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HomeRC & PowerAircraftHelicopterRadio - Servo - Gyro - Gov - Batt › 401 and 9254 issues
05-29-2013 03:26 PM  5 years agoPost 1
dschertz

rrApprentice

Jackson, MI

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Awhile back it I lost my tail control and crashed. I presumed it was just the battery. The battery was bad (and new). The problem is it keeps drifting (tail right). I've set it up and reset the gyro a few times still doing it. Just doesn't make me feel confident. I've read through a bunch of posts stating that the servo isn't that great or reliable and the most post say that the gyro isn't set up right. I can't wrap my head around setting it up in normal mode and then switching to HH mode. It should not matter in heading hold what the settings are in normal mode. I hope someone can explain that other than that's what they do or that's what the directions say. I've never had drifting with JR gyros. I've also set it up in normal mode. Any ideas. Personally thinking about a new gyro/servo combo.

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05-29-2013 10:52 PM  5 years agoPost 2
BeltFedBrowning

rrKey Veteran

Kansas City

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Make sure all the trims and sub-trims for the tail are zeroed out and that revo mixing is turned off. To set it up in rate mode. I mechanically set the tail so that it had a tiny bit of pitch on the tail blades to help counteract the torque of the main rotor. Don't try to use any trims, the 401 doesn't like it.

Mine would not act right if switched between rate and HH without re-initalizing.

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05-29-2013 11:14 PM  5 years agoPost 3
Dr.Ben

rrMaster

Richmond, VA, USA

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It absolutely makes a difference what the rate mode trim is like when you are chasing a drift.

Trim the rudder out mechanically in rate mode at your most commonly used head speed. After doing that, switch into AVCS and let me know if it is still drifting.

The 9254 typically does not fail in a manner characterized by drift. Drift in a GY401, arguably one of the most bomb-proof gyros ever made, is most commonly caused by poor mechanical tail trim and/or vibration.

Remember the gyro must be booted up in AVCS.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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05-29-2013 11:44 PM  5 years agoPost 4
dschertz

rrApprentice

Jackson, MI

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I set it up in rate mode. several times. still drifts. my question remains about setting it in rate mode, what does it have to do with heading hold. again, I want an explanation, not that is just how to do it.

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05-29-2013 11:49 PM  5 years agoPost 5
dschertz

rrApprentice

Jackson, MI

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and all trims etc. are at 0.

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05-30-2013 12:07 AM  5 years agoPost 6
RappyTappy

rrProfessor

Traveling the USA

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With a proper heading lock gyro, rate mode center adjustment has no bearing on HH center because the HH is a dynamic center and constantly changing according to conditions. This is evidenced why a rate gyro that holds in no wind will drift with wind and vice versa, but HH will compensate center and hold no matter the conditions. New HH gyros of today dont even give a hoot about rate mode setup or even give the option as such.

The set it up in rate mode was popular with the 401 cause it did seem to help the 401 sometimes, not always, but I think the 401 is a bit of a wonky gyro in the first place. I've seen them hold one flight and drift the next. I was working at a hobby shop at a time when they were popular and saw many units.

Sometimes I was able to fix drift by setting it fairly close to hover neutral in rate and the 'memorizing' center by flipping the switch from rate to HH a bunch of times (cant remember how many) and end the switching on the HH mode and it would flash for a second then go solid indicating it relearned center or something. Anyways good luck, like I said the 401 is a bit wonky in my experience so your mileage may vary.

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05-30-2013 12:52 AM  5 years agoPost 7
Dr.Ben

rrMaster

Richmond, VA, USA

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It is interesting to hear the opinions on these matters and how they correlate with the best recommendations of the gentlemen, especially Yamamoto-san, who actually engineered the Futaba gyros. I can assure you that up to and including the CGY750, the factory strongly encourages mechanical trim of the tail as best as possible before final trim memorization when you can get no closer than 1/2 turn of the linkage rod. The limitations of updates to written manuals have often resulted in a lag in these facts reaching documentation, but I do know without question that which the factory supports. Multiple times over the years I have explained in detail how proper mechanical trim is critical to piro consistency and in the cases where trim is notcieably off, induction of drift. The search function should locate one of those posts.

While it is possible that this 401 is defective, I would still investigate closely vibration, relocate the gyro to another place on the model, and play with the mounting tape thickness. I have rather lost track of how many 401 I adjusted over the years. Not one drifted. YMMV of course.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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05-30-2013 03:04 AM  5 years agoPost 8
RappyTappy

rrProfessor

Traveling the USA

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I'm not a software engineer nor do I claim to be but im speaking in terms of the definition of rate center and HH center are two different things And its not opinion that heading hold has a dynamic and constantly changing center for which to hold the tail.

You will note that my first paragraph is the definition, then about the 401 and that setting up in rate mode did in some instances help with drift, but did not always cure it.

If heading hold had a fixed center position then it would be called rate mode, lol. Maybe for Futaba it has some other function by rate mode but a heading hold gyro should not drift regardless for a task of simply holding the tail in a hover. Other gyros say vbar don't need even have a rate mode and work the best in the industry for holding and piro consistency.

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05-30-2013 03:31 AM  5 years agoPost 9
Four Stroker

rrElite Veteran

Atlanta

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1) If your tail rotor isn't spinning fast enough, the tail will drift.
2) Make sure there is no trim activated and no classical pitch/throttle to tail rotor mixing (in all flight conditions).
3) When you crashed, you may have bonked it.

Since the 401 does not have individual direction travel adjustment, I usually just adjust the rod so I have full mechanical travel. I never have drift problems.

Would it really hurt to try what Ben said ?

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05-30-2013 03:54 AM  5 years agoPost 10
dschertz

rrApprentice

Jackson, MI

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again, I have set this gyro up the way that it was suppose to be. In rate mode with all trims at zero. it drifted before and after the crash.

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05-30-2013 05:49 AM  5 years agoPost 11
Zaneman007

rrElite Veteran

Texas - USA

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The servo is not a linear output. If the servo is not centered, The servo will have more travel in one direction than the other direction for the same amount of input.

Unless you have a faulty 401, the source of the drift is more likely to be from a vibration than not centering the servo.

I hope that answers your question. But, I'm not sure how a slight drift would cause a crash.

Old Guys Rule!

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05-30-2013 05:56 AM  5 years agoPost 12
Zaneman007

rrElite Veteran

Texas - USA

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I just noticed that you keep repeating that you had zero trim on Radio for the tail gyro. That really has nothing to do with nothing on a 401 when it comes to the Gyro drifting.

But that is not what people are asking. They are asking if you adjusted the linkage for the servo so that when you're flying in rate mode it doesn't drift. This requires about a 7° offset on the tail blades.

Old Guys Rule!

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05-30-2013 06:38 AM  5 years agoPost 13
RappyTappy

rrProfessor

Traveling the USA

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Linear equal throw on a proper heading hold gyro wont do much either in regards to hovering and holding the tail withiut drift other than reducing your piro speed in one direction. I am going off my own experinces here not paper documents or throwing names around. I have purposely set up a way off center tail set up with vbar and 601/611 gyros and more and they all hold the tail in a hover and fly around just fine with just reduced piro rate and inconsistent piro rate one way cause geometrically it runs out of room. Heading hold doesnt go by a fixed center position, but by what position the servo needs to hold the tail.

You can see this action after powering up the gyro if you say give full left or right rudder it will stay full left or right. You have just witnessed dynamic centering in action and what makes a heading hold gyro, well, heading hold. The gyro doesn't care what pitch is on the blades, if the horn is 90, what model you are flying or anything like that, all it knows and cares is that is the position at that moment that holds the tail and in flight that dynamic center is changing multiple times every second.

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05-30-2013 11:11 AM  5 years agoPost 14
dschertz

rrApprentice

Jackson, MI

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Zane, I keep repeating myself because most of the posts keep asking how it is set up. As directions say in rate mode, adjusted the linkage so that the servo is still 90 degrees and the tail holds in hover with no trim adjustments on the radio. The drift did not cause the crash, the crashed was caused because in an instant I had no control of the tail and started spinning counter clockwise. I was only 3 feet from the ground so there wasn't much to do. Battery was infact bad so that was most likely the cause, but the tail still drifts in a hover. I am going to cure the problem by simply ordering a new gyro and servo. Not a 401. I have to go with rappy, heading hold should hold no matter where it is set in rate mode. Center in rate mode doesn't mean much when the heli is moving and heading hold is designed to hold all the time. Unless someone can actually explain how centering works on rate mode then correlates to heading hold, I consider this topic over.

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05-30-2013 07:30 PM  5 years agoPost 15
RappyTappy

rrProfessor

Traveling the USA

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No one can cause it doesn't affect it the only reason to set up in rate mode is to get the horn 90 and equal throws for the tail geometry on to be correct. I've fiddled with oh I say at least few hundred 401s in my day and drifting was very common with these gyros, even sometimes from flight to flight. Personally a el cheapo align 760 blows the doors right off the 401 in every aspect. If anyone has ever set up a vbar, you know there is no rate mode trim, just set if in the computer to get throws equal and horn 90 and then go out to the field and right off the bat have the best performing tail gyro and piro consistency setup on the market.

Forgot to mention there were a few 401s that held the tail better with no drift in rate mode than heading hold. Lol good that 401 is in the past and has been far eclipsed by gyros of today and honestly sits in my 'good riddance' list of gyros.

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05-30-2013 09:15 PM  5 years agoPost 16
Four Stroker

rrElite Veteran

Atlanta

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I have been happy with my 401/9253 for at least 10 years. Over 1000 flights.

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05-31-2013 12:33 AM  5 years agoPost 17
ICUR1-2

rrElite Veteran

Ottawa, Ontario

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Ah the old 401 when it works, it works ok
you can still buy them for about half the price of a fbl unit.

spending time, paying attention

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05-31-2013 05:04 AM  5 years agoPost 18
Zaneman007

rrElite Veteran

Texas - USA

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If you don't set up for zero drift in rate mode, you are constantly applying an input to the servo the second you flip to heading hold.

Have you tried increasing the gain in the radio. If the gain is to low, the gyro will drift in heading hold. Do you have the travel maxed out without binding?
The only other suggestion would be to increase the travel in the radio. This will increase the piro rate allowing for quicker adjustments.

The 401 was a good gyro for its day. But it is now old and tired. If you are planing on getting a new gyro, may I suggest a spartan.

Either way hope you sort it out.

Old Guys Rule!

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05-31-2013 05:26 AM  5 years agoPost 19
Zaneman007

rrElite Veteran

Texas - USA

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Rappy,
Are you taking mechanical gain into consideration? Assume that the servo is way off center to maintain no drift. The distance the servo would have to travel in one direction verses the other would effect it's ability to hold better in one direction than the other, no? It would most certainly respond quicker in one direction than the other. It's just basic physics.

It is my understanding that the piro rate is increased or decreased by the adjusting the end points in the radio.

Also, once you go into heading hold the servo moves to an offset position that will hold the heli in a constant position. If there is no wind, this position would always be the same regardless of set up in the rate mode. So I am not sure how the travel distance from side to side would be effected,

Thus, I stand by my previous statement.

Old Guys Rule!

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