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Old Oct 08, 2012, 07:02 PM
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Originally Posted by ak79 View Post
What battery were you using ? (type and voltage) 5cell eneloop

What Radio system are you using (tx and rx, voltage reg ?) SD10, 10ch rx, no reg

What harness were you using ? I make my own, 26 gauge twisted wire

at full deflection did yours servos hum or buzz ? They were buzzing for sure

I don't think it had anything to do with the harness or battery. I am going to have another look at my linkage as I rushed to build the plane in time for the comp.
Agreed a 6 volt enloop pack "should" not cause that issue. However ANY impedance phsyically will really load up those servos and especialy the pots - Thats the only way I killed 809s - at full deflection I really worked hard to make sure there was no strain on the servos (no buzz) so that when I pulled the stick all the way I had only the airflow to fight and not friction or contact with the subspar or skin etc.

However it does not suprise me that your X survived unscathed. Those models are ___ing tough!
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Old Oct 08, 2012, 07:15 PM
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Here are some photos of the servos and linkage, maybe someone can see something I'm doing wrong.
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Old Oct 08, 2012, 08:02 PM
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hrm there are vast differneces between our linkage installations - mechanical advantages are different as well -

1) There is a dubious lack of clearance at full deflection in that shot. I can see the sub spar is actually touching the control linkage in the one picture. Thats sub optimal but I would have to be a fly on the wall to see if that was causing significant buzz vs a little centering here and there....

2) I actually clear out the sub spar with a hand file from top skin to bottom for total clearance and peace of mind where the clevis passes through. If the clevis's are contacting that sub spar during normal opperatio (flap to aileron coupling assumed here) you create way more heat on these little servos.

Let me post a picture of my 3.5 at max clearance - for good measure - this is an x2 3.5\8 center ection at full deflection which is less than 90 degrees (I see you have more deflection than I run but thats preference) I could set it up for 90 but I dont find it helpful but thats a different lesson in the LZ courtesy of Daryle Perkins...
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Old Oct 08, 2012, 08:44 PM
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Originally Posted by webbsolution View Post
hrm there are vast differneces between our linkage installations - mechanical advantages are different as well -

1) There is a dubious lack of clearance at full deflection in that shot. I can see the sub spar is actually touching the control linkage in the one picture. Thats sub optimal but I would have to be a fly on the wall to see if that was causing significant buzz vs a little centering here and there....

2) I actually clear out the sub spar with a hand file from top skin to bottom for total clearance and peace of mind where the clevis passes through. If the clevis's are contacting that sub spar during normal opperatio (flap to aileron coupling assumed here) you create way more heat on these little servos.

Let me post a picture of my 3.5 at max clearance - for good measure - this is an x2 3.5\8 center ection at full deflection which is less than 90 degrees (I see you have more deflection than I run but thats preference) I could set it up for 90 but I dont find it helpful but thats a different lesson in the LZ courtesy of Daryle Perkins...
Dave, what does your servo arm look like when you are at full flap? Is it laying totally flat so that the arm and linkage basically become collinear? I have been under the assumption that if that is the case then the servo is under less load at full flap since the load is basically being transferred from the gear to the output shaft itself.
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Old Oct 08, 2012, 09:40 PM
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Originally Posted by ak79 View Post
Dave, what does your servo arm look like when you are at full flap? Is it laying totally flat so that the arm and linkage basically become collinear? I have been under the assumption that if that is the case then the servo is under less load at full flap since the load is basically being transferred from the gear to the output shaft itself.
In the picture above the servo arm is relatively flat but not touching the skin. I have about 80 degrees of travel on that panel (and all my x 2 panels)

You could also present better mechanical advantage by not burying the brass horn quite so deep into the surface and reduce the torque requirement especially at full travel. Maybe some of the more "mechancially inclined" would care to comment but I remember experimenting with different depths and found that just 1-1.5 mm of brass horm height really translated to lower servo buzz.
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Old Oct 08, 2012, 09:41 PM
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What clevises are you guys running? Are they the ones where the pins come out to make it easier to attach them to the flap horns? Sorry I don't keep up on the latests trends on these things
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Old Oct 08, 2012, 09:50 PM
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What clevises are you guys running? Are they the ones where the pins come out to make it easier to attach them to the flap horns? Sorry I don't keep up on the latests trends on these things
I use the hays 131 clevis that one does NOT have a removable pin.
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Old Oct 08, 2012, 10:04 PM
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I use MP Jet clevis's the pins come out.
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Old Oct 09, 2012, 09:38 AM
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I used what ever hardware came with the plane... Are those up to the job? I think they were M2-size clevises with accompanying steel pushrods.

Also used the '3 meter JR-competition' servo-combo from SoaringUSA, don't remember the names of the servos though, only that they are JR's, but the flap-servos have about the same torque as most 'standard-size' servos, about 45 to 55 oz-in I think. The aileron-servos has about 70 oz-in but I used them because of the slim profile and convenient frames rather than torque.

What stab incidence do you guys use? I think I used about 0,2 degrees or something on my old Xplorer but am nowhere near sure what I used. Am hoping for some input from all you experts... I've heard about one method in which the incidences are set to zero then the CG is shifted until the plane is trimmed rather than the other way around, or is it set to 0,1 or some other very low value? Any of you guys heard of this way of trimming a glider?

Do most people use a thermal-mode with a preset camber or a 'snap-flap' mixing? I am sort of on the fence about what to do about it. I have enough available switches to try both ways within the same model-memory...
Lastly, is there any benefit of using launch-camber on a high-start? Other than hand-launching high-start is all I have for getting the plane into the air.
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Old Oct 13, 2012, 05:45 PM
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New 3.8 Mk2 in Albuquerque

I just finished my new Xplorer-2 3.8. It was a standard ST versoin in Bob's last shipment. It has white paint with red trim and weighs 64.9 oz (1.84kg). with the balance point at 120mm. It has Hyperion DS-095 servos on the flaps, Airtronics 94809 servos on the ailerons and rudder and a 94761 on the elevator. It has a LiFe 1450mah receiver pack and a JR/Spektrum 9310 receiver. We'll see how it flies tomorrow.

Bruce T.
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Old Oct 14, 2012, 03:46 AM
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Sounds like the servo was stalled. Those are LONG servo arms. Are you using asymmetrical travel on the flap servos to get more down.

I am no expert on f3j, but they seem like very small servos for the flaps of a large model.

Why not just dive out of lift anyway. It's more fun for a start. Do a few loops, bunts, squares or whatever.
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Old Oct 14, 2012, 03:55 AM
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Here is a really useful tool that helps you work out what servo horn sizes you need to get the deflection you want.

Amoung other things it can work out how much servo torque you need with your flap size, linkage setup and flying speed etc. bear in mind manufacturer servo specs are 'optimistic'.....

http://www.envisiondesignusa.com/evd..._Overview.html
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Old Oct 15, 2012, 09:17 PM
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Satinet

Those servos really are not to small. Of course they won't take the abuse that a larger servo may take but they do the job very nicely. I used Futaba 3156 servos on all the surfaces of a 3.5 xplorer and they never had a problem. Even after some heavy flying they never had any slop. Only problem I had was the servo had such a small foot print that I would pop them loose from the skin. At fall fest I was launching it off of mono on a b winch and holding lots of tension. The elevator was so crisp. Next open ship will have the same servos.

Joe
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Old Oct 16, 2012, 03:13 AM
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Satinet

Those servos really are not to small. Of course they won't take the abuse that a larger servo may take but they do the job very nicely. I used Futaba 3156 servos on all the surfaces of a 3.5 xplorer and they never had a problem. Even after some heavy flying they never had any slop. Only problem I had was the servo had such a small foot print that I would pop them loose from the skin. At fall fest I was launching it off of mono on a b winch and holding lots of tension. The elevator was so crisp. Next open ship will have the same servos.

Joe
Joe my comment really was incorrect sorry. small = not powerful in that context. I agree that you can use very small/low torque servos even in a big model if you are careful in a number of ways (linkage geometry, flying speed etc).

How much servo torque you need on a surface is a combination of a number of factors. The obvious ones like surface deflection, speed of the airflow, size of the control surface etc. Linkage setup is important so that the servo given a chance. IMHO it is important to make the servo travel down more than up to minimise servo arm length (some discussion on the pike perfection thread).

An f3j model has a large flap and is fairly fast. If you calculate how much servo torque you need to dive a model like that with the brakes out (big flap, big throw and lots of airflown) it's a lot if the linkage setup is not sympathetic (even a powerful servo wouldn't be up to the job). I think the best thing to do on flaps is make the linakge so that it is "locked out" when full flap is deployed. Therefore the servo isn't really doing any work when the flaps are fully out.

Although, like I say personally I wouldn't be doing any sustained dives with my flaps fully deployed even with an f3b model. Let's face it scrubbing off height/speed is the easy bit (I am something of an expert in landing before 10 minutes are up! ).

This a good couple of diagrams I found ages ago on the xploder thread. Sorry I can't find them again to thank the author.




note at full Crow deployment (green lines) the servo horn is pointing directly down the line of the pushrod. This equals servo not having to work hard. And the gears are less vulnerable if the flaps hit the ground.

I'd rather have the greater margin for error with bigger more powerful servos, but I think the same good practice applies regardless - just more so with tiddlers.
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Old Oct 16, 2012, 09:28 AM
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Joe my comment really was incorrect sorry. small = not powerful in that context. I agree that you can use very small/low torque servos even in a big model if you are careful in a number of ways (linkage geometry, flying speed etc).

How much servo torque you need on a surface is a combination of a number of factors. The obvious ones like surface deflection, speed of the airflow, size of the control surface etc. Linkage setup is important so that the servo given a chance. IMHO it is important to make the servo travel down more than up to minimise servo arm length (some discussion on the pike perfection thread).

An f3j model has a large flap and is fairly fast. If you calculate how much servo torque you need to dive a model like that with the brakes out (big flap, big throw and lots of airflown) it's a lot if the linkage setup is not sympathetic (even a powerful servo wouldn't be up to the job). I think the best thing to do on flaps is make the linakge so that it is "locked out" when full flap is deployed. Therefore the servo isn't really doing any work when the flaps are fully out.

Although, like I say personally I wouldn't be doing any sustained dives with my flaps fully deployed even with an f3b model. Let's face it scrubbing off height/speed is the easy bit (I am something of an expert in landing before 10 minutes are up! ).

This a good couple of diagrams I found ages ago on the xploder thread. Sorry I can't find them again to thank the author.




note at full Crow deployment (green lines) the servo horn is pointing directly down the line of the pushrod. This equals servo not having to work hard. And the gears are less vulnerable if the flaps hit the ground.

I'd rather have the greater margin for error with bigger more powerful servos, but I think the same good practice applies regardless - just more so with tiddlers.
This is a great discussion on linkage setup and I totally agree - all my servo flap setup are locked out at full deflection and I think as consequence I have far less slop than I see on many models with full deflection putting stress on the servo itself.

The thing to remember about the 809 is that until the 3.5 center panel of the X or X2 attains a speed of +80 MPH the servo is pleanty powerful to attain high degrees of deflection from a clean position.

Once the deflection starts the speed drops fast and the servo is well within its margin of performance from a speed / surface area and torque requirment perspective. I deployed full flaps as described numerous times and held them all the way to the ground without the described heat and servo failure. Did I make a habbit of doing that ? no its abusive at best but I needed to see oif they would fail...


I also paid very close attention to both geometry and linkage clearance. Even a tiny amount of binding or recentering will cause huge heat and end the life of these servos which is why I posted about abusive usage scenarios not being within the envelope of typical applications for it. Heat is the real enemy here.

Also just a few mm of surface horn adjustment makes a massive difference. I see a lot of guys buring the brass horn too deep, modifying the horn to do so. I did that on my Pike perfect and then realized my servos were sloppy and ill centering at the end of the 2008 WC. I had to replace them all. My bad. lessons learned -
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