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HomeAircraftHelicopterRadio - Servo - Gyro - Gov - Batt › PLEASE EXPLAIN AVCS MODE vs NORMAL!!!!!!!!!!!!!!!!
01-26-2012 05:50 PM  6 years agoPost 1
bv13

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park city utah

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Im back into helis from the early 90's at th estart of pcm and with mechanical gyros. WOW THINGS HAVE CHANGE. For the most part I the setups from a-z, but it seems more to do with radio setup now a days then at the heli. SO!, Do all gyros get setup on a slave switch to go back and forth between normal and avcs? Is avcs considered heading hold/lock. What percentages are usally used on a futaba 401 or an inertia 360. Normal mode on my 401 is rock solid same as my inertia and avcs is twitchy. is this a gain issue on the gyro or a percent issue on the radio.

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01-26-2012 06:17 PM  6 years agoPost 2
kcordell

rrElite Veteran

O Fallon, MO

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AVCS mode is heading hold (HH). Most actually set the model up and get it trimmed mechanically in normal mode then switch to AVCS. Many never take it out of AVCS once set up.
Amount of gain varies due to headspeed, tail rotor blades, type of servo used, distance from center of wheel on servo for pushrod. Each model is different. You have to find what works for you, but generally the amount of gain in normal can be applied to HH. One last thing to consider is tailrotor linkage. If the linkage is not free and easy, the servo tries to work to hard to correct and you can get the issues you are describing.

Team Futaba, Team Synergy/Rail, Team Scorpion, Team Castle Creations, YS Engines, VelTye

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01-26-2012 06:27 PM  6 years agoPost 3
bv13

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park city utah

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So what are the percentages about on the radio, and do you start at 0 and go from there

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01-26-2012 07:18 PM  6 years agoPost 4
MattJen

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UK

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On a 401,
I am running at 75/80%, see how that feels, i set 0 on the delay ( on the gyro itself)

If you find in the hover or foward the flight the tail oscillates then the gain is too high,and you have to turn down the %.

The way to set one up is as has been mentioned, you need to start the 401 up in HH mode ( solid red light when you swithc on RX) you then switch it out of HH mode on your TX via an assigned switch on your TX,

Take off into wind, take your hand off rudder and see which way the nose drifts, and either shorten or lengthen your push rod until it will hold nose into wind.

Now put the gyro back into HH and leave it..

It depends on what type of flying you want to do, some like scale flying in normal mode, I personally use the 401 on all my models and i fly it in HH.. and i set my TX up in AVC mode.. ( Futaba 10C)

The 401 is a nice simple and effective Gyro..

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01-26-2012 07:25 PM  6 years agoPost 5
wifeorheli

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reno, nevada usa

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NO dont start at ZERO thats zero gain. need to know what TX and gyro. Im on spektrum and a good starting point 65 to 75%

Novarossi Motors U.S.A
www.PLanethobby.com
Team GrandRc.com
Team Byron Fuels
ZRC U.S.A. "PushGlo, SwitchGlo"

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01-26-2012 08:08 PM  6 years agoPost 6
bv13

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park city utah

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Ok, my radio is is the flysky 9x. I know what you guys are going to say. GET A REAL RADIO!!!!!! But just getting back into things, i had to start somewhere, and for what i used to fly. I cant believe I got this thing for $80.00. The options for the gyro are as follows; Standard mode, which offers percentages for uprate or downrate (switch position).
OR, gyro mode??. Which offers percentages 0-100% in normal and 0-100% in avcs in both uprate and downrate. Again the uprate and downrate are switch positions and can swapped. Im guessing its a preferance thing. Im running 30% in both as of yesterday. Now on my 600 electric im running an inertia 360 gyro. On my ergo z230 im running a futaba 401. JUST KNOW THAT THESE HELIS WERE PURCHASED SECOND HAND READY TO BIND FOR I WANTED TO FEEL OUT THE HOBBY AGAIN BEFORE SELLING MY SOUL AGAIN. They seem to be well built, and I went through them both (stripped down and built up) before flying. Like i said they fly great in normal. OH! Im flying anywhere from scale to somewhat tight and aggressive. No real aggresive throttle changes and not really into 3d. YET!!!!

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01-26-2012 08:54 PM  6 years agoPost 7
BarracudaHockey

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Jacksonville FL

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Back to your question.

Heading hold, AVCS, and tail lock, all mean the same thing. AVCS is Futabas acronym for heading hold (Angular Velocity Control System)

A rate mode gyro, or a heading hold gyro operating in rate mode (normal mode) will dampen the rate of unwanted tail movements, meaning it will slow them down to a manageable level.

A heading hold gyro will try to correct that movement as well as fight it.

A rate gyro when facing a wind from the side, will eventually weathervane the nose into the wind. The wind will push it, it will stop the movement and recenter, the wind will push it, the gyro will stop it ect till its not being pushed any more.

A heading hold gyro will add more pitch if the wind increases to the tail doesn't move, and will take it away if it decreases. A rate gyro simply isn't that smart.

Andy
AMA 77227
http://www.jaxrc.com

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01-26-2012 09:01 PM  6 years agoPost 8
wifeorheli

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reno, nevada usa

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not sure about the modes on the radio i run the gain wire from the gyro to aux2 then use travel adjust of aux2 to set the gain + side HH - side normal

Novarossi Motors U.S.A
www.PLanethobby.com
Team GrandRc.com
Team Byron Fuels
ZRC U.S.A. "PushGlo, SwitchGlo"

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01-27-2012 02:22 AM  6 years agoPost 9
dkshema

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Cedar Rapids, IA

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Assuming that you have all the mechanical stuff set up correctly, and you have the gyro set up correctly, the easiest way to set your heading hold gain is to fly the heli in fast forward flight. Increase the gain until the tail of the heli begins to oscillate in flight. Then back off the gain down until that oscillation in fast forward flight just stops.

What radio are you using with your helis and gyros?

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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01-27-2012 04:24 AM  6 years agoPost 10
dkshema

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Cedar Rapids, IA

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A rate mode gyro will sense movement and drive your servo to attempt to stop it. As such, the movement will be damped or stopped, but the heli will not maintain its current heading (direction the nose is pointing). Wherever the nose happens to be pointing when movement stops, that's where it stays till the next upset.

When flying a rate-mode gyro, the gyro will actually fight you in turns as it will not only attempt to stop unwanted movement, it will attempt to stop the turn you've commanded (eventually, some rate gyros had a feature added called "stick priority" that at least made the gyro smart enough to know the turn was a commanded one, and not an accidental one).

Since the rate gyro isn't really too keen at doing much more than trying stop or dampen movement, most transmitters still retain a rarely used feature called "Revolution Mixing" or "Acceleration Mixing". This feature has two adjustable settings -- "UP" and "DOWN".

Typically, to set up a heli that will fly a rate mode gyro exclusively, you would set the tail rotor to have about six degrees of pitch at hover to keep the tail from yawing while hovering. With a rate gyro, you adjust it so that at hover, the heli doesn't want to yaw left or right. Other setup stuff includes setting the travel limits so that at full rudder you don't bind up the mechanics and making sure the gyro knows which way to compensate, so you need to get the direction set correctly.

But, if you then increase pitch/throttle (and add torque into the system) the rate gyro can't keep up, and the nose of the heli turns as it goes up. That is where you adjust the Revolution "UP" mix to stop that unwanted yaw.

Then, as you decrease pitch/throttle, the torque in the system is generally less, the nose goes the other direction. Here, you adjust the Revolution Mix "DOWN" setting to stop that yaw.

These three steps allow you to hover without unwanted yaw, to go up without unwanted yaw, and to descend without unwanted yaw. It kind of worked, but since there were so many variables, it wasn't perfect.

The higher end radios also had a "rudder offset" feature to use with your rate gyro. Everything seems to be set OK for hovering, for going up, and for going down, but when you transitioned to forward flight, the fact that your tail rotor gets additional lift from moving forward also causes the nose of the heli to change direction. The Rudder offset feature allowed you to tweak the rudder trim to be different at hovering than in forward flight.

Rate gyros took a lot of tinkering with to get set up correctly, but gave a more "scale-like" flight performance.

With a rate gyro, the rudder servo is controlled primarily by the transmitter, and the servo follows the stick "normally" and returns to center on its own. The gyro only aids the rudder.

-----

Enter the Heading Hold (tail-lock, AVCS, head-lock...) mode.

With the ability to have better sensors and microcomputers built-in to the gyro, the ability to sense the rate at which the heli is yawing (as opposed to just knowing it's moving) added the possibility of having the gyro not only stop the movement, but to figure out how much compensation to add to the rudder servo to move the nose back to where it was and maintain that position was introduced. This became the basis for the Heading Hold gyro. If you know how fast you're turning and for how long, you know how to maintain heading.

The heading hold mode is a whole different mode of operation. The transmitter really no longer controls the servo, the gyro does. That is why on the ground, if you move the rudder stick, the servo moves, but stops in weird places relative to stick motion, and generally doesn't return to center on its own. You have given up direct control of the rudder in favor of letting the gyro do its thing.

The stick essentially gets relegated to telling the gyro which direction to let the nose turn to a new heading, and how fast it is allowed to get there (heading and yaw rate are about all you get to control in this mode, the gyro does the rest).

With a heading hold gyro, setup is quite different than that for a rate gyro. It is now typical to simply center the tail pitch slider at neutral, and tell the gyro where the mechanical left and right travel limits are (as the stick no longer tells the gyro how far to move the pitch slider). The rudder endpoint settings no longer control travel of the tail rotor, they control the maximum rate at which you will allow the heli to spin. Typically, the endpoints start at 100% and if you want a faster yaw ("piro" ) rate, increase the endpoint number; if you want a slower yaw rate, decrease the endpoint number. In most present-day gyros, the left and right yaw rates can be fine tuned to give you equal yaw rates for left and right, in spite of the system torque differences. This was not really possible with the GY401.

Of course, there are now a thousand additional settings to mess with in the higher end gyros, and USB adapters, Bluetooth adapters, and even Iphone/Android Apps are available so you can really fine tune (or screw up royally) your gyro.

-----

Heading hold gyros typically have a start-up, initialization sequence that last from about three to five seconds. During this time, you need to let the heli sit and not move it. Among other things, the gyro is looking at the rudder channel neutral pulse width, and learning how wide it is.

Once it's learned where neutral IS, it expects it to remain the same until the next time the power is cycled and it gets a chance to learn again.

Therefore, once you initialize a HH gyro in HH mode, the rudder trim in all flight modes must be identical. If you have different rudder trims in different flight modes, when you switch flight modes, the trim changes, and the gyro no longer "knows" where neutral is. It will be angry with you and may drift, or do all sorts of weird, unwanted things.

For the same reason, once you have initialized the gyro in HH mode, NEVER NEVER NEVER use the rudder trim tab on your TX. You'll confuse the gyro and it won't work too well until you re-establish the neutral point.

The GY401 MUST be initialized in Heading Hold mode, or it just won't work well at all. Most other gyros these days aren't that picky. Just don't mess with their neutral settings after you let them initialize.

-----

Gain setting these days in most gyros is accomplished by an additional plug that goes to an unused channel in your receiver. Tradition has somewhat settled on using channel 5 (the "landing gear" channel" in most systems), or in the case of JR/Spektrum, AUX 2 in a receiver having more than six channels.

The gain control is set up such that it looks at the width of the pulse coming down the gain lead from your receiver so the gyro knows which mode in which to operate (rate/Heading Hold), and what the actual gain should be.

If you were to plug the gain lead into your aileron channel for instance, you could essentially move the aileron stick full left and be in rate mode at 100% gain. As you move to neutral, you stay in rate mode, but the gain decreases till you hit neutral and are at zero gain. The gyro is essentially out of the picture at this point. Now continue to move the stick to the other extreme, and the gyro enters Heading Hold mode, and the gain increases from 0 at neutral up to 100% at full stick.

Most transmitters today have a Gyro Sense/Control menu that requires the gain lead be plugged into a specific receiver channel, and the numbers that you enter into that menu select the mode and gain for that mode (simply by adjusting the width of the pulse coming out of the RX channel controlling the gain). These menus typically allow the gain to be controlled by the flight mode (or other) switch, and you can have different gains (and the same or different modes) based on the switch setting.

In the gyro sense menus, the gain numbers may go from 0 to 100, or -100 to +100.

If they go from 0 to 100, then 0 usually sets 100% gain in Rate mode, 50 sets zero gain and no mode, 100 sets 100% gain in Heading hold mode. 25 would set 50% gain in rate mode, 75 would set 50% gain in HH mode.

If they go -100 to +100, then at -100, you would be in rate mode at 100% gain, and as you move to 0, the gain decreases to 0 at 0. As you start going from 0 to +100, the gyro enters HH mode at near zero gain, and the HH gain increases to 100% when you hit 100%. (This is just like using the Gear Channel and its two endpoints).

If you don't use that built-in Gyro Sense/Control menu, you can opt to plug the gain lead into the Gear channel (usually channel 5) of the RX, and use the Gear switch on your TX and its two endpoint settings to control gain. Doing so usually gets you one Rate mode gain, and one Heading Hold mode gain.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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01-27-2012 05:02 AM  6 years agoPost 11
bv13

rrNovice

park city utah

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That is THE BEST explanation ever. I really appreciate your information. And I thank you for taking the time to share it with me. I feel like a diferent person with all that info. I cant wait to try it out now. I see many different aereas where I need to tweek something.

A BIG THANK YOU TO EVERYONE WHO AS ADDED THERE OWN OUTLOOK ON THIS MATTER!!!!!!!!!

ITS GOOD TO BE BACK BEHIND THE STICKS AGAIN

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04-10-2014 06:48 PM  4 years agoPost 12
Jrox

rrNovice

Irvine, California

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Amazing and informative post...thank you! (Also a 90's flyer dusting off the equipment...this was a huge help)

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06-09-2017 01:29 AM  14 months agoPost 13
flying4fun

rrApprentice

Sunny SoCal

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Bump to top very informative on Gyro functioning

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06-13-2017 04:00 PM  14 months agoPost 14
Richardmid1

rrProfessor

Leeds, England

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If it hasn't already been said you can set a rough gain % as a starting point as follows:

Initialize the gyro in AVCS, Heading hold, Heading lock, 'tail stays put' mode!

Rotate the heli slowly while watching the tail pitch slider on the tail shaft.

If you have reached full tail pitch before the heli has rotated 45 degrees (roughly), the gain is too high. If you need to rotate the heli more than 45 degrees to reach full tail pitch your gain is too low.

60% of the time, it works every time!

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07-04-2017 05:04 AM  13 months agoPost 15
fredmillard

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Portland, Oregon

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Dear dkshema, thanks for a really great explanation.

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