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HelicopterHIROBOOther › FFZ-III vibrations problem, which head to upgrade
03-16-2009 08:12 PM  8 years agoPost 1
puneetp

rrApprentice

Bangalore, India

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I have FFZ-III head on my new heli. I was planning to use it for Aerial Photography application.

I have noticed vibrations , which are resonance like while spooling up. This happens at several rpms probably 2-3 times before I reach my desired head rpm.

The heli shakes aggresively. I need to keep giving more throttle and vibrations start to fade away , however the head doesn't seem to be fully stable I can still notice significant vibrations at full head rpm.

What could be the reason for vibration at my final head rpm?
(Head tracks perfect and is balanced as well)

What should be my upgrade choice SSZ-III or SSZ-V ?

( My flying mostly consists of hovers and slow movements for video shoots )

Thanks,
Puneet

( I am new to Hirobo , is this what you guys call mast bump)

Machine over Gravity

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03-16-2009 09:18 PM  8 years agoPost 2
racingstripe

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Sacramento, CA

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What blades are you using?

The FFZ-III is the original Sceadu head with trailing input into the blade holder. This head does not like certain blades or very much slop in the control system.

andy-

Proofread carefully to see if you any words out.

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03-16-2009 09:22 PM  8 years agoPost 3
VinceY

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Newnan GA

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FFZ-III is the stock plastic Evo90 head, not the sceadu head.

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03-16-2009 09:43 PM  8 years agoPost 4
puneetp

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Bangalore, India

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NHP 800mm ( symmetrical )
Gear Ratio 9.3 :1
Engine 91Hz

Yes head is stock plastic EVO90

Machine over Gravity

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03-16-2009 11:46 PM  8 years agoPost 5
uh-1b flyer

rrNovice

montreal,Quebec-Cana​da

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Sounds to me like your problem is in the combination of blades, engine and gear ratio you are using. A 91hz is designed for a much lower gear ratio say between 7.9 and 8.25 to 1 and is not really meant to spin such long blades maybe 710's at most however with that head i would say go down to 690's since the width of the blade grips and yoke is rather large compared to other 90 size machines.

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03-17-2009 12:07 AM  8 years agoPost 6
Dr.Ben

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Richmond, VA, USA

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What is the hovering head speed of your model?

Ben Minor

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03-17-2009 12:20 AM  8 years agoPost 7
racingstripe

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Sacramento, CA

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Oh... EVO90.

800mm blades, wow.

Did you stretch the tail?

andy-

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03-17-2009 06:15 AM  8 years agoPost 8
Quickster

rrVeteran

Victoria, Australia

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You can run 710mm blades with 95 mm tails safely on that model. uh-1b flyer is right. That is the wrong gear ratio for that motor. Thats more for a 60 size motor! I would run 7.9 (12t pinion and 95t main) or 8.27 (11t pinion and 91t main). Have you got the blades too tight in the grips? I know that can cause funny shakes!

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03-17-2009 01:39 PM  8 years agoPost 9
puneetp

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Bangalore, India

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uh-1b flyer and Quickster : I know gear ratio seems to be the culprit but since I swinging very large blades its dificult to be on that same gear ratio as 700m blades. WIth 800mm, the head rpm is much lower maximum you can touch is 1500-1600 that too is very dangerous. 91HZ powerband starts from 14000rpm, I am very close to that.

racingstripe: This is custom heli which uses standard Hirobo mechanics EVO90 mechanics. Everything is same . Tail is extended. I will post a pic.

Dr.Ben : My head is at somewhere 1400-1450rpm. ( similar to Maxi Joker and other 800mm helis ), as you know with these blades its difficult to touch higher rpms.

Issues and suggestion :

- Does FFZ-III have any resonance problem ?

- How is the experience with SSZ- III ?

- How is the experience with SSZ-V ?

( I am assuming the SSZ-IV is not as good for stable application like SSZ-III and SSZ-V , please correct me)

Thanks,
Puneet

Machine over Gravity

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03-17-2009 07:08 PM  8 years agoPost 10
Dr.Ben

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Richmond, VA, USA

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1450 with the standard Evo dampers MAY cause a pretty good mast bump or wobble in hover. If this is indeed the kind of shake you have (is the tail boom bouncing up and down or is the model just shaking all over kind of like it's doing a belly dance?) then a set of SSR-V 60 D dampers will be of help to you.

There is no inherent reasonance problem with the FFZ-III head. The SSZ-III head is a all metal version of the FFZ-III head and shares the same ratios and geometries. The SSZ-IV head can be set up to be VERY stable but its stiff dampening may not play well at these slower head speeds. The SSZ-V is everything you'd expect from a premium Hirobo contest head.

Ben Minor

Team Synergy Team Futaba Team Kontronik USA
Progressive RC

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03-17-2009 07:10 PM  8 years agoPost 11
synodontis

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United Kingdom

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just a quick note

it's the general consensus that you use things according to their specification. If you deviate from that, as you have done, you are basically on your own!

the FFZ-III does NOT have any resonance problem if you use it the way it was suppose to be used...

SSZ-IV is a much better head than SSZ-III.

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03-17-2009 07:44 PM  8 years agoPost 12
puneetp

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Bangalore, India

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Ben Minor : I think you have Hit the nail on the head. This is the exact issue my heli is facing. Your post is very useful.

Please can you tell me what are the standard dampers with FFZ-III which come on EVO90 ?

Is the part number 0404-821 .

Q1: Please can you explain which kind of material is good for slow head RPMs and why.
Q2: Will appreciate greatly your explanation of what is going wrong here in terms of design aspects.
Q3: And your suggestions for correct parts( other than suggested).

Ben, Thanks again.

Kindly comment on : about adding shims to O-rings , making it stiffer, I see side ways movement in spooling up .

Thanks,
Puneet


Machine over Gravity

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03-18-2009 12:10 AM  8 years agoPost 13
Dr.Ben

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Richmond, VA, USA

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Please can you tell me what are the standard dampers with FFZ-III which come on EVO90 ?

>>The 414-389 standard dampers are 60D, but they are functionally MUCH firmer than the 0404-821's.

Is the part number 0404-821 .
>>Correct

Q1: Please can you explain which kind of material is good for slow head RPMs and why.
>>For slower head speeds with higher flybar ratios, along with the correcting delta that Hirobo uses in this head, a softer damper material helps avoid mast bumping.

Q2: Will appreciate greatly your explanation of what is going wrong here in terms of design aspects.
>>Try the softer dampers first. This whole issue may be a lot easier to solve than you think.

Q3: And your suggestions for correct parts( other than suggested).
>>None right now, but I want to see how the softer dampers work, too.

Kindly comment on : about adding shims to O-rings , making it stiffer, I see side ways movement in spooling up

>>With the center teeter Hirobo heads like you have, you run only as much shim as needed to remove the endplay in the grips. Anything more simply binds up the grip bearings.

One other thought, at slow headspeed and with large blades, you can expect it to take a while during spool up for the blades to "feather". It'll will help this if you run the blades a bit looser in the grips than you would on a smaller model.

Ben Minor

Team Synergy Team Futaba Team Kontronik USA
Progressive RC

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03-18-2009 12:41 AM  8 years agoPost 14
Mike0251

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Hills of the Blue​Ridge VA

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Put some grease in those bearings! Open face of the balls face inward to keep the grease from working itself out.

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03-18-2009 07:44 PM  8 years agoPost 15
puneetp

rrApprentice

Bangalore, India

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Ben : I have ordered the part 0404-821. Have done express shipping . Will try and post my results ASAP. Thanks for your response to my questions.

Mike : Thanks for the reminder ,surely will keep the bearing greased from inside.

Cheers
Puneet

Machine over Gravity

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03-18-2009 08:46 PM  8 years agoPost 16
Quickster

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Victoria, Australia

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Thats not a standard evo 90 is it? Look at the swash setup! It has an anti rotation guide yet it has a 90 deg swash!

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03-18-2009 10:31 PM  8 years agoPost 17
Dr.Ben

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Richmond, VA, USA

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Hmmm............Good pick up. I'd like to see the remainder of the ele control loop. Single input ele control is notoriously "soft". Is collective control via 90 D eCCPM?

Ben

Team Synergy Team Futaba Team Kontronik USA
Progressive RC

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03-18-2009 11:27 PM  8 years agoPost 18
synodontis

rrKey Veteran

United Kingdom

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I have FFZ-III head on my new heli
I suppose we weren't listening properly and assumed he had an EVO. Looks like Vario mechanics to me, what else can swing 80 cm blades?

3 servo 90 CCPM? That's pretty awful, but then again 90 CCPM is awful anyway so no change there...

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03-18-2009 11:52 PM  8 years agoPost 19
Dr.Ben

rrMaster

Richmond, VA, USA

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Indeed.

A$$ume too much and you end up looking like the same......

Ben

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03-19-2009 12:09 AM  8 years agoPost 20
puneetp

rrApprentice

Bangalore, India

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Ben and synodontis :

Sure nothing much,a basic setup, three servos directly connected to the swash. No control levers.

On radio , 90 deg type swash selection on jr9xii(jr9303).

As you know , two servos opposite to each other for right left cyclic and one servo for front-aft . So ch2 and ch6 are the right-left cyclic and ch3 is the front-aft cyclic.

Since this is a custom built heli for aerial photography, it borrows hirobos EVO head and drive mechanics as they are known to be stable.

Thanks,
Puneet

Machine over Gravity

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HelicopterHIROBOOther › FFZ-III vibrations problem, which head to upgrade
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