Roban AH-1W Cobra 700 Size Scale Helicopter

[PawPaw]

Details never seem to end or either I’m just making excuses. Sfc, I’m absolutely not trying to hijack your thread but can’t seem to get all my questions on one post: Did you install those “EVA Distancers” on yours? If so, next time it’s convenient would you post a pic? I can’t make hyde nor hair of the pic in the manual. I get the intent of the critters but just don’t find the obvious mounting spot. Thanks!

[sfcfury]

Details never seem to end or either I’m just making excuses. Sfc, I’m absolutely not trying to hijack your thread but can’t seem to get all my questions on one post: Did you install those “EVA Distancers” on yours? If so, next time it’s convenient would you post a pic? I can’t make hyde nor hair of the pic in the manual. I get the intent of the critters but just don’t find the obvious mounting spot. Thanks!

Ppaw!! Good day! I haven't permanently mounted those yet either... I've identified pretty much where I am going to put tho... I will take a picture when I get home.

[PawPaw]

Not hard to figure out there’s few spots to grab on a Cobra once all the scale bits are glued on. All it takes to remember the wrong way to pick it up is having to glue them all back on two or three times.

[sfcfury]

Not hard to figure out there’s few spots to grab on a Cobra once all the scale bits are glued on. All it takes to remember the wrong way to pick it up is having to glue them all back on two or three times.

Looking good! I like the camo version... To be honest I usually pick mine up by the rotor head... Of course I don't just snatch it up, but I figure that's weight is while it's flying. But yes... with all the small pieces attached, it's a test of patience on picking it up or loading up without knocking something off.

[DCORSAIR]

Not hard to figure out there’s few spots to grab on a Cobra once all the scale bits are glued on. All it takes to remember the wrong way to pick it up is having to glue them all back on two or three times.

Sweet, looks awesome...........

[PawPaw]

Not exactly Cobra related, but I’m spoiled here. Specing out a 700 B407 & curious about motor nomenclature: I read the 1st two digits of a motor is the stator diameter & the 2nd two digits are the stator thickness, but what would the practical difference be between a 4035 and a 4025 when both motors have the same kV rating? Heat dissipation? Pickings are getting slim in the marketplace & doesn’t appear new stock is flowing yet so don’t want to pass up a 4025 that’s available now if there’s not a major difference. Thanks!

[sfcfury]

So out the gate... again i'm not a SME... but from what I've read (at least concerning scorpion motors) 4025's are listed as for 600 size helis. 4035 is for 600-700 size... usually if you get into the numbers, the 4035's can handle more peak power draw (watts/amps).... which in scale flying probably wouldn't be an issue... except for that one time lol.

[sfcfury]

With that being said.... (and throw extra confusion and indecisiveness lol) if you go back and look at scorpion motors... you have different 'series'... so like HKII, HKIII, HKIV etc... and when you compare their older HKII 4035 motors to a HKIII 4025... even the peak power draws are similar.

[PawPaw]

Yeah, it’s that one time for sure. I did see the general write ups say the 4025 is a 600 class motor, even with the same kV as a 4035 which is 700 class. The Scorpion 4035-560 is a good fit in my Cobra with the camera pcb mounted cockpit rear but your 4500 series would likely touch it. The B407 is pretty tight in the doghouse anyway so need to figure out how much diameter there is to work with there. Thanks for the info!

[F106DeltaDart]

I’ve been slowly plugging away on my build. Built up a test rig for the mechanics, and started working on wiring. The stock tip on my new soldering iron proved too thin to heat up the 10AWG wiring for the ESC, so now it’s another week waiting for the new tips to show up.

I am struggling to figure one thing out though.. I am using an AR12310T Powersafe Spektrum receiver. This has 2 inputs for batteries to connect to the rx. If one is starting to run low, it automatically switches to the other. What I’ve been trying to figure out, is whether I can connect a Castle Pro BEC to one of those battery inputs. That way I only need one rx battery, and it only serves as a backup in case the BEC fails. Anyone know if this is ok? All I’ve been able to find searching around is people who have used batteries only..

[PawPaw]

I guess it would depend on that receiver’s diode circuit. A 2S pack is 7.4v and BEC’s run 6.0v so my thoughts are you would benefit more from using the BEC as primary & 2S as backup as you suggested. Would be easy to test with a multimeter on the bench too.

[PawPaw]

Oh, forgot to add that it might be a good idea to couple the 2S ground to the ESC ground as is suggested in the Roban manual “ Certain configurations without this ground interconnection have led to a loss of signal at the ESC from the receiver due to EMC effects.” The receiver switching circuit probably has this already but can’t say for sure.

[sfcfury]

What Ppaw said. Lol... I'm here to ask Delta questions not the other way around ... I just don't have enough experience in general to give any worthwhile thoughts on it

[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.

[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?

[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]

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.

[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]

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 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.