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HomeAircraftHelicopterBergen R/C Helicopters › tail rotor glitch demystified (tail kicking, wagging, etc)
11-07-2004 05:11 AM  13 years agoPost 1
kas1903

rrNovice

groveland, ca

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howdy,

to get right to the point, my GY401 has gone wacky; with gyro, servo kicks all over the place, without it is smooth...now for the details:

i built my bergen gasser about 5 months ago. after one gallon of fuel, everything was going just great. then i started to get a tail rotor glitch. when i would start up for the weekend, the tail would kick or wag (depending on your personal vocabulary). because i am a scholar of runryder, i researched and i thought it to be a tuning problem...afterall, if your tail is kicking, the engine is rich!!!. in fact, this was reinforced because what i did was fly for a few minutes and it went away....what i figured was that the plug was a bit "fouled" because of priming or temperature changes (coincidentally this problem occured with winter's onset). so i flew with the tail kicking all over for a few minutes, then it cleared up. this happened for 3 or 4 tanks over the course of 3 or 4 different flying days. now, as time went on and i did more experimentation with video cameras and such, it got worse. it got so bad that the tail went completely nose in from a tail-in hover.

i simply couldn't shake it. i leaned the damn thing till it wouldn't lift off the ground. i then tried the standard settings and tried flying for a while to see if it would "clean up". well sh**%. didn't work. so i did more reading and saw that people were having problems in the past with the GY401.

i talked with chris (bergen...of course) for quite a few private messages. he had some great ideas. first off, check your mechanism for binding. mine is really smooth, smooth as a baby's bottom. then i tried all the tuning changes, rich, lean, even tried the damn setting that gave a perfect hover for the first gallon.... and THAT didn't work! chris had a very great idea, check the voltage. did this happen on a new charge and then as the battery voltage dropped a bit, it worked?

the GY401 is rated for 6V operation, and i chose the S9254 because the S9253 doesn't have any torque. at $100 a servo, this is a tough lesson to learn all by itself. as we all know, futaba recommends 4.8V nominal for the digital servos.

i am using 6V batteries, but before you go wild and accuse me of over-voltage, i have diode-isolated my dual battery pack system and i have a second diode on the tail rotor servo just to reduce voltage for the digital 9254. (diodes always have a voltage drop in them). almost fully charged, i have 5.5V going to my gyro (and the entire system) and since i have a second .7Vff diode going to the tail rotor servo, it is seeing about 4.8 volts.

so i had time today to try some things. i took it to the field and started it up. at idle, the servo was kicking all over. it moved like no tommorow. i put it on the ground and tried all engine RPM's and rotor speeds. the damn thing was very erratic all the time, i thought it was going to break the boom...it was rotating the servo arm about 20 degrees at random.

i went home.

i was desperate so i put in a trusty S9202 on the tail rotor an bypassed the GY401. now when i ran it, the servo was very very smooth. this poses two questions, was it the S9254 digital or the GY401? easy question to answer. i plugged the S9202 that operated smoothly from 0 to 1700 RPM headspeed into the GY401. now when i ran the engine up, the servo was going crazy!

so, apparently the GY401 has a problem. i am not sure if i have had any sort of voltage spike, if perhaps my sparkplug resistor has lost it's resistance or if something else has occured. i do know that i have seen elsewhere that the GY401 apparently had a bad batch and i wonder if i had one? maybe digital servos just don't work with the gas engines that well? naw, i know that isn't the case becuase everything used to work....

the real puzzling thing is that i started out with a perfect flying machine. everything was real smooth and over the course of 2 gallons of fuel (not starting until after 1 whole gallon), it started wagging all over the place, the tail is kicking like a donkey! i never changed anything except that i have mounted video equipment, etc. and of course i removed that stuff for the sake of the the scientific method. it didn't make any difference.

so my GY401 and my servo are going to futaba for a checkup. i will update the post when the stuff comes back and i re-install them. it is kicking now and it never did before with the exact same equipment so after service, this should be a good experiment for the whole tail wagging problem.

kas

http://www.heli-chair.com

fly like ya live!

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01-19-2005 01:02 PM  13 years agoPost 2
kas1903

rrNovice

groveland, ca

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problem solved - update
sent equpiment to hobby services as described above and they returned it saying that nothing was wrong with it. i re-installed everything and it flew just great, the tail kick went away. *shrug* didn't change anything except the gyro and servo and according to hobby services, they didn't do anything to those either. maybe the fact that it took me several months to get back to flying the helicopter accounts for a change in the position of the sun and moon.

kas

fly like ya live!

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01-21-2005 02:49 AM  13 years agoPost 3
gigi

rrVeteran

Port-au-Prince, Haiti

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Do you have a GV-1 on-board?
Kas,

I don't know how relevant this will be, but at the very least, it might make for some comedy relief with this serious problem: I had a CSM 540 with a JR 8700G on my Intrepid. It worked beautifully until I added a GV-1 and Stator Gator, at which point, the tail kicked the same way you're describing. UNFLYABLE! Well, disconnecting the Stator Gator from the GV-1 or the GV-1 from the RX solved it, but since I had shelled out a couple of C-notes on the combo, I kept trying to make sense out of it. To make a long story short, the Intrepid is now flying beautifully with its GV-1 and Stator Gator... But with a GY401 instead of the CSM540. Hahaha!

'Gotta admit I never figured out why in the world the CSM540 wouldn't play nice with the GV-1. I seem to recall you have one on your heli. Food for thought or crazy idea, I don't know.

Kind Regards,

Gigi

My heli spending has gone way down since I got a Honda 919 :-)

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01-21-2005 01:21 PM  13 years agoPost 4
kas1903

rrNovice

groveland, ca

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yes, i am using a GV-1 with the stator gator

that's quite a good troubleshooting idea. i never thought to just unplug the governor and see if that did it. as soon as the problem comes back, i will unplug the GV1 to see what happens (this problem can't be gone forever, can it??)

along these lines, i guess there was one other small change in my "re-installation" of the GY401 after service. i did have the receiver and GV1 packaged in an 'avionics box' where their separation was approximately 1/4 inch. i have repositioned them and they are now about 1" apart. maybe that GV-1 is bringing in some noise?

i have to ask myself how much noise that stator gator is creating. it has such a long ignition lead and then you have the servo wire coming out of the 'black box'. those things are like antennas, radiating energy everywhere. i only have one digital servo on-board, the tail. I thought about putting one on the throttle but i would hate to have it doing what the tail rotor did!

kas

fly like ya live!

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01-21-2005 02:06 PM  13 years agoPost 5
gigi

rrVeteran

Port-au-Prince, Haiti

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Link
Supposedly, the wire from the Stator Gator to the RX is as benign as any other wire from the RX to a servo.

Just in case you're interested, here's the link to my CSM 540 to GY401 story... http://www.runryder.com/t149224p1/

Best of luck finding the solution if the problem does come back.

Gigi

My heli spending has gone way down since I got a Honda 919 :-)

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01-21-2005 06:21 PM  13 years agoPost 6
JKos

rrProfessor

Redondo Beach, CA

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> i have to ask myself how much noise that stator gator is creating.

It shouldn't be making any. The lead coming from the kill wire is shielded. Also remember that the voltage levels on the kill wire are MUCH lower than on the HT lead and thus does not cause any where near the same RF levels. As gigi said, the wire from the SG to the governor is as benign as any other servo wire.

In fact, there are noted occurrences in which connecting the SG to the kill wire eliminated interference problems by putting a small load on the kill wire as opposed to an unterminated wire.

The SG has been tested with the receiver antenna wrapped around it with no interference found.

- John

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