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HomeScaleAircraftScale HeliScale Helicopter Main Discussion Docs  Approach Engineering "Whiskey" Cobra build..
02-23-2016 05:35 AM  34 months agoPost 41
coptercptn

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Mesa AZ. USA

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So today "Jim's ManCave" was renamed "Gepetto's workshop"!!!
All day was spent carving and sanding...
The result was I turned this;

Into this;

Still some minor filling and sanding before poly... But mostly there...
So the next step is fitting and making work the cockpit/canopy section.
I did deviate from the instruction here ( I know.. Shocker!! Right?)
The instructions want you to apply wax paper and then blindly glue the fiberglass canopy frame to the mount rails... I could only see epoxy running inside and bonding everything in its path... And then having it wrong??!
My solution ;

Place the rails in the fuselage, trim the canopy cover/frame to fit, and the drill for about a half dozen small screws to locate its position.
Now I can remove the assembly and properly glue and clamp everything together using the screw placement for a guide....

More tomorrow...

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

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02-23-2016 01:43 PM  34 months agoPost 42
ssmith512

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Indianapolis, IN USA

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I am jealous!!

Amazing work. Looking outstanding so far and will be nothing short of awesome when finished!

Thanks for sharing the build so far!

Steve

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02-23-2016 02:54 PM  34 months agoPost 43
GyroFreak

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Orlando Florida ...28N 81W

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I am really enjoying this thread with the fine details.
.
Question: Not being that familiar with the T Rex 600 series, I assume this is an electric ? Some details on the power setup would be interesting, motor, gear ratios, expected lipo ratings and I believe you were going for 700 size blades.
.
Keep up the great picture and description of the build.
Paul

I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?

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02-23-2016 03:08 PM  34 months agoPost 44
coptercptn

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Mesa AZ. USA

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Thanks guys...
Yes Trex 600E is the base mechs for this build ( w/custom lowered side frames ) that being said, the other option I would recommend would be the 550 frames. Advantage here is that you can upgrade to larger gear surfaces, and main shaft...( KDE, or 700 )
Power will be on 12S with 700-750 blades at around 1200 Hs

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

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02-23-2016 03:14 PM  34 months agoPost 45
prototype3a

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Christiansburg,VA

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Why 12s if you're only running 1200rpm?

~Drew

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02-23-2016 03:56 PM  34 months agoPost 46
don s

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Chesapeake, VA

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Probably due to blade size and/or motor selection.

E820, Raptor G4N, X50F/E, E620, Forza 450, and some planks.

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02-23-2016 04:03 PM  34 months agoPost 47
prototype3a

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Christiansburg,VA

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I realize his heli is probably considerably heavier but I just built a 1200rpm logo 600se running an xera 4025-560 on 6s and it is a VERY efficient setup. ~12A / ~88% efficiency in a hover and the efficiency just goes up from there with peak efficiency around 40A.

~Drew

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02-23-2016 06:35 PM  34 months agoPost 48
ScaleCrazy

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Salem, OR-USA

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Prototype3a, the other reason could be for COG purposes. A lot of weight back there to compensate for.

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02-24-2016 03:25 AM  34 months agoPost 49
coptercptn

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Mesa AZ. USA

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So, to continue, after aligning the canopy with the mount teeth the next step is to adjust the fiberglass. This is really easy as all that was needed here was a heat gun and a spreader/brace. The canopy was a bit tight toward the nose where it tapers.
So a little gentle heat over the whole shell and it all adjusted itself.

After I got the fiberglass shell fitting, I discovered that there was quite a difference where the fiberglass part met the balsa fuselage side...
My solution was to add a 1/16th balsa strip on the outside of the frame between it and the canopy.

Time to mix up some 30 minute epoxy, and glue it up... Lots of clamps, and of course the screws for alignment.

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

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02-24-2016 03:36 AM  34 months agoPost 50
coptercptn

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Mesa AZ. USA

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There are a few reasons we scalers like 12s ( or more) for the bigger helis..
First is because it takes a lot more power (watts) to fly them..now power comes from volts and amps... More amps causes failures/heat and poor efficiency...
More volts (cells) require less amps for the same power... We usually use gearing and motor KV to adjust our headspeed.
Second, as was mentioned earlier is for balance. Especially in this case, there is a long, heavy tail that will require counter weight for balance..so, it only makes sense to use the batteries to make up this weight.

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

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02-24-2016 03:42 AM  34 months agoPost 51
coptercptn

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Mesa AZ. USA

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Ok, back to the build...
But first a little builders "Tip"
If you have to clamp an area that the clamp wants to slip off of ...here's a quick tip.

Take a piece of sand paper and place it under the clamp...
It works great!!!

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

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02-24-2016 04:35 AM  34 months agoPost 52
coptercptn

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Mesa AZ. USA

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Flex drive 101.....
I thought I would share what I have learned about using cable/ flex/wire drive (whatever you wish to call it?)
i have used these for years in all sizes of Helis all the way up to my 49# Turbine and have great faith in them.
But, you have to know a bit about the set-up for them to be reliable. So, let's go into the procedure for ...well let's call it "good cableing"?
The first thing to consider is of course the cable.. Three important issues here;
First, size...(yes, size matters) you can buy cable in all sizes, but most common for our use is 1/16,1/8,1/4" and some metric equivalents. Personally, I tend to steer away from the smaller size...
Second, "Wrap" or "lay" .. Cables are "layed up" in left or right twist. If you have ever heard a cable driven helicopter that has a sound like it is winding up and unwinding ...? It is because the cable was the wrong "lay" or wrap. You always want the lay to be so that the direction of rotation tightens the wrap or the direction of turns. So, to test this, look aft ( from the mechanics) and notice which direction the tail rotor drive turns. Now look at the cable and visualize it trying to tighten itself or unwind?
Three; type of cable... On a small 450 or smaller, you " can" get by with a single wound cable ( like a speedometer drive) Anything larger, you really want a double wound type.
A great source for this cable is the nitro boat guys. They use it all the time and it works great!

Now on to making the cable.
All the cable sizes have a corresponding liner (usually Teflon) to allow it to move freezing with low friction... (You still need to lube it though).
Also needed is a support tube (brass) that guides it through the fuselage and keeps it from flexing under load.
One important thing when routing the tubing is to try and incorporate an "S" curve into the routing. This wil help prevent resonance at the high rpm's the cable spins at.
Next is to cut the cable to length.. Pretty self explanatory here so I won't elaborate on this.

Next step is to silver solder the ends.. They need to have at least 3/4-1" soldered on each end.. Word of caution here be sure that your tubing bends are very gradual, and kink free or the cable won't go through it! (Ask me how I know this?

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

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02-24-2016 05:14 AM  34 months agoPost 53
coptercptn

rrElite Veteran

Mesa AZ. USA

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So, here's how I made the drive for this project ...
I won't go back over the basic tube install cuz you saw that earlier... But here's the cable and connectors for the Trex .
Starting at the front (mechs) end I cut a short piece of boom to go inside the rear frame to support the cable end.
With this I took a torque tube and cut off about 4". Long enough so it would engage the splines but not stick out the end.

Next, I pushed a torque tube bearing and rubber dampening support into the tube, using the torque tube section for alignment.

Next, because the cable is smaller than the I.D. Of the TT shaft, I had to come up with a way to sleeve them together.. ?
A few short sections of brass tubing stacked on each other did the trick...!

I silver soldered the sections together and pressed them into the TT shaft.
Because you can't solder the TT shaft I will epoxy and pin this assembly together..
But now you can see how simple the setup is?

This end of the cable will be permanent, and inserted into the mechanics by slipping the TT through the bearing and into the splines of the drive gear. Then the "open" end of the cable is pushed into the tubing and walked in with the mechs.
Once in place, the tail rotor end will be attached using grub screws and the tail rotor gearbox installed....
Easy peasey??!!!!

One last thing....after I finish with all the upper fuse work I will be adding one final support brace at the end of the tubing. More on this later, and pics when it is installed...

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

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02-24-2016 06:51 AM  34 months agoPost 54
prototype3a

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Christiansburg,VA

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So, you ignore the efficiency curve of the motors.

~Drew

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02-24-2016 08:31 AM  34 months agoPost 55
Andy01

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Brisbane, Australia

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Drew

No you don't. A commonly used calculation would be something like;

RPM = kV x (3.7V x # of cells) x 0.9 (efficiency) / gearing

Most of us do not run throttle curves, but rather a simple governed headspeed, so there is no motor efficiency curve to worry about - just aim to govern between 90-95% throttle and you should be in the sweet spot of most larger motors.

The main reasons that most of us go for 12s with the larger scale helis is amps - the higher the voltage, the lower the , and generally less amps means less heat, and (as said above) more weight is often needed up front to offset the heavy tail boom, so the weight may as well be useful (ie. lipos).

I am running a 12s setup in a 800 sized EC-145 at 1050rpm (with a XNova 4035-300kV motor), and many others are running slower headspeeds than that. You just need to run slower motors to suit the gearing.

I also run two Xera 4030-470kV motors in smaller 12s scale helis (both running 1350rpm), and they are good motors. All 3 of my helis are 19 lbs or heavier which is quite different from a pod and boom that probably weighs less than 10 lbs. Many larger scale helis weigh well in excess of 20 lbs.

Colin

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

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02-24-2016 02:15 PM  34 months agoPost 56
old nitroman

rrVeteran

Naples florida

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Great job

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

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02-24-2016 02:21 PM  34 months agoPost 57
prototype3a

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Christiansburg,VA

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A good friend of mine has a 25lb+ 700 size AP heli and I've also flown a 35lb 750 size at just 1100rpm. At 1550rpm, in a hover, he is well outside the peak efficiency band of his motor on 12s. Though, he's only using a 'crummy' rewound Align 700mx.

For instance, on your Xera 4030-470, it doesn't get up to 90% efficiency until about 20A on 12s. I would bet you're just below that on your bird at 19 or 20lb.

As I said before, you're ignoring what the efficiency curve of the motor. You're ASSUMING a flat 90% which may or may not be an accurate approximation.

~Drew

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02-24-2016 08:35 PM  34 months agoPost 58
teamdavey2001

rrApprentice

Sunnyvale, California, USA

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Prototype3a

You are right of course. Out of interest, I just ran some numbers on my 12 cell scaler which uses an XNova 4035/400. Based on some rough numbers I give up about 1.5% efficiency in the motor alone by running 12 versus 6 cells (and doubling the current) at my hover current. Of course when wiring etc.losses are included the difference in less, unless the rest of the wire etc. resistance is cut to a 1/4 of what I have now!

Of course, in a hard climb (or if the model was heavier) the advantage would go to the 12 cell set-up.

I had wanted to use a motor with lower max Eff current for that model for just this reason. However, life is a trade, and the motors I looked at with lower max Eff current also had much lower efficiency anyway - and I could not get hold of a 4035/300 which would have been ideal, except that it would maybe not cool as well at the reduced rpm - but I digress

This is one of the disadvantages of using motors essentially optimized for 3D for scale applications.

Jim Davey

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02-24-2016 08:42 PM  34 months agoPost 59
prototype3a

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Christiansburg,VA

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You could also run 10s or 8s. My research has shown that in some cases, dropping the voltage, and going to a smaller but slightly higher kv can result in an overall higher efficiency with similar peak power capability.

It just so happens that the optimal setup for my 600se (using commercially available motors) is with the 4025-560 on 6s.

~Drew

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02-24-2016 09:21 PM  34 months agoPost 60
teamdavey2001

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Sunnyvale, California, USA

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Agreed.

Oddly enough another of my scalers uses a 4025 frame on 10 cells - bear in mind it is going to be heavier than your 600SE!

Another thing to mix in is the total run time wanted - I plan on 10 minutes with 20- 30% reserves which drives total battery energy required. Since I really don't like to parallel packs and 4000 and 5000 seems to be the sweet spot for cost/availability, higher volts is where we go.

On some other models I have used 14 pole aero motors on the basis of getting close to the best efficiency. While the numbers work and are born out in practice, they do tend to run hot - probably due to the poor airflow through the motor.

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