Roban AH-1W Cobra 700 Size Scale Helicopter

[DCORSAIR]

First of all... cool that yours came with that motor mount. Mine didn't... and I bought it after market from scaleflying.de. I also plan on getting their gear upgrades; that replace the top two gears that are above the belt gear and motor pinion. I have a touch of slop in mine as well... but some will be taken out of the drive train when you mount the motor/belt. Just be careful to not over tighten the belt, as too much tension will pull the belt gear down ever so slight and it will rub the top of the vertical drive shaft that goes to the tail boom; the spacing between those two gears is minimal. Here's video I found just about a month ago, that will show how to mount the motor bracket and belt tension. It's in German, but it's easy to tell what he's doing and get the idea.

Did you get the pkg of shims?, but no support bracket?

[DCORSAIR]

Here is a picture of how the motor shaft support bracket mounts to my Hughes 500 and a picture of my instruction manual for the Hughes 500-800 size, hope it helps you guys with yours, there is a top and bottom to the bracket, those standoffs fit into little round holes in the bottom of the bracket.

[sfcfury]

First of all... cool that yours came with that motor mount. Mine didn't... and I bought it after market from scaleflying.de. I also plan on getting their gear upgrades; that replace the top two gears that are above the belt gear and motor pinion. I have a touch of slop in mine as well... but some will be taken out of the drive train when you mount the motor/belt. Just be careful to not over tighten the belt, as too much tension will pull the belt gear down ever so slight and it will rub the top of the vertical drive shaft that goes to the tail boom; the spacing between those two gears is minimal. Here's video I found just about a month ago, that will show how to mount the motor bracket and belt tension. It's in German, but it's easy to tell what he's doing and get the idea.

[DCORSAIR]

Well, if you have backlash in all the umbrella gears and add all that up by the time it gets to the tail, you will have some play, my Bell 212 was the same way so I added a few shims and it still had a lot of play by the time you got to the tail, I would still check all the gears to make sure you don't have one with excessive backlash.

[PawPaw]

Thanks! Makes sense now that you explained everything. I’ve already learned that just because the factory assembled it one way doesn’t guarantee it’s the correct way. The main unit gears are smooth. The slop at the tail rotor hub must be in the elbow itself unless the shaft spline races are wallowed out some.

[DCORSAIR]

Well, I will give it a try on your questions, yes the long side of the elbow goes on the long boom coming from the mechanics, yes you will have a little play in the gears but go through all the gears and make sure you don't have some that are about to skip teeth, a little backlash on the gears is fine, if too tight then you will get excessive wear, and the T looking part in your picture with the bearing in it and those long standoffs are for your motor, if it has a long shaft sticking out past your motor pulley, you add that part to help support the long shaft, if not enough shaft is sticking out past the pulley then that part won't fit and you just leave it off, those washers you see in the bags are shims for the gears and such if you have to tighten up some of the umbrella gears, hope I am right on some of your questions, if not, I'm sorry.

[PawPaw]

[PawPaw]

Oops....hit the wrong button:

1. The tail rotor torque tube “elbow” has a longer end & a shorter end. The grainy pic seems to show the longer leg on the long tube. Is this correct? I had to reverse the linkage triangle to install it this way.

2. My tail rotor hub has 1/2” play back & forth before the torque shaft bevel gear will rotate the main. Is this normal? I can’t imagine one or both of the tail shafts stripped before my motor even arrives.

3. I have what looks like a different design tail rotor shaft bevel gear bearing block & shims from what was installed at the factory. Was in a separate plastic bag. A separate amendment sheet says nothing about replacing the existing bearing block nor a diagram of this part. Ideas?

Thanks for the help!,

[PawPaw]

HELP, y’all! I’m still trying to rationalize this sketchy manual with such a precision machine. Hopefully I’ll get a thumbs up on my guesswork so far:

1. The

[DCORSAIR]

Okay, didn't know if you seen that is was off, my big 800 has the predrilled hole in the boom as well but its not perfect either, I have to be able to move mine a little to get the vertical T tail straight then tighten the two clamp screws, that screw is on there to hold the tail unit from coming off is all, so on mine, the hole is a little bigger than what it comes from the factory, you might have to do the same to be able to get everything straight and then you will be able to move the tail pitch arm over so the rod doesn't hit the fuselage? I'm sure I will have to do the same on my Magnum Pi version as I did on my AH-6.

[sfcfury]

I see it; I just don't know where that tilt would come from. You have the nipples that are inside the elbow... on each end. For the long tube side and short tube, and those are aligned. The tail assembly itself is aligned in the pre drilled hole as well.... I'm going to take it apart and double check everything.... *shrug. Clearly it needs some duct tape...

[DCORSAIR]

So your whole tail rotor is not off then? In your pic is doesn't look square with the fuselage?

[sfcfury]

Yea I was thinking of finding a way to push it center (foam etc), in fact I was thinking about putting some extra foam/dampening material before the elbow as well. The tube caught the notch/nipple that's in the elbow/gearbox. Perhaps i can try to push the mechanics in front to the right lol... not that there's any wiggle room.

[DCORSAIR]

The upper tail pushrod catching at the very top... It's like the boom is just a hair off center. I dremeled a little bit off already, but it's still touching.

Sounds great to me, but looks like one of the reasons the rod is hittiing maybe, you need to square up your tail rotor shaft with the fuselage, that will swing the control rod back to the left, the whole tail unit looks off to me, I had the same problem with my Roban Bell 212, but it just needed a little dremel work at the top of the fuselage, had a little lip on it and was snagging the linkage also I put some foam around the top of the boom and a little more on the right side and this pushed the boom over a little to clear the linkage even more plus I always add foam anway to help dampen any vibes back in the tail section, just make sure you don't stuff to much and jam the rod.

[sfcfury]

The upper tail pushrod catching at the very top... It's like the boom is just a hair off center. I dremeled a little bit off already, but it's still touching.

[sfcfury]

So I did my first run up with the fuselage on... just looking for any crazy vibrations... seems okay. Gonna have tinker with the the upper tail rod link; its catching on the very tip of the tail piece... here goes the dremel again lol.
The first speed it spools up to is 1050 which its at about the 25 thru 30 sec mark, then I pass through 1350 for about a second lol, and then the end 30-35 secs is at my throttle 2 which is 1400rpm (which I think will be my flying speed).

[sfcfury]

I think more what might scare me... it just seems tall... like it would wanting to teeter... a little bird with stork legs . I like it tho! Likes like it flies nice!

[DCORSAIR]

I like the look of the tall struts myself, just not on the AH-6, it needs the short struts to look right, oh well it is what it is, maybe one day I will experiment with the idea of cutting down the strut length, I do have a brand new set to experiment on, or wait until I crash it, then it will have shorter struts I'm sure.

[sfcfury]

Nice! I ended up trimming my skids by an inch on my 500 AH-6 as well. It has always confused my why they went with the tall skids on the 800 versions.

On another note, this thread has caused me to get the Cobra down from the shelf and look at getting back to it. I’m planning on rigging the FLIR and gun for servo movement, and am considering adding a spinning barrel to the gun as well. I’ve though about using a jack screw (like the LX actuators) but I think it would look too slow. Anyone have any suggestions on a small motor/mechanism to spin up the barrel?

That's above my skillset!! LOL... That's the reason I come here to see how to do those kinds of things

[F106DeltaDart]

I actually cut an inch off of my skids... going into the frame and the actually 'skids' lol. I've been looking at the 800 size AH6 (and there's a white navy OH6)... they just look so tall to me... like the skids seem dis-proportionally sized. Yea I saw that you had flown yours as well! I swear these roban kits should be labeled as 'you will need to purchase a dremel tool'!

Nice! I ended up trimming my skids by an inch on my 500 AH-6 as well. It has always confused my why they went with the tall skids on the 800 versions.

On another note, this thread has caused me to get the Cobra down from the shelf and look at getting back to it. I’m planning on rigging the FLIR and gun for servo movement, and am considering adding a spinning barrel to the gun as well. I’ve though about using a jack screw (like the LX actuators) but I think it would look too slow. Anyone have any suggestions on a small motor/mechanism to spin up the barrel?