Anwar is talking about the case where he uses same symmetrical pitch curve for all flight modes. In that case, mid throttle stick is not the hovering position. It'll be a little above mid throttle.

For the gyro question, answer is yes.

Please see my response to Vinay :  http://www.rcindia.org/helis/hk-450-mt-build-thread/msg12654/#msg12654

Basically, when you do the physical setup, you always go for -10,0,+10 (with a linear pitch curve in the radio at -100,0,+100 or 0,50,100 depending on the radio). So at mid-stick, you will have zero pitch. 

After the physical setup is confirmed AND if you decide to have separate pitch curves for various flight modes, you adjust the pitch curve *for normal flight mode* so that you are -3,+5, +10 on the blades (which will translate to something like -30, +50, +100 on your radio). 

Or, you can follow what I have been doing, which is a single pitch curve for all modes, so that you will hover around 65% of the throttle stick position.  In this case, you adjust the throttle curve so that you do not have too much head speed around mid stick. But you will leave the pitch curve at -100,0,+100.

Regarding the gyro; for a solid setup, you should put it in rate mode with enough gain, adjust your mechanical setup so that the servo arm is perpendicular, but the pitch slider on the tail has a small amount of pitch (so it will not be in the center).  How much is that offset, is determined by flying the heli in rate mode, and adjusting either the length of the tail linkage rod, or by moving the whole tail servo on the boom (keeping in mind that the you want the servo arm as close to 90 as possible when you are not applying any rudder input).

Thanks Anwar/Rajesh,
That helped !

I am going to try and fine tune the gyro/rudder servo linkage today. Tell me something, suppose i have my heli hovering in rate mode, how will know if the rudder linkage needs to be increased/decreased ? In your last post you mentioned that there will be some drift. Wouldnt the drifting be compensated by cyclic trim ?
Perhaps i should have someone observer the heli from the side to see if the arm is perpendicular or not, and then land the heli and adjust and try again ?

In rate mode, when you have drift, you will be applying some rudder input to correct the drift. Note which side you are applying the input (let us say you were moving the stick to the left).  After landing, apply the stick to the same position, and see which way the linkage rod moved.  That should tell you if you should lengthen it or shorten it.

Or you can just do trial and error, and if you did it wrong, you will realize it while test hovering as you will have to apply more and more rudder.  If you see that is the case, do the opposite adjustment.

The drift we are talking about is tail drift, and has nothing to do with "cyclic trim", which is only elevator and aileron.  Tail drift is when the heli tends to pirouette by itself, and you are forced to apply some rudder input to keep the tail pointed towards you in hover.

The "servo arm" being perpendicular is something you can see on the ground, after the heli is powered up with the gyro in rate mode with NO rudder input.  Remember that we are not talking about the "tail pitch slider" being perpendicular.  You need to be clear about the difference between the two.

Anwar,
I have some results and more questions. I tried to do what you said above a few minutes ago .
First I switched my Gyro to Normal mode, and took the heli to a hover. I noticed that the heli wanted to turn left. and i needed right rudder to keep it straight.
So i powered down, and adjusted the servo linkage/position ( finetuned with subtrim )  so that in Normal mode, the heli was pointed straight in a hover with no need of rudder. At this position the servo arm was perpendicular to servo, BUT the tail blades were considerably pitched to the right.

So then i switched the heli back to Heading hold mode, but now it wanted to spiral to the right !! The Gain is set to 50 ( recommended in the Gyro manual )


The Gyro works fine, because yesterday only i flew in HH mode with the nose locked in .

One more observation. Suppose i put the heli on table and switch to Normal mode, The servo at this point is centered.
Now if i switch to heading hold mode ( motor and everything is OFF, and i do not even touch the heli ) , i notice that the servo  gradually tries to change the pitch of the blades to the right, till it reaches the end ..
Possible that i did something that damaged the gyro/servo ?

Please remove the sub-trim when you do the adjustment in rate mode.

It is normal for the servo to have some creep in heading hold mode, but not going all the way to one side (from what I can remember/imagine).  I think this is also an effect of the subtrim you have.  Please get rid of all trim and subtrim on rudder (channel 4), do the mechanical setup in rate mode again, and you should not have any problems. It is OK if the servo arm is not exactly perpendicular, so avoid sub-trim. Just do the best you can.

Please report what you see after trying the above setup.

Thanks Anwar.
I will try this first thing tomorrow morning. SO i will get rid of all trim/subtrim on rudder, then go back to normal mode on gyro and get the fly to track straight with no rudder input and servo arm at 90 deg.

Then will attempt to get on to the heading hold mode.

Is it normal to have the tail blade pitch almost at 75-80% travel in normal mode for the heli to track straight ?
Another question, that though i have tried to understand what the Gyro does, I am still a little fuzzy on what it does really in the normal mode.
In the HH mode it locks the heli to one heading, and counteracts the affect of wind/torque.
But what does the gyro do in normal mode ?

Best thing is that i am not crashing and getting to know the dynamics of heli better.

Oh one last thing.. Currently i have an odd ball mix of subtrims, and trims to have my heli hover without much cyclic . Is this OK ? Or should i attempt to get rid of trims by tweaking the linkages .
My objective is to have as close as a perfect setup as possible.

Thanks a ton !

It is NOT normal to have 75% travel to the side for the heli to hold its tail. You have to measure it *while you are actually hovering*, which is a tough task. It seems like the 75% is an exaggerated visual estimate.  It would be much smaller. If I were to guesstimate, something like 10% to 15% (again, I am pulling a number out of thin air, will try to confirm later).

Regarding the differences between rate and heading-hold modes, please see this : http://www.rcindia.org/servos-gyros-and-all-electronics/gyro-modes-normal-and-heading-hold/

My experience is that you will end up with some sub-trim on the swash servos (unless you get lucky by turning the servo arms OR you have a digital servo whose center can be adjusted with a "servo programmer"; some people I know do that on bigger helis, with Hitec servos).  Trim is something you can pretty much get rid of with careful setup.  At your present stage, I am not sure if it is worth the effort.

Ok i have some results and more issues/questions.
I reset the trim/subtrim on rudder channel to 0 . Then i got back to Normal mode and since i couldnt really get to the point for the heli to track straight on hover ( without any revo mix ) , i left it like that ( i read from the gyro links above that in normal mode the heli will slip a little to the left, unless revo mix is used to correct ) . The pitch at this point is slightly to the right, around 15% as you said.

Now i went to HH mode. the tail was good but then after about 10 seconds of hovering it started to move to the right. not a continuous turn but like a turn-stop-turn-stop...I had to give left rudder to get the tail pointed towards me. This was with 50 gain. I increased the gain to 75 and the tail wag came in , but even then the heli wanted to shift to the right.

Re trim/subtrim, though i want to have a perfect setup, i will not bother with it as of now, as the trims/subtrims i have are not too much, and plus i want to concentrate more on learning to fly now.

The battery is on charge right now. i will try to make a video and post it when i go home for lunch. I am a little worried that there may be a problem with the Gyro or the tail servo . Is that possible ?

Are you making your gyro changes from the radio (switching from heading hold to rate or adjusting the gain) ?  How are you confirming that the gyro has indeed switched from one mode to another ?

Yes I am making this change using the CH5 channel assigned to a 2-position switch on my TX. I have hooked up the CH5 on the RX with the Gyro, as indicated in the manual. Theres a LED on the Gyro, that turns red when in HH and Green when in normal mode , that is what i use to determine the mode.

The Gyro i have is Thunder Tiger 6100 gyro, and i believe it does not allow you to remotely set the gain using the TX. At least this was not said in the manual anywhere. Thus I assumed that CH% would not be used to adjust the gain, rather simply switch between HH and Normal modes.


Is it possible, that this CH5 may be the culprit ? Now that you have mentioned, I was not connecting this to the TX at all during my initial flights where i had the tracking better than what i experienced today

Just as I had suspected   The single green wire from the TG6100M is for remote gain adjustment, and it does provide the gyro with the gain value also (AFAIK).  So you should control the gain % from the GYRO menu of the radio, if you have that green wire connected to channel 5.

You da man !
Have you used the TG6100M Gyro ? Yes i have the green wirer connected to the Ch 5 .
Nowhere in the manual does it say ( unless i missed it somewhere ) that the Ch5 can be used to adjust the gain. It only says that it is used to switch between HH and normal modes.

Opens a can of questions. So now does the gain set from the TX and transmitted via the Ch5 override the physical gain set up ( using the small dial ) in the gyro  ?
Also, does the CH5 perform 2 tasks ? switch the Gyro mode +  adjust gain ?

Wow !

Yes, if you connect the remote gain wire then the gain is taken from whatever is supplied by the radio.

And it also switches between rate and heading hold based on the same signal. On most gyros, if, let us say the range of gain signal value is between 0 and 100, then 0 to 50 on the signal corresponds to 100 to 0 gain in RATE mode on the gyro AND 50 to 100 on the gain signal from the radio corresponds to 0 to 100 gain in HEADING HOLD on the gyro. JR/Spektrum radios work exactly like this. Futaba has this translation done slightly differently.

Hmm, That clarifies so many things. I will go home and see whats under the Gyro gain in TX and then perhaps set it up.
I will make a video of the entire setup and post here.
Thanks.

Ok, i read the Futaba TX manual and activated the Gyro Sense menu .
So now i can set the gain in the TX independently for Rate mode and HH mode. ALso using the 2-way switch i can switch between modes.
The gain setting on Tx for both rate and HH mode goes from 0 - 100 . However i am not sure how this translates to gain in the Gyro . Will 0 in TX be 0 in Gyro gain ? or will it be opposite ? Perhaps it works the right way in Rate mode and opposite in HH.

Well i flew with 50 as gain ( middle position ) and in HH mode. Even with no trim/sub trim, i had to touch the rudder to keep the tail locked in . I then tried to set the gyro gain to 0 in TX and flew . This time the heli wanted to yaw to the left. I tried with gain to 100 and even then did not notice the tail wag ..

I am not sure why my Gyro doesnt lock the nose in one heading, as it should .

BTW had one question, when in HH mode, suppose you lift the heli and move it to a different place / direction, the gyro would be trying to rotate the heli in the original direction. How do you reset this ? perhaps by switching to rate mode and then back to HH mode ?

On Futaba, the gain values are translated directly as in 0 to 100% is the same on the gyro, as it is on the radio (for both HH and rate modes). 

Apparently you are doing something wrong  

First of all, since this is a HH capable gyro, you should set the "MODE" to "GY", have you done that ? (For a non HH gyro, you will keep that at "STD" which we don't want in this case).

Make sure the whole gyro thing is "ACT"ivated (moved out of "INH").

Then, as you change the gain number alone, you will see it moving between HH ("AVC" in Futaba world) and rate mode ("NOR" in Futaba world).

So all you need to do is put it in "NOR 50%", and get your mechanical setup right.  After that, switch to something like "AVC 40%" and fly.  If you feel slight drifts, increase the gain in "AVC" side until the tail starts to wag quickly, then reduce it a little bit. Absolutely DO NOT PLAY with things like REVO mixing, if you have anything like that, disable ('INH') it right away.

Always remember to NOT move the heli for the first 3 to 5 seconds after you plug in the battery, this is the time the gyro initializes and "learns" what the default/stable position is.

Before i work on tuning this tomorrow, i wanted to verify something.
When i adjust the linkage, in rate mode, my objective should be to  adjust the linkage so that the heli hovers without any drift AND does not require any input to track straight ?
Now this should be done without the Revo mix ( which i have as INH at all times )  ?

From what i read so far on how Gyros work how will this be possible, because in rate mode the gyro merely dampens the yaw movement, so the heli will not immediately swing to the left, but gradually it will keep turning to the left , isnt it ?

So is it really possible that in rate mode, without Revo mix , we can get the heli to point straight ?

Now you are officially declared as reading too much

Yes, it is quite simple.  Go to 50 gain in rate mode, and adjust linkage or servo position till you fly without any drift or rudder input.  Forget you ever learnt the word "Revo" for now   I never brought it up for discussion, if you remember.  None of that is needed.

To oversimplify it, HH works better because it can handle the effects of wind, pitch, throttle & rudder input better; because of its ability to remember/calculate the orientation it needs to hold.  Rate mode itself can hold the tail without any drift, given favorable/reasonable wind and main blade rpm/pitch conditions. Rate mode is affected by sudden pitch/throttle changes, but that is not the case in either hovering or stable forward flight; so for your test in rate mode, the simple answer is that it will hold pretty well in a hover. Point the nose of the heli into the wind.

If you continue to read about Revo mix, you will realize that is old school, when gyros like the HH ones now were NOT available   If you want to read about Revo-mixing, here you go :

http://www.raptortechnique.com/gyroinfo.htm

Anwar, what is the need for rate mode to be included in an HELI GYRO when there is HH mode?

For one, it allows you to do the mechanical setup properly. 

I also read about some pattern pilots using rate mode, although never found a really good explanation for why that was called for (or may be I did not look enough!).

One example is when you do a roll on FF. In rate mode, the tail "weather vanes" to make the roll more axial. In mode 2, it is easy to introduce tiny bit of rudder input when changing pitch for the roll. Rate mode hides this to some extent.

Just looked this up, thank you Rajesh.

http://www.rchelicopterfun.com/heading-hold-gyro.html  (see the headings "Heading Hold gyro limitations" and "Heading hold gyro benefits for aerobatics").

Also, elsewhere someone suggested that rate mode may actually help beginners with forward flight, as the weather-vane effect will keep the tail in line with the direction of flight, without the flyer having to "fly the tail".

PS: I like this sentence from the last part of that page, which reads :

"A lower quality HH gyro paired with a fast digital servo, will outperform the best HH gyro paired with a slow analog servo."  Reiterates that a good/fast servo is a must for good tail performance !