Roban AH-1W Cobra 700 Size Scale Helicopter

[PawPaw]

Yes that makes more sense now. Thanks for posting the how to vid also. Your AH-1W looks great & glad you got the vibe issue sorted. Still got mine to do but been distracted with the B407 last few days. I’m thinking I’ll end up shortening my short vertical tube to get a better shaft lockup but we’ll see.

[DCORSAIR]

And well hey... you gotta have a lil slo mo action too right??

Looks great, once you get it up a little higher out of ground affect and out in the open I bet it will settle down some, oh and now I understand how you did your blades and why one is heavier, sorry, at first I thought you just stuck some weight on one blade and made it heavy and went for it, but now I see you found the CG on each blade then added the weight, thats how I do it, maybe not as perfect as he did in the video, but close.

[sfcfury]

And well hey... you gotta have a lil slo mo action too right??

[sfcfury]

So my first video in the air.... Well the good news is that I think that I have eliminated most of the vibrations that I can... feels pretty solid. The bad news is that my piloting skills were sucking butt... and the harder I tried to keep it in one spot the more it didn't want to stay!! In my defense that was my new gopro stand, and I was trying to not get too close and blow it over! (that's one of my excuses and I am sticking to it!)

[sfcfury]

Definitely not a bent shaft... and I never did all that with my blades before I started chasing down my OH6 tail issue last month... although it's not like I've built a lot of heli's either! But I had found a video about blade balancing for the helicopters, and after I had noticed tail vibrations on the test bed... but then noticed that there were zero vibrations in the tail when I did a full run up with out them... like the tail was rock solid... I figured blade tracking, balancing etc... My tracking was pretty solid out the gate b/c I use the soko ( I really like that thing). I think I ended up only making 1 half turn adjustment on a blade for tracking... so that left balancing. The first time I put them them on the prop balancer, it was very clear that one blade was heavier than the other. I had watched this video, and another with a guys putting his 500 blades on a prop balancer.

[DCORSAIR]

Wow! Awesome vid sfcfury...now I gotta copy you again & buy sounds. Odd on the blade balancing. Doesn’t seem to make sense, unless you had a bent main shaft...which woulda showed up before now. Better check mine!

I was thinking the same thing, that is odd that he had to balance the blades like that to keep the vibes down, I never had to do any that way.?

[PawPaw]

Wow! Awesome vid sfcfury...now I gotta copy you again & buy sounds. Odd on the blade balancing. Doesn’t seem to make sense, unless you had a bent main shaft...which woulda showed up before now. Better check mine!

[sfcfury]

Managed to chase get most of the vibration out of my tail... had to break out the prop balancer on the blades!! The blades were all kinda out of whack... trying to get them to match on the center alignment, I actually had to add weight to the 'heavier' blade... which made it that much more heavy... So I ended up having to add 4grams of putty and then sanded it down a touch. When I tried to spool up with the blades at identical weight the vibration in the tail was horrible. So added weight, took it off, back on the balancer, back off, sanded some more... so now they are pretty dialed in, one blade weighs 188.69 grams and the other is 189.22... go figure!

[sfcfury]

So, doing a little sound check... I have an APU sound initially, and then I toggle the actual engine start up.... I think I will set the Nav lights to be on initially, and then the strobes will come on with the engine start up.... nothing exciting. Matching the blades with the spool up is a task lol... while my engine spool up is pretty slow actually, the blades start turning much quicker than scale! Shutdown is easy tho

[DCORSAIR]

Yes- this one HN7053B 700N Metal Tail Torque Tube Unit.... Just b/c I was trying different things... when it came in, it's slightly wider than the Roban. That's when I ordered the Align 600ESP Metal Tail Pitch Assembly / Black AL-H60250... which fit perfectly on the roban assembly. The 700 size one fit the tube and the drive shaft, was just slightly wider. I don't have a complete 600 size assembly, but I would have to believe the entire assembly would be a drop in replacement.

But the fact the replacement tube is a 1.3inches longer than mine, got me wondering about the mechanics and size of everything. I know your mechanical setup for the tail that's in the main mechanics is different from mine.

Roban did make improvements since the RCAerodyne days, now that MRC has picked them up there seems to be some improvements along the way, so your new tail tube will put the tail rotor up taller out of the fuselage?

[sfcfury]

Yes- this one HN7053B 700N Metal Tail Torque Tube Unit.... Just b/c I was trying different things... when it came in, it's slightly wider than the Roban. That's when I ordered the Align 600ESP Metal Tail Pitch Assembly / Black AL-H60250... which fit perfectly on the roban assembly. The 700 size one fit the tube and the drive shaft, was just slightly wider. I don't have a complete 600 size assembly, but I would have to believe the entire assembly would be a drop in replacement.

But the fact the replacement tube is a 1.3inches longer than mine, got me wondering about the mechanics and size of everything. I know your mechanical setup for the tail that's in the main mechanics is different from mine.

[PawPaw]

A 700 Trex unit?

[PawPaw]

A 700 TREX unit?

[sfcfury]

So in my ongoing tail endevours, I put a complete 700 tail assembly on the tube... and the only real difference between the roban and 700 assembly was that the 700 was a little bit shorter. It took all the slop out... in fact it was going to be a little bit too tight on the drive train. But the fact that the tube I ordered came in too long.... just got me curious about how the kits are coming now.

[PawPaw]

Mine is assembled but I’ll measure the shaft when it comes apart again. Curious if the slop I’m feeling is due to the shaft not seating fully because the tube is too long or bevel gears need shims. Only have a couple mm’s clearance between fin top edge & tail rotor gearbox so hate to think cutting the fin for a shorter tube is only option.

[sfcfury]

So question... I ordered a short tail tube, and when it came in it was 1"+ longer than the tube that came with mine. So now I'm curious about the the measurements etc... If you guys get a chance, shoot some measurements... I didn't measure the short tail drive shaft, I will when I get back home.... The black tube is the new tube, the silver is what came with my kit. I really need to measure the drive shaft...

[PawPaw]

If you can get 7.4v from the CC then the only issue would be how the AR12310 reads the capacities of the two different power supplies. Talking off the top of my head here I would need to know what the amp rating of the BEC is & compare that to the LiFe pack...seem to remember my Talon is 20a max but lots more capacity so wouldn’t want the BEC to act as a 20a unbalanced LiPo to LiFe battery charger when connected. Just don’t know if the AR has any kind of isolation circuit to prevent that.

[F106DeltaDart]

Gotta backtrack on my post: Just read in the AR12310T manual they specify that both battery packs be of the same voltage and capacity so that would seem to rule out a BEC as an option for one of the two power supplies. It appears the circuit is wired in parallel & doesn’t use a switching diode but could be wrong on that. Also, manual mentions something about an optional voltage regulator so perhaps their intent is to allow mismatched power supplies to work together?

The interesting part here, is that I can set the Castle BEC voltage in the Castle Link software and configure it to be 7.4V, or any other common voltage. Don't really know where the line is drawn. I have 2 LiFe packs that I can use if I need to, but then this becomes a 4 battery machine.. 2 X 6S 5000s for primary power + 2 RX packs.

[PawPaw]

Gotta backtrack on my post: Just read in the AR12310T manual they specify that both battery packs be of the same voltage and capacity so that would seem to rule out a BEC as an option for one of the two power supplies. It appears the circuit is wired in parallel & doesn’t use a switching diode but could be wrong on that. Also, manual mentions something about an optional voltage regulator so perhaps their intent is to allow mismatched power supplies to work together?

[PawPaw]

Well, I’m no expert by any means but it certainly appears the design intent of the AR12310T is to do exactly what F106 wants & unless the receiver specs advise against using a BEC for a power source it will work great. My only concern, and minor at that, would be the switching rate as designed in the receiver’s circuit. Easy to connect everything on the bench w/blades off, then pull the BEC wire from the receiver with one hand while holding a cyclic input on the Tx with the other hand. If nothing stutters or quits good to go.