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Old Oct 20, 2009, 01:53 AM
I fly, therefore, I crash!!!
SteveT.'s Avatar
San Jose, CA
Joined Jan 2008
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Boosted end points, VS. longer servo arms..

Hi Guys...

A quick question for you.

The plane in my avatar is an Aero-Works .90-1.20 size Yak 54 that I have converted to electric power. It flies great, but it lacks in rudder authority. I have the pull-pull cables hooked to the inner holes on the control arms on the rudder, and on the outer holes on the longest arms that came with the Hitec HS-7985MG digital servos (essentially the same length as the Dubro long arms for these servos).

Today, I was checking the throw on the rudder, and found that the end point adjustments were set to 100$, but with my JR X9303, I can set them higher. I set them up for 145%, and get a lot more throw on my rudder, however, I am getting a fairly pronounced buzz at the extreme ends of the throw. Or, I also have some longer carbon fiber extended servo arms that I can use.

In your opinions, which way is better?? to over drive the servos, or to use the extended arms??

Thanks in adavance...

SteveT
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Old Oct 20, 2009, 01:58 AM
R/C Airplane Executioner
Melbourne, Australia
Joined May 2006
1,934 Posts
If your getting buzz, there may be one or more of a few contributing factors. Could be that its overloading the servo, but also could be that the hinges are a bit stiff and the servo's binding. If your servos are up for it, go the extended arms. Not only will you get better throw, the arm will need to move less which means it gets there quicker. The risk is the servo may not be up for the job, and you may get blowback in say, the bottom of a KE loop, which is no good 'tall.

You could also keep it the way it is and make up some SFG. That should be an all round improvement to the plane.
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Old Oct 20, 2009, 02:00 AM
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Threshold's Avatar
London UK
Joined Jul 2004
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I believe the idea is to match the distance between the control horn holes and the servo arm holes. If you have one bigger than the other you will get binding and buzzing. Then increase the EPA to get the throw you want.
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Old Oct 20, 2009, 02:06 AM
I fly, therefore, I crash!!!
SteveT.'s Avatar
San Jose, CA
Joined Jan 2008
26,097 Posts
Quote:
If your getting buzz, there may be one or more of a few contributing factors. Could be that its overloading the servo, but also could be that the hinges are a bit stiff and the servo's binding. If your servos are up for it, go the extended arms. Not only will you get better throw, the arm will need to move less which means it gets there quicker. The risk is the servo may not be up for the job, and you may get blowback in say, the bottom of a KE loop, which is no good 'tall. You could also keep it the way it is and make up some SFG. That should be an all round improvement to the plane.
Nope, no binding that I am aware of, and it is in both directions....usually surfaces don't bind in both directions at exactly the same point (not to say it can't happen) Also...the surfaces are quite heavily beveled...And...I believe the servos are up to the task, as I went for stronger than called for.

Quote:
I believe the idea is to match the distance between the control horn holes and the servo arm holes. If you have one bigger than the other you will get binding and buzzing. Then increase the EPA to get the throw you want.
They are pretty well matched as to distance...but I will check them again later today....

Thanks Gents..

SteveT
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Old Oct 20, 2009, 02:17 AM
R/C Airplane Executioner
Melbourne, Australia
Joined May 2006
1,934 Posts
Definitely go the longer arms IMO. Dont forget when measuring the distance between the two holes, your measuring from the hinge point to hole, not base of control horn to hole. (Not that I think that a small difference will cause much problems.) Let us know how it go's either way. Its a very cool plane.
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Old Oct 20, 2009, 02:29 AM
I fly, therefore, I crash!!!
SteveT.'s Avatar
San Jose, CA
Joined Jan 2008
26,097 Posts
Quote:
Originally Posted by maiden-crash
Definitely go the longer arms IMO. Dont forget when measuring the distance between the two holes, your measuring from the hinge point to hole, not base of control horn to hole. (Not that I think that a small difference will cause much problems.) Let us know how it go's either way. Its a very cool plane.
Thanks, I will...

As to the plane, It is as I said converted to electric, and has an AXI 5330-18 motor, a Hacker/Jeti Master Pro 90 amp esc, running on 2X 5S 4000mAH 25C packs, and is swinging a 19 X 10 prop, which gives me seven minutes of flight time. I have a JR two cell 4000mAH lipo for the receiver and servos, which is run through a Spektrum 10 amp regulator, that drops the voltage to a usable 6 volts.
It has Graphtech carbon fiber gear. Unfortunately the plane weighs 12.8 pounds ready to fly....but it has pretty good power at 2467 watts, which is basically 199 watts per pound.

It is also a couple of firsts for me, it is the largest plane I have ever flown, and also the first gas to electric conversion I have ever done...

SteveT
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Old Oct 20, 2009, 02:29 AM
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theKM's Avatar
central PA.
Joined Sep 2004
20,158 Posts
the buzzing problem: the servo is stalling. The rudder cannot move as far as the servo is trying to drive it. You need to reduce the end points of the servo so that this buzzing doesn't happen, you're making your servo unhappy. Reducing travel means that you're losing operational resolution of your servo. If anything, reduce the size of the arms and maximise the end points in the radio to take advantage of the servo capabilities.


Either way... you do not want longer arms, your servo is already complaining that the rudder isn't going where it wants it to go. You can only drive your rudder as far as the servo can drive it, you have hit that limit. It will take changes at the rudder in order to get more throw.

A common setup technique for getting maximum throw is to adjust the end points until the servo starts buzzing and then back off until it stops.

step one: see if you can get the rudder throw you want without stalling your servo. There's no point in tweaking other things like horn/arm equality if you can't achieve this.
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Old Oct 20, 2009, 02:50 AM
R/C Airplane Executioner
Melbourne, Australia
Joined May 2006
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KM, Draknep has already mentioned the surfaces were heavily bevelled. That was my first thought too, that the servo's were being overloaded because the rudder was already at its limits of throw.

It def wouldn't hurt to double check that the rudder can freely move further, though.

Draknkep, very cool pictures, awesome color scheme. How does she 3D at that weight?
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Old Oct 20, 2009, 05:10 AM
Time For Me To Fly!
Get Real's Avatar
Illinois
Joined Feb 2006
4,963 Posts
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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Old Oct 20, 2009, 10:00 AM
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cwojcik's Avatar
United States, NH, Epping
Joined Oct 2005
2,628 Posts
Digital servos buzz when there is any load on them at all. It is natural for the control surfaces in any airplane to have light resistance towards the extreme end of their movement.

I would try this: First, make sure that the distances between the holes on the rudder servo horn and the holes on the rudder horn are equal. Set the EPA or DR so that the rudder will see about five or ten degrees more than it sees right now (if you are currently at 100%, this might be 120-130%). That will make a big difference. Now hold the rudder stick hard over and apply light pressure with your finger to the rudder in the same direction as it is moved (ie if it is deflected to the left, push it further to the left). If light pressure makes the buzzing go away, you'll be fine. It it requires lots of pressure, or it the rudder itself deflects significantly before the buzzing goes away, then you need to check your geometry and find what is binding.

But definitely try to use more than 100% of the servo's throw if possible. You will have more torque and more resolution, at the expense of some speed, but that servo is really fast so you probably won't notice it.
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Old Oct 20, 2009, 01:58 PM
I fly, therefore, I crash!!!
SteveT.'s Avatar
San Jose, CA
Joined Jan 2008
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Hi Guys....

Thanks for your suggestions, and I will most certainly try them...

Last night, before bed, I did go out into my shop for just a moments, and tried something. I manually moved the rudder, and it will go WAY beyond the point where the servo moves it and with no binding I can feel. The one thing I think might be causing this though are the springs on the tail wheel assembly. They seem like they are possibly a bit tight, but if too loose, you don't get good steering response while taking off or taxiing.

And...

Quote:
Draknkep, very cool pictures, awesome color scheme. How does she 3D at that weight?
I will admit, I am more of a sport flier, with a few 3D "moves" thrown in. The plane only has about 8 flights on it, and while it has lots of power, I hadn't started to dial in the throws, (which is why I was asking about the servos, and servo arms etc.. ) She does have as I said right at 199 watts per pound, and even though she is a bit portly, she doesn't feel that way.

You can see one fly on fuel here just scroll down to the video...I think mine actually flies better....the guys at my field have all commented on how much power she has.

SteveT
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Old Oct 20, 2009, 05:37 PM
anything Yak
Joined May 2007
443 Posts
Possibly offset?

http://www.swbmfg.com/rudex.html
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Old Oct 20, 2009, 07:19 PM
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Xpress..'s Avatar
Joined Oct 2007
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If they're digital servos, they're going to buzz.

Also, make sure you setup the controls so that the rudder doesn't get within 1" of the elevator. This ensures there is plenty of room to keep the rudder from touching the elevator
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Old Oct 20, 2009, 09:58 PM
blucor basher's Avatar
United States, PA, Lancaster
Joined Jun 2003
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Also, make sure you setup the controls so that the rudder doesn't get within 1" of the elevator. This ensures there is plenty of room to keep the rudder from touching the elevator

Not. Maybe you added the "wink" because you're joking? Who knows?
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Old Oct 20, 2009, 10:40 PM
I fly, therefore, I crash!!!
SteveT.'s Avatar
San Jose, CA
Joined Jan 2008
26,097 Posts
Hi Guys....

I have determined (at least I'm pretty sure) that since I have a lot more rudder throw (due to the large bevels) available than the servo is moving the rudder, that the tail wheel springs are causing the problem. I meant to purchase some new springs today, but didn't get a chance to.

SteveT
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