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Old Nov 19, 2012, 01:46 AM
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United States, CA, San Jose
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Originally Posted by pilot_keeter View Post
I accidentally cut down my push rods based on the inner hole and not the outer hole. I have at least half the insertion length of the metal clevis on both ailerons. Should this be enough to still get a strong enough connection? I'll be using 30 min. epoxy for the strongest possible bond.
It doesn't sound as though you don't have any choice. Try what you have, with 30-min epoxy, and test them. I was able to really pull quite hard on mine and they didn't come apart.

If you find they won'y hold, you may need to go back to PA and get replacements. If you do this, I would recommend not cutting them at all. I was able to accomplish a good fit by using a sanding block alone. I simply sanded the rod's to length.

And one last thing; don't forget to use a small jewelers file, or the edge of a file, to create small grooves in each end; as per the instructions. This is really important to get a good hold...
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Last edited by bobmixon; Nov 19, 2012 at 01:48 AM. Reason: I forgot something...
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Old Nov 19, 2012, 07:59 AM
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United States, GA, Pooler
Joined Nov 2008
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Originally Posted by bobmixon View Post
It doesn't sound as though you don't have any choice. Try what you have, with 30-min epoxy, and test them. I was able to really pull quite hard on mine and they didn't come apart.

If you find they won'y hold, you may need to go back to PA and get replacements. If you do this, I would recommend not cutting them at all. I was able to accomplish a good fit by using a sanding block alone. I simply sanded the rod's to length.

And one last thing; don't forget to use a small jewelers file, or the edge of a file, to create small grooves in each end; as per the instructions. This is really important to get a good hold...
I filed everything per the manual

I went ahead and glued everything last night. Let it set overnight and tested everything this morning. The movements themselves are fine and I tried pulling the rod from the metal clevis almost as hard as I could with no budge at all. I wish I had a little more length to ease my mind, but I think everything will hold up.
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Old Nov 19, 2012, 11:20 AM
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Originally Posted by demonGti View Post
Use the outer holes. The geometry is such that the control rods will be 90 to the control surface at full deflection, which is where you need the most torque from the servos. When the ailerons are neutral you end up with control rods that are not parallel to the ribs in the wing but this is as intended.
But didn't you use red lock-tite on the screw and nut, making it impossible to move the linkage to another hole? That's what they tell you to do. It's one example of why this is a frustrating plane to build -- to answer a question posed recently. They use techniques other companies don't, perhaps to save an ounce, but they are difficult. Like cutting out slots for the control horns and gluing them in. The slots are not the right size, so you need to sand the CF horns, and of course it's hard for them to come out perfectly straight, putting strain on the linkage when in use. It looks good, but it's 10 times more work and a lot easier to make a permanent mistake (because those are glued with epoxy -- you only get one chance, unlike screw-on horns used on most models).
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Old Nov 19, 2012, 04:50 PM
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Originally Posted by bmschulman View Post
But didn't you use red lock-tite on the screw and nut, making it impossible to move the linkage to another hole? That's what they tell you to do. It's one example of why this is a frustrating plane to build -- to answer a question posed recently. They use techniques other companies don't, perhaps to save an ounce, but they are difficult. Like cutting out slots for the control horns and gluing them in. The slots are not the right size, so you need to sand the CF horns, and of course it's hard for them to come out perfectly straight, putting strain on the linkage when in use. It looks good, but it's 10 times more work and a lot easier to make a permanent mistake (because those are glued with epoxy -- you only get one chance, unlike screw-on horns used on most models).

Those pictures I took were of the push-rod test fitted, not loctitied yet.

I kept testing those rods this afternoon, trying to pull apart from the clevis pretty hard with no indication of weakness. I think they'll be okay. The real test will be in high stress/force maneuvers. I'll just have to keep an eye on them.
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Old Nov 19, 2012, 05:23 PM
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Australia, ACT, Kambah
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Originally Posted by pilot_keeter View Post
Those pictures I took were of the push-rod test fitted, not loctitied yet.

I kept testing those rods this afternoon, trying to pull apart from the clevis pretty hard with no indication of weakness. I think they'll be okay. The real test will be in high stress/force maneuvers. I'll just have to keep an eye on them.
The servos are only capable of about 2.5 to 3 kgcm torque. If you're using say a 2.5cm servo arm, the maximum force the servo can exert is only 1kg. If you're confident your testing is well over that force, you should be good.
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Old Nov 19, 2012, 05:34 PM
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Originally Posted by scirocco View Post
The servos are only capable of about 2.5 to 3 kgcm torque. If you're using say a 2.5cm servo arm, the maximum force the servo can exert is only 1kg. If you're confident your testing is well over that force, you should be good.

Good to know, thanks for the assurance!! I'm pretty confident that it will hold. I did my best to roughen up the CF as well I putting plenty of notch groves in the rod.
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Old Nov 20, 2012, 01:54 AM
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Originally Posted by scirocco View Post
The servos are only capable of about 2.5 to 3 kgcm torque. If you're using say a 2.5cm servo arm, the maximum force the servo can exert is only 1kg. If you're confident your testing is well over that force, you should be good.
That's static loading. Dynamic loads could be much higher.

A person abseiling will exert say 80kg of static load on the rope and anchors. However, if they tie themselves with that same length of rope and leap off the edge of a very tall cliff (a "factor one" fall), dynamic loading on the rope could easily exceed 800kg or more, depending on the rope material (how much it stretches).

A servo linkage capable of (barely) holding 2.5kg statically may easily fail when the plane does a high-stress maneuver like a wall or tumble.
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Old Nov 20, 2012, 04:21 AM
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Originally Posted by H2SO4 View Post
That's static loading. Dynamic loads could be much higher.

A person abseiling will exert say 80kg of static load on the rope and anchors. However, if they tie themselves with that same length of rope and leap off the edge of a very tall cliff (a "factor one" fall), dynamic loading on the rope could easily exceed 800kg or more, depending on the rope material (how much it stretches).

A servo linkage capable of (barely) holding 2.5kg statically may easily fail when the plane does a high-stress maneuver like a wall or tumble.
I wonder whether I'm missing something here. I'd have thought that higher loads than the servo is capable of resisting would just drive the servo backwards. It's not like the control linkage is connected to an irreversible worm drive, or is like a rope fixed to a immovable anchor.

I gather holding torque, ie resisting movement, can be a fair bit higher than dynamic torque, but most vendors quote the higher static/holding torque only - Hyperion is the only one I've seen with both figures, with dynamic torque half static.
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Old Nov 20, 2012, 04:37 AM
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Originally Posted by pilot_keeter View Post
I filed everything per the manual

I went ahead and glued everything last night. Let it set overnight and tested everything this morning. The movements themselves are fine and I tried pulling the rod from the metal clevis almost as hard as I could with no budge at all. I wish I had a little more length to ease my mind, but I think everything will hold up.
You should've just trimmed the rod a bit shorter and then sourced some Dubro Threaded couplers of the appropriate size (similar to these http://shop.dubro.com/p/4-40-threaded-coupler-qty-pkg-2 ) and glued one to one end which would've fixed your problem and given you an adjustable length control rod like every other manufacturer (hint hint PA).


Quote:
Originally Posted by scirocco View Post
I but most vendors quote the higher static/holding torque only - Hyperion is the only one I've seen with both figures, with dynamic torque half static.
Which is the reason why most Hitec servos appear to be quite strong compared to the competition, the reality is they are just over rated.
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Old Nov 20, 2012, 03:39 PM
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If it comes apart in flight then so be it... I'm almost to the point of not caring anymore. I've gotten so frustrated with this build. I've tried to be patient and delicate with everything, but I always seem to break or mess something up through the process. Maybe I'm just clumsy and too inexperienced to be building this plane.
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Old Nov 20, 2012, 05:18 PM
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Quote:
Originally Posted by scirocco View Post
I wonder whether I'm missing something here. I'd have thought that higher loads than the servo is capable of resisting would just drive the servo backwards. It's not like the control linkage is connected to an irreversible worm drive, or is like a rope fixed to a immovable anchor.

I gather holding torque, ie resisting movement, can be a fair bit higher than dynamic torque, but most vendors quote the higher static/holding torque only - Hyperion is the only one I've seen with both figures, with dynamic torque half static.
It would be interesting to see a graph of force over time applied to say the elevator linkage as the plane goes into a 'parachute'. It's the extreme transients that break stuff, and given a solid carbon fibre rod there is no stretch or compression to lengthen the time over which force is absorbed and thereby reduce the transient amplitude. It's just a short, massive jolt.

My guess is that even a relatively small 3D plane like the Bandit would generate 100N of force or more for a split second - way more than the servo's ability to hold. The impulse is so short-lived that it's difficult to observe without test equipment. Unfortunately, it would also mean the link has to be capable of holding more like 10kg - rather than just 1kg - if it's to survive.
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Old Nov 20, 2012, 06:22 PM
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Originally Posted by pilot_keeter View Post
If it comes apart in flight then so be it... I'm almost to the point of not caring anymore. I've gotten so frustrated with this build. I've tried to be patient and delicate with everything, but I always seem to break or mess something up through the process. Maybe I'm just clumsy and too inexperienced to be building this plane.
Don't worry it's not you, it's just PAs way of doing things that makes everything 3 times harder than it needs to be. I've built several ARF, traditional kits, short kits, laser cut kits, and a scratchbuild or two. None of those have been as irritating to build as the Bandit.
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Old Nov 20, 2012, 07:04 PM
I'm torquing to you!
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Wattle Grove NSW Australia
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And none of them fly as nice as the Bandit either
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Old Nov 21, 2012, 02:25 AM
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Originally Posted by mr kamikaze View Post
and none of them fly as nice as the bandit either
+1
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Old Nov 21, 2012, 10:10 AM
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Panama
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Originally Posted by luke352 View Post
Don't worry it's not you, it's just PAs way of doing things that makes everything 3 times harder than it needs to be. I've built several ARF, traditional kits, short kits, laser cut kits, and a scratchbuild or two. None of those have been as irritating to build as the Bandit.
I have been in this hobby for over 15 years, and i have built kits and many arfs. The PA planes are easy to build, the instructions are very clear, yes they use different methods than standard, but if you take the time to read the instructions it isn't hard. Also they are planes that will last for thousands of flights!
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