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HomeScaleAircraftScale HeliScale Helicopter Main Discussion Docs  Approach Engineering "Whiskey" Cobra build..
02-24-2016 09:46 PM  32 months agoPost 61
Mojave

rrElite Veteran

Palos Verdes, Ca. USA

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As Jim stated, it's all a trade off, there is no magic bullet. I fly 12S on all of my scale machines and I get great flight times, motor runs cool, lipos don't puff and I never run into a situation where the motor has to struggle to get me out of trouble. The 300KV Xera in my big R22 flies on an average of 38 amps and sees 70 amps on hard climb outs. IMHO, the key is to buy high efficiency/quality motors, correctly match the final drive ratio to the motor KV, lipo cell count and expected head speed. The rest is gravy... But on the flip side of that coin, I have seen Gary Wright fly and extremely low head speed 3D routine on 6S and a higher KV motor with his 800 size TT pod/boom machine. I watched him fly a 10-12 minute routine and he still had 30% left in the lipos. But his motor was a bit on the warm side. It's all about the combo...
Barry

All helis and planes have an expiration date stamped on them...you only find it after you crash!!

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02-24-2016 10:24 PM  32 months agoPost 62
prototype3a

rrApprentice

Christiansburg,VA

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FWIW, Gary's setups are more of a compromise since he won't build a purpose built low headspeed heli.

Honestly, I mainly asked because I figured scale helis are the closest analog to a heavy AP heli or a 'drone' where you're lugging around a payload.

One of my newer pet peeves is how the motor manufacturers don't actually give you enough specs on their motors to make intelligent choices when it comes to your powersystem. This is one reason I personally like Xera/Xnova motors. From what I've seen, they have market leading efficiency and I've personally verified their published specs.

Something I'm very curious about is how the efficiency and flight characteristics of the helicopter change as you add more blades to the rotorhead.

~Drew

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02-24-2016 11:55 PM  32 months agoPost 63
Mojave

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Palos Verdes, Ca. USA

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Yeah, I get it. Those were merely my thoughts on the situation. I'm not an electrical engineer, I just have a combo that works for me. There really is no perfect world when it comes to finding the sweet spot in a combo, there will always be some sort of compromise. Also, the scale side of this hobby is much smaller, so the motor mfrs don't cater to us like they do the pod/boom crew. But you can always have a motor custom wound to your specs. I do agree, the Xera motors are by far some of the best available. I have also had great luck with Axi motors, they are complete power house motors, quite reliable and efficient.
Barry

All helis and planes have an expiration date stamped on them...you only find it after you crash!!

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02-25-2016 03:28 AM  32 months agoPost 64
coptercptn

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Mesa AZ. USA

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Today, I spent the majority of the time setting up the mechanics.
But first I finished the tail drive... After mounting the mechanics in, and securing the forward end of the cable drive, I was able to measure off of the tail gearbox and adapter and cut the cable to length. It requires a bit of trial and error, but in the end you want a little free play so when the cable expands, it doesn't bind up..

In the pics you can see how I made the adapter by cutting off the end of the torque tube and machining a sleeve that allows the cable to be captured on one end ( with grub screws) and the splined drive on the other.
In order to assemble the drive in the helicopter this end has to be removable. To get to the grub screws ( to secure the cable on the adapter) I drilled a hole in the section of tail boom. When the gearbox is mounted on the Heli, it covers this up .

Home of the "Sea Cobra".....

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02-25-2016 03:53 AM  32 months agoPost 65
ScaleCrazy

rrNovice

Salem, OR-USA

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Protoype3a,

Answer this. If he did run this on 6S and discovered he needed nearly a pound of weight as ballast for optimal COG then what do you think that is going to do to your performance/efficiency quotient?

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02-25-2016 08:35 AM  32 months agoPost 66
Andy01

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Brisbane, Australia

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I think that this motor talk is hijacking a very good build thread, but I suspect that Prototype may be over simplifying things.

As said above - what is more inefficient - carrying 2 lbs of useless lead ballast and having a marginally more efficient motor, or carrying a useful battery that allows for either longer flights or two flights on a single flight pack (minimising sometimes awkward lipo changes) and sacrificing a percent or two of efficiency..

For the record, the XNova site indicates that my 4035-300 is at max efficiency at fairly low amps, and coincidentally I tend to fly around 25A mostly.

http://www.xnovamotors.com/xnova-4035-300kv/

Anyway I am very happy with my motor that is designed for 800mm 12s helicopters with fairly constant power draw - seems perfectly suited to my 820mm 12s helicopter that has very constant power draw when flown in scale circuits

No more on the subject from me. Back to the very interesting build.

Colin

Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )

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02-25-2016 10:54 AM  32 months agoPost 67
Mojave

rrElite Veteran

Palos Verdes, Ca. USA

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Nice work Jim! This project is really coming along nicely. Have you decided what head speed you're going to run on this heli?
Barry

All helis and planes have an expiration date stamped on them...you only find it after you crash!!

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02-25-2016 01:06 PM  32 months agoPost 68
doorman

rrProfessor

Sherwood, Arkansas

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Agreed...
I am with Colin.. this is a good build thread and hope it stays on track..
Jim, it really is looking great!!!
Some nice wide cord blades would look good on it!!! Hit Darrell up...
Any idea yet as to the finish weight vs an all glass fuselage??
Stan

AMA 2918-Team Spin Blades,,Castle Creations, Unique Aircraft

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02-25-2016 01:21 PM  32 months agoPost 69
old nitroman

rrVeteran

Naples florida

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Great build, wish I had time to do a build like this, great job, like the tail drive.

E5s and E7se,and a 766, Roban bell 222 800 superscale,450 bell 4 bladed head,gobby 380and 420 ,180cfx

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02-25-2016 02:02 PM  32 months agoPost 70
prototype3a

rrApprentice

Christiansburg,VA

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For the record, the XNova site indicates that my 4035-300 is at max efficiency at fairly low amps, and coincidentally I tend to fly around 25A mostly.
That's at 30v or about 8s. However, using the information Xnova provides you can calulate the curve for 12s. Raising the voltage will push the curve towards higher current and higher peak efficiencies.

Peak efficiency for that motor on 12s is about 32A and at 25A on 12s you're using about 1050w of mechanical power. Not a bad setup actually.

I wouldn't suggest anyone to ever add lead to a flying model. But I guess that is your only option if you feel you can't parallel packs or use a cell size other than 5000mah.

~Drew

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02-25-2016 04:03 PM  32 months agoPost 71
coptercptn

rrElite Veteran

Mesa AZ. USA

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Hey Barry , guys, yes at this time I have a set of 716 blades on it ( cuz I had them laying around ?) may go to 750..? Dunno yet. And am gearing for 1150-1200 hs. Not sure about weight yet Stan but it feeling fairly light and, (to my surprise ) nose heavy!!!!
This is all a little pre-mature though as I haven't added a lot of details that can change things.. I'll be finishing up the nose and forward fuselage next, but wanted to get it all "flight ready" first...and it is!!! Gearing came out ;
118T main gear W/11T pinion (mod 1) 330kv motor on 12s castle120.
This gives me head speed options from 1147-1204, with esc operating above 90%

Home of the "Sea Cobra".....

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02-25-2016 06:21 PM  32 months agoPost 72
coptercptn

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Mesa AZ. USA

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Ok, just a couple of update pics that I didn't add yesterday


As you can see, plenty of room for batteries ( those are 6S 5000) .
Also you can see the spreader/brace I added for the cable behind the mechs

Home of the "Sea Cobra".....

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02-25-2016 08:07 PM  32 months agoPost 73
coptrdr2

rrApprentice

Huntsville, Al

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Frames
Looking good and making me want to build one. Where can a guy find the shortened frame halves?

Ken

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02-25-2016 09:28 PM  32 months agoPost 74
Mojave

rrElite Veteran

Palos Verdes, Ca. USA

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Hey Jim, if you can fit 800's I have a pair of MAH at home that flew very nicely on my UH1B. I think they have a 12mm root and wide chord, semi sym. Let me know if you can swing them.
Barry

All helis and planes have an expiration date stamped on them...you only find it after you crash!!

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02-26-2016 03:13 AM  32 months agoPost 75
coptercptn

rrElite Veteran

Mesa AZ. USA

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That may be an option Barry, I let you know after I get it in the air...
Today I finished the front fuselage weapons bays and lower avionics bay...
All that's left is the stub wings and I'll be ready to start glassing and finishing

Home of the "Sea Cobra".....

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02-27-2016 01:26 AM  32 months agoPost 76
doorman

rrProfessor

Sherwood, Arkansas

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Sweet!!
Coming right along!!

Stan

AMA 2918-Team Spin Blades,,Castle Creations, Unique Aircraft

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02-27-2016 01:31 AM  32 months agoPost 77
coptercptn

rrElite Veteran

Mesa AZ. USA

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Ken, I'm not sure where you can find these frames...? But, my second choice would be the 550 frames w/700 upgrades...

Home of the "Sea Cobra".....

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02-27-2016 03:51 PM  32 months agoPost 78
Mojave

rrElite Veteran

Palos Verdes, Ca. USA

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You may be able to get those shorter side frames from RCA. They were originally designed for the UH1B kit. I believe I already gave my spare set away...
Barry

All helis and planes have an expiration date stamped on them...you only find it after you crash!!

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02-27-2016 04:54 PM  32 months agoPost 79
prototype3a

rrApprentice

Christiansburg,VA

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I should have the cad model for the old Trex 600 frames. If you gave some critical dimensions, I might be able to modify them and send them to Custom Heli Parts to be cut for you.

Alternatively, you might be able to ask CHP to adjust their EDL frames to your required dimensions.

~Drew

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02-28-2016 04:20 AM  32 months agoPost 80
coptercptn

rrElite Veteran

Mesa AZ. USA

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Yes the aerodyne ones are what I had, except that these were the prototypes from TF models when they first made the b model 600 Huey . Kin sent me a few sets to check out... This was my last pair...

Home of the "Sea Cobra".....

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HomeScaleAircraftScale HeliScale Helicopter Main Discussion Docs  Approach Engineering "Whiskey" Cobra build..
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