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Old Mar 06, 2014, 09:46 AM
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Trex 550 and 3gx Help

I had a problem with my esc. The regulator crapped out and sent the whole 22volts through my system frying everything. Luckily Align replaced all the servos, the esc and the 3gx.

So I just put it all back together and since I was doing all the work, I upgraded to a 600 DFC Head. Everything is setup correctly I re-calibrated everything on the 3gx per the manuals recommendations. I was flying on an older software version and now it is the current 4.0 release.

So I think I have a torque problem with the new DFC head. When I do an aggressive back elevator 180 degree inversion roll for example the tail kicks to the right about 90 degrees. I have kicked the gyro up to 85% which is about the max before I get tail wag. I also played with the aileron and elevator gain adjustments on top of the 3gx unit just in case it had something to do with the swash mix. If I do a more gentle roll it seems to hold fine. If I do an aggressive pitch climb it holds fine.

So my question is, does this sound like I need to increase the gear ratio on my tail? It still has the stock gear from when I bought it with the non-DFC head.

FYI. I am using a JR X9503 radio with two Satellite receivers. The 3gx unit is mounted at the rear of the main frame on top of the tail boom.
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Old Mar 07, 2014, 04:48 AM
Grumpy old git.. Who me?
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The DFC head doesn't change the gear ratio, it shouldnt make any difference to the holding power of the tail.. maybe you programmed in more collective pitch when you set it up?.

The Trex 550 and 600 are optimised for very high head speeds so have a low gear ratio on the tail. This is fine if you run the high ungoverned head speeds that Align intended, but if you run lower speeds the tail can blow-out in hard 3D.

It is possible to change the tail gear ratio but it's simple to do. You can also fit larger tail blades which is easier to do. Just check that you have clearance between the tail and main blades, this can be an issue with the 600 but shouldn't be a problem with the 550.
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Old Mar 07, 2014, 08:31 AM
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I have 95mm tail blades on now. I'm running 100% throttle, so I don't think my head speed is an issue. Maybe I am missing something on my setup. I going to start from scratch and re-program. I'll see if that helps.
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Old Mar 08, 2014, 02:59 AM
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On my 600 I use the 105mm tail blades off a Trex 700. On the 600 they have to be trimmed to a little over 100mm to avoid possibility of striking the main-blades but that likely wouldn't be a problem on the 550.

But you are right, if your running 100% flat throttle curve then tail blow out shouldn't be a problem in the first place. Maybe you have too much collective pitch?
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Old Mar 17, 2014, 08:17 PM
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Yes I agree too much pitch would do that. What version 550 do you have? Any idea how much pitch you running?What size main blades you running? End points on the tail travel set well? Do you have the DFC type tail gear ratio or the faster older style? At 100% throttle that tail should hold like a rock. Depending on the gear ratio and motor you could overspeed the older tail gear ratio.
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Last edited by TURBOOMNI; Mar 17, 2014 at 08:22 PM.
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