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11-28-2005 10:51 PM  12 years agoPost 1
hoverboy

rrNovice

Kailua-Kona, Hawaii

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I'm building my Vario Benzin trainer right now, and I'm ready to install the 4 servos into the wooden tray. I'm hesitating beacuse I've been told by a few vario owners that they experienced binding with the standard 4 servo arrangement and switched to 3. I wanted to get the groups take on flying with 3 servos instead of 4.

-Hoverboy

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11-29-2005 12:34 AM  12 years agoPost 2
Christopher J

rrElite Veteran

Kansas City, MO Californian lost in land of Oz

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I've done both and prefer the 3 servo 120 setup. Others use the 4 x 90 with no problems either. I've noticed less chances of binding when using the 3 x 120 setup (for myself), but with good mechanical setup as well as attention to detail a person could achieve the other set up with no binding as well.

Overall, it's really a personal preference for pilots, both ways work quite well.

Christopher J
same as I ever was
"Still all set & Flying the original"

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11-29-2005 12:41 AM  12 years agoPost 3
DStJohn

rrApprentice

Ft. Collins, CO

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I have used both and for the gassers I prefer the 4 servo. I have never had a problem with binding using JR 4131's or 8101's.

Dan St.John
East Coast Scale Helicopters Vario Field Rep

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11-29-2005 12:42 AM  12 years agoPost 4
Phil_Mart

rrVeteran

Newcastle UK

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I've got the Sky Fox /Airwolf combo flying with the 120 degree 3 servo set up and the Gasser Alouette flying with the 90 degree 4 servo set up. To be honest in flight I really cant tell any major difference between these two. However if I were to run the gasser on 3 servos I might, because of the blade size, but then maybe not!

What I did do for the servo set up was to get it set up mechanically as spot on as I could and then bench test it with an ammeter connected to the system. This showed up a small amount of binding in the servos, which lead to a few minor adjustments to the set up. Flies just perfect now

BTW, if you've got any major binding issues you will see the wooden tray flexing !


Philip Martin.

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11-29-2005 12:04 PM  12 years agoPost 5
doorman

rrProfessor

Sherwood, Arkansas

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3 OR 4 Servos???

I started out with the 3 servo set up on my Benzin and it flew fine, and that was using 9202 servos.... then I flew one with the 4 servo set up with 9202's and you could really feel the differenece mostly during the turns in the collective... it just felt a lot stronger (and it is!!!)
I now fly both of my Benzin's with the 4 servo 90 degree set up and like them a lot... and no binding issues at all.... as mentioned it is the set up... it must be right.
If you do go with the 3 servo 120, use a good 80-90 oz servo and you will be fine... I am certain that they would give the same "feel" as the 4- 9202's, and that is what you are realy looking for...
As far as the 4th servo adding a little security if one servo should fail, it may have some merit, but I think it would have a lot more to do with "Lady Luck".... Haven't had a call to find out and I hope that I don't!!!
Best of luck with your new heli.... you are going to like it..... a lot!!!!

Stan

AMA 2918-Team JR, Spin Blades, East Coast Scale Helicopter,Castle Creations

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11-30-2005 05:18 AM  12 years agoPost 6
hoverboy

rrNovice

Kailua-Kona, Hawaii

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Thanks for all the great answers!

I want to try using 3 S9206 servos instead of 4 9202's. Do any of you have recommendations on how to setup my servos and the linkages to the swashplate assembly?

-Hoverboy

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12-06-2005 09:12 PM  12 years agoPost 7
raybee

rrNovice

Sacramento, CA

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The 4 servo 90 degree setup will bind with cyclic input to varying degrees. This binding is nil with collective at, we'll say "centered". "Centered" being 0 degrees collective pitch and all bellcranks at 90 degrees in a typical 3D type of setup. The binding will be exacerbated the further the collective pitch is from "center", and as cyclic input is introduced. We all know we don't hover and fly at 0 degrees collective. No binding with collective-only inputs and cyclic neutral, no binding with cyclic-only inputs and collective "centered".

The simplest way to observe this is to watch the center of the swash plate of a 3 servo 120 degree eCCPM setup as described above for 3D. Center the collective and rock the cyclic around. The center of the swash plate doesn't rise or fall on the mainshaft. Now go to maximum +9 or +10 degrees of collective. Rock the cyclic around. You will note the swash plate drop relative to its original position as more cyclic is introduced. When you input -9 or -10 degrees of collective and rock the cyclic, you will see the swash plate rise.

Now imagine you tag a fourth servo to the swash plate anywhere opposite one of the original three, or better yet, we'll just jump to the 4 servo 90 degree setup. It will be fighting that drop or rise in the swashplate. This happens because our control setups are not of linear design throughout their travel.

Personally I don't like 4 servo eCCPM. I have heard stories of fellow pilots praising the fourth servo helping them get a helicopter down safely when one servo fails. My thoughts are that the failed servo died because of the constant bit of abuse throughout its life, and that it would be likely that none would have failed if it was a 3 servo eCCPM setup in the absence of binding.

Other factors are your choice of servos. If you do want to go with the 4 servo setup, stay away from digital servos. With a little binding the digitals will try to correct harder than analog servos, draw more current, have to dissipate more heat, create more stress on control links, and shorten battery life. A better choice of servos would be a high quality analog servo. Select something with reasonably high torque and whatever speed is appropriate for the application. Any high quality, properly selected, analog servo should perform well in a 4 servo arrangement.

If you do go with the 4 servo setup, do check the current draw statically as Phil_Mart suggests. This will ensure that the servo links are set up as accurately as possible and minimize any binding issues.

- Ray

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12-07-2005 04:21 AM  12 years agoPost 8
JWPage

rrNovice

Petaluma, CA

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Why use 3 over 4 servos?

Is there a reason to use one over the other?

If 3 is good, then 4 is better? There got to be more to it than that.

IRCHA #2527, AMA #846152

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12-07-2005 09:24 AM  12 years agoPost 9
Phil_Mart

rrVeteran

Newcastle UK

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I personally don't subscribe to the redundancy theory, that with a 4 servo set up if one should fail you still have 3 to control the heli. I've tried this on the bench and the swash really isn't happy when you disconnect any one of the servos.

My Airwolf is running a 120 degree 3 servo setup, but then its only running 620 mm x 65 mm chord blades. The servos on this setup are the Hitech HS635HB and I have to say I'm very pleased with this set up.

The Alouette on the other hand is running 750 mm x 75 mm chord blades and will eventually run a 3 blade head. On this I'm using the 90 degree 4 servo set up. This with 4 Futaba 9202 servo's. To me its all about available torque to the swash, with 4 servos you get a lot more. Also both Elevator and Aileron inputs are a true push / pull action.

Yes 3 servo is a lot easier to set up with a negligible risk of servo binding, but then we invest so much time and energy into getting every thing else absolutely spot on, why not do the same with 4 servo eCCPM ?

Philip Martin.

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12-07-2005 12:33 PM  12 years agoPost 10
Notar

rrKey Veteran

Taxachussetts

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The standard benzin trainer with the wood tray can do 3- 120, 4-90 or 3-90 ccpm set up.
Joe

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12-07-2005 12:39 PM  12 years agoPost 11
doorman

rrProfessor

Sherwood, Arkansas

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3 OR 4.....

I have had both set ups on my Benzin Trainers... I started with the 3 servo set up, and then converted to the 4 servo set up... it just felt a lot more positive, especially in turns..... and both of mine use the servo tray and linkage as stated by Heli_jack...
But I must agree 100% with both Heli_jack & Phil_Mart.... it is the set up that counts....
I have not had experience with the frame mounted ccpm in a Vario, but I can tell you that I have no binding in any position with my set ups... and also keep in mind that mine are not set you for 3D, but there is plenty of throw for general sport flying, loops, rolls, & inverted.
So I am certain that I am not trying to get the throws that someone else might be trying for...
It depends on what you are going to be doing with the unit and you type of flying.... but the bottom line is the set up must be proper wether 3 or 4 servos are used...
Good Luck... Stan

AMA 2918-Team JR, Spin Blades, East Coast Scale Helicopter,Castle Creations

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12-07-2005 01:50 PM  12 years agoPost 12
FCM

rrElite Veteran

Surrey, England

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If you do want to run 120 eCCPM with long blades and/or a high weight then use digital servos. The Futaba S9151 servos I use on my cyclic are rated at 11kg.cm torque - more than you will probably ever need and also more than 4 x 9202 coreless servos can produce.

You will also benefit from that unmistakable 'digital servo feel' i.e. rock steady precision, that I really appreciate even when flying AP.

Paul.

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12-07-2005 02:40 PM  12 years agoPost 13
Phil_Mart

rrVeteran

Newcastle UK

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Not that I want to cause a servo war

But, according to Midland Heli web site, the S9151's are rated at 9.5 kg (assume at 4.8v) whereas the 9202's are rated at 5.5 kg. It also seems that, according to the above site, 9.5 kg is the highest rating on Futaba servos, you have to go to JR to get up to 11 kg or Hitech to go as high as 15 kg.

However, does any one else find that there is now a bewildering array of servo's with varying speeds, torques and gear train materials ?

As to the comment about the Airstar side frames. I was interested in swapping out the side frames on my Benzin for these, like the idea of frame mounting the servos, smaller linkage routes and doing away with the wooden mount. Christopher J commented that these frames were taller than the Vario ones and kindly sent me some pictures of a heli fitted with them. Sure enough the frames were sticking out of the fuse, but interestingly the servos were mounted vertically in the frames. Next a chap from AS finally sent me some pictures of their frames matched against the Vario ones and they were the same hight. A design change had taken place and the servos were now fitted horizontally. Problem is that despite an email requesting further info, little things like postage rates and availability and TWO phone calls to their flippin answer machine from the UK (cant wait for that phone bill !) I still have had no response from them. Kind of backs up the bad reports about their sever lack of customer service that have been reported here on RR. Guess I will just have to wait for Vario to bring out a similar upgrade

Philip Martin.

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12-08-2005 02:00 AM  12 years agoPost 14
FCM

rrElite Veteran

Surrey, England

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That's interesting re: the S9151 torque that Midland's web site quotes. I got my info from the Futaba servo packaging and it is also at 4.8v. Doesn't matter to me whether 9.5 or 11 really - still plenty of reserve power

I use 3 point frame mounted servos with the servos mounted vertically in the frames as horizontally mounted servos will twist under load. I make my own sideframes for AP use though - no good for fuselages.

Good luck with Airstar Phil - I'm affraid I had to give up on them earlier in the year due to their lack of customer support. They make nice stuff though - it's just difficult buying it from them

Paul.

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12-08-2005 09:11 AM  12 years agoPost 15
FCM

rrElite Veteran

Surrey, England

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I just ordered my Vario Acrobatic this week from Joe.
And not before time either Tom - now you will get to see how a gasser really should be built

Paul.

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12-08-2005 09:16 AM  12 years agoPost 16
Phil_Mart

rrVeteran

Newcastle UK

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Admission is free, advice is free, but I'm sure we can find something to charge you for

You will not be disappointed with the Vario kit. The engineering is just superb, as is the customer support from them


Philip Martin.

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12-09-2005 05:17 AM  12 years agoPost 17
hoverboy

rrNovice

Kailua-Kona, Hawaii

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Wow! I started off quite the discussion

Again, thanks for all the input!

Everyone has left me with quite a bit to think about....

-Hoverboy

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