Flickering LED on 401 gyro - RC Groups
Thread Tools
Mar 21, 2006, 12:36 PM
Registered User

Flickering LED on 401 gyro

If the LED on a Futaba GY-401 gyro flickers off intermittently during flight while in Head Hold mode, is that a definitive indication of an electrical glitch? None of the other channels/servos are acting up. Can I then conclude the glitch is "downstream" of the RX (not RF link)? Could the flickering LED be caused by anything else non-electrical (eg: vibration, slow TR servo, slop in TR etc... all of which I likey have to some degree)?

PS: radio is powered up in HH mode and LED is solid before and after flight. Tail is "twitchy", but not a periodic wag. TR servo motion seems to indicate that twitch is being induced by the control system (ie: servo moves jitters first, tail jumps in direction produced by servo motion). Tail is not twitchy with GYRO disconnected (just more challenging to keep in line).

Moving the GYRO to front didn't seem to do much. Adding double foam tape... no change. Swap GY240 in both locations... same symptoms (with no LED of course).
Sign up now
to remove ads between posts
Mar 21, 2006, 12:44 PM
What helicopter?

Sounds like a glitch caused by static buildup from a belt-drive. Should be an easy fix.
Mar 21, 2006, 01:09 PM
Registered User
Just got me 401 today and flew it succesfully in my hornet. I didn't read the manual but as far as i'm concerned the blinking led just says that you aren't giving the gyro a neutral pulse (basicly it indicates you turning the heli on your TX)

It's no indication of a glitch or something, in fact i wouldn't think the 401 has such a feature, again i didn't read the manual.
Mar 21, 2006, 01:24 PM
Moving to Crouch, Idaho
Sounds like its working right..
Mar 21, 2006, 01:27 PM
Will fly some day
willfly's Avatar
I think this happens when ever there is a signal change on CH4 (tail) - like moving the yaw lever.
Mar 21, 2006, 01:47 PM
FPV Enthusiast
martinic's Avatar
This sounds perfectly normal. If the GY401 senses rudder input while in HH mode, the LED will flash. This happens whenever you move the rudder from center/neutral. Check it on the ground - power up in HH mode and then move the rudder stick - the LED should flash.
Mar 21, 2006, 02:23 PM
Guys, a "twitchy" tail is not normal with a 401...

The flashing isn't the important factor, it's what the tail is doing in the air that we should be worrying about.
Mar 21, 2006, 02:37 PM
FPV Enthusiast
martinic's Avatar
Chucky - Then the subject was poorly chosen and the main body of the post places the emphasis on the wrong concern. The mention of the twitching is in the PS part of the post. You're right - the twitchiness should be the concern and main subject - the LED probably doesn't matter (our point).

Twitchiness is a different issue. It could be caused by many things. What is the setup (servo, heli, headspeed, RX, ESC and component placement, etc.).

Some things to try: Check for the easy things first - is the motion of the tail slider smooth (remove link from tail servo, operate by hand to verify if any binding). Is there slop in the tail system (move the grips and slider with everything connected to see if there is slop)? Check wire routing to ensure power is well separated from radio equipment. Have you replaced the servo to see if the fault persists?
Mar 21, 2006, 04:27 PM
FPV Enthusiast
martinic's Avatar
Same issue on RR at this thread. Issue seems to be incorrect crystal for the 146 RX. This is a Trex SE with GY401/9650.

Looks like you're going to see if the crystal will fix it. (OmegaDot a.k.a ckoelliker). Please let us know if it fixes it in order to close off the thread for others who may have similar issues.
Mar 21, 2006, 06:42 PM
Registered User
Post at lunch time and have feedback by the time you get home. Isn't the internet great!

Firstly, to martinic - I'm not familiar with the RR thread and I'm certainly not "a.k.a" anyone but OmegaDot. First and only post by me on this subject was today, here.

FWIW, I'm currently using an Electron6 but just happen to have a new-in-box R146iP to go with my new 9CAP Xmtr. I was going to try this if the concensus was that the flickering LED was RF glitching.

Perhaps the subject was poorly worded, but it addressed the first burning question I had. Trying to eliminate one potential cause at a time and was planning to start a new thread if gyro was ruled out... But since you asked!

The heli is a Shogun with shaft drive, original tail pitch slider, a carbon TR pushrod with ball links, and a GWS (PICO+F?) BB TR servo (ie: lots of potential contributors). HS56-HB everywhere else. Head speed is 2400RPM. Rx at top front, ESC to right and just in front of DH-400 motor. TP3S2100. Gyro has been variously located below motor, under main frame, at back of battery compartment (makes no difference). Haven't tried it with the gyro on the bench next to the heli. It has "twitched" for a while now, but is flyable. "Twitch" = sudden unexplained jump of tail by 1/2 to 3 inches, in "random" directions. I believe the jump is PRECEDED by servo movement. I'm sure many will tell me to spring for the fastest digital servo and all will be fixed (so says the LHS). I wanted to eliminate electronic causes before I threw money blindly at the problem.

For ~18 months, up until this weekend, I ran the heli with a homebuilt PIC micro based Auxillary BEC/LipoAlarm/Throttle/CP/REVO/Gain mixer module onboard and a non-heli 5ch Tx. Though I was 99% sure the twitch had nothing to do with my mixer, I never tracked down the real source(s). Now with a new 9CAP Tx, the onboard mixer is gone, along with the other nice features... but the twitch behavior is still exactly the same.

With the heli on the carpet, light on the skids, same yaw position as where power was first applied, TR servo nominally centered, and with hand off the left stick... The LED still sporatically flickers and the TR servo jitters. With GYRO in rate mode, same symptoms, minus the LED indicator. Without the gyro, under the same conditions, the servo is fine. I have swapped the servo "in kind" to no effect. I really don't see how the servo or mechanical slop can cause the GYRO LED to modulate?

Hmmm, here's an experiment... Y-connect the TR servo and gyro INPUT to rudder channel at Rx, leave gyro OUTPUT hanging, spool up and see if gyro still blinks and if servo is steady???

If the LED blinks when you make an intentional TR stick input, wouldn't it also blink if the Rx intermittently tossed a bad rudder pulse?
Last edited by OmegaDot; Mar 21, 2006 at 06:58 PM.
Mar 21, 2006, 08:23 PM
FPV Enthusiast
martinic's Avatar
Sorry for leaping to conclusions - it was just remarkable coincidence.

Seems logical that you could be getting RFI. I would swap the RX and see what happens. I would also replace the tail servo and run HS56 all round. If the gyro is bad, it should mess up in bench testing too. If you get desperate, strip out the gear and bench test it all to try to isolate the issue. I'm just guessing like you - you sound like you're doing the right things to try to resolve it.
Mar 22, 2006, 03:36 AM
That tree again!!!!
thanhTran's Avatar
I also observe this problem on one of my heli. With same 401 gyro, if I use with eclispe 7 TX and with electron 6, it will intermittently blink when the left stick at highest position. Main motor is not running. Remove all servos, ecs, doesn't seem to help. This blinking doesn't seem to interfere with my flying. Maybe they are very short changes. When I use this same gyro with a DX6 system. It's not flickering. I then did some modification to use the Eclipse 7 with a spektrum module (https://www.rcgroups.com/forums/show...umize+eclipse), the flickering goes with the TX. so I'm pretty positive that the TX causes this. My flying with this TX doesn't seem to have any problem. When glitch really happens, the light is also blinking, and I sure see tail wag or heli shaking.
Mar 22, 2006, 04:04 AM
Mad Heli Scientist
BigS's Avatar
I have also had my GY-401 get 'twitches' and the light flicker when using a electron 6 receiver. It turned out to be the recevier was on the way out. I use a Futaba 8uhps TX.

The gyro will also twitch/blink if there is interference coming back from the servo wire too.

Mar 22, 2006, 04:12 AM
Registered User
buzzsaw 46's Avatar
The flickering led is glitch, had this problem on my Eolo. intermitant tail wags and a blinking led are the sure sign. I switched from a JR 549 RX to a Berg g3 6ch and the problem went away. Let me guess the ESC is a CC?
Mar 28, 2006, 09:35 PM
Registered User
After a bit of experimentation I have determined that the blinking GY401 is indeed normal and indicates that the TR stick was being held ever so slightly off center. The actual pattern is blink-blink-pause-blink-blink-pause. I think the non-uniform timing, combined with the fact that it only occurs when the stick is biased off center had me thinking the blink was random.

My twitchy tail has been vastly improved by shortening the TR servo arm from 10mm to 6mm (shaft center to ball link).

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
401 Gyro on a Shogun newman Mini Helis 10 Oct 05, 2004 11:17 AM
Art Newlands old Futaba 8U, 401 Gyro on zoom setup help. Dino Mini Helis 12 Aug 21, 2004 12:02 AM
Tail hunting on Zoom 400 With 401 Gyro?? theviper Mini Helis 21 Aug 15, 2004 12:51 AM
What's the best price on the 401 gyro?? Dr Honda Micro Helis 8 Jul 12, 2004 09:46 AM
Futaba 401 gyro on a Hornet? maiv Electric Heli Talk 5 May 26, 2002 01:52 PM