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Old Oct 20, 2009, 05:10 AM
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Flippin Multirotors
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Joined Feb 2006
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Lets get a fresh start and rule some things out. Just to be sure and this is quick and easy.. remove the the servo arm from the servo with the cables attached etc and make sure theres plenty of slack in the cables,now check for any binding by moving the rudder back and fourth by hand to the desired throw your asking the servo to move it.. does it move freely? Make sure your not trying to drive the surface further than the servo can move it as mentioned.. it will only stall,it will also stall if the servo doesnt have the torque to begin with for the surface its being used to move.

Now if the first step went well,check the clevises on the servo horn for binding. then run the servo itself back and fourth with power and check for any binding with the servo arm back on and gently creating some light resistance with your fingers on the servo arm as you run the rudder stick back and fourth to feel if the servo has any noticeable resistance in the servo gear train.

I know this sounds tedious but its part of diagnosing the problem,id guess the servo is marginal in power myself though for this size and weight plane,but why spend money if you can work with what you have to get maximum performance and acceptable results with what you already have.

The longer the servo arm,the harder the servo works to move the control surface.. this reduces effective power of the servo.. its just bad leverage(less mechanical advantage in rc plane terms),you gain overall throw but lose power and stall the servo easier and youll feel the difference in the air.

The servo is rated for 172oz of torque,and it is digital.. very sensitive and precise.. but also emits quite a bit of buzzing. The slightest touch or resistance is easily noticed with digital servos more so than non digital servos.

On resolution.. think of it this way if you run rc cars,32 pitch versus 48 pitch,by maximizing epa but using a shorter servo arm or moving the linkage closer to the center of a larger servo arm you can still get the same throw usually with much smoother feel and response to stick movement.

Food for thought.. two servos,for example one has 150oz of torque and .10 transit time. The other servo has 300oz of torque and .15 transit time. In a high torque application like a rudder servo with both servos having identical servo arms and linkage placement the higher torque slower servo will probally have the same deflection speed on the control surface or even faster because it doesnt struggle to move it while the faster servo struggles its transit time slows because its struggling. Deflection rates and movement on the ground can be quite different than when the plane is in the air with additional drag or resistance in flight.. easy way to get some idea of the blow back a or loss of torque the control surfaces can experience in the air.. Full elevator deflection on the ground.. now hit wot and watch the elevator.. make sure the tail of the plane is secured ofcourse.

With planes i usually go with the suggested servos for the plane.. a couple months ago i ran into a similar problem as your probally having now,using the suggested servos for the plane and some extended arms for use with hitecs that were recommended for the plane and the linkage locations pictured in the manual etc. On the elevator in particular the response etc didnt feel crisp and walls and other pitch manuevers felt like crap compared to similar planes in this size that i had used them in before in the past,ok check the servos.. all seemed well but i swapped servos around just to rule out it was completely a servo issue causing things in the air.. no avail. I chucked the elevator aftermarket horn and went with the stock hitec servo arm.. i lost some of the control surface deflection but because the servo was struggling with the after market arm and getting blow back.. it flew much crisper to elevator imput and pitch was much better in the air even with less throw because the servo wasnt struggling anymore using the stock hitec arms instead of the overkill aftermarket arm.

Hope some of this makes sense.
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Last edited by Get Real; Oct 20, 2009 at 05:20 AM.
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