder for a quick moment then gets back to steady hover???? it is the 450 pro fbl with 3gx.. any ideas where to start looking for the problem? cheers peeps

[HeliSmith]

Loose links/parts then bearings

[Lee777]

All seems tight with no slop

[HeliSmith]

Is it possible the tape got knocked loose? Checking bearings make sure you test side load

[Lee777]

what tape????? the 3gx foam tape??

[HeliSmith]

For the 3GX

[Lee777]

No the 3gx is in the body of the pro and just checked and it is solid....

[Victor Kovalev]

I am not an expert but in my experience, when replacing a main shaft I have found the bearing in the upper bearing block to be damaged and/ or gritty necessitating replacement.
Definitely look for and find the cause of your problem to prevent failure or damage.
Vibrations like you describe are typically mechanical in origin.

Check your main rotor tightness. Maybe too loose?

Make sure your cyclic servos are running smooth. Maybe the elevator servo or the others lost a tooth.

[kheinink]

feathering shaft bent?

[cafediablo_30]

This could be any number of things...if all is tight and and gyro secure with no slop to be detected then maybe a gyro gain adjustment is in order.

Sometimes new parts like bearings and what have u may make for a smoother drivetrain and so gains would need to be dialed down some....just an option

Another is the motor pinion...ive had a motor pinion have just a tiny bit of back and forth play....almost unoticeable...and of course with the slight change in head load it would shudder...

Good luck with the duagnostic...keep us posted.

[CrashNburn420]

Feathering shaft, bent torque tube, bad bearing, damaged tt gears....

Did you spool it up without blades on to check for vibes?

[jazsop]

How tight are your main blades in the grips. Dfc doesn't like to loose of blades. Mine was doing the same thing on spin up. It would just start shacking at 3/4 speed before lift off. Tightened the blades a little and it all went away. I never flew it this way before it tightened them. But it flew fine after I tightened them. Know has 35 flights on it and that was all I did to correct it. Just something else to check maybe. Hope this helps.

[HeliSmith]

Lee did you get this resolved? Never heard back from you on the PM so I keep watching this thread

[DWill]

My 450 DFC Pro had a similar issue after maybe 15 -20 flights.

It would shudder every now and then especially in hover. It turned out to be worn main bearings. I had the same thing happen with my 500 DFC Pro. With the 500 I replaced the stock bearing blocks with KDE thruster bearing blocks and that solved the problem permanently.

Sadly KDE doesn't have thruster bearings for the 450.

[Lee777]

Hi Lads,

replaced feathering shaft and the wobble on spool up calmed a lot, but still has a really bad few second shudder in steady hover about every 40 seconds, gonna try the bearings next in the blocks and see if that solves it, the tail isn't holding very well either

[Tasteles]

I had a shudder on my 450 when I had the stock BL450M, 3500 KV motor. It would shudder around zero pitch and quit as soon as I gave it a little pitch.

After I swapped in a scorpion motor and castle lite ESC, the shutter went away. That was the only thing changed on the setup. Don't know why but the shutter quit.

Sent from my SAMSUNG-SGH-I537 using Tapatalk

[aevans692]

Will be interested to see what it is , I had a shake / shudder on my 450 I searched everything , and replaced loads , still get it now and the but turning the gain down stopped it

[Sefrez]

I am unsure what you mean by "shudder". Is it a violent shake that seems to suggest balance issues, or could it be electronically induced? It would seem if it becomes stable in hover and only unstable after specific maneuvers, that it is gyro related. Cyclic wobble is supposedly a symptom of too high aileron/elevator gain on the 3GX (the two pots on the unit).

[Tasteles]

In my case when mine was doing it, the shutter was kinda like blade flutter. The heli didn't shake or anything, it just gave off a fluttering sound. Changing to different kind of dampers did nothing. Gain settings on my beastx did nothing.

I upgraded my motor and esc just because I got a good deal on both. I was wanting the logging and governor capabiltties of the castle so since I got the deal, I changed out both. Never had the flutter again after that.