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Old Apr 13, 2005, 07:41 AM
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Mr. Boogie's Avatar
Morristown, New Jersey (excl EWR), United States
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Ed,

Sorry your maiden didn't go well. Your raptor was/is a beauty. You mention that you were fighting to keep her straight during the takeoff roll. Could you offer a little more information, was she bouncing, steering left/right, etc.

I know the next attempt will be more satisfying, and I can't wait see/hear about a successful maiden.

Mr. Boogie
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Old Apr 13, 2005, 08:27 AM
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Wow, the description of the stall sounds just like kriptonics harrier... quite the bummer.

Paul
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Old Apr 13, 2005, 10:46 AM
a really nice guy, really
Ralph Brekan's Avatar
Phoenix Intl, Arizona, United States
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Yeah Ed, you know my Scale mastery is for want. But I was refering to the crashed nose-less version.
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Old Apr 13, 2005, 11:49 AM
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Ed Waldrep's Avatar
Las Vegas, NV
Joined Dec 1996
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Quote:
Originally Posted by Mr. Boogie
Ed,

You mention that you were fighting to keep her straight during the takeoff roll.
Mr. Boogie
Well it was yawing side to side, I really had to be on top of it and give tiny inputs or large inputs, depending on what it was doing. I made 3 attempts before getting it. I have the same motors that I did in my 45" A-10 and it was sometimes tough to take off, hard to keep it straight. I think most jets are like that, with the "push" in the back they want to swap ends. A lot of the turbine jets use a gyro for that reason I think. There are differences in when the motors come on at low throttle and I wonder if they are putting out the same power. I think so, one pulled 25 amps and yesterday full throttle with both was 50 amps. When they are spooling up I have asymmetrical thrust for sure, but once going they match I think. I have some tow in on the mains wheels. Once it got going a certain speed it was easier to keep straight.

Before with the A-10 I was using a Smile 40 on one motor and a Smile 30 on another, so I thought that might account for some thrust symmetry problems, but now I'm using two Smile 40 controllers. The problem is the motors don't both get "recognized" at the same throttle postition. One does the "beep beep beep" think as soon as I plug in the power, with the other I have to lower the throttle trim some to get it to activate. Then, when I throttle up, the one motor starts before the other as I slowly advance the throttle. Does anyone have an idea why? Both controllers are set to mode 3, airplane mode, no break. I've also tried to plug in the power with full throttle on, hoping it would calibrate, but they controllers are still different. Could motor wire length create a difference? Mine aren't even, one motor has 3 inch longer leads. Also, both controllers are wired together in a parallel setup off of the main battery, and both becs are running to feed the receiver. I know everyone always says only use one BEC, but I've been flying the A-10 that way for 2 years without a problem. I don't see how the BEC supplying power to the receiver could affect the calibration with the throttle but then I'm not expert on ESCs.
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Last edited by Ed Waldrep; Apr 13, 2005 at 11:56 AM.
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Old Apr 13, 2005, 11:53 AM
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Ed Waldrep's Avatar
Las Vegas, NV
Joined Dec 1996
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Quote:
Originally Posted by stumax
Bummer, Ed! Are you sure the CG wasn't too far back? 25% MAC on that plane seems a little aft to me.

Stu.
I'm not sure Stu. Actually, to balance level I had my fingers about 1/4" (1 cm?) in front of the 25 percent mark, maybe more. I'll have to look at my Wattage F-22 again and measure but just glancing at it the cg might be a bit farther forward than 25%. I haven't flown it in ages so I don't remember how it behaved.

The twin was probably level at about 22% or so.

I'll have to lengthen the nose gear, build a new nose, and go for it again. Maybe a gyro is in order on the nosewheel.

Oh and to whoever asked, no flaps or ailerons, tailerons only. A positive AOA will fix some of the problems I think.
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Old Apr 13, 2005, 01:29 PM
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Oshkosh, WI
Joined Nov 2002
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Sorry to hear about a hiccup on your Raptor maiden. The bright side is that the damage is repairable. The lesson of more AOA is one I have embedded in my brain for my F-4. Hope to see you fix it up & be back for another attempt soon.

Cheers,

Phil
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Old Apr 13, 2005, 01:31 PM
Capt. Z
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Tonopah, Nevada
Joined Dec 2004
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Capt Zaner say's

Good afternoon ladies and gentelman my name is Capt. Zaner, Larry the Cable Guy would tell ya.."Git er done" and if ya know Ed like I do he will have it back in the air in no time.
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Old Apr 13, 2005, 02:46 PM
2014 EDF JET JAM We be Jamming
Kevin Cox's Avatar
St. Louis Intl, Missouri, United States
Joined Jan 1997
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I'm sure Ed will get it sorted out in due time. Set it in a corner for a couple of days and then restart.

I always start with my CG at 20% for conventional models and even more forward when a big LEX is involved.

As fas as ground handling goes my Super Hornet does the same thing.I know most of mine is due to the slop in the main gear but a functioning rudder would fix it.

Here's to a rapid rebuild <clink>
(Sunkist on ice)
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Old Apr 13, 2005, 03:00 PM
go fly! no crashes!
Synwpn's Avatar
Honolulu, HI
Joined Jun 2003
2,845 Posts
Hey Ed, when i ran my dual fan test setups with 2 CC 45s, they never started up in sync. i was always either a second off or i had to increase the throttle another click to get the second one going. this was off of one battery also. i did make sure that i had the leads the same all the way throughout this system, or at least to withing a 1/8th of an inch. i never did get it to fire up in synchro nicely. on mines, i'm thinking maybe the soldering on the deans connectors may be causing the slight difference.
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Old Apr 13, 2005, 05:28 PM
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Hi Ed

That was really hard luck with your maiden, but it does look repairable.

FWIW I think the guys are correct ref the CG being too far aft. Around 18% of MAC ought to do it, plus lengthening the noseleg to give about 3 degrees angle of attack on the ground.

Hope you've got the repair scheme planning underway

Gordon
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Old Apr 13, 2005, 07:19 PM
Watts is life...
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Hi Ed,

I sure hope you donít get discouraged by the rough maiden; this is a really tough plane to make work. When I saw the picture of the nose smashed, I could sense the disappointment. FWIW Iím highly inclined to think the CG is more forward than you might have thought. Iím only posting this to share what I found. The pencil marks the CG that I found to produce a good glide. Let me quickly say, Iíve havenít flow this with power yet but I did dozens of hours of glide tests without the fan installed. I also built two chuck gliders; a ľ scale and a full sized model version.

The smaller glider was an accurate miniature with scaled CG markings out to 10%. The CG worked out to 14% and I just didnít believe it. I just thought it was a scaling thing so I built a quickie cardboard one at full model size. I ended up with the same CG.

So Iím posting this only to offer some experience I had and remember this plane has only RC glide tests, NO powered flight. Of course the powered flight means the most but Iím quite sure the CG is where it needs to be.

I really need to ask a question, you previously said the plane was very nose heavy, something like 8oz worth. When you did the maiden, what did you do? Did you add tail weight or did you run it as is?

Bob.
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Old Apr 14, 2005, 10:11 AM
Mad Max meets the Thinker
Cyberman's Avatar
Pittsburgh, PA
Joined Apr 2004
569 Posts
Quote:
Originally Posted by Ed Waldrep
Before with the A-10 I was using a Smile 40 on one motor and a Smile 30 on another, so I thought that might account for some thrust symmetry problems, but now I'm using two Smile 40 controllers. The problem is the motors don't both get "recognized" at the same throttle postition. One does the "beep beep beep" think as soon as I plug in the power, with the other I have to lower the throttle trim some to get it to activate. Then, when I throttle up, the one motor starts before the other as I slowly advance the throttle. Does anyone have an idea why? Both controllers are set to mode 3, airplane mode, no break. I've also tried to plug in the power with full throttle on, hoping it would calibrate, but they controllers are still different. Could motor wire length create a difference?
Yes it will make a difference, 3" doesn't sound like a lot but in the right conditions it might make the controler see a different inductive value. Wires act as an inductor. You should match the lengths. The other possibility is the longer length allows for subtle interference.
Quote:
Originally Posted by Ed Waldrep
Mine aren't even, one motor has 3 inch longer leads. Also, both controllers are wired together in a parallel setup off of the main battery, and both becs are running to feed the receiver. I know everyone always says only use one BEC, but I've been flying the A-10 that way for 2 years without a problem.
Just because you haven't been struck by lightning yet doesn't mean there isn't a possibility. The reason you should never connect the BEC from both controlers is they will FIGHT each other. The LDO's commonly used in the BEC's of motor controlers aren't likely pefectly matched, in fact it would take a miracle if they were. 2% variation in ouput is often for a 5V LDO, which means 4.90 to 5.10 volt output. Basically you wire them together and they will fight each other to keep the BEC voltage to what they want. This wastes battery power and can lead to weird voltage variations in your control system, just use one (or use UBEC instead).
Quote:
Originally Posted by Ed Waldrep
I don't see how the BEC supplying power to the receiver could affect the calibration with the throttle but then I'm not expert on ESCs.
Hmmm depends on how it was designed really. Anything is possible considering that you have electronics and software sitting together there. It all depends on how they calibrate themselves.

Cyb
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Old Apr 14, 2005, 12:37 PM
gasless
Seattle area
Joined Jun 2004
631 Posts
Quote:
Originally Posted by Cyberman
The reason you should never connect the BEC from both controlers is they will FIGHT each other. The LDO's commonly used in the BEC's of motor controlers aren't likely pefectly matched, in fact it would take a miracle if they were. 2% variation in ouput is often for a 5V LDO, which means 4.90 to 5.10 volt output. Basically you wire them together and they will fight each other to keep the BEC voltage to what they want. This wastes battery power and can lead to weird voltage variations in your control system, just use one (or use UBEC instead).
Without knowing the exact BEC regulator part and circuit, it is safest to assume they will fight each other. One crude way to check is to make an IR temp measurement on the BEC part on both controllers after they have been powered up at 0% throttle for a minute or so. If they are both hot, or one is much hotter than the other then they are fighting. Also, a difference in board temperature between 2 controllers could possibly lead to minor differences in throttle detection, due to oscillator temperature variations.
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Old Apr 14, 2005, 02:02 PM
smug in granny panties
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NorCal Silicon Valley
Joined Aug 2002
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My RBC A-10 would get a glitch here and there upon start up, single battery dual ESC setup, and I later found that it was each ESc trying to initalize BEC mode, dropping one BEC fixed it. Setup is x2 Astro Micro Fans with both ESC's.

Barry
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Old Apr 14, 2005, 02:57 PM
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Las Vegas, NV
Joined Dec 1996
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Hmm, thanks for the bec explinations guys....I'd always heard "don't do this" but never knew why. I should probably just add and ulitmate BEC, I'm using 4 servos, two of them digital so the load might be high. Running just once BEC off of a controller might lead to a crash if it shuts down. That might cure the thottle asymmetry as well.

I'll take the plane with me to Best In The West, so anyone there can check it out. Ted and Patrick and I will be there both Friday and Saturday. I'm bringing my little Hawk EDF conversion so I can fly something after hours (don't want to pay 60 bucks to fly around a tiny little foamy). I still have the 45" A-10 but the motors are in the F-22.
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