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T-REX 450 › Center of Gravity
12-03-2007 12:58 AM  10 years agoPost 1
cowboychris

rrApprentice

Pittsboro, NC, United States

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The center of gravity on my 450SE was towards the tail. I moved my ESC forward and the RX forward, and although it helped, it still wasn't perfect. I ended up installing one lead weight (1/4oz) under the battery tray. The CG is perfect now. I even put it on my plank CG machine to prove it. I set up my swash plate with a leveling tool. I would have thought that when I test hovered, it would have been "spot on." It wasn't. I still had to add forward trim to the elevator. This trim screws things up when inverted. Anyone have any thoughts? Thanks.

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12-03-2007 01:03 AM  10 years agoPost 2
jimboflies

rrElite Veteran

Beaumont, Texas;

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Mechanicly adjust the swashplate for forward elev. using the ball-links...

EP8 EX twinring frame
Quick of Japan
EP8v2 EX
EP9

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12-03-2007 03:06 AM  10 years agoPost 3
ckd

rrApprentice

Saugus CA

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Mechanicly adjust the swashplate for forward elev. using the ball-links...
but then that ends up messing it up when you go inverted. Add more weight is what I was always taught. I added a small plate on top of my V2 battery plate so I can get my battery more forward to help with the cg.

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12-03-2007 10:46 PM  10 years agoPost 4
702nitro

rrKey Veteran

Las Vegas, NV

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I wouldn't recommend using trim for anything, especially for the reasons posted above. Best bet is to play around with your battery position on the tray, or move the tail servo closer to the boom clamp.

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12-03-2007 11:27 PM  10 years agoPost 5
The_Widowmaker

rrElite Veteran

Bear Valley Springs, CA

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I wish I had that problem. My CG is forward because of 4S. I have no room for battery adjustment. ESC, wiring, gyro, rx and tail servo are as far back as I can get them without any mods and it still takes two nickels on the tail to bring the CG back.

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12-04-2007 02:39 AM  10 years agoPost 6
joey79

rrNovice

Edmonton, AB

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I had the same problem. CG was dead on, but the heli would still drift backwards while hovering. I adjusted the links from the washout arms to the flybar cage. Lengthened one and shortened the other, and it hovered level after that. Just check which way the cage tilts when you apply the elevator so you know which to shorten and which to lengthen.

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12-04-2007 01:30 PM  10 years agoPost 7
The_Widowmaker

rrElite Veteran

Bear Valley Springs, CA

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As much as I like the power of the KP 4S setup Im going either have to go to 3S or another brand battery that is not quite so heavy.

I have screwed the ball caps on the tail rotor linkage all the way in so besides buying a shorter rod, my tail servo is as far back as it will go. I moved my ESC to the bottom of the heli and it extends out past the back of the bottom plate. It is about centered on the brace of the rear landing gear. Can't really go back any farther. The 6100 rx is sticking out the back of the bottom plate. My wire bundle was next to it on the bottom plate but since it actually weighs more than the RX, I moved the bundle back and fastested it to one of the tail boom braces. Battery is as far back as it will go. My only option now is to add weight and Im just not going to do that.

It took two nickels placed on the vertical tail fin to get the CG correct and Im just not going to add that much weight to the back. Moving forward around tail boom block, I would probably have to add 3 times that or more.

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12-04-2007 04:57 PM  10 years agoPost 8
The_Widowmaker

rrElite Veteran

Bear Valley Springs, CA

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Ok I figured the difference in weight between the a 9257, which I currently am using, and a 9254, which I had but sold. Looks like I should have kept it going 4S. The difference is weight is 23grams (approx 4 quarters). I put 4 quarters on the 9257, making it the same weight as the 9254 and it balances perferctly.

I could just add 23 grams of lead at that location but instead I would rather pick up something in the process other than just weight. The 9254 and 57 spec about the same on speed and torque except the 54 is a little faster.

Anyone wanting to trade for a 9254 for a 9257?

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12-04-2007 07:11 PM  10 years agoPost 9
The_Widowmaker

rrElite Veteran

Bear Valley Springs, CA

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Whats going to be better,

7 grams added on vert fin or 23 grams added where tail servo is mounted?

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12-04-2007 09:34 PM  10 years agoPost 10
T-Rex-Flyer

rrElite Veteran

Panama City, Fl

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I am no expert, but to my way of thinking, I wouldn't want the extra mass out at the end of the tail where the servo would have the work harder to move.

Where's the engineer when you need one (I like to fly not do math).

If the wings are traveling faster than the fuselage, it's probably a helicopter.

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12-04-2007 10:18 PM  10 years agoPost 11
The_Widowmaker

rrElite Veteran

Bear Valley Springs, CA

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I just got back from testing. The 7 on the tail did not seem to bother the tail holding but with the weights on the fin it gave somewhat of a vibration. It probably exaggerated a small vibration. I went with 21 at the servo and it seems to be fine.

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12-04-2007 11:51 PM  10 years agoPost 12
AAKEE

rrApprentice

Boden, Sweden

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Ive got a 450SE and I use #s 2200mah lipos (184g)

I needed a small coin in the canopy to get it perfect in CG.
I also did a thourugh job on leveling the swash plate in its hole movement (from max to min pitch).
Didnt need any trim at all and it hovers hands of both normal and inverted.

Its a big improvement since before. The swasch didnt travel leveled so I got strange behaviour with low pitch angles. It made 'cork screw' loops and when flipping back from inverted it almost pirofliped.

I guess most improvment came from getting the swash travel in level.

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T-REX 450 › Center of Gravity
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