Can't figure vibration out

[DWayte62]

I have a 600EFL I converted into a 600L Dominator. Ever since I moved away from the stock white gears that came with the kit and moved to the black gears the heli doesn't run smooth like it used to. Upon take off the landing gear shakes until I kick it up to 2300 RPM. Upon landing there is no shake but I have noticed as it spools down the tail boom goes up and down and the swash seems to pivot side to side a little looking at the ball links. I have tried several different main shafts and a couple different center hubs as well as main gears, auto gears and main gear case sets. Running Rail main blades and am assuming todays blades really don't need to be balanced or do they?

[peptod]

Try another pair of main blades. Every pair must to be verified on CG . If you must to put some weight put on CG.
Do not get to much tight on main rotor holder.and tail rotor holder as well.
Be sure if the Blade tracking is ok.
Use digital pitch gauge do not trust in your eyes.
If the armature of your motor is no good this cause vibration.
Be sure the torque tube and Bearings is ok.

[RC/DC_5000]

This is the part I hate about this hobby. Chasing down a shake and shudder. It could be so many things and it sounds like you tried a lot already.

Did you crash it or have any rough landings since changing to the black gears?

You might also look into the tail drive gear system. TT gears and the TT itself. You can also take the blades off and spin it up and look and listen for any problem areas.

And even when my Trex600L is at its best, it will occasionally skid shake at -1900 HS and the wind is blowing. Its just the ultra stiff head dampers.

[nabl74]

Chasing down vibrations is not as hard as most people make it out to be. But it does require patience and a logical process. If you don't apply logic, then you will spend so much time chasing your tail that you get frustrated with the hobby as RC/DC mentions.

When I first started up in this hobby I had my fair share of vibration issues. My experiences have been

a) vibrations due to incorrect gain settings and gyro settings in general
b) vibrations due to torque tube being slightly bent (some times very undetectable until you roll it on glass sheet
c) slightly bent tail rotor shaft (again minor bend only)

I've never had any shakes caused by rotor blades being out of balance, bent main shaft / bent feathering shaft / excessive play in head, poorly set up rotor head or even warped autorotation gear but all these also come up quite frequently on forums and at the field. Also becauae ive changed these out most times after a crash anyhows.

As you can see there are far to many reasons. Sometimes youll strike it lucky based on process of elimination and logic. Ie just had a crash, tail strike and focusing attention on tail. Other times you will have no clue. What works everytime for me (yes its a pain) but it works is to strip back to basics and go through things logically. ie.

a) take tail blades / main blades off.
b) spool heli up and using your finger or even an extention such as a screw driver trace over every part of your heli scanning for abnormally higher vibrations in key areas. I mean touch the tail rotor housing / scan your finger along the tail boom, grab the torque tube housing at rear, move your hands around near the main bearings of the main shaft, move it closer to the motor.

As you get better, youll be able to know what is normal and pick up where the vibrations are coming from and allow you to focus your attention there.

Be prepared to break it down even further as required. Ie take the main rotor housing off and spool up just to see if main shaft is spinning concentrically (do the vibs go away ??), take the tail boom off and spool, do the vibes go away (if vibrations are picked up in tail boom).

Eventually you get to a point where you have no vibrations and you gradually add one element back on at a time, ie rotor housing, tail boom, tail blades, main blades until you hit vibrations and sure enough youll narrow down the cause.

You may find its a combination of factors but you wont know until you work through methodically (often when you buy second hand helis with poor upkeep).

Trust me if you are slow and detailed in your approach youll find the root cause every time.

Íve had to do this once or twice (where process of quick elimination and numerous flight testing didn't resolve the issue) but slow deduction allowed me to find the problem.

[strat1960s]

DWayte62,

As you can see the forums are a good source of information and support.

When dealing with vibration on spool up and spool down, a majority of the time I've found it to be due to main blades being too tight. Over time, I've learned to spend as little time in spool up and spool down. It's kind of like I was asking for trouble if I did.
How is it vibrating on the ground; is the head wobbling side to side or is the tail bouncing up and down? What's it look like in the air? Are the skids vibrating? Is the tail fin vibrating? Hows the blade tracking. Knowing how and were its vibrating will almost always point you in the right direction.
Anyways, Once I have narrowed down where the vibrations are coming from, (i.e. head, tail, drive) I make a list and check each item on the list to eliminate "what its not".
I hope you get it figured out. There's nothing worse than losing confidence in your heli.
Ted

[DWayte62]

Looks fine in the air, It's just a bad wobble upon lift off which seems to mellow out with a quick pitch pump then seems to completely go away when idle up is engaged. Pitch was set with a Doka set up tool and tracking looks perfect. Even checking the pitch digitally the blades at zero pitch are within 2 to 3 tenths of a degree as well as full positive and negative. Crashed it over the weekend, aileron servo screw backed out to the point that the servo horn came off the spline. Now I will go thru the rebuilding process and apply what nabl74 was talking about. I can't have servo horn screws coming loose and backing out in mid flight....Geez

[strat1960s]

Very sorry to hear about the crash.
Without seeing the heli and being able to feel how tight the blades are, it really does sounds like the blades were too tight. Once up to speed centrifugal forces extend the blades and the lead/lag is good. I may not be using the right terminology there. Lead/lag is when the blade grips are spinning faster than the blade tip. Once everything is up to speed, the blade tip is in line with the blade grips.

Ted

[DWayte62]

Rebuild complete. Put one component on at a time and did the finger test. I don't know what's normal in regards to vibration but around the motor mount and support bearing the vibration was very very minimal. Around the main shaft bearing blocks and the tail boom case is where the vibration was the most intense. All the gears on the heli are brand new including all gear and main shaft bearings and were assembled carefully. Finishing set up this morning and will report back if landing gear shake still remains.

[szaki75]

Originally Posted by DWayte62

...Around the main shaft bearing blocks and the tail boom case is where the vibration was the most intense...

this is why I love vbar and its spektrum analyzer that comes with the pro upgrade. debugging is easy with that.
if the head generates the vibration that is equal to 38Hz @ 2300rpm. if the tail, then it gives a 148Hz vib to the vbar.
(if the motor, it will be a 323Hz signal)

[peptod]

the spirit have this feature too. it is very usefull.

[DWayte62]

After flying yesterday the excessive vibration resonating to the landing gear is gone. My best guess is the vibration was caused by the main gear. The new one that was installed ran true on the main shaft where others have had a slight up and down wobble, some more than others. This was seen by simply putting the main gear on a new main shaft held in my hand and spinning the main gear.

[nabl74]

Originally Posted by DWayte62

After flying yesterday the excessive vibration resonating to the landing gear is gone. My best guess is the vibration was caused by the main gear. The new one that was installed ran true on the main shaft where others have had a slight up and down wobble, some more than others. This was seen by simply putting the main gear on a new main shaft held in my hand and spinning the main gear.

great news.

main gears (autorotation gear especially) always warp if you over tightenn the shaft bolt. sounds like your back in action and you now have a better feel for what vibrations you can expect during future vibration tests !!