CTX-5FBL a proper coax - RC Groups
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Feb 02, 2015, 01:49 PM
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CTX-5FBL a proper coax

After having played with the finicky Heli Baby and spent countless hours trying to get the Volker Jung coax to stop vibrating, I was wary when I saw the CTX-5FBL on Sovereign Technologys website, but, at the price, I thought I'd give it a try. It would make excellent mechanics for a nice KA 32 or KA 52 if it was smooth and reliable. So, I spent the money and bought one. This is how it went together.

  Opening the box. Inside you find a nice printed manual, a checked off parts list and 3 boxes. A long thin box contains the blades and tail boom. A big box contains the canopy with the mainmast assembly, chassis assembly and landing gear parts inside. The last box contains bags of parts all labeled.   Reading the manual, it explains to start with bag A and progress through the bags, not opening more than 2 at a time or you will get in a mess. All pretty straight forward so far, so lets get to it.

  The first construction page shows the finished assembly that you are about to build. Then it tells you how to build it and which bags to use. So we start with bag A. This is what you get and opening the bag you find the item is fully assembled and a quick check shows the screws are loctited. Easy so far.

  On to the next step, assemble the swashplate. Bag B

  Push rods already with the ball links on, close to the required length. Final adjustment will be made when the assembly is complete. So, opening the bag and checking, all is good and everything that should be loctited is loctited.

  Now for the top rotor head, in bag C.

  As you can see, it is fully assembled and taking one of the blade grips off shows the thrust bearing is greased and a quick check of the ball links shows they have loctite on them as well. Even the swash driver is assembled.

  Now we get to do some assembly.

  Take the plastic pushrod guide out of the center of the main mast. Slide the swashplate onto the main shaft, slacken off the 3 locking screws in the rotor head and slide that on. Now we get to use that bottle of loctite which has been sitting around. Remove the three 3mm cap head bolts from the head, apply loctite to the first one and screw it in looking through one of the other holes for one of the three locating holes in the top of the main shaft. Once the first screw is properly located, loctite and fit the other two 3mm bolts

  OK, this bolt by bolt assembly is getting tedious, suffice to say, all the other main parts come out of their bags properly assembled.

  These parts go into the bottom rotor assembly and the manual is clear about how to assemble it.

  This is the lower rotor head assembled, and for the first time, you will have some parts left over after the assembly. There should be two 3mm cap bolts left, which we will use later.

  Now the top rotor head assembly is slid into the lower mainshaft
  I got a bit ahead of myself fitting the links from top to bottom, the guide needs to be bolted to the bottom rotor head first. There is a small projection on the bottom of the guide which fits into a locating hole in the top of the rotor head. Once it is in, the two 3mm bolts secure the two parts together.

  Next is simple. The aluminum bearing holder is slid onto the bottom of the lower mainshaft followed by the bottom gear. The three cap head bolts locate into 3 holes in the lower mainshaft.

  Next we fit the yaw control mechanism. These are the parts we use.

  First thing to do is to remove the two locknuts from the bottom of the shaft.

  Then the bottom plastic rod guide is removed. The yaw control mechanism is slid over the bottom of the mainshaft, the plastic guide replaced and then one of the 3mm locknuts is replaced. Then the rod is fed through the yaw control unit and the other locknut is fitted. The top assembly has two pins which locate in the top rotor head and prevent it from turning. Now the links can be popped on.

  The next step in the manual is called final assembly! Opening these bags and assembling the whole mechanism took about an hour. Photographing it took 2 hours, I’m no photographer.
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Feb 03, 2015, 08:07 AM
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To continue....

The next part to assemble is the main chassis and you start off by inserting seven hexagonal rods into one side and screwing them in place, not forgetting to Loctite screws.

There also two canopy mounting standoffs which have to be screwed to the other side.

You need to note carefully the top two hexagonal rods orientation. These are used to mount the servos and the front two are close together and the back ones further apart.

Next the assembled mechanics are slid into place and four screws are used to bolt them into the side frame.

Then the other side of the chassis can be fitted, but not before inserting the two standoffs with the canopy from the inside. Then a lot of screws are used to clamp it in place.

Then the landing gear is assembled and bolted to the bottom of the chassis, four bolts, four washers and four locknuts.

This is the main Pinion and it is hardened and is running on a hardened steel shaft. The white gear contains the one way bearing for autorotation if it is needed.

I wanted to keep the cost low, so I purchased a Hobby King 1220 KV motor rather than a scorpion 1400 KV motor. Unfortunately this has a 6 mm shaft and the hole in the pinion is 5 mm so I had to drill it out on my lathe.

This is the pinion assembly fitted waiting for the motor. As I am using a Hobby King ESC I have decided to set the ESC up with the motor mounted in a vice rather than trying to do it in this assembly without any servos fitted. I'll be back when its done.

Feb 03, 2015, 01:36 PM
It flies!!! ... so who cares ?
erdnuckel2's Avatar
Latest blog entry: Random Pictures ...
Feb 03, 2015, 06:59 PM
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mihcmac's Avatar
can't wait to see it fly......
Feb 04, 2015, 09:34 PM
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Gregco10's Avatar
Good luck with this, will be following....
Feb 04, 2015, 09:45 PM
mono's Avatar
Was looking at this beast last week after noticing an ad for it on helifreak.
Price is reasonable, no more than a trex 500 combo, which seems like fairly good value to me.
Parts are reasonable too, but I'm wondering about those blades, whether they are weighted in the tips and if other blades could be substituted without affecting operation.
Just have to wait for Mr Wales to finish the build for all the info and verdict.
I do wish they would make the manual available for download, I always like to study manuals to get a better idea of the inner workings.
Feb 05, 2015, 06:42 AM
Registered User
The blades are described as trainer blades. They are solid plastic and are quite heavy. If you like flying this heli, they are the first thing to change. I took mine off and put trex 450 blades on. I found a willing retailer, prepared to go through his stock of trex blades and match me up sets to get to sets of 4 matched blades.

However for the purpose of this write up, I have to stick with the supplied blades.

I have also ordered some sets of JR Forza 450 blades which should be in next week. They make them in sets of 3 for about $50 a set and if they fly like the trex blades, they will be the upgrade of choice.
Feb 05, 2015, 07:17 AM
mono's Avatar
Ah, good, thank you for the clarification, I hoped it would be able to make use of alternative blades.
For me, this will be the most interesting build log in a long time.
Feb 05, 2015, 10:54 AM
Cá bhfuil an linn snámha?
spykez's Avatar
Originally Posted by Peter Wales
The blades are described as trainer blades. They are solid plastic and are quite heavy. If you like flying this heli, they are the first thing to change. I took mine off and put trex 450 blades on. I found a willing retailer, prepared to go through his stock of trex blades and match me up sets to get to sets of 4 matched blades.

However for the purpose of this write up, I have to stick with the supplied blades.

I have also ordered some sets of JR Forza 450 blades which should be in next week. They make them in sets of 3 for about $50 a set and if they fly like the trex blades, they will be the upgrade of choice.
That's interesting. I must have misunderstood, I thought this was "500"/430mm size heli. Didn't know it was that small.
Feb 05, 2015, 01:14 PM
mono's Avatar
on the product's webpage, rotor diameter as listed as 926mm, main blade length as 400mm (supplied blades).
Feb 06, 2015, 01:39 PM
Registered User
At last the sun is shining, but we have 25 mph winds. At least I can take some photos and explain a bit about the setup.

This is the tail boom assembly. It is very simple, just a tube which fits into a nicely injection molded carrier which is bolted through the side frames. It does have the platform on the top which I have used to hold the ESC. The supports are aluminum again with some nicely injection molded ends to bolt to the frame and stab carrier.

The ESC mounted with the on off switch glued to the boom

This is the yaw control pushrod

And the elevator pushrod on the servo

I used the same servos all round as the yaw servo is not pushing a small tail rotor, it is pushing the same size disk as the other three, albeit only one disk not two

The two front servos are fitted in the other way round with an arm pointing out each side

The rest of the electronics and the battery in its molded in holder

And thats all there is to it, except a nice canopy of course

Now for the setup, pay attention I will ber asking questions later

If you have setup a flybarless helicopter before.......then you know how to do it!

There is no phasing of the rotor heads, imbalance in the lower is countered by the upper.

For those who haven't done it before, here is a quick run down, and the actual detail depends on which gyro you select. I used a mini V-bar on my first one and was not pleased to be told I would have to pay an extra $50 to have it detuned to run rate mode. So for this one I bought a Tarot ZYX which cost $39, $11 less than the cost of the V-bar upgrade, and its seems to be working just as well although I have not yet finished the fine tuning.

Start off by setting up your gyro and servos so that the servo arms are all at 90 degrees. Hook up the servos and the set the lower swashplate level and then ensure the upper swashplate is level. It should be if the links are exactly the same length.

Now fit the blades, move the collective to mid stick and adjust the pitch curve so that you have 5 degrees of pitch on one blade grip which is exactly over the center front of the model. Without moving the helicopter, turn the rotor and adjust the next grip to 5 degrees and then the last one, then do the upper 3. Then adjust the bottom pitch curve to be -2,+5, +12.

Sovereign recommend using a linear throttle curve so you end up hovering at 50% throttle. Not many ESC's like that ,so I have a throttle curve of 0,90,90,90,90.
This allows the rotor to spool up before lift off. Now comes the only tricky part. Setting the gain on the tail gyro and getting it centered. The V-bar wants 25% but my radio goes from -100 to +100 so if your radio goes 0 -100 you would need 62%. The zyx wants a similar amount, and while not full optimized yet, I am at 60%. You need to use servo centering or mechanical adjustment of the pushrod to get the model to track correctly

And thats it, you are done doing unusual things. Take it outside and run it up, and finish optimizing gains and throws to make a nice smooth flying heli
Feb 06, 2015, 03:19 PM
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I'm awaiting your flight report to decide if I buy one of these or not, i have a couple of questions for you, I have flown rc helis for many years and have been interested in coaxials for a long time, but have no experience with their properties, so please excuse my ignorance

1) when you placed your order, how long did it take to arrive to you from China?

2) what special setup conditions, if any, are required for the yaw " collective bias" ? Do you have to mix rudder to pitch to compensate for total lift change factor?

3) once flown, I would like to know, is the tail required for weathervane effect or will it track correctly witout it and is only used for visual orientation? This is important because if I buy it, I would like to mold a Kamov 32 fuselage for it
Feb 06, 2015, 04:02 PM
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It took about 4 days to get mine, I have heard of others getting theirs in 2 days, so they are very fast, but expensive.

If you fly in a scale manner, you dont need to add any controls for adjusting the collective when you turn, you will do it automatically as if you were losing and gaining height into the wind. If you want to keep it at the same height regardless, you can add a rudder collective mix which will compensate for the rise and fall. Its just a straight line and on the turbine one I had I added 7%, but that had no head gyro.

The tail is needed for the weather vane effect. These things fly in any direction equally well. East Coast Scale Helicopters is having some KA 32 fuselages made for it and they should be available shortly. Contact them also for the CTX kit, you may find shipping a lot cheaper.

web site is eastcoastvario.com. details are on the site
Feb 06, 2015, 06:59 PM
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Gregco10's Avatar
If you would be so kind to explain. How does this heli accomplish yaw? Does it change the pitch on both or just the top rotor?
Feb 06, 2015, 09:25 PM
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If you look at this picture

The rotor disk is attached via a long rod down to the yaw servo. Along the sides of the piece under the disk are 3 mixing arms which adjust the top rotor pitch when the head disk goes up and sown with yaw servo movement