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Old Jan 21, 2012, 07:13 PM
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Mini-HowTo
Helicopter Tail Gyro FAQ & Check List

Most contemporary gyros support both a Rate Mode and a Heading Hold or Tail Lock mode. Rate Mode allows the tail to "weather vane" in the direction of flight, smoothing out and coordinating turns, but will resist smaller changes, like a gust of side wind in a hover or torque from increasing or decreasing throttle and pitch, allowing the helicopter to be controllable by mere mortals (I learned to hover on a GMP Cricket without a gyro... damn... that was hard!). Heading Hold mode attempts to keep the nose of the helicopter pointed in a constant direction, regardless of how much wind is pushing the tail, allowing for flight in all orientations including sideways and backwards. Most pilots today fly exclusively in Heading Hold mode.

Gyros typically have a "gain" setting, which controls sensivity: how much movement it will allow before trying to oppose it. Too little gain, and the tail will "blow out": either allow the helicopter to weathervane into the wind, or allow the helicopter to spin counter to motor torque. Too much, and the gyro ends up fighting itself, causing the tail to wag back-and-forth as the gyro overcorrects. Gyros with a controllable gain setting will have two receiver plugs: one to receive the rudder signal, and the other to receive the "gain" signal. The gain plug usually has only a single wire and is generally red or orange rather than black in color. Gyros without a controllable gain usually have a pot for adjusting this setting. Heading Hold gyros consider the mid-point of the gain signal to be 0% actual gain, the low end-point to be 100% Rate Mode Gain and the high-point 100% Heading Hold Gain - though some, like Nine Eagles, are the reverse of this, so again check your manual.

Consult your transmitter manual for how to set gyro gain. Some transmitters, such as most Spektrum models, have a "Gyro Gain" setting that runs from 0% to 100%, which controls the signal sent to the "gear" channel of the receiver, where 50% is the mid-point. Adjusting up from the mid-point adds Heading Hold gain, while adjusting down adds Rate Mode gain. So, 30% transmitter gain means 40% Rate Mode gain (50-30 = 20*2 = 40) and 60% Tx gain means 20% Heading Hold gain. There are generally different settings for both up and down positions of the gear/gyro switch, allowing one to change between two different gain settings (two Rate settigns, two Heading Hold settings, or one of each; most people set one of each). Some transmitters may use a different range, such as -128 to 128, or may not have a "gyro gain" setting at all, in which case you can adjust gyro gain via the "end-point adjustment" of the channel the gyro's gain plug is connected to (you can even do this with Spektrum Tx's and avoid the 50% messyness - thanks for the tip pmackenzie!). Other transmitters may just have a knob that can be twisted to change that channel's value.

The "limits" setting available on some gyros sets how far the gyro can move the tail servo when making corrections and in response to rudder input. Therefore, the rudder channel does not directly control the position of the servo, it instead informs the gyro how quickly to yaw or pirouette the helicopter; setting the "end-points" on the transmitter controls piro speed, not servo throw. The limits should be set to provide the maximum throw without stalling the tail servo. On the Trex 450 v2 and clones, setting the limit too far can cause the tail linkages to "lock" on one side, making the heli uncontrollable, so be sure to check for this. If your gyro does not have a limits setting, the same effect can be achieved mechanically by moving the ball on the servo horn in for less throw and out for more throw. To get more throw in one direction than the other, simply offset the horn by more or less than 90 degrees. Moving the ball in also provides more torque and resolution, allowing for a higher gain setting before the tail starts to wag.

Gyro delay, available on some gyro models, helps to compensate for the speed of the tail servo. The most noticable effect of too low a delay setting is that the tail will "bounce back" several degrees when quickly stopping a piroutte, or "hunt" back and forth a few times. Too much delay makes the tail feel "mushy". Counter to "common wisdom", delay is not just for Analog servos: the performance of digital servos can sometimes be enhanced by adding a delay setting, depending on the servo, helicopter, and other mechanical factors.

Here's my gyro set-up check list to get both heading-hold gain and delay set properly for any class helicopter with any kind of tail servo.

INITIAL SETUP
  • Power up the transmitter (Tx).
  • If gain can be controlled by a gear/gyro switch, program the Tx to give 20% Heading Hold in one position, and 20% Rate Mode in the other. On a Spektrum Tx, this means 60% and 40% Gyro Gain.
  • If there's only a single setting available, use 20% Rate Mode for now.
  • Change the "Analog" or "Digital" switch on the gyro to match the type of tail servo you have. The Analog setting is safe for digital servos, but may impact performance. The Digital setting will most likely cause permanent damage to an Analog servo in a matter of minutes.

MECHANICAL SETUP
  • Power up the model, but make sure the motor won't start up accidently by either disconnecting the motor plugs, or hitting throttle hold (the former is HIGHLY recommended).
  • Zero the rudder trim & make sure the servo horn is at 90-degrees to the pushrod. Adjust with subtrim.
  • If supported by your radio gear, rebind the Rx to lock in fail-safe value for the now-centered rudder.
  • Adjust the tail linkage so the tail-control slider ball is roughly in the middle. In a hover, there needs to be about 6-8 degrees of pitch pushing the nose to the left in order to counter torque from the main motor.
  • Switch Tx to Rate Mode
  • Adjust "Limits" on the gyro to give the maximum tail slider movement without binding. Check both sides! This setting must be done on the gyro, not on the transmitter. Some gyros don't have the ability to set limits, or can only set overall limit rather than separate limites for each side, in which case you can try offsetting the servo horn away from 90-degrees to mechanically give more throw one side than the other.
  • Turn "Delay" up to maximum. Don't try to fly this way - the helicopter tail response will be very mushy if you do.
  • Power off, plug in the motor, then power back up (outside!)
  • Switch to Rate Mode
  • Bring the helicopter light on the skids and watch for rotation.
  • Mechanically adjust the tail linkage to remove helicopter rotation, until the tail is stable in a hover.
  • If the model spins uncontrollably in one direction, double check your gyro's servo reverse switch. When you rotate the heli by hand, the gyro should provide a counter command to the tail servo.
  • If a rudder input spins the heli the wrong way, correct the rudder channel reverse setting on your transmitter: left rudder stick should move the nose left.
  • If you made any adjustments, recheck the limits for binding and locking.

GAIN ADJUSTMENT
  • Increase Rate Mode gain on the Tx until the tail starts to wag in a hover, then lower it a couple of points. On a Spektrum Tx, this means LOWERING the Gain Setting to increase Rate Mode gain. Go figure.
  • If you are capable, do a few 360-piros clockwise and CCW with a hard stop, to make sure there is no wag. Adjust gain if necessary. The stops will be mushy, because you still have max delay.
  • I like to lower Rate Mode gain an extra point or two here (increase the Gain Setting on a Spektrum Tx), just in case I start getting a Wag of Death in HH mode... in which case I can try switching to Rate Mode and Idle-Off to avoid a crash.
  • Land and switch to HH mode.
  • Repeat the above, but this time INCREASING Tx gain until the tail starts to wag, then DECREASE a point or two. Again, do a few left and right piros with hard stops to make sure the wag is gone.
  • Switch to Idle Up and make sure there is no wag.

DIALING IN DELAY
Now let's find your servo's ideal delay setting.
  • Use divide-and-conquer to find the best setting that gives a hard stop after a full piro, but no kickback, in both directions.
  • Lower delay to 50% and check for kickback.
  • If there is kickback, try 75% delay. Or, if no kickback, then try 25%.
  • Keep going zeroing like this to get the best response.

DIALING IN THE PIRO RATE
  • Finally, adjust your Tx rudder end-points to give a consistent piro rate in both directions, at a speed that you are comfortable with: lower end-points will give a slower piro rate, higher a faster rate up to the mechanical limit of your tail.
  • Make sure to check and adjust both left and right setting.
  • To tame the tail down at mid-stick, but still have a fast piro rate, add some Expo to the rudder channel (see your Tx manual to determine if the Expo should be + or -). I tend to use between 15% to 25% on most of my models.
  • Take her up and have some Fun!

VIDEO OF DIALING-IN GYRO GAIN
As an example, here's the maiden flight of my HK250GT after installing a Tarot ZYX 3-Axis Gyro and Flybarless head. At first, I had the rudder channel reversed on the transmitter, plus ran into The Wag of Death a few times due to starting tail gain being way too high.

HK250 GT FBL with Tarot ZYX - Maiden Flight (11 min 3 sec)
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Old Jan 30, 2012, 08:22 PM
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Thanks!

just a quick note to say thanks- i finished the build on my 550 3gx and could not figure out why my rudder kept going hard right and the heli would not stop spinning one way. i got it now from reading your notes and finally i was able to get it up on its maiden hover and it felt great - hovered nicely and no wag, no drift and best of all, no crash.
thanks again for taking the time to post it.
cheers
GP.
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Old Jan 31, 2012, 12:03 AM
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You are most welcome, GP.... Glad to be of service :-)
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Old Jun 12, 2012, 08:54 PM
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this is so good I'm going to print it out pending my tarot fbl 450 arrival..... Is there a "sticky" section for FBL stuff? too lazy to look
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Old Jun 13, 2012, 08:56 AM
What goes up, must come down..
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Originally Posted by atkin View Post
this is so good I'm going to print it out pending my tarot fbl 450 arrival..... Is there a "sticky" section for FBL stuff? too lazy to look
Cool

The only "fbl setup" faq I've seen that really digs into the details is for quad copters and even that isn't straight forward... frankly, adjusting PID settings is still a black art to me.

That said, I *finally* got the "cyclic shakes" out of my 450TT Pro and fixed the touchyness around mid-stick. Turns out I had way too much mechanical throw and had the "pitch limit" turned down to 60 and aileron/elevator at 80. Moved all three servo balls in one hole and flies much better now on the default Hard Core 3D setting (one down from Extreme 3D). Pitch limit set to 80 and aileron/elevator limt now set to 100, but still have 12* pitch and 10* aileron/elevator throw.
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Old Jun 20, 2012, 08:44 PM
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is that about hole 3 of 5? (with 5 being the farthest out) that you have yours on now?


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Originally Posted by ZeroPitch View Post
Cool

The only "fbl setup" faq I've seen that really digs into the details is for quad copters and even that isn't straight forward... frankly, adjusting PID settings is still a black art to me.

That said, I *finally* got the "cyclic shakes" out of my 450TT Pro and fixed the touchyness around mid-stick. Turns out I had way too much mechanical throw and had the "pitch limit" turned down to 60 and aileron/elevator at 80. Moved all three servo balls in one hole and flies much better now on the default Hard Core 3D setting (one down from Extreme 3D). Pitch limit set to 80 and aileron/elevator limt now set to 100, but still have 12* pitch and 10* aileron/elevator throw.
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Old Jun 21, 2012, 09:28 AM
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Originally Posted by atkin View Post
is that about hole 3 of 5? (with 5 being the farthest out) that you have yours on now?
Yes, 3rd hole from the center on an HK-933MG.
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Old Sep 11, 2012, 07:48 AM
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Yes, 3rd hole from the center on an HK-933MG.
Hi, I'm having just a single trouble on three different heli, all equipped with ZYX.

I'm trying to understand how bad is the situation, I'd like to post a question:

if you stay in hover with your hely, in HH mode, without touching the rudder, will it keep the nose in the same direction for indefinite time? (or very very slow rotation will be considered normal?)

If you stay that way for... 1 minute... how meny degrees (about nose rotation) will you get?

I'm asking because all my helis rotate very slowly while hovering in HH mode (about 30 degrees per minute) and I'm triing to find out if it's normal for the ZYX.

thanks
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Old Sep 11, 2012, 09:10 AM
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Quote:
Originally Posted by michelevar View Post
Hi, I'm having just a single trouble on three different heli, all equipped with ZYX.

I'm trying to understand how bad is the situation, I'd like to post a question:

if you stay in hover with your hely, in HH mode, without touching the rudder, will it keep the nose in the same direction for indefinite time? (or very very slow rotation will be considered normal?)

If you stay that way for... 1 minute... how meny degrees (about nose rotation) will you get?

I'm asking because all my helis rotate very slowly while hovering in HH mode (about 30 degrees per minute) and I'm triing to find out if it's normal for the ZYX.

thanks
I don't think I could keep my fingers off the sticks for a full minute, lol, so no clue. I'm constantly making unconscious corrections...

It sounds like maybe you might have some rudder trim or subtrim set? Try flipping your gyro switch rapidly until the zyx lights blink. This will reset "neutral" rudder. Set the switch to "rate mode" and mechanically adjust the tail pushrod to get no drift, then flip to heading hold mode and see if that fixes the problem.
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Old Sep 11, 2012, 09:23 AM
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Originally Posted by ZeroPitch View Post
I don't think I could keep my fingers off the sticks for a full minute, lol, so no clue. I'm constantly making unconscious corrections...

It sounds like maybe you might have some rudder trim or subtrim set? Try flipping your gyro switch rapidly until the zyx lights blink. This will reset "neutral" rudder. Set the switch to "rate mode" and mechanically adjust the tail pushrod to get no drift, then flip to heading hold mode and see if that fixes the problem.
Hi, thanks for the reply,
not 'hands off the stick', just do not touch rudder to observe if tail points the same direction as it should.

I got a lot of suggestions, as well as yours, as you can see in the following post.
http://www.rcgroups.com/forums/showp...postcount=4831

nothing helps, and I just would like to know if it's normal, so I asked to you, cause I read that you have a ZYX equipped 250, if you could do the test, just a minute in hover without correcting the ruddere to observe how much 'error' the tail gets in HH (shoud be zero?)

I made a small video of mine too, to show how much it rotates without touching the rudder (very evident at the end of the video when i realign the eli)

thanks

ZYX drift (0 min 42 sec)
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Old Sep 11, 2012, 02:59 PM
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Originally Posted by michelevar View Post
[...] I just would like to know if it's normal, so I asked to you, cause I read that you have a ZYX equipped 250, if you could do the test, just a minute in hover without correcting the ruddere to observe how much 'error' the tail gets in HH (shoud be zero?)
I've actually got 3 ZYX birds: a 250, a 450ProTT, and a frankenheli Blade 400.

Never noticed any drift, but I hardly ever sit still for that long either ;-) Having learned to hover WITHOUT a Gyro, anything that holds the tail even CLOSE to a single direction is a big blessing, lol.

Next time I break one of these out, I'll put it to the test and let you know! Have a couple of glider projects on the bench right now, so haven't done any heli flying for quite a while...
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Old Sep 12, 2012, 06:45 AM
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I've actually got 3 ZYX birds: a 250, a 450ProTT, and a frankenheli Blade 400.

Never noticed any drift, but I hardly ever sit still for that long either ;-) Having learned to hover WITHOUT a Gyro, anything that holds the tail even CLOSE to a single direction is a big blessing, lol.

Next time I break one of these out, I'll put it to the test and let you know! Have a couple of glider projects on the bench right now, so haven't done any heli flying for quite a while...
Thanks a lot...
In the meanwhile, on the other thread there are already some confirmations about same issue from ZYX owners.
Altought it's not a big issue, i'm looking for a solution
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