Head Shake unresolved on Goblin 570

[Grees01]

Hello all. I'm grateful that Synergy is willing to offer support to people who are having issues with other brand helicopters, so thanks in advance for any and all help. I built a Goblin 570 about this time last year. All stock with the exception of the lynx main gear, as at the time Goblin had not come out with the delrin cnc gear. I had done some reading about the failure of the earlier style molded gear and didn't want to run into any issues on a 2000.00 + heli build. No cheap parts were installed on heli. BK 8001hv on the cyclic, and 8005hv on the tail. FBL unit Ikon, Castle talon 120hv speed control (I liked the option of 6 or 12s and the heavy duty bec circuit) less complicated just no logging, and rpm out. Pulse 5000 mah 45c batteries, Quantum 4125-1100 kv motor. Didn't have any issues with the assembly nor the setup. I have flown this (basically a little hovering in my yard) probably a dozen times since I built it last year. It has never been crashed. The radio is set up to run external governor controlled thru the Ikon with head speeds of 2100, 2200, and 2300 rpm. In order to get this head speed I needed to increase motor pinion by 1 tooth from 21 (stock) to 22 (factory SAB part). Sorry forgot (It does have a hobby wing rpm sensor wired into the motor wiring and to the Ikon for rpm signal.). The helicopter files, but I have a shake in the head that I just have not been able to get rid of. Very annoying. At 2100 rpm, normal mode its almost not noticeable, you can see it if you look real close and the heli is close to you. At 2200 way more pronounced, cant miss is, a little uncomfortable for a novice pilot like myself, at 2300 still there only the frequency of the vibration is faster. I checked the balance on the stock SAB 3d black line blades with a Maglev balancer, but I don't have a digital scale that can read that high, but on the balancer one blade is heavier. Ok, so I checked both blades for cg and marked them. Aligned the blades at the root and tip and cg is very very close between the two. OK, so added some scotch tape on the cg point of the light blade until they balanced, and tried again. The same issue. Double checked set up, swash level, collective pitch +-12%, cyclic +-10%. Blade tracking, no real progress, left it alone for some months, later again trying to resolve shaking, ordered SAB cnc version delrin main gear and installed, slightly tighter lash, (I like the fit better) re checked set up again, no faults found. Tried running with slightly looser blades, and tighter a few flights, no real significant changes, still shakes. Called helidirect, that's who a bought the kit from, talked to them for a while, recommended to double check main shaft, and feathering shaft for straightness, I didn't pull the main shaft out, but did spin it up with no head and no tail blades and shaft looks straight to me, the feathering shaft I rolled on a nice piece of glass and I cant see that its bent.  Searched all forums and Google for answers, seems to be quite a bit of discussion of low rpm wobbles, with several recommended ideas, none that consistently worked. Found out that SAB manufactures a set of delrin dampers for the head that is supposed to eliminate head shake, OK, I ordered them and tried it, seemed to change the rpm that the problem occurs, but only slightly. Tried lowering the gain in the Ikon settings by selecting a 500 sized model instead of 600. lowered the cyclic gain by a few points doing that, maybe very slight change in vibration, but problem still evident. The very last thing that I tried was replacing the main aluminum center hub, have heard of some issues with machining being slightly out, and I was able to talk helidirect into sending me one. Re assembled with stock dampers and re checked, no changes still wobbles / shakes.  I need some help here, I'm not real comfortable flying this machine and I spent a lot of time not to mention money to have a nice helicopter, and it is nice, but doesn't fly nice IMHO. Thank you in advance for any help that is offered.
Side note (I'm working on the cash to buy a synergy e5) have read a lot of good press on Synergy products. 

Glen

[curmudgeon]

There are a number of issues:

1) Main shaft straightness.  Very hard to tell if the shaft has a slight bend with just the naked eye.  You either need to roll it on glass or use a dial indicator.

2) Head shakes.  Mechanical issues include notching main blocks bearings, bent main shaft, unbalanced blades.  Electronic issues include exposure of FBL unit to high vibrations (high bona fide helicopter vibrations and/or not enough padding) or too high gains.

3) Blade balance.  Generally speaking, most CF blades from reputable companies come pretty well balanced.  However, if there is a concern about blade balance, you would need to measure the (1) respective weights, (2) the chordwise COG, and (3) the spanwise COG.  With the Maglev balancer, you are only balancing the spanwise COG.  The Maglev balancer does not tell you about weight or chordwise COG.  I believe the best blade balancer for chordwise COG is the Koll Rotor Balancer (which also balances spanwise COG just as well).  Still, you would need a decent digital gram scale, ideally one with 2 decimal places like the AWS 200g/0.01g scale.  The SAB 570mm blades weight about 113.99g each (5.09g for stock 95mm SAB tail blades), so a 200g max scale should work fine for this purpose.

4) Top main block bearing.  Make sure to not overshim this bearing in an effort to remove all the up/down play.  My bearing fell apart mid flight.





On postmortem, the top main bearing (bottom left) fell apart, the main shaft got notched, and the shims (bottom right) were all deformed.


On the rebuild, I used a Synergy shaft collar (10mm ID) to remove the up/down play.


I used a few shims on top of the main bearing so that the Synergy collar would not interfere with block assembly.

Top of main bearing without shims.


Same area with shims added to the top of the main bearing.


I then added the Synergy collar on top.


With similar electronics, my Synergy E5 with 556/96 blades weighs 2,930g (without LiPo's) which is 188g more than my Goblin 570 with 570/95 blades at 2,742g.  After flying the Synergy E5 and the Goblin 570 back to back, I decided to just sell the Goblin 570 and keep the Synergy E5.

The following pictures demonstrate the size difference between the Synergy E5 and Goblin 570.

Goblin 570 (bottom) and Synergy E5 next to G570.


Goblin 570 (left), Align T-Rex 550 v1 (middle), Synergy E5 (right)

[Grees01]

Thank you Curmudgeon for the reply. I will take a look at the scale and balancer. I am unable to see any pics listed or linked to your reply however. Something I am doing wrong?
Glen

[Grees01]

Ordered the scale, no biggie less than 20.00 amazon, be here Monday. The Koll rotor balancer however is another story. Not in stock at the linked location, and fairly pricey. Likely 200.00 + with shipping.

[Grees01]

I did add enough shims to the main shaft to eliminate any up and down play as per the manual. And when checking for any drag as the result of being shimmed too tight, I found it to rotate normally with very little to no drag. Is this lack of vertical play something that could cause a wobble / vibration problem, or only possible damage to bearings?

[Danny Dugger]

I did add enough shims to the main shaft to eliminate any up and down play as per the manual. And when checking for any drag as the result of being shimmed too tight, I found it to rotate normally with very little to no drag. Is this lack of vertical play something that could cause a wobble / vibration problem, or only possible damage to bearings?

No the lack of vertical play is what you want but you do not want to put any axial preload on those radial bearings. It's important to shim it just right in very small increments, I know SAB sells shims in a variety of thicknesses, Amain caries some nice bearing shim sets from Yokomo that have lots of 0.05mm, 0.1mm, and 0.2mm thicknesses in each pack. If you've gotten the slop out to within 0.05mm you know you're not preloading the bearing.
   If the harder dampers made a change in the RPM range of the wobble then that's probably where you should concentrate. Did the delrin dampers push the wobble to a higher or lower RPM? Have you tried running a faster headspeed? You might also try the stock dampers and play with how many shims you preload them with.

[cml001]

Not to thread jack.. But I have a similar issue.. No play in the main shaft.. But I get the shakes on E7SE. My desired head speeds where 1400, 1900, & 2150. I am fine on the low 1400 & high 2150.. Which were to be my "play'n round" head speeds.. Figured I'd stay in 1900 normally.. But I'm unable to run it.. The heli shakes between 1750-2025 range. Being unable to tune this out via the FBL unit or following the manuals mechanical order.. Even tried Ralph's Progressive damping system(blue,blue,blue & blue,blue,green) still shake'n.. So I just run 1400, 1700, & 2150. Love'n the bird but really want the 1950 in place of the 1700.. It's just too low for my preferred normal feel in the air. I end up just staying on the 2150.  Danny, are u saying I could use different shims to give different preloads on my head axle/spindle/dampers? I have the stock 1mm shim on each side of the head block against the dampers per manual. Suggestions.

[Danny Dugger]

Cml, you will see those shakes with stiffer dampers. Ralphs system would probably run smoothly for you using blue, green, white with the blue ones inside and white ones closest to the blade grips. Softer dampers should get you right. You can preload the dampers with shims to make the head tighter. Tighter dampers usually have some wobble in lower rpm ranges. Softer dampers let the blades flap a little and soak up the wobbles that can be associated with certain head speeds.

[cml001]

Thanks, I'll order some color from Ralph then & try out that combo..

[Danny Dugger]

Get extras The softer ones can wear a little quicker if you beat on em. Plus you might find that you want to soften it up a little more to make it happy

[Grees01]

Hi Danny, thanks for the reply. "Thread Jack" that's comedy. Well I tried re balancing the blades again. Was a little off with the maglev, but not much, its currently assembled with the stock dampeners. In terms of shims, there are only 2 brass spacers on each side of the center head block according to the manual, doesn't say anything about adding more shims, the only shims that I have are the ones that came with the delrin dampeners. There is another spacer between the outer blade grip bearing and the inner thrust bearing. I don't have anything like these. To the best of my recal with the stock dampeners the wobble was more prevalent at 2100 and improved slightly at 2200 and 2300, with the delrin dampeners more prevalent at higher rpms and little better at lower rpms. I'm doing a little flying this morning, just some basic hovering and orientation exercises, maybe these dampeners need to "break in"? Wish I had a set of rail main blades to mount up just to check.

[Grees01]

See attached image please.

[Grees01]

Can anyone explain why I can not see the pictures that was supposedly listed in curmudgeon's reply?

[Danny Dugger]

I just didn't know if you were running any shims to tighten up the stock dampers, in which case you could remove some to soften it up. I used to have a G630 and they recommended running some shims after break-in to keep the head super tight. I would recommend flying it for a while at higher headspeeds to break in the dampers. I would wager that around 2450 it should smooth out. Goblins tend to like more headspeed anyway. Give it some stick time at higher speeds. Maybe drop it back down and see if it doesn't clear up after half a dozen flights or so.

[curmudgeon]

Can anyone explain why I can not see the pictures that was supposedly listed in curmudgeon's reply?

Maybe the web browser?  I am using Firefox.