Questions about servos.

[SkyEye]

I just got a Park Zone T-28 BNF (not the micro), and I tried plugging in the battery to test the controls on the ground.

Whenever I apply full right or left aileron, I hear this weird grinding noise. I've consulted with episode 9 of the beginner series where they talk about servos and how to check if their working or not. I turned the servo by hand to their farthest extent and heard no clicking which indicate broken teeth.

Also I notice that when I apply full left or right aileron, the servo does not go to it's farthest extent. (which makes it approximately 3mm short of what they state in the manual.

Please help, should I never mind this and proceed with my maiden, or try to fix this.

 

[quorneng]

SkyEye
From what you describe it sounds like one or more of the servos is hitting an obstruction before it has reach its full travel. The noise you are hearing is it 'stalling'.
You really should disconnect the servo from its linkage and see if it then moves equally both ways without making the same noise. If it still does at full travel then the servo itself is damaged.
If it moves freely with no grinding then obviously the problem is with the linkage or the control surface itself.
If your manual gives a travel distance then you should investigate what in the linkage is stopping it. You should not attempt to fly it until you have the specified travel and without the servo stalling at the travel limit.
A servo does not take kindly to being stalled on a regular basis.

 

[SkyEye]

Thank you, I will try your suggestion.

 

[SkyEye]

Ok I see no obstructions, but did you mean obstructions on the outside or the inside of the servo.

 

[ViperTech]

Some servo's "growl" ,kind of normal and if the hinge is tight, that can make it worse. The servo's manually move almost 180 deg. but the movement from the radio is always less and I don't know why? In my radio I can add 25% more movement. If you need more movement you could check the radio to see if you can change it electronically or it can be gained by changing positions on control horn mounts or servo arms. It is possible that you could be having control rod flex also limiting the amount of movement and that might make some noise also. Worst case is some thing is not together correctly and that would be a disaster in the making. If your not sure try to find some one who is may be more experienced and have them physically inspect it.

 

[SkyEye]

Thx, I've been wondering about that sound.

 

[quorneng]

SkyEye
What I mean is that something is stopping the servo from travelling to it full limit. Disconnecting the linkage from the servo is a good way to test that it is not the servo itself that is making the noise.
In this video the flap servo travel has had it full travel artificially limited so it then becomes stalled and 'growls'. In other words it cannot reach the position it wants to get to.
Does it sound anything like this?

 

[airhawk]

if all these dont work which they should try clearing the sides of the ailerons just a little

 

[SkyEye]

Quorneng, that's exactly what it sounds like. I will test all of these suggestions. I actually just got back from the hobby store, and you will not believe how many flite test planes I found. 2 FT Viggens and 4 Ft Guineas. Flite test rocks. Thank you all.

 

[SkyEye]

Ok, it was not the servos, and there's a little adjuster thing on the control rod that I will loosen to get better results. Any fixing suggestions would be great although I know I have asked a lot from you guys.

 

[SkyEye]

Um, I can't find a position where both ailerons, make no noise.

 

[quorneng]

SkyEye
What type of hinge are you using?
If we assume the control surface can be deflected to the required degree and there is nothing else in the linkage that is preventing movement then the hinge itself (particularly the plastic 'bend' type) require more force the further they deflect and this may simply be over loading the servo.
If this is the case you could reduce the travel (and increase the force at the control surface) by moving the linkage 'in' one hole on the servo arm but the much better solution is to use a free moving hinge!