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Tail drifting (rotating CW) slowly with AVCS

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Tail drifting (rotating CW) slowly with AVCS

Old 10-21-2006, 02:40 PM
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Default Tail drifting (rotating CW) slowly with AVCS

This is sort of related to the other thread about the tail mis-behaving but I didn't want to thread-jack. I have a 450XL using GY401 and HS-65 on the tail. Bob's video asked that we set up the servo so that when it is centered, the tail slider is in the middle. I see a problem with that, because centering the slider means 0 pitch for the tail rotor. That means with no stick movement and the main rotor spinning, the tail would just rotate CCW uncontrollably. Shouldn't the tail slider be at a position where when the servo is centered and the main rotor spinning, the tail should stay put? (relatively of course) Eventhough I thought about that, I still followed bob's direction and centered the tail slider. This produced 3 problems:

1. In AVCS mode, I can barely make the heli rotate CCW. I get a fast CW rotation but not CCW.
2. The tail drifts slowly CW over time. If I understand correctly, adjusting the rudder trim under AVCS won't do anything. How do I cure this?
3. If I flip over to normal mode, I have to trim the rudder over 35% to the right to barely keep the heli from rotating. This is due to what I mentioned earlier, bob asked that we center the tail slider when the servo is centered. I did try to adjust it the way I think it should be, but I get slow CW rotation but fast CCW. So I think it needs to be some where in between what bob said and what I had in mind. Does this make any sense at all?
Old 10-21-2006, 05:02 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

First off that servo isnt made for running on a 401, that aside....

The "correct" way to set up the tail is to set the linkage length so that the heli will hover in rate mode w/o drifting with the servo arm at 90 degrees.

Unfortunately on the rex the tail pitch sider is so short that doing it "correctly" leaves almost no throw one direction since on the 401 you can only adjust total throw, not individual end points (and dont try to do it with radio atvs). The good news is you dont need much throw to turn with torque doing the work for you.

The other issue is you need a fairly short servo arm to get the limit pot as high as you can with the trex and make sure there's no binding or excessive slop anywhere in the tail rotor control system and make sure you are running sufficent head speed so that the tail rotor is fully effective.
Old 10-21-2006, 05:11 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS


ORIGINAL: BarracudaHockey

First off that servo isnt made for running on a 401, that aside....

The "correct" way to set up the tail is to set the linkage length so that the heli will hover in rate mode w/o drifting with the servo arm at 90 degrees.
That's exactly what I meant.

Unfortunately on the rex the tail pitch sider is so short that doing it "correctly" leaves almost no throw one direction since on the 401 you can only adjust total throw, not individual end points (and dont try to do it with radio atvs). The good news is you dont need much throw to turn with torque doing the work for you.
That's what I experienced in 3 that I mentioned above. So you're saying even with limited throw, using the torque, I can make it rotate CCW quickly? I guess I just have to adjust the slider a little so I get more throw for CCW rotation?

The other issue is you need a fairly short servo arm to get the limit pot as high as you can with the trex and make sure there's no binding or excessive slop anywhere in the tail rotor control system and make sure you are running sufficent head speed so that the tail rotor is fully effective.
I have the tail linkage rod on the hole closest to the center of the servo. The tail is as slop free as a XL can be. I have a 430L 3550KV motor on a 11T. My DX6 is set up to have 0, 90, 90 throttle curve. Would that be sufficient head speed? (I stripped the thread for the locking nut on the 13T pinion because I got a bit torque-happy)
Old 10-21-2006, 06:06 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

I'm running a 65 on the tail and I have just a bit of a drift maybe 1/8 turn over 1 min nothing that you don't get used to after awhile. As for the servo arm hole make a new one as close as you can to the center this will help you out so you can run a higher gain. As for the pinion size 11t should give you plenty of HS. Remember to do all you trim settings in Non-HH play with moving the servo for and aft until you have it dead on. It will take about one battery worth to get it correct. As for doing CCW spins make sure you have max throw on before it binds on you Gyro set up and you should be good to go.
Old 10-21-2006, 06:15 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

ORIGINAL: NVSFlyer

I'm running a 65 on the tail and I have just a bit of a drift maybe 1/8 turn over 1 min nothing that you don't get used to after awhile. As for the servo arm hole make a new one as close as you can to the center this will help you out so you can run a higher gain. As for the pinion size 11t should give you plenty of HS. Remember to do all you trim settings in Non-HH play with moving the servo for and aft until you have it dead on. It will take about one battery worth to get it correct. As for doing CCW spins make sure you have max throw on before it binds on you Gyro set up and you should be good to go.
I will drill a new hole for it. I just noticed that it is doing a slight bit of hunting eventhough I'm down to 25% in the DX6 for gain. More resolution should help a ton. thanks.
Old 10-21-2006, 06:45 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

I'm using a DX6, 401 and 65 all the way around only difference is I'm using a 450th motor. My gain is set at 91% on my TX and it holds great on max climb outs. You will need to have your Delay set at about 65 or you will get a bounce after fast turns.
Old 10-22-2006, 03:26 AM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

After moving the servo rod closer to the center and adjusting the slider position, it rotates much much better now. I had to lower the travel a bit to keep it from rotating too fast. But my main problem of it drifting CW over time slowly in AVCS is still there. I got the expensive GY401 so the heading would be rock solid, not drifty. Do I HAVE to go with a digital tail servo to eliminate this? I thought the GY401 is supposed to be rock solid even with a HS-65.
Old 10-22-2006, 12:43 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

Yesterday I did a bunch of searching over forums and I think I figured mine out. I mount my Gyro upside down and I had placed a tight strap to make sure it didn't come off. I think that I was getting vib through it an it was causing issues. Make sure your Gyro is secured down with the Gyro tape and that it's not rubbing on the frame.
Old 10-22-2006, 09:16 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

I have my gyro on probably 10 layers of mounting tape to make up the volume under the frame at the back. Then I have a piece of plastic then it's sitting on the mounting tape that came with the Gyro. I think I'm ok as far as vibration goes. Actually, adjusting the trim does correct for some drift in AVCS mode. I think I'm ok now. I'm just not used to the tail being so precise.
Old 10-23-2006, 01:05 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

10 layers? Its probably too spongy. 1 or 2 layers is what you want.
Old 10-24-2006, 03:49 AM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

ORIGINAL: rcboosted

I have my gyro on probably 10 layers of mounting tape to make up the volume under the frame at the back. Then I have a piece of plastic then it's sitting on the mounting tape that came with the Gyro.
If you have a CF frame there is an [link=http://www.modelhelicopters.co.uk/acatalog/VarUpgrades_MicroHeli.html#aMH_2dTX4001LGM]underside mount[/link] available now that bolts in the rear.

The mounting foam that comes with a GY401 is designed to absorb vibration from the frame at the frequencies that the piezo sensor works at. Putting a cable tie or some other fastening over the 401 will bypass the damping foam.

Any gyro needs to be mounted as firmly to the frame as possible, several layers of servo tape will act as a spring and the gyro will be bouncing all over as the heli vibrates. Not good for performance. The only tape you should have is the supplied damping foam.
Old 10-24-2006, 11:25 AM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

I just have a plastic frame, so I can't use that mount. I did make a mount myself using an eraser and a piece of plastic. It's mounted using regular mounting tape that comes in a roll. These are thinner and less springy as the futaba ones. I will see how it does tomorrow. The thing with the strap though, you want to make sure you don't lose the expensive gyro so you strap it down, but the safety from the strap changes its behavior. Just can't win.
Old 10-24-2006, 12:41 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

Get some 3m outdoor mounting tape, its grey tape with red backing, use two layers, it needs some vibration islolation while giving a bit of dampening. A soft strap is fine to keep it from fallling out but invariably it ends up transmitting frame vibration to the gyro, mount it correctly and you wont have to worry about a strap. Also you would have to worry about it even less so, most of the foam tape problems come from fuel getting inbetween the layers of the tape and degrading the foam, since you dont fly wet it shouldnt be an issue.
Old 10-26-2006, 01:02 AM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

I'll look for that mounting tape. In the meanwhile, my eraser mount worked great. I can bump up the gain to 60% instead of 35% previously without hunt.
Old 10-26-2006, 12:36 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

My Trex XL has a GY401 and I use a Futaba 3107 on the tail. (I know it is not the best servo but it is what I had at the time) I get absolutely NO drift on the tail for an entire run. I am running just a tick over 3000 head speed and one thing that may be helping it is that I have the complete Duzi Tail Rotor setup on it. It also Piros fast in either direction. My post is here because there should be no drift with a 401 reguardless of which servo/tail rotor you are running. It sounds like the GY401 is not being allowed to completely initialize in AVCS mode before the heli is being moved. The heli has to be on a solid surface with absolutely no movement at all while the gyro is initializing (The ground works fine as long as the wind can't wiggle the machine even the least bit as again the AVCS gyros are very sensitive to the slightest movement while they are initializing). Good luck getting it sorted out.[8D]
Old 10-26-2006, 01:52 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

It's difficult to keep it steady the whole time it is be initialized. Because as soon as I have the deans together, the servos move a bit before centering. Also I have to get the deans connected enough so it doesn't fall back out. That takes time, so the first second often have movments. I'm not sure if those movements are still causing vibrations to the frame afterwards. I also find out that I CAN trim the rudder while in AVCS mode.

BTW, the deans spark everytime I connect them, is this normal? My balance connector spark somtimes too when connected to the charger.
Old 10-26-2006, 04:01 PM
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Default RE: Tail drifting (rotating CW) slowly with AVCS

You dont want to use rudder trim in AVCS mode, it will take it as a command to turn.

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