Tarot ZYX, ZYX-S & CopterX 3X-1000 Advanced Tuning and Troubleshooting Guide

[Dr. M]

Foreword

It seems to me there's a lot of knowledge about these gyros floating about, but not a succint and easily understandable summary, so here's my attempt of doing just that. This is not a setup thread, but rather a guide for the pilot who is past the basic setup and trying to get the most out of these FBL controllers.

If you're looking for setup help, there's no better place to start reading than the very first post on the RCG ZYX Thread. So I'll go ahead and assume you've done that and have set up your mechanics and controller as well as anyone could do.

This tuning guide starts after you've completed the basic mechanical and gyro setup. Or perhaps you've been flying the ZYX for a while and just feel it could fly better. Now you're contemplating the myriad of options check boxes and numbers in the Advanced settings window.

Let's get started

OK, so if you're new, I suggest you start with the "3D Soft" preset. Otherwise, use whatever settings you're currently flying and work from there. But first, read the definitions of the advanced parameters here.

Before you do anything I must emphasize the importance of a proper pre-flight checklist. Use it every time you plug in a flight pack before you arm your ESC:
- check the compensation directions on all axes. Pick up the heli and tilt the chassis around watching the swashplate. It sould swing in the oposite direction of your tilting, attempting to stay level. Do it along the elevator and aileron axes. Then rotate the heli around the main shaft (Yaw) and watch the tail blades - the trailing edge should swing in the same direction the tail is traveling.
- check response to stick inputs: set the heli on the ground and watch the swashplate as you move collective and cyclic, and the tail blades for yaw.

[Dr. M]

Before you fly for the first time Stop! Examine your setup one more time, make sure everything looks and moves right.

In particular, if your Collective Range number is lower than 60 and you still have 12° pitch at the top, your swashplate servo arms are too long: move the linkage balls one hole closer to center. Conversely, if the number is higher than 80 for 12° of pitch, your swashplate servo arms are too short: move the linkage balls one hole further from center.

For you first flight you'll want to take it easy and make sure nothing bad happens. I recommend you set your Tx tail gain to whatever value reads 36 in the Monitor screen of the PC software. Set the Roll and Pitch gains on the main screen to 25. This will help prevent possible violent oscillations caused by too much gain.

Deadbands

CX and ZYX firmware older than 3.5 had a bug in the way the stick deadband was implemented ("Deadband RC"). The defaults were far too high and, together with the bug, caused odd, twitchy, or jerky behaviour. A simple solution is to reduce this parameter to a value no higher than 15, or else upgrade the firmware to ZYX 3.5.

The other parameter, "Deadband Gyro" refers to the way the gyro talks to the servo and functions correctly. Keep this one at default, or the lowest setting you can get that will not cause your servos to overheat.

Maiden Flight

Spool up with your lowest HS and pick up into a hover 10-12ft AGL. If the tail isn't wagging, give a few stabs of the rudder stick. Observe for any wobble or instability in the rotor disk. Give some small, but quick stabs to the cyclic stick (both nick and roll). It may feel pretty mushy, but the disk should not wobble. If it does, stop. Something is wrong - either cyclic servo arms are too long (see above), servos are too slow/weak or you've got some serious binding in the head mechanics.

Let's say the tests above went well, switch to your highest HS. And repeat the tests. Decrease your tail gain if you get wags, but you should not need to decrease the cyclic gains. If the tail is stable, increase the Tx tail gain a few points at a time until the wags just start appearing, then dial it back 2%.

Also, start increasing cyclic gain 5 points at a time and test by giving quick stabs to the cyclic stick. Keep increasing the gain 5 points at a time until you see the disk wobble after quick stabs to the cyclic stick, then go back down 5 points.

By this point you should have a pretty solid foundation to move on to advanced tuning. The cyclic and tail gains should be pretty close to optimal, though perhaps a bit on the high end, we'll tune them next.

Fine-tuning main gains

Finally, do some FFF and decrease the tail gain a bit if you hear it wagging. Also watch the disk for any signs of wobble. Particularly, fly some gentle FF descents with the disk unloaded (0 or slight negative pitch - think autorotation, but don't turn off the motor): if you see any wobbling, drop the cyclic gains 3 points.

Final note: optimal gains depend on your servo speed/accuracy, ball-to-center distance on the servo arms, HS, as well as overall geometry, mechanical condition and setup of the head.

[Dr. M]

Now that we've got the baseline gains settled, let's make that tail hold a perfect line.

First, you'll need to check your mechanical setup in Rate mode: hold a hover and switch your gyro to RM using the gear channel switch. Adjust the length of the tail push rod such that the tail holds steady with the gyro in RM, i.e. there's little or no drift either direction. I can't emphasize enough the importance of this step to getting good performance and symmetric behavior out of the tail.

The following tests should be done with the gyro in HH mode, and with precompensation set to 0.

Performance Tuning
Here we'll tune the Acceleration values in the Advanced Settings. Hold a steady hover at your highest HS and quickly move the rudder stick to max in one direction and do a whole 360 piro. Listen to the sound of the blades as the tail starts piro'ing. If you hear a loud bark or sputtering, your Acceleration Rate for that side of the piro is too high; if the start feels vague or mushy, your Acceleration Rate for that side of the piro is too low. Adjust the Accel until you get the performance you're expecting on that side, then do the same thing for the opposite side piro.

Piro Stops Tuning

The most common tuning problem with these gyros is a bouncy CW piro stop. Start by setting your tail D-gain to 10 in the Advanced Settings. Then, hold a hover and test the piro stop by doing one or more full 360 piros CW, then suddenly, but precisely return the rudder to center. Do the tests at your highest HS, and highest piro rate, and make sure the stick does not bounce when it returns to center. Most likely, the first time you do this, when you let go of the stick, the tail will coast a bit and return (i.e. it will bounce only once). Decrease the Deceleration Rate for the CW piro until this bounce is minimized. If you go down too low, the stops will feel vague and mushy. At this point, aim for the lowest Decel rate that does not act mushy, even if it still has some bounce to it.

To eliminate the last bit of bounciness, increase the Tail D-gain 2 points at a time. If you go too high, the tail will start wagging at the piro stop (more than 1 bounce). Optimal D-gain is generally in the 10-20 range. If you've gotten to 20 and the CW piro stop is still bouncy, start Increasing P-gain 2-3 points at a time. You might start seeing some wags if you do this, in which case, go back to the Main screen and decrease your overall Yaw Gain to 90 (default 100). Keep adding P-gain until the CW piro stop is crisp and precise.

Finally, tune the CCW piro stop using the Deceleration rate - aim for the lowest Decel rate that does not act mushy. This side of the piro is usually pretty easy. But, if you have a marginal tail servo, it may feel bouncy even at low Decel rates. If that happens, you'll need to drop the tail I-gain 2-3 points.

Note: if you don't have a high-end dedicated tail servo, don't expect flawless performance out of your tail. You'll have to live with some bounce on piro stops and some vagueness around center.

Final PID Gain Tuning
With the piro stops sorted out, it's time to take the heli for some FFF and FBF to see how the tail behaves. Start with a few high-speed passes FFF down wind and listen for wag. If you hear any, decrease your Tx gain. Then, move on to FBF, shallow tail slides, and right-rudder funnels (tail up and down). Again, you're looking for wags - decrease Tx gain if needed.

Finally, do some full 360-piros while moving in FF. The piros should look smooth, consistent and effortless all the way around. If the tail hesitates as it approaches 90° to the direction of flight, then quickly whips around the other side, your I-gain is too high. Decrease it by 5 points.

Pre-compensation Tuning
With the gains all settled, it's time to tune how the tail holds position in high-pitch maneuvers. First, test some pitch pumps. If the tail swings when you apply sudden bursts of collective, add 5 points to the Coll>Tail compensation box. Make sure it goes in the right direction by watching the tail blades as you push collective from center to the top - the leading edge should swing towards the boom (use -5 if they go the wrong way). Keep adding more pre-comp to the Coll>tail box until the tail holds steady when you apply bursts of max collective pitch. This number is rarely >10. If you need to go much higher than this, your throttle curves are probably too shallow or your governor isn't tuned well.

Whatever final number you end up with in the Coll>Tail compensation box, copy it to the Cyclic>Tail box as well. Test by doing multiple continuous stationary flips or rolls (2-3 flips without stopping). If the tail tends to drift CCW, add 1 more point to both Coll>Tail and Cyclic>Tail; if the tail drifts CW, subtract 1 point.

[Dr. M]

In all my experimenting and reading I've not found any value in tuning cyclic roll and nick any differently on these units, so I'll discuss them both at the same time.

I think it's easier to have the tail figured out first, and endeavor into tuning the cyclic feel last. If you followed this tuning guide so far your gains should be pretty well tuned already and the tail should be very well behaved. You could very well stop with the fiddling and just go fly. In fact, I recommend you do just that: fly your newly tuned heli for 10 or so packs just to get used to the feel of these units, then go ahead and proceed to tune the cyclic to be closer to your ideal feel.

The purpose of this section is to help you get the best feel out of the cyclic controls and compensation that these gyros are capable of delivering. As before, do the tuning using the highest HS you plan to fly.

Let's start with the easy parameters:
Acceleration: When this value is high the swashplate will tilt fast when stick is moved. The default is 125 in all default configurations, and I've never found a need to change it.
Deceleration: just like the tail, this parameter control stopping behavior when a stick input is suddenly released. The effects are not quite as dramatic as the tail though, but decreasing this will make the stops softer, while increasing it will make the more crisp. The defaults are pretty good starting points; tune up or down to get the feel you're after.
Agility: this is the maximum roll/pitch rate. Adjust to taste.

The hardest parameters to tune are the PID gains. These will have dramatic effects on performance and feel. The general guidelines are as follows:

P-gain has a the largest impact on stick response; increasing it makes the cyclic feel more connected and responsive, particularly around center. You can't go too high though, increase 2-3 points at a time. Decreasing P-gain will soften the cyclic response, making in more robotic. Most often, the best tuned values are in the range of 80-110. If you keep increasing P-gain and you start noticing disk oscillations in the hover, or unloaded FF descents, decrease the main cyclic gains 5 points and continue tuning the advanced parameters.

I-gain determines both how well the gyro will maintain attitude, as well as how hard it will fight your inputs. For the most connected feel you'll want to tune in the lowest I-gain possible, while still maintaining an acceptable level of attitude hold. I tune my I-gain by doing moderate speed passes and taking my hand off the cyclic stick. Watch carefully how well the disk holds attitude as the heli flies down the flight line up and down wind, right, inverted, as well as sideways. If the disk drifts up, and the heli slows down considerably, increase I-gain 2-3 points. I found values in the range of 90-105 produce the best compromise between attitude hold and connectedness. Values higher than this range will feel increasingly disconnected and robotic, and may even cause low-frequency oscillations and bounce back on stops. Value in the 60-90 range feel extremely quick and jittery, but may be well suited for smack 3D flying style.

D-gain similar to the discussion for the tail, this parameter controls stops. You need to test fly both quick jabs to the cyclic stick, as well as continuous flips/rolls and observe the stops. If the stops bounce, you can increase D-gain, and if they wobble, or coast, decrease it. However, if the disk stops cleanly, but just feels a bit vague, increase the Deceleration value and leave D-gain alone. Caution If you're using ZYX firmware 3.5, do not go above 20 for the cyclic D-gain, as this can cause violent oscillations.

Final tests
The most conclusive test of cyclic feel comes in stirring maneuvers, such as piroflips. If you can't fly these, don't worry about it, but if you can, try them out really slowly and deliberately. Keep that piro rate low, and carefully sync the cyclic stir, then slowly increase the piro rate and piroflip as fast as you can controllably- if you feel like the gyro is fighting you, increase P and decrease I-gains 2-3 points. If the cyclic feels inconsistent or sloppy, decrease P and increase I a bit.

Revisiting the tail
Now that you have your cyclic set up to the right feel, it's time to check the tail just to make sure it's perfect. One of the best tests you can do is sideways (aileron) tick-tocks. Do these with the starboard side down (i.e. the TR facing the ground). Keep them swift and tight, and observe if the tail drifts. If you notice a CCW drift, increase your governor gain , or add 1 point to the Coll>Tail and Cyclic>Tail precomp values. But be aware that the best tail performance is always a balance between how well your motor maintains HS in hard maneuvers and the gyro pre-compensation. There's really little any gyro can do if you're shedding 200-300 RPM with each collective move

[Dr. M]

Pro Tips
- Always check compensation and stick inputs before spooling up. Do it for every pack you plug in!.
- If you're not using the Conditions switching function, make sure the parameters for the 2 banks are set identically to prevent an inadvertent switching of the Conditions mode from causing a crash.
- Quickly Flicking the Gear switch 3-4 times, switching between HH and Rate mode will cause the gyro to reinitialize. Don't do it in flight!
- If you use John_NZ's PC App (fbl.net.nz) you don't need to connect to the ZYX to update the firmware

ZYX-S Satellite binding issues
Solutions:
https://www.helifreak.com/showpost.p...7&postcount=26
https://www.helifreak.com/showpost.p...6&postcount=24

USB drivers in Windows 8
http://www.rcgroups.com/forums/showp...postcount=6420
http://www.prolific.com.tw/US/ShowPr...id=225&pcid=41
http://www.rcgroups.com/forums/showp...postcount=6444

Static issues
These gyros are extremely sensitive to ESD. If any part of your avionics system gets zapped by static, the gyro will lose its initialization data and either stop responding, or cause the Swashplate to tilt all the way to one extreme. Symptoms of ESD in flight are easily recognizable: tail twitch followed by a tendency for your heli to want to tilt in one extreme cyclic direction. It usually takes full cyclic input in the opposite direction to maintain a level disk. I suggest you hit TH immediately if you see this happening - this is an extremely dangerous situation and could cause you to lose control. Once the heli is on the ground, examine the Swashplate - it will be tilted all the way to one side and it will not return to center unless you power cycle the gyro.

Take steps to mitigate the static dangers by grounding your tail shaft to the motor mount and using anti-static lube on the belt and plastic gears. For some reason, using a large electrolytic capacitor plugged onto a Y-lead next to the gyro seems to help as well. I use a 3300uF 16V low-ESR cap on my ZYX helis.

Tipover on spool-up or shortly thereafter
Most often these are caused by an incorrect compensation direction on cyclic. Read about the recommended preflight checklist in the first post.

Other possible causes include ESD and vibes.

Here's an example of working thru the possible causes of a flipover (with video): http://www.rcgroups.com/forums/showp...postcount=1953

Brown out testing
Test conditions: used a 4-cell NiCd Rx pack almost depleted. The Rx pack has two leads, one was plugged into a voltage monitor/charger, the other plugged into a free Rx port. I wiggled all sticks until bad stuff started to happen, then started the charger to increase voltage.

Results: the CX-ZYX will brown out around 3.44V. The aftermath of a brown out depended on how long it took for voltage to be restored at operating levels:
1. Fast (<1sec): no reset, everything returns to normal operation with no loss of control. Swashplate level.
2. Medium (1-3 sec): temporary loss of control (feels like a hiccup). All activity returns to normal when voltage is brought back up; the gyro does not reset. Swashplate level.
3. Long (>3 sec): complete loss of control, gyro resets (all leds blink), then fails to initialize (blinking blue led). There's no response from any of the servos, or any other input. Swashplate is frozen in an odd position, cyclic servos buzz, tail servo unpowered. A power cycling is required to restore normal operation.

Bonus testing: I also wanted to see what happened if voltage was maintained at marginal levels for a longer period of time. I set and maintained the input to the system at 3.44-3.45 V. All servos were randomly twitching. There was still response to inputs, but the swash was not level and tail servo wanted to be at the fore extreme (cw piro). Stick inputs resulted in correct response, but upon release, the servos returned to the previous behavior. Increasing voltage above 4V returned the gyro to normal operation (Swashplate level, tail centered).

Known issues without solutions for ZYX FW 3.5
- collective mushyness, doughy feel, particularly in reversals and around center
- random (minor) tail drift in HH mode in a stable hover
- abrupt pitch-up behavior in FFF

[lcc014]

Should this post be pinned ?

[bionicbone]

Good idea Dr.M - subscribed

[Dimitris K]

Dr. M has been very helpful to many members of HF,
giving great advice on this FBL unit and of course he
is not the only one helping people. This guide reflects
a great know how that has been build up in these threads and
has been layed down nicely. I think it would be vey helpful
to be pinned as a sticky post.

Dr. M, thanks for your effort

[Dr. M]

Thanks for the support, guys, and thanks to Dominic for the sticky.

Please feel free to add your own ideas, problems and solutions to the thread.

[u8at711]

what to do if, piro hover is not flat ?, both upright and inverted ?

[Dr. M]

Originally Posted by u8at711

what to do if, piro hover is not flat ?, both upright and inverted ?

Most likely you need to adjust your CG so it's directly on the main shaft. Otherwise, make sure piro optimization direction is set correctly and that your cyclic gains are tuned to their optimum values. Finally, the CX or ZYX prior to firmware 3.5 never had great piro stability, even with the best of tuning. So, if you haven't done so, upgrade to the latest firmware.

[pinguin]

I just built a new X2. I use 415M for cyclic. Set the servo as 1520us. I have no trim nor sub-trim on the Tx. Some trim for pitch and elevator servo in ZYX-S software.
Why my zero pitch keep changing. Sometimes when I do full throttle and 0 throttle and back to mid stick, it's not zero anymore. Sometimes after turning off and on again, it's not zero anymore. It can be positive pitch or negative pitch. It's give me headache setting min/0/max pitch curve.

[Mikej]

Sorry - I have not heard of this before on the ZYX

One thing that I do to ensure that I have mid stick is to set a pitch curve in Hold of 0, 50, 50, 50, 100 - this way anywhere between 1/4 stick and 3/4 stick will give middle - it probably won't help, but it does make things easier.

[Dr. M]

Originally Posted by pinguin

I just built a new X2. I use 415M for cyclic. Set the servo as 1520us. I have no trim nor sub-trim on the Tx. Some trim for pitch and elevator servo in ZYX-S software.
Why my zero pitch keep changing. Sometimes when I do full throttle and 0 throttle and back to mid stick, it's not zero anymore. Sometimes after turning off and on again, it's not zero anymore. It can be positive pitch or negative pitch. It's give me headache setting min/0/max pitch curve.

I suggest you use subtrim on your Tx to make the ZYX see 0 at mid-stick when looking at the monitor screen. And also when Mikej said with the setup pitch curves.

[Chillout47]

I am getting a difference in the zero points when I switch TH on and off, the swash moves slightly when switched between the two. Any ideas???

[ricoalonso]

Originally Posted by Chillout47

I am getting a difference in the zero points when I switch TH on and off, the swash moves slightly when switched between the two. Any ideas???

Is it possible you have different sets of pitch curves between HOLD and the other conditions?

[Mikej]

Originally Posted by Chillout47

I am getting a difference in the zero points when I switch TH on and off, the swash moves slightly when switched between the two. Any ideas???

What Tx are you using? Most Tx's will allow you to set different pitch curves for Hold / Normal / Idle 1 / Idle 2 - it sounds as if this is the case in your Tx

[pinguin]

Originally Posted by Dr. M

I suggest you use subtrim on your Tx to make the ZYX see 0 at mid-stick when looking at the monitor screen. And also when Mikej said with the setup pitch curves.

On the monitor screen, everything is zero. Throttle/pitch is zero, the same on the servo screen on 8FG. I suspect the problem is with ZYX. I will try to flash the ZYX again.

[pinguin]

Originally Posted by Chillout47

I am getting a difference in the zero points when I switch TH on and off, the swash moves slightly when switched between the two. Any ideas???

Check for any mixing. It happened to me once. I was setting a new model, but when flipping a switch, the swash move. When I check my Tx, there is mixing assign. I never use any mixing. I don't know how it was possible.

[Chillout47]

Ok, thanks lads, I'll check that out tonight. I'm using a standard DX7. Funny though, when the swash moves between switching, it only looks like the elevator servo is dropping the back of the swash slightly, then switch and it pops back up to level again.

Cheers, Mark.