Gyro: Normal mode vs. heading hold

[ArthurKnowles]

I was testing my setup on my Lepton out back just a few minutes ago. What I noticed is that normal mode on the gyro required some trim. And in normal mode it seemed to keep drifting. I have a Futaba 401 with 9650 servo. When I centered my trim and set the gyro in heading hold mode, the tail was locked in. Even though I know my mechanical setup needs adjusting (based on what I saw in normal mode).

So a question occured to me... Do people even bother to set up their tail for normal mode with a centered trim? By that I mean setup the mechanics for zero drift. Or do most just use the manual and set up the basics and let the electronics zero out the tail and always use heading hold mode?

I know it is going to take me quite a while to zero out the drift in my tail in normal mode. Particulalry as it is going to take x number of turns on the ball link (yes I did that mode doing the build thankfully) on the tail. Hover. Adjust. Hover. Adjust. Hover. Adjust. I just wonder if it is worth it in the end.

PS: I know many set up a normal mode throttle/pitch/gyro just in case they have a gryo failure or gryo reset, but just wonder if it is really needed/worth the effort.

[HeliLover]

Actually ARTHUR, you are supposed to center the GYRO in non-heading hold,(Normal) this is the correct way to do it, also for a small tip, on the radio set your Non-heading hold higher, some where around 60 and your heading hold to around 30-35 to start, you do NOT want the numbers to be too close to each other, i have noticed that these numbers are almost right in the ball park, hope this helps.......Ivan!

[ArthurKnowles]

Ivan,

That's pretty much how I have it set. It is centered in normal mode, but requires a bit of right rudder to keep the chopper from rotating. That's the mechanical part I'm talking about. Is it really worthwhile to get the tail perfectly centered in normal (rate) mode.

As it stands now, my gyro settings are normal (50) and AVCS (HH) 50. That means in non-futaba speak about 25 (norm) and 75 (HH) if you convert the settings to EPA/ATV values. Both of the settings equate to a 50% setting if I remember correctly. I have not tried to tweak either setting to lock in the tail yet.

The tail is not hunting currently and is pretty good as is. Later I'll try tweaking it (get it hunting then back off a bit). But I'm still trying to decide if I need to adjust my linkage for the rudder to eliminate the drift mechanically or not. I know I need to eliminate the electronic (TX) trim needed in normal mode or it will cause problems in HH mode. But I can set an offset (if I remember my TX options correctly) for normal mode only that would apply the trim needed to eliminate the drift. That would be easier than mechanically adjusting the linkage.

I'm just not sure what is the best method. Mechanically neutral or electronically neutral. I guess if I don't get any input here I'll try the electronical neutral first and only go with mechanically neutral as a last resort.

[DebianDog]

You should have it mechanically centered in rate mode. You move the linkages or servo mount to do so.

What is electronically centered? Trim???

[ArthurKnowles]

So, mechanically centered it is. :arggg: I hope the time getting it just right is worth it in the end.

As for electronically centered, if I remember my manual and TX (9C) correctly it has the ability to set an offset (basically electronic trim) for a servo for various flight modes (normal, idle 1, idle 2, etc.). So I could use that to trim out the drift in normal mode.

[DebianDog]

Head holding is head holding (as far as I know)

I mean if you tail is "true" in rate mode and you flip it to HH mode the tail should "lock" in. There is no adjustments (other than gain for the gyro). If it start to drift in HH mode then you turn up the gain.

Harkey?

[kgfly]

Well there are two camps on this. I think Finless says "Why worry?" if you are not going to fly in Rate mode then don't waste time getting it perfect. Others feel that getting it drift free in Rate mode is the "right" way to do things. Take your pick :lol:

However you cannot use trim to get it drift free in Rate mode as this will upset HH mode. So if you want a perfect Rate mode you have to mechnically adjust out the drift.

[DebianDog]

I will bet Finless does not do a lot of good tail slides with his 401 :lol:

[DavidH]

However you cannot use trim to get it drift free in Rate mode as this will upset HH mode. So if you want a perfect Rate mode you have to mechnically adjust out the drift.


Yes you can use the trim to get it drift free in Rate mode. And as for AVCS mode, all you have to do is flip the switch 3 times between AVCS mode and Normal mode within 1 second. And then both rates have the same neutral. That is in the instructions.
An AVCS gyro is an angular velocity command type gyro. The gyro constantly
compares the transmitter rudder operation signals and gyro internal
reference signal (transmitter rudder neutral signal) and controls the helicopter
tail rotation speed accordingly. Therefore, for the AVCS function to
operate normally, the rudder neutral signal must be memorized in the gyro
before flight.
•Rudder neutral signal memorization methods
[Method 1] When the gyro power is turned on, the transmitter rudder signal
automatically received at that time is assumed to be the neutral signal and
is memorized. The gyro is normally used in this state.
[Method 2] Rapidly switch the transmitter sensitivity switch between the
AVCS and normal modes at least 3 times at a 1 second or shorter internal,
then set the switch to the AVCS mode position. The monitor LED flashes
instantaneously and the rudder signal is memorized. If the trimmer was
moved during flight, the memorized neutral position can be updated to the
current neutral position by repeating this operation. When performing this
operation, land the model and hold the rudder stick in the neutral position.

I adjust the tail mechanically in rate mode. I do this to assure that the mechanical setup is centered and the travel should be equal for the servo.

David

[kgfly]

Yes you can use the trim to get it drift free in Rate mode. And as for AVCS mode, all you have to do is flip the switch 3 times between AVCS mode and Normal mode within 1 second. And then both rates have the same neutral.
Yes indeed, but then be sure to have the *same* trim set on the Tx in Normal/Idle1/Idle2 otherwise when you switch flight modes in HH you will no longer have a neutral rudder. But at the different headspeeds, the trim for Rate mode won't be the same, will it ?

I adjust the tail mechanically in rate mode. I do this to assure that the mechanical setup is centered and the travel should be equal for the servo.
My experience on the T450, and IIRC as observed by Finless, is that these two conditions - mechanically trimmed for no drift in Rate mode and equal travel are mutually exclusive. Why ? Well to hold in Rate mode you need non-zero tail blade pitch. On a T450 this means the pitch slider is offset along the tail shaft and hence has unequal travel range. Finless advises setting the pitch slider in the centre of its range for this reason, particularly for a GY401 which does not have separate travel adjustment for each direction (which the new L2100T does :) ).

David has far more experience than I do so perhaps this is not so on other helis ?

[DavidH]

Yes you can trim the rudder in rate mode with the electronic trim on the transmitter. Then when you switch to AVCS mode, YES the tail will drift. To make it where the neutral ( trim ) is the same as Rate mode or vice versa, you flip the switch 3 times (Within a second) between the two modes. Now both modes will have the same neutral ( electronic trim).

I have not messed with a Trex much. But I would just set it up like I do most helis. I would mechanically adjust the tail to hover straight ahead with no rudder or trim input in rate mode. Then I would switch to AVCS mode. As for equal travel, the heli does not need much input to piro left, it wants to do that naturally with a clockwise rotating main rotor heli. You actually need more right rudder input to piro the same speed right as left.

David

[DebianDog]

:noteworthy Thanks David that is exactly how I do it. :D

[ArthurKnowles]

Thanks for your input guys. Out of curiousity do any of you use the Tx offset function to set up different trim settings for different flight modes?

The most common use for that is to adjust the rudder setting for forward flight. With HH gyros, this isn't really needed but was common for use with rate gyros. The offset can also be used with cyclic commands (to adjust for pitch up/down or left/right). It's really just another way to add trim as far as I can see.

[DavidH]

Only time you would use Rudder offset is if your going to use the gyro in Rate mode all the time. For AVCS or HH mode, you will need the trims to be the same in all flight conditions for the rudder.


Don't see a need to use offset for the cyclics. Best to set the swash neutral and trim the model for FF with horizonital fin and C/G.

David