Weird DX7 tail/gyro issue

[sireric]

Hi.

I hadn't flown in 2.5 weeks due to various reasons. This evening at sunset, I decided to take a flight on both my Trex 450 and 600. Both are using DX7 as models 1 and 2, with AR7000 receivers.

Nothing had been touched on the T-rex 600, while I did rebuild the tail and head on the 450. I might of messed with the transmitter, but I don't think I've played in the 600 model.

Anyway, took off and flew the 450 in standard mode without a problem. I switched to idle up and the head spin went up (expected) but the tail started drifting quickly. I tried to adjust the trim, but no go. Almost felt like it was in non-HH.

I landed and switched to the 600. Same thing! I checked the gyro light while on the ground (though it's hard to check in idle-up 1), and it seemed to be steady, though I had to give so much tail control that I can't really be sure.

Any idea what could of affected the two models like that? I checked the settings for gyro, and they are both in the 70's with the rudder switch switching modes. I don't see a difference there between std and idle-1. I checked the trim, and it's almost the same between std and idle-1.

Any ideas? A little stumped.

[fireup]

Yep, happens to me too sometimes. It's because the gyro boots up faster than the receiver sometimes. When this happens the gyro sees an invalid signal and don't initialize properly. That's why your heli feels like it's not in HH mode even when you get a solid light.

The only fix at the moment is just unplug and plug back power again and make sure the cyclic servo initialize first before the tail.

[sireric]

Ok. Strange that it would happen twice. But why would it work fine in std mode but not in idle-1?

Thanks for the help!!

[Danal Estes]

Fireup, very interesting that this is happening to you. I have not experienced this nor heard it from any of the dozens of people flying DX7s and GY401s around here.

Any possibility that your reciver still has an exact "mid channel" setting on the Gyro gain channel at startup? In other words, after you completed the full setup for you heli, did you re-bind? A rebind memorizes your HH gain and therefore the RX is putting out a clean HH signal at startup... prior to the RX linking to the TX... If, however, the factory bind is still in effect, the gain channel will be exactly at middle and the gyro could have trouble booting.




Sireric, you say "I checked the trim...and it's almost the same..." trim on what channel(s)? Rudder trim should be zero in ALL modes, agree?

Also, perform the following check:

1) Power everything up, but don't spool up.

2) Move the rudder stick and recenter. Tail blades should move and NOT recenter (because you powered up in HH mode, and the heli hasn't changed heading, the gyro will keep trying to change the heli's heading).

3) Throw the appropriate switch to enter Rate mode. Tail blades should immediately recenter. While still in this mode, move rudder stick & recenter, blades should also move and recenter.

Switch back to HH and verify as in Step 2 again. Repeat 2 & 3 if desired... (I'm really hard headed sometimes)

I do a variant of this (power, bump & look for blades to stay over, switch and look for blades to recenter, switch back to HH) before every flight (along with a quick cyclic check). It has saved me from some mistakes (like powering up with the switch wrong) a couple of times.

[sireric]

Thanks. By trim, I mean I'm using rudder trim to center the gyro, per the 401 instructions. I could do mechanical centering, but prefer electronic centering. It's set at gyro initialization and doesn't change afterwards.

I've changed the gyro gain without rebinding, and I saw that it did work. I'll try to rebind and see if it helps.

Thanks again!

[Jermo]

don't use rudder trim on anything for the rudder. Use subtrim only. Rebind after changing anything with the rudder/gyro. Note: Trim is mode specific. If you have rudder trim in idle 2 it will be different in idle1 and/or normal unless you put it in.

Up in the Finless Helifreak techroom there's a vid for the GY401 and I did a DX7 video. Use those if you still have issues after fixing trim and rebinding.

[DavidH]

Why would you use any type trim at all? Subtrim is really no different than the normal trim. It is just a way to do some trimming and leave the trims on the transmitter centered.
No trim of any type should be used with a HH/AVCS gyros.


David

[Jermo]

On the DX7 subtrim is for all modes and allows you to get the tail servo exactly 90 degree's. I think we can all agree with DavidH about really not needing any since the servo has more than enough travel to move the slider.

[DavidH]

On the DX7 subtrim is for all modes and allows you to get the tail servo exactly 90 degree's

Why can't you get the tail servo horn 90 degs without subtrim or trim?

The majority of the servo horns or wheels can be rotated and the position that is needed can be found. That is why the spilines are offset and the servo horns had numbers at each position.

Just a pet peeve for me to see people put on servo wheels and then start using trims and such and never have tried to position it correctly. I have seen many models that the builders have done this. They try to take the easy way out, than spending a little more time and doing it the correct way.

David

[sireric]

thanks. I ended up resetting all trims and gyro settings and it appears to work on the 450...

[TMoore]

Jermo, the only gyro on the market that can truly handle subtrim is the JR 500T because it doesn't depend on the TX to set the gyro/rudder neutral.

Subtrim isn't any different than trim. They both do the same thing.

TM

[Defuser]

I have a Trex 450se, a DX-7, a 401 gyro, and the servo is a Fatuba s9650. When I stick left or right rudder, then let the stick center, the s9650 or the hs-50 (that I had) does not return to center. I can move the servo completely in both directions with the stick, but when I let go of the stick the servo just moves a little. Is it a setting in the radio or???? All other servos are fine and center beautifully.

Defuser :dontknow

[Jermo]

That's normal in heading hold mode. ;)

[Defuser]

Slowly but surely my Trex will fly.

Today when I spun up the Trex450se w/ Gyro401(in normal mode), as I gave it more power, everything was fine until around 1/2 stick+. It just spun around in circles on the gound completely out of control(no matter what I did to the Rudder). I tried this a half dozen times or so..... same thing. Anyone? :arggg:

[tppjr]

Slowly but surely my Trex will fly.

Today when I spun up the Trex450se w/ Gyro401(in normal mode), as I gave it more power, everything was fine until around 1/2 stick+. It just spun around in circles on the gound completely out of control(no matter what I did to the Rudder). I tried this a half dozen times or so..... same thing. Anyone? :arggg:

Reverse your rudder servo in the TX. The gyro senses tail movement from the spinup and adusts the rudder in the wrong direction adding to the problem creating a run away situation.

Thomas

[fireup]

Slowly but surely my Trex will fly.

Today when I spun up the Trex450se w/ Gyro401(in normal mode), as I gave it more power, everything was fine until around 1/2 stick+. It just spun around in circles on the gound completely out of control(no matter what I did to the Rudder). I tried this a half dozen times or so..... same thing. Anyone? :arggg:

Reverse your rudder servo in the TX. The gyro senses tail movement from the spinup and adusts the rudder in the wrong direction adding to the problem creating a run away situation.

Thomas

No, reverse on the gyro first. You may need to reverse on your TX also depends on if the nose move in the same direction of your stick.

[Defuser]

Problem solved....Reverse switch on gyro...THANKS!! I don't remember touching the switch before though :dontknow

[tppjr]

Slowly but surely my Trex will fly.

Today when I spun up the Trex450se w/ Gyro401(in normal mode), as I gave it more power, everything was fine until around 1/2 stick+. It just spun around in circles on the gound completely out of control(no matter what I did to the Rudder). I tried this a half dozen times or so..... same thing. Anyone? :arggg:

Reverse your rudder servo in the TX. The gyro senses tail movement from the spinup and adusts the rudder in the wrong direction adding to the problem creating a run away situation.

Thomas

No, reverse on the gyro first. You may need to reverse on your TX also depends on if the nose move in the same direction of your stick.

Got it, thanks,

Thomas