Tail moves right on takeoff

Tail moves right on takeoff
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Tail moves right on takeoff - 9/2/2006 10:52:54 PM

georgeb3dr

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From: , TX, USA
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TREX SE, 401 Gyro, 9650 tail servo.

I'm pretty new to this, but I've tried everything. I've followed videos for setting up the 401/tail and although everything I check seems to be right, when I try to take off, the tail rotates right, and the nose left.

Mechanically it all seems sound. The pitch slider is in the middle. There isn't a lot of binding. Channel 4 seems setup right. Reverse on the Gyro seems right (all going by Bob White's vids). I'm just stumped.

I don't really know what to do to debug this, since I'm so new to everything. I'm sure I just missed some step along the way.

I'd love some tips and info on where to look.

Post #: 1

RE: Tail moves right on takeoff - 9/2/2006 11:02:31 PM

BarracudaHockey

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When you say "moves right" do you mean it drifts right or it tries to spin like a top?

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RE: Tail moves right on takeoff - 9/2/2006 11:11:43 PM

georgeb3dr

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quote:

ORIGINAL: barracudahockey

When you say "moves right" do you mean it drifts right or it tries to spin like a top?

Hmmm...I'm going at fairly low speeds, as I don't want to lift off that way, so as it start to lift off, I stop. But I punched it a couple of times and the faster the main rotors went, the faster, and more forceful the tail would rotate to the right. So, it's not slight drift, that you can adjust with trim (I assume)...it seems to be tied to main rotor speed.

Did I mess up the belt? When I turn the main blade clockwise, the tail rotates counterclockwise, up into the downwash, and I thought that was correct?

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RE: Tail moves right on takeoff - 9/2/2006 11:17:48 PM

georgeb3dr

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Yeah, after watching a video of some guy with a tail rotating in the wrong direction, I'm not seeing that. It's not nearly so violent, and spinning like a top. It's more like drift to the right. I did try adjusting the trim on the rudder and that didn't seem to really be the solution, even going to the far ends of the trim.

< Message edited by georgeb3dr -- 9/2/2006 11:21:20 PM >

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Post #: 4

RE: Tail moves right on takeoff - 9/2/2006 11:35:31 PM

BarracudaHockey

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Well lets start with the basics.

Are your tail blades turning the right way, looking at the right side of the helicopter the tail should turn counter clock wise, that is, the blade going forward should be moving up and into the down wash from the main rotor.

If thats correct.....
Give Right rudder, the servo should pull the rod. If thats wrong reverse the rudder channel.

Pick up the heli, set the gyro in HH mode (solid light) and turn the nose couter clockwise, again, the servo should pull the rod towards the front, if thats wrong reverse the gyro.

Make sure you boot the gyro in heading hold mode (power it up, wait for 3 seconds before you touch the rudder stick or move the heli at all) and the light should come on solid. If its flashing 1 flash per second its not getting a signal from the gain channel or your are booting it in rate mode.

Check that, let me know.

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RE: Tail moves right on takeoff - 9/2/2006 11:43:27 PM

georgeb3dr

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quote:

Are your tail blades turning the right way, looking at the right side of the helicopter the tail should turn counter clock wise, that is, the blade going forward should be moving up and into the down wash from the main rotor.

Check.

quote:

If thats correct.....
Give Right rudder, the servo should pull the rod. If thats wrong reverse the rudder channel.

Check, as long as you mean right rudder to be (moving the rudder stick right), and 'pulling the rod" meaning the rod on the tail serve is pulled toward the front of the heli and not pushed toward the tail.

quote:

Pick up the heli, set the gyro in HH mode (solid light) and turn the nose couter clockwise, again, the servo should pull the rod towards the front, if thats wrong reverse the gyro.

Check.

I really appreciate the help. It has to be one silly little thing.

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Post #: 6

RE: Tail moves right on takeoff - 9/2/2006 11:57:18 PM

BarracudaHockey

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DS mode =ON

Delay to 0

Rudder atv's to 100

Hole closest to servo spline (i drilled one as close as I could get) used for the linkage.

Limit pot set so that the linkage doesnt bind in either direction.

No drag on the rod from that hole under the horizontal fin? I enlarged that a few sizes with a drill by hand.

What radio?

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RE: Tail moves right on takeoff - 9/3/2006 5:11:49 AM

georgeb3dr

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I have all those setup correctly. I did not drill any new holes for the tail servo, though, and am just using a hole that puts it at 90 degrees to the tail boom.

Could the problem be as simple as the tail blades not being centered properly and misaligned, so it pulls it to the right? From eyeballing it, they sure look straight, and there is an equal distance on both sides of the tail pitch slider.

One more detail. My 401 is mounted under the boom, but it's not 100% level. It's close, but it's on some foam and probably 3-5 degrees off being level with the boom. A potential problem?

< Message edited by georgeb3dr -- 9/3/2006 5:45:44 AM >

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RE: Tail moves right on takeoff - 9/3/2006 6:21:22 AM

georgeb3dr

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So, I think I did an interesting test?

I took the 401 out of the equation. I set the Futaba Gryo settings to all Normal mode at 50%. That basically removes the Gyro, right? It certainly had no affect on things and the 401 light was blinking and not steady.

Well, the tail still moved to the right, so now I'm thinking it's some mechanical setup thing?

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RE: Tail moves right on takeoff - 9/3/2006 12:51:20 PM

Remyrw

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Sounds to me like you just have a tiny bit of negative pitch in the tail at what the gyro thinks is neutral. I bet if you could get airborne the gyro would get it under control in heading hold mode, but it can't deal with the throttle changes on the ground. If it was a Blade CP I'd say you need a bit more proportional, giving the tail more push power for a given throttle setting but I know the T-rex operates differently and I'm not sure how you'd accomplish the same thing.

< Message edited by Remyrw -- 9/3/2006 1:12:24 PM >

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RE: Tail moves right on takeoff - 9/3/2006 1:05:20 PM

BarracudaHockey

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The 401 is really too much for the tail pitch slider on the rex.

Get the linkage as far in as you can towards the servo spline and set the limit pot so its not binding. You are going to get more throw one way than the other if its set up right and the reason that isn't a problem is because torque is spinning you one way, the tail rotor is over coming torque to spin the other so it needs more throw.

The bottom of the gyro needs to be 90 degrees to the main shaft, if you are using some kind of cushy foam get you some 3m outdoor mounting tape at wallymart, its grey with a red backing. Use two layers and mount the gyro.

What transmitter are you using?

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RE: Tail moves right on takeoff - 9/3/2006 4:09:06 PM

georgeb3dr

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I'm using a Futaba T7CAP.

quote:

Get the linkage as far in as you can towards the servo spline and set the limit pot so its not binding. You are going to get more throw one way than the other if its set up right and the reason that isn't a problem is because torque is spinning you one way, the tail rotor is over coming torque to spin the other so it needs more throw.

I do notice now, that when trying to move the tail left (with right stick) it just barely compensates for the tail spin to the right. I see a lot of deflection in the blades, but it's as if it just doesn't do much at all.

When you say get the linkage as far in as I can on the servo spline...

On the 9650, there is the little round hub that attaches to the servo, with a set of holes, labeled 1-4. I just screwed the linkage into one of those holes (the one that got it closest to 90 degrees). Is this really not sufficient? Are there any links to pics of where people have drilled thier holes, for reference?

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RE: Tail moves right on takeoff - 9/3/2006 6:20:29 PM

georgeb3dr

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Hmmm...think I found the root of the problem.

No matter where I put the 9650 on the boom, I cannot seem to get 100% full deflection on both sides, using the rudder. Seems like I should be able to peg both ends, then just back it off with the limits on the 401.

What mechanically could be wrong to cause this?

EDIT: Nevermind...was the 401 limit (putting it at 100 solved this).

< Message edited by georgeb3dr -- 9/3/2006 6:36:20 PM >

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RE: Tail moves right on takeoff - 9/3/2006 7:09:17 PM

georgeb3dr

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From: , TX, USA
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Well, I give up

With everything set properly (far as I know). I power up and the tail starts rotating right. I slow down a little and watch and I see that the Gyro has the tail pitch slider pretty far from center, so when I try to rotate left, I get virtually no play at all.

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