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HomeAircraftHelicopterHelicopter Main Discussion › Heading hold gyro question
02-08-2008 04:11 AM  10 years agoPost 1
Nicros

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San Diego, CA

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Hi,

I have the TRex450SEv2 with a GY401. I had a pretty nasty crash a bit back, and while the repairs seem all good, I have noticed something with the HH Gyro.

Occasionally, the tail will wag really quick, like a shudder- but it doesnt happen often (I have it on digital as I have a 9650 servo) and doesnt seem to affect much.

I also noticed that when I am in a hover, if I give full power the tail spins quite a bit- the heli does a few pirouettes as it climbs. Before the crash I could give it full power and the tail would not move.

I had to adjust the blade pitch all over again after the crash- so Im wondering if the pitch is too positive- so the tail rotor cant keep up with the power and pitch.

Or maybe the GY401 is damaged? I also notice that when I fly the red light is sometimes flashing and sometimes steady...

Any ideas anyone?

Thanks!

Ever notice how crash rhymes with cash?

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02-08-2008 04:44 AM  10 years agoPost 2
tadawson

rrElite Veteran

Lewisville, TX

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Do a setup on your 401 in normal mode, if you have not done so already. If you don't you really don't have any idea where the servo is centering in flight . . . also make sure that your tail rotor is running in the right direction - I have heard of things like this happening if the belt goes back in twisted the wrong way . . .

- Tim

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02-08-2008 08:30 AM  10 years agoPost 3
astro-g

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Wellington, New Zealand

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Are you sure you haven't lost a tooth on the tail belt?

Beating the air into submission

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02-08-2008 10:25 AM  10 years agoPost 4
tlankford01

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Amarillo, TX 79110

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possilby need to increase your gain a bit if it piro's in a climb.

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02-08-2008 12:26 PM  10 years agoPost 5
Way2slow

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Jeffersonville Ga

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I have two different 450 size heli's, both have 401's with S9257 servos, both have the tail centered perfectly, neither have anykind of a tail twitch/wag when flying or hovering and both will kick the tail around when you slam the stick forward if you are just hovering at or flying at low rpm on the motor. I've assumed it's just the torque of the motor is a lot more and a lot quicker than the servo can compensate for. Figured it would not do that if it was in an idle up mode so the blades were already spinning at full speed so it didn't have all that motor torque to compensate for.

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02-08-2008 12:59 PM  10 years agoPost 6
helimatt

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Lafayette, IN

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The 401 gyro can hold the tail in full pitch climb-out if set up properly and the head is not bogging too much.

After you are sure the tail is properly set up, the gyro holds in rate mode, and that you don't have any bent shafts or other sources of imbalance and vibration then:

1. Check the gyro mount tape- not torn or loose.

2. If all that is good, likely the gyro is damaged. The occasional quick wag is a symptom that something other than just insufficiently high gain is at work here.

Never, ever, ever, ever give up.

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02-08-2008 03:40 PM  10 years agoPost 7
Nicros

rrApprentice

San Diego, CA

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I will check the gain, but it sounds like something got damaged in the 401. There is most definately an occasional quick wag, not consistent at all.

Only other thing I wonder is if maybe the servo was damaged. I blew out all 3 of the ds285s, and it was a tail strike so that would make sense too.

How can I check to see definitively if it is the servo or the 401 (or both) that is bad?

Ever notice how crash rhymes with cash?

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02-08-2008 07:59 PM  10 years agoPost 8
helimatt

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Lafayette, IN

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Just put a little load on the servo , powered up and see if it moves smoothly throughout its range. Wiggle the wires, tap on it, etc, to see if you can get it to be jumpy or freeze up.

You can do the same with the gyro, but tapping on it should make the servo jiggle, so harder to tell.

Ultimately you could swap in a known good servo.

Never, ever, ever, ever give up.

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02-08-2008 08:40 PM  10 years agoPost 9
crofty

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Phoenix, AZ - USA

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I had the exact same problem. I crashed my 450 so many times I assumed the problem was one crash too many on the servo (9650). At times it would kick a full 90 deg on power others just a bit.

I set it up in rate mode to ensure the gyro was in the right place and that stopped it kicking as much but it still wagged on fast turns and would wag all the way around a funnel. (My first crack funnel, beat that Dzsabo. )

I've since replaced the 9650 with a JR3400 and so far so good. I am working down the gain to get rid of the final bit of wag but it's generally flying a whole lot better.

I'll repost if I get the wag to go completely this weekend although my new nitro is supposed to get it's maiden this weekend so the 450 may have a weekend off!

I have nerves of steel but thumbs of jelly!

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02-08-2008 10:22 PM  10 years agoPost 10
Andy from Sandy

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Bedfordshire, UK

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I am going with a faulty servo. When the gyro wants to stop the tail from moving whilst in HH it will move the servo a large amount to get the helicopter back in shape as fast as possible. The result is you don't see the helicopter move or only a very small amount. If the servo is damaged what you are seeing is the servo is not centering properly so the tail kicks but then the servo does move and the helicopter stops.

As already mentioned, put the gyro in normal mode, then hold the servo horn and keep moving the rudder left and right and feel for a dead spot.

I have had the same problem with a 9254 connected to a GY401.

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02-08-2008 10:29 PM  10 years agoPost 11
payne1967

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uk

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have a look and make sure your tail belt drive pulley at both ends of the belt are not slipping on their shafts

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02-09-2008 07:46 AM  10 years agoPost 12
Nicros

rrApprentice

San Diego, CA

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So far as I can tell (I checked tonight) the belt is still good and there is no slippage.

There also doesnt seem to be any issue with the servo or the gyro, everything is smooth. So maybe my pitch settings are too positive?

Would that make sense?

Ever notice how crash rhymes with cash?

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02-09-2008 01:08 PM  10 years agoPost 13
tlankford01

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Amarillo, TX 79110

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No the gyro can keep up with full size heli's so I do not see how a 450 is going to over torque the gyro at all. We have had this trouble some on our 450's and it just took setting it up correctly in the radio. Hope that you can figure it out. Also if you think that the head speed is too high you can lower the top of your throttle curve a bit.

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02-09-2008 05:48 PM  10 years agoPost 14
Sam2b

rrElite Veteran

Tacoma, WA

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My few thoughts are:
Occasionally, the tail will wag really quick, like a shudder- but it doesnt happen often
Check for a possible bad or loose wire. On the work bench (with your motor unplugged) gently wiggle the tail servo wire all the way from the receiver port to the servo and look for any servo jitter. Just keep the heli flat on the table and not moving while wiggling the wires.

If you have wires tied up with a zip-tie, inspect them for wire damage. A crash might have cause a yank on some wires. I also agree with the other suggestions above.
if I give full power the tail spins quite a bit- the heli does a few pirouettes as it climbs
My knee jerk thought was try increasing the gain. BUT if your servo horn, linkage, and servo travel is not set up correctly, the gyro will not work efficiently. (that reminds me to create my own document)

If anything, you should only see a small twitch when you give full collective pumps. If it does an entire piro, I'd question the entire gyro/servo/linkage setup.

_Sam B_

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02-09-2008 06:36 PM  10 years agoPost 15
Nathan

rrApprentice

Elkhart, Indiana

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Hope you find out what this is. Because I have a brand new 450 and 401 w/9650 and it does the samething. I have chased this for almost a year.

Nathan

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02-10-2008 12:21 AM  10 years agoPost 16
Nicros

rrApprentice

San Diego, CA

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An update:

I think Sam is right, I dont have the gyro/servo/linkage set up properly after the crash (he kindly offered to help with a howto).

I discovered this by decreasing the pitch, and noticed that I could hit full power with no spinning. But then I have to give too much power to get the thing off the ground- so I need to tweak things better- maybe it wasn't right even before the crash.

Ill keep updating till I get it fixed!

Ever notice how crash rhymes with cash?

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