Roban AH-1W Cobra 700 Size Scale Helicopter

[F106DeltaDart]

Following all of the discussion on the mechanics closely. Hoping to get mine to fly on the test rig soon. I am continuing work on the gun turret at the moment, and finished up adding the servo for gun elevation. Used a 5 gram servo that barely fit inside the housing and some old 450 ball links to get it working. The movement range actually mirrors the real thing pretty closely. I also cut open the bottom of the turret, as the real is open as well for maintenance and ejecting casings. I’m still debating whether to add the cover plate on the turret or not around the barrel. In the States, it is kept on, but it is usually removed in combat environments for accessibility to the gun.

One other thing I’m still trying to figure out is a mechanism to trigger the gun barrel rotation. As of now with the retract motor board, the barrel spins for 4 seconds when triggered. Does anyone know of a receiver activated switch that I could use to trigger it? Would be nice to be able to fire it for different intervals other than 4 secs.

[sfcfury]

I think the mechanics for the 700/800's are all about the same... seems like the only changes are whatever they do to adjust for the type of tail drive train setup... but the top half seem to all be identical.

[DCORSAIR]

Oops right...sorry..700 size.
I also have the Airwolf, Huey and 500 which are 800.

Dean

I had to go back and look to make sure it was 700 size, not that it matters, I don't know how big your 800 Huey is, but these Hughes 500 are very big, that is one reason I bought another one, but that Cobra is on my list.

[Helijet]

Oops right...sorry..700 size.
I also have the Airwolf, Huey and 500 which are 800.

Dean

[PawPaw]

According to the video mine is set ok. My Scorpion is a 38mm shaft but I was able to get the lower shaft bearing support plate installed & a couple mm’s of shaft is still protruding. Not as long as in the video but enough to get the full benefit of the bearing.

[DCORSAIR]

Thanks! I have posted that video a couple times in the thread as well... I found it after the fact of course tho!

Same here, after the fact....

Thanks for your help sfcfury, really appreciate it.
So I went back and adjusted my belt again, made sure I could twist it a little and squeeze it together like the video, it does seem to turn smoother, so now I will for sure adjust my AH-6, its way to tight.

[DCORSAIR]

Here is how to do it

https://youtu.be/iEqE7KebqmY

Belt tightening around the 6:00 minute mark.
The Cobra is my favorite of the 800 series.

Cheers
Dean W.

Well thank you for the video link, mine is coming back apart for sure, by that info, I have my belt a little to tight on my Magnum PI and for sure on my AH-6, I noticed he put his pulley with the set crews at the top near the motor, I tried that but with the short shaft on my motor I was not able to track the belt properly because I couldn't go up anymore, mine works great with the set screws at the bottom, kind of wish I would have bought the Hacker like he has so I could use that extra bearing support, oh well, I'm not buying another motor right now, in this thing too much already..............

Helijet, I do believe the Cobra is a 700 size??

[sfcfury]

Here is how to do it

https://youtu.be/iEqE7KebqmY

Belt tightening around the 6:00 minute mark.
The Cobra is my favorite of the 800 series.

Cheers
Dean W.

Thanks! I have posted that video a couple times in the thread as well... I found it after the fact of course tho!

[Helijet]

Here is how to do it

https://youtu.be/iEqE7KebqmY

Belt tightening around the 6:00 minute mark.
The Cobra is my favorite of the 800 series.

Oops..right its the only 700 I have. The others are the Airwolf, MPI 500 and Huey

Cheers
Dean W.

[sfcfury]

DC, I would imagine the belt would give a little bit after some use... and if it has caused any problems you should be gtg. I knew by the 3rd hover flight that something was messing up. Just something to just watch for. I think if you can pinch the belt in some and give a little bit of twist, that should be right about were you want it.

[DCORSAIR]

I think I originally had my about how tight as DC is describing on his AH6... so much I probably could barely put any twist on the belt; but I don't know the tail mechanics setup on the AH6 800 size... but that amount tension lead to the problem. This go around I have it so that when I squeeze the belt from the middle (middle being from motor pulley to big gear) I can get about a 1/2 in of push... and about a quarter twist in the belt. I had it a little bit looser than that at first, and that actually gave a lil slop in the tail mechanics as well.

I thought the belt on my AH-6 was to tight when I got it, just haven't taken it apart to adjust it yet, so on my Magnum PI version I have the belt adjusted with a little less tension on it, so hopefully I have it about right, it's a little tight, I'm thinking is will loosen up a little more after a few flights anyway and should be just right.

[PawPaw]

Maybe so. Mine looks the same from your pics but a long way from trying to install it. Can’t tell if the vertical tube’s plywood bulkhead in the tail is drilled the same ‘tho.

[sfcfury]

I would wait and see... again my whole kit is a lot older than yours... and even after I double checked the tail rotor vertical alignment (and actually shifted it a smidge to the right to make it completely vertical and aligned) it didn't correct the problem... it kinda made it a little bit worse... Your's might align perfectly dead center... I think it's just one of those things when it comes to these types of kits...

[PawPaw]

Sorry, sfc....didn’t see your answer after my question! I guess I need to order those crank arms also, then. Figure mine will need ‘em too.

[PawPaw]

Never mind....answer is yes. Pretty simple to reverse the 3 servos in the FBL programming so all is well.

[sfcfury]

So I remembered I had ordered these crank arms from microhelis.de and it can be built up kinda as tall as you needed, and set for left or right... and just so happens that the servo arm itself was a touch longer! So that's my fix for my tail pushrod!

[sfcfury]

Shouldn't affect the swash plate... I just looked at the talon card, so yea it says reverse it on the transmitter for futaba.... Pitch slider is what affects the swashplate going up and down...

[PawPaw]

Anybody using Futaba with a CC Talon ESC? It arrived today & I read that I must reverse the throttle direction in the Futaba for the Talon. Will that affect my 3 swashplate servos in collective as well?

[sfcfury]

I think I originally had my about how tight as DC is describing on his AH6... so much I probably could barely put any twist on the belt; but I don't know the tail mechanics setup on the AH6 800 size... but that amount tension lead to the problem. This go around I have it so that when I squeeze the belt from the middle (middle being from motor pulley to big gear) I can get about a 1/2 in of push... and about a quarter twist in the belt. I had it a little bit looser than that at first, and that actually gave a lil slop in the tail mechanics as well.

[DCORSAIR]

Thanks again, guys. After studying it for awhile I made peace with 2 bolts: The belt tension adjustment bolts maintain center-to-center distance while the 2 motor bolts are loaded mainly in compression. Figure any sheer on the bolts from rotation would be very small.
Please clarify too tight? I have my belt adjusted with about 1/4” deflection when pressed in midpoint between pulleys. Kinda feels “firm” but not solid.

Good question, I have mine tight, just a little slack when I twist it, thats on my Magnum PI version and on my AH-6 it is really tight, you can play music on it, it was that way when I bought it and I think its too tight, so now that I see how my new one is, I am going to loosen that other one up a little, you don't want to loose and not to tight, kind of a hard decision what is right, I say snug and leave it, I don't want to loose because mine has 5 blades to pull.