Urukay Building Tips

[A VIKING]

Fit and finish of the Urukay in my kit was outstanding...including the tail boom. In past 770 builds I had to sand a little here, grind a little there to make it fit the fuselage mount but the Urukay boom was a perfect fit in every way requiring no re-work.

Three bladed heads:
In building up the Goblin heads, main or tail, be it two or three bladed, you must get the thrust bearing race stack up correct on the spindle. The thrust bearing race with the larger ID must be installed first on the spindle. Just looking at them is very hard to get it right with a size comparison if you don't use a micrometer and you do not want to get it wrong.
....so take a trust bearing race and slide it over the spindle, now rock it back and forth with your fingers....the bearing race with the larger ID will rock back and forth noticeably farther than the one with the smaller ID, its very easy to see and feel the difference. If you go through all of the races before assembly and create two separate stacks, one with larger ID and one with smaller ID, you can quickly and confidently build up the head assembly.

The fit of the Urukay head on the mast shares the same play between the two that I had on the 770s. With the two bladed heads you have two pinch bolts to squeeze the head on the mast which for me on two 770 builds was never enough to do the job, I would always find the head loose on the mast after several flights. More torque on the pinch bolts never corrected this.
With the three bladed Urukay, you only have one pinch bolt for the head.
My fix on the 770s was to put a little blue thread lock on the mast before installing the head and after installing and torqueing the attaching hardware I never saw the head loosen again and this is with hundreds of flights.
This trick will be utilized on my three bladed Urukay as well.

I mentioned this before, but installing the nut plates in the tail boom for the tail rotor box should be done accurately the first time. The nut plates are installed with double sided tape to hold them in place and you have to put them inside the small end of the tail boom lining them up with the bolt holes then stick them to the tail boom wall.
The tape is real sticky so you get one try...make it's the only try.
I stuck the bolts through the tail boom holes to capture the nut plates first then pulled the nut plates back against the tail boom wall, sticking them in perfect alignment with the holes.
I am surprised they used thick foam double sided tape to secure the nut plates in this location. To really secure the tail box and keep good belt tension the clamping of the tail box to the boom is very important so a solid torque on the bolts is needed. The foam tape will compress and not provide the solid clamp up I would be looking for.
If I loose belt tension constantly, I will remove the tape and go with the nut plates solid up against the boom wall.
If the belt tension stays set...SAB was correct in the design.

Overall I was very impressed with the fit and finish of the Urukay, its fantastic.
I am still coming up with ideas with what to do with all that space under the canopy.

[jsbach#1]

Have you given much thoughts to the power system ? I see in the manual they don't list 14s as a configuration. I suppose its not necessary for the style of flying that the urukay is intended for ?

[A VIKING]

Originally Posted by jsbach#1

Have you given much thoughts to the power system ? I see in the manual they don't list 14s as a configuration. I suppose its not necessary for the style of flying that the urukay is intended for ?

I'll be staying with a 12 cell Pulse and the Quantum motor. I don't fly hard smack so for me this should be perfect. Passing 670 flights with the Quantum in my 770 so that's why I will stick with them. I am going to try out a 45C Pulse 12 cell battery in the Urukay. That will be a 300 gram weight reduction compared to the 65C batteries I fly now in the 770.
Looking to get the magical greater lift from the 3 bladed system and lighter weight to enhance it even further.
That's my plan anyway.

I see they offer a Derlin guide for the anti rotation pin of the swash plate.
This is a good thing as I have worn out three pins on my 770. The carbon fiber of the guide just saws through the pin making a lot of play.

[Joe Bailey]

One point I picked up on in the manual, they tell you to CA the rods into the carbon push rod. From many years of personal experience this is a sure fire death sentence. I've had this method fail on countless planes and 3 helicopters.

Epoxy all the way for me.

[A VIKING]

Agreed Joe...epoxy all the way when building up tail control rods.
I build them old style by seating the threaded rod in the carbon control tube with epoxy.
I scratch up the smooth shank of the threaded rod with course sand paper.
I put some epoxy in the tube with a little on the threaded rod then slowly turn the treaded rod while pushing it into the tube. This insures a good bond line over the entire end of the threaded rod in the tube. If you just put some epoxy in the tube and push the threaded rod in, it will push the epoxy down the tube and not provide as much bonding over the entire shank of the threaded rod with the carbon fiber tube.
Once the epoxy dries then its black tread wound around the end of the carbon tube set in place with CA glue, then follow that with heat shrink to make it pretty.

I do a couple other things when building up tail control tubes.
I never build the control tube up until I have the tail boom built up completely and installed on the fuselage with tail rotor drive belt tension set and the tail servo installed.
Set the servo arm to mid travel and the slider bell crank of the tail rotor to 90 degrees then use the dimension between the two to set the exact length of the control rod with the threaded plastic control rod ends in the center of their adjustment....Perfect!
If I try to set up the dimension of the control rod per the instructions, I always seem to get it a little long or short so I have learned, for me anyway, its best to do it last.

The very last thing I do after tail rigging is paint the silver portion of the threaded rod that protrudes from the carbon fiber control tube flat black. This does two things. It makes it pretty but more importantly if your bond in the tube should start to fail and the threaded rod start to pull from the tube, it will create a silver ring in the flat black paint that is very easy to see letting you know failure of the tube is close at hand.

[A VIKING]

This should work for most servos if yours have a flat surface to work from.

Always trying to get it perfect and after 3 Goblin builds I finally figured out something when setting up the servos, servo links and pitch links to get the perfect level swashplate at mid stick with pitch.

The instructions say to set the servo horns at dead center with pitch at mid travel, set the length of the servo links which I do with a micrometer to get them matched, install the servos, install the servo links, then set swashplate level at mid pitch.

Every time I get to this point I always see the swashplate is off level? How could this be, the servo arms are set to dead center and the servo links are matched as a set, so the swashplate should be level with no adjustments right?.

I finally saw the error in my ways. When I read "install the servos", I just install the servos.
Anyone notice how much wiggle room you have with the servos in the mount before tightening the screws...there is a lot. When tightening the servo screws, where is the servo in the mount? At the top of that slop, at the bottom or tilted sideways?

So now I use a precision steel scale from my square to insure the servos are all mounted in the same plane and are not cocked in their mounts.
Just lay the steel scale across to adjacent servos and look for any gap between the servo and the scale.
If you see daylight at any point the servo is either cocked or at a different height compared to the other.
Loosen up the hardware and reposition the servo to eliminate the gap between it and the scale and you have just matched the two servos together on their mounts.
Now do exactly the same thing for the third servo, comparing it to the other two, adjust the servos as necessary and now you have all three servos mounted in the same plane.

Now check swashplate level...it should be level or super near level if you set everything up properly and with no servo link adjustments.

Now go have a piece of leftover turkey.

[A VIKING]

Regular heat shrink is good for protecting chafing wire but I found something even better. Marine Heat Shrink.
This stuff has a rubber glue inside which melts and provides a water tight seal as the tubing shrinks.

I am not looking to prevent water intrusion but I am looking for something to "glue" the heat shrink in that special spot to protect the wires.
For whatever reason regular heat shrink has a tendency to be to big or small to fit over the standard size plug used in my harnesses but the Marine Heat Shrink has a slightly larger diameter I believe because of the sealant which allows the tubing to just slip over the plug end of the wire with a little push through the tube using a small Allen Wrench or similar pushing device to gently push the plug through.
Once over the plug you can slide it to the location where you want it to reside and shrink it down with a lighter.

There is one other benefit to using this stuff...it moldable before it cools off.
If the wire you are protecting goes around a corner or the edge of something, you can mold or bend this heat shrink tubing to what ever curve you want and wait for it to cool holding that shape.
When cool, you have a perfect curved protector for your wire.

See my photos in this thread to see it in use.

[A VIKING]

Anyone else have a good building tip for the Urukay or any other Goblin as these ideas are good for all.
Feel free to post your ideas here!

[A VIKING]

I used the Marine Heat Shrink in some more areas on my Urukay and I am telling you I can't recommend this stuff more highly.
Let me give you a run down of what I have discovered.
It's a heat shrink of course but in a very different way, it has sealant in the tube that melts with heat.
This was meant to produce a water tight seal but it does something amazing in protecting our wire harnesses.
I mentioned earlier that it fits over the standard 3 wire servo plug so you don't have to remove the plug to slide it over the wire like you would standard heat shrink.
Standard heat shrink, after it has been shrunk down, likes to keep a straight line.
The Marine Heat Shrink can be bent into any shape you want and after it cools will maintain that shape. The sealant inside the tube acts like sand in a pipe when bending it. It prevents the tube from collapsing when being bent so you have a beautiful radius bend without a kink.
If you have an area where you want to both protect and provide a route for the wire to travel you just have to shrink the tubing over you wire and while its still warm and soft, route the wire on your ship holding it in place while it cools. Once cool, the tubing will maintain that special shape to match the contours or edges of the ship.
If you have a long route with many bends you can measure and draw the route out on a piece of paper, cover your wire with the Marine Heat Shrink, heat it up to shrink the tubing and melt the sealant, then simply place and hold the harness over your drawing and like magic you have a custom harness that fits perfectly in your ship and the wires are bullet proof.
If the harness you made doesn't fit perfectly, no worries, you can heat up the area that needs tweaking and try it again over and over and over until you get it perfect. The sealant reacts to heat and as such can be melted over and over again without damage.
You guys in the U.S. can find this stuff at Harbor Freight.
I recommend this stuff highly. Try it out, you will love it!

[jsbach#1]

I've seen this enough times its worth mentioning. Some peoples servo is jammed in the corner against the bearing housing very tight. In these cases where the servo sizing is such that you are jammed up against the centre bearing housing you should put a shim (provded in the kit I believe) between the servo and the mounting lug so its clear, this will minimize vibrations going into the servo, also minimize strain on the servo housing as the bolts are pulling the housing in a cantilever effect if you know what I mean. Attached a pic to show the location I am referring to.

In turn pulling the servo away so its clears the centre bearing housing may introduce a new problem, the outside right corner of your servo is lodged up against the goblin fiberglass canopy. No all canopies are the same but its also common to see the paint cracked there.

570 canopy is extra large in this area its never a problem, but my 770 is tight.

[A VIKING]

Thanks jsbach#1.

I never noticed that issue until you pointed it out to me.
I checked the servos on my 770 and yes they just barely touch as well and your right the 770 canopy is tight against the right hand servo.
The Urukay has plenty of room.
The servos sit squarely on their mounts so the contact is slight but its still there.
I think there may be enough play in the mounts when installing the servos to allow them to "slide over" a bit so the contact isn't to great.
I have 670 flights on the 770's with just a small dark rub mark on the bearing housing.
Doesn't mean it's ok, just means I have been lucky.

I'll make up a shim to provide a little clearance. It won't take much.
I have learned something new today.

I appreciate it and so do my servos!
Thanks!!

[jsbach#1]

My pleasure ! I suspected from the pic and the Savox servos appearance, yours was either just clear or barely touching. A little is okay I suppose reinforced by your results after 670 flights but I have seen them bad, where its really contorted looking.
Now just imagine how much vibrations the nitro birds have in their servos, much more than what that centre housing will transfer.

[A VIKING]

Just took my Urukay out for its maiden flight.
On the first spool up, I never made it to flight RPM.
I had noticed the lateral guide for the tail rotor control tube was within an 1/8" of the belt after installation. The belt was properly set in tension.
I had an issue with my 770 where the belt would contact the top of the tail servo wearing the paint off the top right hand rear screw. I fixed this by adding shims to the mount of the servo effectively lowering the servo out of the way of the belt. This contact would only occur with heavy loads being placed on the belt.
The Urukay has two guides in the assembly, one primary guide for the rod and one that controls lateral play of the rod in the primary guide.
This lateral guide sticks up higher than the primary guide and put itself in harms way of the belt.
During spool up, all was normal until the acceleration of the motor became greater which loaded up the tail belt causing it to sag slightly allowing contact and a very loud grinding sound as the teeth of the belt passed over the lateral guide.

This is a fixed installation at a fixed point in the boom so a new guide will be necessary for me.
I will try to mod up a better guide for this location as this one for me does not work as it should.
Those of us who take pride on running a straight control rod better get used to running one with a pronounced bow in it.
The Urukay is one of those ships that a bow will always be present. Doesn't seem to affect flight however so no worries.


So the lateral guide was removed and I tried it again.
This time smooth quiet spool up to my initial target RPM of 1100, which by the way, don't go there, its way too slow. The Urukay wallows around like a drunken sailor at 1100 RPM.
So I switched to Idle 2 which was set to 1500 RPM and that was much better and will be my normal RPM setting.

So at 1500 RPM, my wife said it best when describing the sound of the Urukay in a stabile hover....she said the refrigerator makes more noise.
And she is right, the ship is so quiet its unbelievable.
And before I am tormented with comments that we need a new fridge, the fridge is only a few years old, the Urukay is just that quiet.

So for those building this ship, take a look at the tail control guide before you maiden to ensure it won't contact the belt and scare the crap out of you with the noise it makes.

I need to make some flight control adjustments and bump up the RPM again but now that the maiden is over...it's a piece of cake.


For me there are no other issues, I like this bird!

[Joe Bailey]

I find 1500 a bare minimum for 3d on a two blade heli, that's all tik tok manoeuvres, funnels waltzing loops, piro loops etc. any less and you struggle for power and grip almost in the air.

[Joe Bailey]

I've just looked down my boom and damn that clip is close, what have you done to make room inside the boom?

[A VIKING]

Originally Posted by Joe Bailey

I've just looked down my boom and damn that clip is close, what have you done to make room inside the boom?

I just removed the lateral guide from the boom and left the primary guide in place.
So far I don't detect any rubbing.
I am going to mod the primary guide to prevent any possible excessive lateral movement of the control rod in the guide.
Shouldn't be a big issue. I really would like to know SAB's thought process on this set up and why it was designed that way.
I may mod the guide to be not as tall also. That would remove some of the bend from the control tube and free it up to slide past the guide a little easier.

...on a side note I had the same issue with binding that I have had with all my Goblins with the tail control slider.
After build up the slider would bind and if you couple that with the bend in the control tube I am sure you would end up with the tail wag from hell. I had to loosen all the hardware of the tail box and flex the assembly around until I found the spot where the slider would slide freely with no binding.
The issue comes from the tail rotor drive shaft not being supported squarely by the side plates.
If they are not perfectly positioned with their support bearings being on line with each other providing a perfect 90 degree orientation of the shaft to the right hand side plate where the tail slider assembly is mounted, that miss-alignment will cause the slider to bind on the output shaft.
I really wish SAB would address this as it becomes a pain to correct every time.
On my 2 770's I had to shim the tail box assembly to the tail boom to fix the slider binding on them. The ID of the tail box assembly was larger than the tail boom OD and when you bolted the two together the side plates would be forced inward to the tail boom causing the tail shaft to be driven off the needed 90 degree position to the right hand side plate which would cause the slider to bind.
The tail box fits well on the Urukay tail boom requiring no shimming, but the problem still persists with the binding slider because of the design.

And again...these issues are pretty small, just wish they would be corrected.

[jsbach#1]

So I'm curious what are your thoughts on how the heli felt being a 3 bladed head and having individual spindle shafts vs a 2 bladed head with a solid shaft. And how about the "floatiness" factor vs your 770. I will get a red one as well

[A VIKING]

Originally Posted by jsbach#1

So I'm curious what are your thoughts on how the heli felt being a 3 bladed head and having individual spindle shafts vs a 2 bladed head with a solid shaft. And how about the "floatiness" factor vs your 770. I will get a red one as well

Not enough flight time in yet to make a proper comparison with the 770.
I am still in the tweaking phases with the FBL and RPM selection.
Weather and work have prevented advancement with adjustments.

All I can say for fact right now is that its super quiet which for me flying just outside the subdivision is being a good neighbor. With the 770 some of my neighbors in the beginning who didn't see the ship flying thought I was using a wood chipper.

Second...its very low in vibration. After the first flight, I downloaded my Skookum files to have a look and couldn't believe how smooth it was.

You'll enjoy this ship. It was a pleasure to build...just don't use the lateral support for the tail control rod unless you like the sound of a baseball card in bicycle spokes.

I would like to hear from anyone else who has had that issue so we can ask SAB...what's up with that.

[A VIKING]

We got into a discussion about different methods of tail control rod build up on another site and to see just how strong the 5 min.epoxy (not CA) joint was with holding the threaded insert in the carbon control tube I did a little test with an old control rod from a crashed 770 of mine. The results were what I expected, check it out.


So how strong is the threaded insert set in epoxy with thread wrapped around the carbon fiber 4mm control tube soaked with CA with heat shrink over the thread wrap?

Check out the photos.
That's a 50 pound bag of concrete followed up with a 100 pounds of concrete supported only by the tail control rod assembly.
I used the standard SAB ball ends threaded on the inserts.
I put drill bits fitting the holes of the ball ends to distribute the load properly in the plastic ball ends.
Then gave it the heave hoe.
Any questions of strength?
Like I said earlier, those who have crashed ships with control rods built in this exact same way, did it wrong.
This control tube had 421 flights and hit a tree in the 770 crash and still pulled 100 pounds with no issue...other than my back.

Check out the split test of the rod with the threaded insert.
The steel threaded insert bent but the carbon fiber tube did not split.
Lets hear it for the strength of CA soaked thread!

One last point of instruction with this...DO NOT thread the ball ends on the inserts until at least 12, but preferably 24 hours of cure time has elapsed for the epoxy. I know it says it's "5 minute" epoxy but in this area you can't take the chance of failing the glue joint before it truly cures.

[A VIKING]

A couple more notes on the Urukay.
When setting up this ship think speed and power for the drive train.
Like the 770 its a big ship so in order to find flight performance like the advertising video, a good power system is necessary. Set it up with a good ESC, motor and battery combination.
I think the advertising of the performance of this ship is correct also in order...sport...F3C...3d.
With 3D being softer like the 770.

It still amazes me how quiet and vibration free the ship is.
I have revised my normal RPM setting to 1500 and that is a slow rotor speed for this ship but a good cruising around setting. idle up speeds should be a fast as you can spin it, with 1900 being the recommended high side rotor speed as per the manual.

I thought I could run a lower rotor speed with the 3 bladed system but I find myself back with 2 bladed speeds which is just fine.

The bigger issue is the tail control rod guide.
I am removing it today for modification. I can not pull any significant power at all without banging the tail drive belt into the guide making a big noise.
I am going to cut it down in height at its mount to make it sit lower in the tail boom and hopefully get enough clearance for the belt to dance in the boom during 3D without contacting the guide.
The tail control rod has a significant bow in it anyway from the guide position so lowering the guide will also eliminate some of that as well and allow for smoother control rod movement.

If I can create a better situation with the guide I will post photos. Flight tests will tell the story.
I just don't see how SAB made the OEM guide work for them.
It very straight forward in it's installation. It can only be installed one way and can't be screwed up by the builder. I don't get it?