Rudder travel inconsistant left and right - HELP!! - RCCanada - Canada Radio Controlled Hobby Forum
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Old 09-20-2006, 07:36 PM   #1
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Rudder travel inconsistant left and right - HELP!!

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Hi there, I have a scratch built profile 3D fun-fly airplane. It is similar in design to the Tower Hobbies Fun-51, only it is made of foam insulation and has a little different fuselage style. The engine is an OS .46AX and the radio is a Futaba 9CS.

The rudder is giving me some problems. It travels fine to the left, but when I shove the stick to the right I get about 1/4 to 1/3 less travel. Is there anything I can do to adjust for the inconsistant travel? I have the servos mounted in the tail and I am using 4-40 rods directly connecting the flaps to the servos (I know they are large for this size model, I took them from the stock I have for my giant scale project ). I have the clevis on the closest hole to the flap.

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Old 09-20-2006, 07:53 PM   #2
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Things to check...

are the holes on the servo horn in line with the hinge line?
is the control horn centred properly on the servo?
is the push rod at right angles to the hinge line?
Steve Hayes, MAAC 51896
4206'15"N 8305'40"W

Sun Parlor RC Flyers Tower Field
4210'13"N 8302'49"W

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Old 09-20-2006, 08:05 PM   #3
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Well to start, the holes on the horn are as close to the hinge line as I could get without mounting the horn on the bevel.

The servo is mounted below the horn (if you look at the airplane strait down the thrust line, where I centered the wing and elevator). The reason for that is I had to either moun the horn above or below one of the hinges on the rudder, if I went below then the push rod would go through the elevator so I had to go over it. The servo couldnt have been mounted much higher because of the amount of foam surrounding it, if I went to high the mount would be real weak.

So that leaves the horn on the servo to check. Ill run out and play with it and see what happens.

Is it possible that I could put a slight Z bend in the rod to get the angles right? Or will this add too much flex and not control the flap properly?


PS.. the picture shows the rudder linkage, so you can see the angle of the rod. Its hard to see the horn on the servo though.
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Old 09-20-2006, 08:11 PM   #4
michel gravelle
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Steve , I read this thread and I asked the same questions . It seams to be a simple math question . I just want to stay in touch with the thread Thanks

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Old 09-20-2006, 08:43 PM   #5
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I just played around with the servo arm angle and the programming in the radio and I think I got it all worked out. I feel pretty stupid for posting this now Easy fix and I could have thought of it on my own

The rudder moves about 45deg both ways now, and actually I had to knock the high rate down a bit because after I adjusted it the rudder was smacking the back of the elevator. (Maybe Ill just trim the elevator a bit so I can get the max deflection out of the rudder ) I have the high rate at 120 right now. If there is any difference in flight characteristics right and left because of the angle of the rod I can adjust the travel by playing with the travel adjustment in the programming.

I looked at the alignment of the control horn in respect to the hinge line and it is withen 1/8". I didnt measure it, I just eyeballed it.


Ill have to wait until tomorrow to see how it works Actually, this airplane hasnt flown yet. The weather turned crappy right as I got it done. Maybe I can get it out tomorrow. We'll see.
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Old 09-21-2006, 11:46 AM   #6
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Steve, I see your problem I think. Make sure the servo arm and the pushrod are at 90 degrees to each other.
Michael Gyger
MAAC 58295
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Old 09-22-2006, 12:36 AM   #7
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Why did you do your rudder pushrod like that?
Imac # 4751
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