Roban AH-1W Cobra 700 Size Scale Helicopter

[PawPaw]

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.

[RCjetdude]

Definitely following this thread as the Cobra is another of my favorites. Looking good so far!

[sfcfury]

Yes the bolt pattern on my scorpion was the same... so I ran with two bolts, (I mean that's all I've ever had on my 500 size)... I only did a couple hover flights with it on the test bed, but the bolts didn't come loose at all. That's when I found out you can have the belt tension to tight! So it had to be torn down and get that gear on the vertical tail boom drive shaft replaced. That's when I saw all these tiny upgrades here and there... that motor mount etc. So as I started getting the lil parts coming in, I saw the tengu motor, and you can select a long or short shaft when you order it. (i also ordered a longer shaft for the scorpion- but it got here 3 weeks after the tengu motor came in!)

[DCORSAIR]

If you need another motor to try and dont mind used??? I will send you an Align 750mx 530KV, I bought it used and never tried it, you will need to order a new shaft though, which comes with new bearings to, the shaft on it is to short for these Roban belt drive units, I will send it to you for free if this will help you out and you could send that Scorpion back if this Align motor will work for you??

[DCORSAIR]

Harmonics? Didn’t think about that. Hopefully the rubber will dampen everything. Got my Scorpion 560Kv today & discovered the bolt mounting pattern will not match the Roban plate for 4 bolts. It will match 2, but the motor’s pattern has the other 2 holes closer to center at the 3 and 9 o’clock positions. Looks like a diamond shape. I checked the website and sure enough, you can see that pattern in the picture if you look closely. Can’t elongate the plate holes either....just not enough “meat” there. Has anybody seen this before?

Yep, some motors come with both bolt patterns 25mm/30mm, kind of universal I guess, but I have seen guys using the Scorpion motors on the Roban models, don't know how they are doing that.

[PawPaw]

Harmonics? Didn’t think about that. Hopefully the rubber will dampen everything. Got my Scorpion 560Kv today & discovered the bolt mounting pattern will not match the Roban plate for 4 bolts. It will match 2, but the motor’s pattern has the other 2 holes closer to center at the 3 and 9 o’clock positions. Looks like a diamond shape. I checked the website and sure enough, you can see that pattern in the picture if you look closely. Can’t elongate the plate holes either....just not enough “meat” there. Has anybody seen this before?

[DCORSAIR]

Yeah, using only Microbeast myself, never set one of those up, two turns on the ball link from neutral?

Pawpaw, so on your bearings, you went 9 1/2 on each end? Its better to do like 9 1/2 on one end and then put the other bearing either farther out or in, not equal distance, I know it sounds strange but it's better to have the bearings different distances apart, I wouldn't take it back apart though, it may work just fine like it is, try it first. There is a theory why you don't do equal distance but I'm not going to go into that.

[sfcfury]

Sorry... I've never used that gyro... the beastx just has you set left and right limits, and the proper gyro sensor direction.

[PawPaw]

How do you interpret this? Set up my Demon 3X FBL programming & it’s 90% finished, except for gyro tuning, etc. I’d rather set a tail rotor blade pitch value with a gauge than the “two ball link turns” method....but in the real world what did y’all do? Thanks!

[PawPaw]

No, I assembled it myself. I installed each bearing 9-1/2” from each end which gives the shaft support in 4 places...roughly 10” spacing. However, those support bearings are free to migrate inside the tube with just a friction fit so gotta believe the engineers allowed for any vibration in the design. Thanks for telling me what I wanted to hear, guys.....didn’t want to take it apart again!

[DCORSAIR]

I don't think your supposed to grease those bearings either, guess a guy could put just a drop of oil before you slide them in, I just sprayed some WD-40 down my boom and the rubber slid right in place, did you guys remember to offset them so the drive shaft is supported at different measurements and not equal distance from each other??

[sfcfury]

Dang... the tail tube assembly came completed as well? I just used a silicone spray... definitely made it easier to get them down the tube and overall shouldn't damage the rubber bushings. I don't think I would put any type of grease on them.

[PawPaw]

No...gears are all straight cut. I’m only seeing a difference in the side plate open hole locations. I was trying to orient my support arms in relation to yours when I noticed the difference. Obviously, the tail boom dictates how these arms must mount on the frame to still slide inside so I figured your setup worked. Probably a good thing I haven’t installed them yet as I’m thinking I should disassemble the entire tail tube assembly to add some grease to the 2 internal shaft support bushings. I decided against the lube at first thinking grease would eventually soften the rubber & assembled the tube dry. Now I’m thinking shoulda used silicone grease. Whatcha think?

[sfcfury]

Did you kit come with the helical gears and pinion on top as well? If so, thats awesome! Interesting that your frame is different too... I used the the hole with the metal cross-support tube... and it had a larger and longer bolts in it... so i just figured that had to be where they wanted it to go lol.

[PawPaw]

That cannon looks awesome, F106.
Thanks, sfcfury...it was confusing because the shims were in the same bag as the motor mount. I did notice from pics you posted your frame is different than mine. I was trying to see which holes you used for the tail tube support arms (copycat again) and the hole orientations are different. Not a big deal...
Thanks, DCCORSAIR....my motor arrives today & I think it’s a short shaft. We’ll see.

[sfcfury]

Just got the rotary cannon functional for my Cobra. Ended up building it out of spare parts. The cannon assembly is mounted on 2 Trex 450 bearing blocks and a piece of the main shaft. It is run by a retract motor out an old HobbyKing gear. Works like a charm so far! Next will be adding the pan/tilt system for the turret.

Wow looks good.... I would like to see what your going to use to rotate the turret...

[F106DeltaDart]

Just got the rotary cannon functional for my Cobra. Ended up building it out of spare parts. The cannon assembly is mounted on 2 Trex 450 bearing blocks and a piece of the main shaft. It is run by a retract motor out an old HobbyKing gear. Works like a charm so far! Next will be adding the pan/tilt system for the turret.

[DCORSAIR]

I didn't get either; I got my kit almost two years ago, when they were still being sold by rc aerodyne... I think they evolved/improved the kit over time... I think the scaleflying de guys had alot of input on those kits.

Oh okay, that explains it, yes these newer kits have the helical cut gears already installed, better main shafts, the motor support bearing optional but included, for some reason though my AH-6 has the regular gears but is very quiet, can't wait to see your Cobra flying, it's looking nice.

[sfcfury]

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!,

#3.. You don't have to replace the bearing block; just add one or two of the washer shims to help get the gear mesh as best you can.

[sfcfury]

I didn't get either; I got my kit almost two years ago, when they were still being sold by rc aerodyne... I think they evolved/improved the kit over time... I think the scaleflying de guys had alot of input on those kits.