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Old Jul 30, 2012, 04:43 PM
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Well, that answers THAT!

The wattmeter test said it all.

(All numbers are averages)

On the 3S, 3000 35C: 60Amps, 640 Watts, 10 Volts.

On the 4S, 4000 40C: 110Amps, 1500 Watts, 14 Volts AND...

The wires from the ESCs began to smoke and where extremely hot to the touch. I immediately throttled off and unplugged it. The smoke subsided and I may have saved it from any major damage.

Sooooo...It's safe to say this setup wants a 3S only.

I may not even bother trying to maiden on my 3S 3000...It will likely fly like it's made of heavy wood...So, Don, I will be requesting another same setup from you soon.
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Old Jul 30, 2012, 06:04 PM
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Quote:
Originally Posted by Aros View Post
Well, that answers THAT!

The wattmeter test said it all.

(All numbers are averages)

On the 3S, 3000 35C: 60Amps, 640 Watts, 10 Volts.

On the 4S, 4000 40C: 110Amps, 1500 Watts, 14 Volts AND...

The wires from the ESCs began to smoke and where extremely hot to the touch. I immediately throttled off and unplugged it. The smoke subsided and I may have saved it from any major damage.

Sooooo...It's safe to say this setup wants a 3S only.

I may not even bother trying to maiden on my 3S 3000...It will likely fly like it's made of heavy wood...So, Don, I will be requesting another same setup from you soon.
Glad you found out at Groundspeed = 0. Now you'll have time to make the whale tail mods and see if you can tell a difference...
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Old Jul 30, 2012, 06:12 PM
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What's weird is I just heard back from the original owner and he said 3S was too sluggish so he used 4S. WTH? Is it the C rating that would cause that? The red and black wires running from the ESCs to the dean's connector are a smaller gauge than the wires from my battery...
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Old Jul 30, 2012, 06:24 PM
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Quote:
Originally Posted by Aros View Post
What's weird is I just heard back from the original owner and he said 3S was too sluggish so he used 4S. WTH? Is it the C rating that would cause that? The red and black wires running from the ESCs to the dean's connector are a smaller gauge than the wires from my battery...
The C-rating only allows the battery to supply the power that the ESC/motor are "requesting". If the C-rating is too low, then the motor will essentially be sucking the power out of the battery instead of the battery supplying what's needed. He may have been running a lower C-rating battery and didn't have a problem because his battery could only supply so much power (or, maybe he did have a problem, and that's why he sold it...)... but with a 40C pack, your battery was able to give everything that the motors were asking of it.

The C-rating doesn't "push" extra power down the wire... that's what the Voltage is for... the C-rating is really more of a battery chemistry thing... it's the max draw that the battery can sustain before damage (to the battery, usually) occurs. Higher C-ratings just mean that the battery can discharge at a higher rate...

The gauge of the wires may also be part of it. Think of it as a garden hose... or a fire hose... 10psi of pressure (or 14.8V), in a small hose will only deliver a certain number of gallons of water per minute. 10psi (or 14.8V) in a fire hose will produce more gallons per minute. That's why you see thicker red/black wires on a 60A ESC than you do on a 30A ESC. The ESC is kinda like the bucket at the end of the hose... the motors are kinda like a suction pump... and on 4S, they're sucking more water (or power) through that tiny hose... and with electricity, when the wires aren't big enough for the power draw, things start to get HOT... quick!

Does that make sense... or did I confuse the issue???
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Old Jul 30, 2012, 06:44 PM
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That makes perfect sense...Thank you very much!

Well, either he's not being straight with me or he was using a smaller battery. I have a 4S 2200 that I could try to see what happens...I'd like to try to fly it if I can...Thanks again!
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Old Jul 30, 2012, 06:53 PM
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The general rule of thumb is going from 3S to 4S will almost about double the total wattage. Mathematically the factor should be 1.78 times the watts so if you get more than that then one of a few things are happening. This first is the motor is highly inefficient at the higher power level so watts are just being wasted as heat, the other thing that can happen is the under load cell voltages may be too far from each other in this case for example

640/60= 10.66 volts/3 = 3.55 volts per cell
1500/110= 13.64 volts/4 = 3.41 volts per cell

This tell me the 3S setup is holding more volts per cell than the 4S setup so I would actually expect the ratio of 4S to 3S to be less than 1.77 to one. In actuality it is 1500/640= 2.34 so that tells me the system is highly inefficient on 4S. Now if you buddy was flying a 4S lipo that did not hold voltage well it may have been only 1000 watts on 4S or maybe less. But your new 4S lipo can hold voltage well so now it runs everything beyond what it was before on 4S when your friend had it. My guess based on the watts you have on 3s is that the motors are ~4800KV motors and that would be a 3S only setup in a 64mm fan.

Don
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Old Jul 30, 2012, 06:57 PM
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Thanks Don! Since math made me break out into hives in school I will take your word for it. LOL.

So 3S only on this setup it appears. She's got to be a slug at 600 watts? Only one way to find out...

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Old Jul 30, 2012, 07:00 PM
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Well a better 3S lipo might help some as 10.56 volts is a little low these days, you should be over 11. That is how I flew my first SR-71, it was the LX version and that is the video on my Youtube page (see the beginning of this thread). Thrust tubes will help as well.

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Old Jul 30, 2012, 07:02 PM
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Yes that battery is old...I'll see what else I have in the inventory.
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Old Jul 30, 2012, 08:17 PM
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I ran a different 3S 3000 in her...Grabbed her like I would hand toss her, cranked her to WOT and boy if it didn't feel like it had hardly enough thrust to keep her afloat if I tossed her. Even after just 30 seconds of WOT, those wires were white hot. The guts in this bird are junk.

So it appears I spent $120 bucks on an old, beat up airframe.

Redlite, I should have taken you up on your offer of two brand new MJ kits for $200.
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Old Jul 31, 2012, 08:48 PM
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Mission #8 was great last night, especially since my buddy (a professional photographer) surprised me by bringing his camera with him! So I should have some sweet shots to show off as soon as he can send me the photos. I never thought that I would see the day that flying the SR-71 doesn't make me break out into a cold sweat the entire flight. I'm getting comfortable with her (but not complacent). I know she - more than ANY other RC plane or jet I've ever owned - can bite at any moment you let down your guard or focus.

I still fly her with a heightened since of focus more than any other in my hangar, but I don't feel as intimidated as I used to. As long as my release is smooth and purposeful on the hand toss, and I keep her nose and the throttle stick where it should be, it's very predictable.

I've already broken my own record. I've never flown one single SR-71 airframe 8 times in a row.

Look out redlite, I'm coming for your record.
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Old Aug 01, 2012, 08:57 PM
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MISSION #9

Flew her without any problems...Ho hum. LOL! But I have to say, it will NEVER get old flying her!
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Old Aug 02, 2012, 01:07 AM
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MISSION #10

This will be the final report of each flight with #9. Now that I have flown 10 flights straight on the same airframe without having to fix, glue or tape anything, I'm going to simply enjoy her like I enjoy all my other planes I fly hundreds of times. I'll keep documenting my Habu flights in my blog.

Another fantastic flight. Easy hand toss into the dusk skies, and the usual 8-10 cycles in the pattern. Landings are dead stick with a touch of down. Non-events now.

I'll post something of significance (A crash, hairy flight or exciting or strange circumstance) if and when it occurs but other than that I won't bore anyone further with each sortie, lol.

Thanks again to everyone who has helped me finally achieve success with this storied bird. My persistence and stupidity saw it through, lol. Until next time, hope your Habu stays happy and spotless!
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Old Aug 02, 2012, 08:36 PM
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Here's some photos from Mission #8, including Anatomy of a Habu Hand Toss.
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Old Aug 05, 2012, 02:59 PM
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Flights #5 and #6...

Well... good news... got flights 5 and 6 done today! The weather was beautiful, and the wind was really light (which is very rare here where I fly). Both flights were without incident, but my landings kinda sucked today. On flight #5, I tried to slow her down a bit more, then tried to aero-brake a little after landing... and I got to see the dreaded pitch-up at the end. Luckily, she was almost out of energy, and there was no damage. After watching the video, it looks like I was just scraping the tail down the runway as she bled off speed. It's amazing how easily the nose wants to come up, especially at such low speeds! I got lucky with this one... she was only inches off of the runway... could have been ugly otherwise. The videos were shot with my iPhone, so the quality is a bit low...

Here's the Flight #5 video:
SR-71 Flight #5 (2 min 47 sec)


The landing on flight #6 was faster (intentionally, after seeing her pitch up on flight #5), but I overshot my planned speed a bit. The first attempt resulted in an unplanned go-around... she was headed for the dirt, and it just didn't look right. The second attempt wasn't much better... a little too aggressive on the flare, and she popped right back up... the actual landing wasn't too bad... it sounded worse than it really was. I think I'm going to put some plastic skids on my wingtips... you can see that my runway is kinda concave in the middle of the road, and with the Habu sitting so low, I'm starting to notice a little more wear and tear on the wings that I like.

Here's the Flight #6 video:
SR-71 Flight #6 (3 min 21 sec)


Cheers,
Sully
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