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HelicopterCentury Radikal G20-30 N640 Hawk Predator › Carbon Predator Owners w/ GY611 (Futaba s9256) please chime in.
11-25-2006 12:02 AM  11 years agoPost 1
asong26

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VA

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I am still struggling with getting the servo throw correctly without affecting the end points too much. My goal is to obtain anywhere between 110 to 115% end point movement in both directions.

For those of you who has a similar configuration please chime in:

1. Predator Carbon w/ Metal Tail Box.
2. Using GY611 front mounted servos (pushrod / bell-crank config)

Let's start off with the servo horn. The manual states that the distance between the center of the horn screw to the link ball should be at 13.5mm. I believe this may be outdated or wrong. When I use this setting, the pushrod from the bell crank to the servo slopes down.

My bell crank has 3 holes on the longer bottom arm, and 2 holes on the opposite side (which point up). On the 2 hole side, I am using the first hole from the center (lower position). Even at this position, the push-rod still points down. This is why I believe this manual is outdated, or not accurate. To correct the slop, I believe it should be at around 20mm from the center of the servo horn screw to the ball link.
Anyone using a similar config?

Also, if I do raise it up this high, this will obviously increase the throw of the servo arm, which will result in manual adjustment to the servo travel.

Does anyone have any suggestion as to where I should be placing my ball-link ball on the servo arm (distance from center) to achieve maximum throw while obtaining 115% servo limit on both sides? Or is this not possible on the Predator due to the length of the the tail rotor output shaft? I want to make sure that this expensive servo doesn't die on me too quickly due to too much movement limit.

Thanks.

Andrew

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11-25-2006 12:34 AM  11 years agoPost 2
coolice

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Northamptonshire, England

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Hey Andrew,

With a little playing around you can sort this out no trouble.
The intermediate bell crank, which connects servo pushrod to tail pushrod, I feel from your explanation is where the problem lies.

The servo connecting rod to intermediate bell crank, if you move that point further out on the arm (2 hole side, outside hole) the servo will have to travel further to achieve the same movement on the other end.
Conversely on the 3 position side, which connects to the tail pushrod, if you move this ball inwards then it will again have to move further around it's arc of travel to push the tail slider further along at the back.
It all comes back to the what is known as the fulcrum (spelling?) or pivot point in relation to the connecting points on the arm.

I ran two (now one Freestyle) Carbon Predator's and forward mounted tail servo's and GY601's with the limits set to 110~120% both ways.

It comes down to striking a balance between ball link position around the centre pivot point and servo arm length. I'd stick with the 13.5mm for now and see if by changing the ball positions on the arms you can bring things where they need to be.
.

Ian Contessa
Team Robbe SchluterUK
Midland Helicopters

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11-25-2006 12:47 AM  11 years agoPost 3
asong26

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VA

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Coolace,

Thank you for that intuitive explanation. "Fulcrum" eh?

Please let me restate what you're saying to make sure that I understand you correctly.

In order to get maximum throw within the limits of the output shaft of the tail, I would use the very top hole (second hole from the center) on the bell crank.

What about the bottom side (3 holes) of the bell crank? I am currently using the second hole on the bottom side of the crank. Should I go any lower than that? The only reason I am not using the first hole on the bottom side of the crank (closer to the middle) is because I did not want to potentially strain the servo (amount of torque required to move the tail pitch slider)

Lastly, if I follow your advice of using the second hole on the top side of the bell crank, I would assume that my ball-link spacing from the center of the servo would end up being greater than 20mm. Because even at 13mm w/ first hole, the push rod slopes down. Am I making sense?

Andrew

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11-25-2006 02:28 PM  11 years agoPost 4
D.Magee

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kansas city mo.

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On the bell crank the top holes the closer you get to center with the ball link the more the tail blades will move with the same input.
the closer you get to center on the botem holes the tail blades will move less.

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11-25-2006 02:48 PM  11 years agoPost 5
asong26

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VA

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I've adjusted the hole placement last night.

First, I am using 19.5mm from the center of the servo horn. From there, I am connecting the shorter rod to the top hole on the bell crank. This give me the perfect parallel from servo to bell crank.

On the bottom side of the bell crank, I am using the hole closest to the center (first hole). With this setup, I am now able to get close to perfect limit of both A and B of 115%.

Andrew

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11-28-2006 03:53 PM  11 years agoPost 6
asong26

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VA

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What is the recommended settings on the Gyro Gain?

Also, how does the gyro gain on the gyro unit settings vs. radio's gyro gain differ, or related?

Andrew

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11-28-2006 07:37 PM  11 years agoPost 7
Scott99

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Nelson, New Zealand

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9256

Correct me if I am wrong, the aim here is also to minimise torque loading on the servo also, which means keeping the servo ball position on the arm as close to the center as practical (13.5 may be a good position?)
I am theorising here, but because the 9256 is so fast, the fact that it may need to travel a wider arc in operation given a shorter ball position (in search of reduced torque loading to servo) is maybe not such that it affects its performance adversly?

This issue concerns me, as we have all seen many 9254 servos burnt out, due to possible set ups? and that the 9256 has the same specs bar the frame rate? - the point I am getting at is the 9256 is also still only 3.4kg - again theorising, but surely there is quite a torque loading difference on the tail servo generally between nitro and gas machines meaning particular attention to setting up a 9256 on a gasser is perhaps a bit more vital?

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11-28-2006 08:16 PM  11 years agoPost 8
asong26

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VA

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I am trying to achieve both. I am trying to make find the best setting that will not only minimize the torque strain (look at my above post) yet get it in the spot that is good enough (from torque perspective) that will give me the most amount of servo movement left and right (end points)

Andrew

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HelicopterCentury Radikal G20-30 N640 Hawk Predator › Carbon Predator Owners w/ GY611 (Futaba s9256) please chime in.
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