700X tail pushrod short? - HeliFreak
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Old 12-03-2016, 12:45 PM   #1 (permalink)
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Default 700X tail pushrod short?

Anyone else find that the Trex 700X tail pushrod is a bit short? Even with the links screwed out as far as I dare i still had to offset the servo arm slightly rearward to get the tail correctly set. I've built two Trex 700X airframes and both were the same, my buddy had the same problem too.

The fix is pretty easy. Take the pushrod and hold a soldering iron to the threaded rod. Once the rod gets hot the glue holding it in softens and you can pull it out quite easily with pliers. Clean off the glue residue from the rod and from the hole in the pushrod then use epoxy to glue it back in, but leave it sticking out about 4mm more than standard (it's easily long enough). Repeat at the other end.

This allows the ball links to be screwed fully in and the servo arm set at 90 degrees.
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Last edited by Grumpy_Old_Man; 12-04-2016 at 05:44 AM..
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Old 12-03-2016, 02:26 PM   #2 (permalink)
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It's not short in fact, you should put the correct ball link to the tail slider. Two ball links of the tail slider are different from the ones which are used in rotor head assembly. I had exactly same hesitation while building my 700x kit, but I realized that the length of the ball links are not all same. It is stated as 700NFL ball link in the manual.
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Old 12-04-2016, 03:18 AM   #3 (permalink)
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No, I'm using the correct ball links on the pushrod. I just double checked to be sure, they are 20.5mm overall length which is correct for the 700NFL link. They are slightly longer than the ones on the head but still not long enough to get the servo arm and tail mechanism properly centred unless the balls are screwed out so far that they are only catching on the last thread or two, which is a disaster waiting to happen..
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Old 12-04-2016, 03:48 AM   #4 (permalink)
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No issue on my end..Ball link threads in more than enough..No concerns..Make sure the boom is fully seated with the pin screw lined up with the hole in the boom..
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Old 12-04-2016, 03:58 AM   #5 (permalink)
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Well i just checked my two airframes (purchased separately from different dealers) and the pushrods are indeed short. The manual says that the pushrod should be 766mm between the outer ends of the metal ferrules. The two pushrods on my helis are exactly 760mm long, so that's 6mm shorter than the manual says which explains the problem quite nicely.

My buddy had the same issue and he's in a different country, maybe this is just a bad batch but if so it was a large batch.

It would be interesting if others could measure the actual length of their pushrods.
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Old 12-04-2016, 04:20 AM   #6 (permalink)
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I think that the mystery is solved. The 700X pushrod is according to the manual supposed to be 766mm long (page 20 of the manual). This makes it a different part to the 700L pushrod which according to part number H70073AT are 760mm long.

So it seems that the pushrod in the kits that I and my buddy have are the old 760mm 700L pushrod (part #H70073AT) and not the new 766mm rod specified in the 700X manual. I'm not even sure if Align actually make a longer rod, maybe they thought that the old rod would be 'good enough'?

So the mystery is how come everyone hasn't had the same problem?
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Old 12-04-2016, 05:03 AM   #7 (permalink)
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Good find..Hopefully we can get some answers
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Old 12-04-2016, 05:17 AM   #8 (permalink)
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That is another reason why I'm still skeptical about getting the claimed "best" Align model.
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Old 12-04-2016, 05:43 AM   #9 (permalink)
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Quote:
Originally Posted by RFCXPerT View Post
That is another reason why I'm still skeptical about getting the claimed "best" Align model.
It's a minor detail, certainly nothing to put you off buying the heli. If you follow the procedure I mentioned in my original post it can be fixed in ten minutes.

Worry is the guys who dont spot it and maybe have the links screwed out too far so that they pull off in flight.
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Old 12-04-2016, 10:17 AM   #10 (permalink)
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Quote:
Originally Posted by RFCXPerT View Post
That is another reason why I'm still skeptical about getting the claimed "best" Align model.
Really? Don't let this stop you.. like I stated mine is fine a well as many others
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Old 12-04-2016, 10:48 AM   #11 (permalink)
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grumpy,

Any way you can actually measure the rod supplied in your kit? I do see the manual does state 766 however there is no part # associated with that to the best of my knowledge. There are 2 control rod versions part # H70073A which is 760mm and # H7NT005XXT which is 778mm.


I just compared a NIP H70073A to what came on my 700X and they are exactly the same length, and the links screw into enough thread.
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Old 12-04-2016, 10:50 AM   #12 (permalink)
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And here is a shot I got with them lined up. I believe the 766 in the manual is a typo, and if yours is indeed not the right length, there may have been a short run of a bad length. There are many kits out there now, and I haven't heard of anyone having this issue so I may just assume it's a one off issue. Just reach out to where you purchased the kit, I'm sure they will supply a replacement.
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Old 12-04-2016, 11:09 AM   #13 (permalink)
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Mine are both 760mm but that's not really long enough. If i screw the ball links out far enough to get everything lined up correctly then the links are only hanging on by three threads. This is made worse by the fact that the first couple on mm of the link bore is not threaded.

I've just double checked. The ball centre to centre of my assembled pushrod is 804mm. With the supplied 760mm rod that literally gives three turns of thread engagement on each end, that's not not enough for comfort IMHO. Added to that if the builder didnt exactly equally distribute the thread engagement he could end up with one link hanging on by a single thread.

It's not an issue for me as i have fixed it as explained in the first post.
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Old 12-04-2016, 11:36 AM   #14 (permalink)
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I understand what you're saying. My servo horn is at 90 degrees and everything lines up fine with enough threaded in on each end of the control rod.
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Old 12-04-2016, 02:26 PM   #15 (permalink)
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It looks like mine is no different from anyone else's and all ll the rods are 760mm rather than the 766mm specified in the manual. I just wasn't happy with only 3 turns of thread engagement into plastic on such a critical component. Possibly I'm worrying about nothing but it's such any easy mod and costs nothing that in my mind it's better to be safe than sorry.
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Old 12-04-2016, 02:34 PM   #16 (permalink)
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I just measured mine, it's 760mm. I have a little less thread showing than nynextel and everything is 90. The difference could be what is considered 90 on the tail linkage. Pics?
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Old 12-05-2016, 03:58 AM   #17 (permalink)
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The image in post #11 is exactly what mine looked like.
I know it looks like there is plenty of thread engagement but what you dont see in the pic is that the first 2 or 3mm of the plastic ball link has no thread, it's a loose fit over the rod. The actual part that takes the thread starts close to where the plastic link thickens. I can see in that pic that nynextel only has about three threads engaged. If he's happy with that then fine but I wasnt.

Here is an illustration to show what I'm referring to:


But dont take my word for it, check how many turns of engagement yours has.
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Old 12-05-2016, 05:12 AM   #18 (permalink)
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Here's a video to show the issue:

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Old 12-05-2016, 11:32 AM   #19 (permalink)
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Mine stayed the same.
So far no problem
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Old 12-05-2016, 12:48 PM   #20 (permalink)
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I'll just add I have numerous flights on my 700X with no issues, and hundreds on my 700N with the same length push rod and links as well.
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