Difference between revisions of "Tuning Guide"

Latest revision as of 08:04, 2 April 2024

This guide should help you with tuning your helicopter to obtain optimal flight characteristic. The tuning guide expect the Advanced parameters are set to default.

First from all, you should try a default settings that are recommended. There are basic parameters that you have to set at the beginning (for example in the Setup wizard) but other are useful to adjust feeling and flight characteristics. Basically, you can set the behavior so that it is very similar to any known flybarless or flybared system.

If you are in condition that the helicopter is flying, but you need to do some corrections, you should start with the rudder settings first.

1 RUDDER TUNING

Prerequisite step - You can verify that the rudder servo limits are not too low or either not too high.

If the values for Rudder End-Points in the Limits Tab are less than 70, then it is too low. That mean that servo precision vs mechanical gain is not optimal. You can fix the issue with putting ball link closer to the center at the rudder servo so that limit can be higher. In case the value is more than 170 there is mostly too high servo precision vs mechanical gain. You should put longer servo arm, so the ball linkage can be further. Be sure you have configured limits so that tail slider is moving from end to end, but without any mechanical binding (servo buzzing). In case your tail mechanics allows a pitch higher than 45°, do not set limits that high. It is not absolutely necessary that limits for both sides are equal.

1.1 Tuning Procedure

1. Set Sensor/Rotation Rate for the rudder - this parameter determine how fast the rudder will rotate around its axis. Values between 8-11 are used by allmost all pilots. Default value of 8 is fine for beginners. While value of 11 is good for 3D maneuvers where faster pirouettes are needed.

2. Set Advanced/Rudder Delay accordingly for your servo type - please see the Servo list where you can find optimal range. For Futaba BLS servos and ultra fast servos it is fine to set 0. Slower the servo is, the higher value should be configured. If you are not sure, leave this parameter (value of 5 should fit for average digital servos).

3. Set Gyro Gain (usually in your transmitter) to the value, that tail is holding well, but not oscillating in any maneuver (for example Pitch pumping). This value should be as high as possible always. If you are observing tail oscillation, you should decrease the gain to eliminate it. Please note that it is recommended to change the Gain only in this step. In case that you have achieved 100% Gyro Gain with no oscillation, please increase Sensor/Rudder Common Gain which will multiply the Gyro Gain.

4. Now, when your gain is configured, your tail can still not hold the position exactly. That's because your mechanical gain is not high as necessary. You can fix it by increasing the Advanced/Piro Consistency value. Increase it by 5 gradually until the tail will hold. The value should be nearly in all cases between 155 - 190. With higher values the rudder will rotate more constantly and so can be even more sharp. With bigger size helicopter the value is often higher. It depends mostly on the helicopter construction (manufacturer), servo arm and servo type. For Futaba BLS servos or similar, it is needed to increase the value even more (in rare cases to value of 200). You shouldn't set the parameter too high if not necessary (always set only as high as really necessary), otherwise tail oscillation in high extent can occur. You can verify it in a fast forward flight or pitch pumps whether the value is too high and you can see any oscillations.

5. If the tail is still not holding well the problem could be:

• Head Speed is holding poorly or too agressively during load. (can be improved by Governor settings or Throttle Curve change).
• There is a mechanical issue. Check by spooling up the motor with no blades, then move with the tail push rod carefully by hand from end to end. (push rod disconnected from servo).
• Tail servo is too slow (0.07s/60° or higher) - increase the Advanced/Rudder Revomix to value 1-4. Higher values are not recommended.

6. When above steps are done, you can tune the Stopping Behavior. For this purpose use the Advanced/Rudder Dynamic parameter. Value determine how aggressive the rudder stops and the steering is. If you like sharp stops, you should set value between 6 to 8. If you like extra sharp behavior, then value higher than 10 are good for you. But high values are very demanding for servos and mechanics, so you should be carefull. If you like smooth stopping so that steering is also very smooth, you should set values between 5-7. If value is too low, the rudder reaction can be even delayed. In case the tail stopping is not equal or overshooting to one side, you can decrease the Rudder End-point for such side (mostly closer to the tail blades) by 0,5-1mm.

2 CYCLIC TUNING

Make sure the Cyclic Ring - Aileron/Elevator range is as high as possible without binding even in min/max collective pitch. Ideally it should be equal angle with your max. collective pitch. But it is extremely important to not exceed angles allowed by the model manufacturer. With models of size 600 and bigger risk of boomstrike is very high with lower RPM.

2.1 Tuning Procedure

1. Increase the Sensor/Cyclic Gain if you can observe the cyclic is not level during pitch pumps or flight is not precise. Mostly values around 60% are optimal for all models. You shouldn't set the gain as high as possible always. If it is too high, steering can be even delayed little bit and not that comfortable. Mostly values above 80% are unwanted. If gain is too high, you can see Aileron oscillations, especially when descending slowly or while doing Tic-Toc maneuver. Sometimes it is caused by too soft head dampeners or non-flybarless blades as well. But if you can achieve values higher than 50% then it is optimal. In some cases, if you want very natural feeling, you can set the Cyclic Gain to e.g. 40%, but you will loose some precision. Stability will be still good.

2. Set the Sensor/Rotation Rate parameter to the extent that flips and rolls are fast enough. Be carefull to not set it higher than your mechanics can handle. The highest value for the most models is between 11 - 13. If the value is too high, steering is not precise and sometimes you can observe that rate is not constant (Once you finish the cyclic input it will continue for a fraction of second).

3. If input reactions are delayed, you want likely to increase the Advanced/Cyclic Feed Forward which plays very important role in overall behavior. If you are switching from e.g. Microbeast, you will be comfortable with values between 4 - 6. If you are switching from V-Bar you will like 6 - 8. If you are switching from Bavarian Demon, you will love values of 8 - 10. The higher values are more demanding for the servos. In bigger helicopter you can even risk Boom Strike with too high values. Too high value will induce too sharp movements and also elevator bounce-back. Too low value will cause very delayed (smooth) steering.

4. Now it is time to set the General/Flight Style. This is the last parameter that determines flight characteristics. If you like very linear movements from the stick center to full stick deflection then you will like low values. If you like flybar behavior, so that feeling around center is smooth but with faster input you will get a sharp response, then you want to set high value. With various combinations of Flight Style and Cyclic Feed Forward you can change Cyclic feeling a lot. If you are switching from e.g. Microbeast, you will be comfortable with values between 4 - 6. If you are switching from V-Bar you will like 6 - 8. Difference between settings can be seen especially in a pirouette maneuvers and also Tic-Tocs. If value is too high, then blade' efficiency can decrease and motor can be overloaded. With higher value a sharp movements are transferred faster to the servos. Also if you are doing aggressive maneuvers, it will stop faster when stick is returned to the center. If the value is too low, then a Tic-Tocs can't be done fast enough, Piroflips can't be done precisely, etc. For beginners we recommend to leave default value. This parameter is only about your preference and both low and high value has its positive and negative side. For example, if you want smooth feeling around center with natural characteristics, you can set value of 8 for the Flight Style and Cyclic Feed Forward to 6 - 10.

5. Lastly, you want to eliminate possible Elevator Bounce-Back effect. This can occur with high Cyclic Feed Forward, but it can be reduced by increasing Advanced/Elevator Filter parameter. Value between 2-3 should be fine for almost all helicopters. When using an aggressive blades you will need value of 4. Especially for bigger size helicopter, the value can be higher. In case of too high value, elevator movement can be too smooth and in some cases elevator can oscillate with low RPM during hovering. Set it only as high as really necessary.

3 Unable to Tune perfectly

In some cases even after proceeding according this Tuning Guide you can be unable to make the model to fly well. The most issues are result of poor rudder performance. This can then transfer to Cyclic whenever tail will kick to a side on its own.

3.1 Tail mechanics check

In order to not waste time with tuning procedure it is recommended after each build or rebuild to remove Tail servo arm from the tail servo. Then check the following steps.

1. Move with tail push rod in full extent and make sure the mechanics is butter smooth.
2. There must be basically zero friction. Any friction you feel has direct impact at the tail performance.
3. The easiest way to make sure it is really smooth is to tilt model - the tail slider should move on its own back and forth.
4. If you remove all rotor blades and spoolup up the motor you should see only moderate increase of required force to move with the tail push rod. Imagine the servo must overcome the force all the time - if you feel it is already too much there is high chance something is wrong with axial bearings in the tail rotor hub or something does not fit at a correct place. Even a single missing washer can cause very big difference.
5. With some models it is absolutely necessary to use a Ball reamer. Without this tool push rods might never move smoothly even after 1000 flights.

3.2 Tail hunting

Tail hunting is the first, but the most common sign there is something wrong with the tail. It is enough to hover the model when there is no wind. Tail should be rock solid without any movement. If there is a movement during hovering then continue reading.

• In almost all cases it results from mechanics not moving smoothly.
• Basically any parameter of the FBL unit will not improve this issue whatever you will do.
• If your servo frequency was configured to the higest possible your tail mechanics is either still not smooth or servo is not up to the task.
• Faster servo will always improve Tail performance and could reduce the issue even if mechanics is not butter smooth.
• In less common cases the hunting comes from very high Governor P gain (ESC governor) or very high Governor Response (Spirit Governor).
• Make sure you used Spirit double sided tape.

3.3 Tail kick

Tail kick could be result of more problems at the same time. If you checked tail mechanics the biggest improvement will come after a proper setting of the Pirouette Consistency parameter and Gyro Gain.

• Make sure that Head Speed is holding correctly. If using Governor make sure the Governor Gains are not too high but not too low. Both cases will result in tail kick. Too high Governor gain can be distinguished by audiable noise coming from the motor. Your motor might be reaching higher RPM than required in that case.
• If using only Throttle Curves without a Governor it is necessary to set a proper V-shape curve. Too high or too small difference between center throttle percentage will cause tail kick too.
• If servo is too slow and there is nothing else you can do with the mechanics the only real improvement can come by using Revomix parameter. In the most cases it should be not higher than value of 4. Revomix value should be configured to be only that high as really needed. Too high value will introduce tail wag problem and other imprecision.
• You can improve the performance by adjusting mechanical tail center position by adjusting push rod length. When tail servo arm is at the center then there should be 3-4° angle between tail blades. Tail slider should be closer to the tail boom.

3.4 Tail stopping is unequal

To get the best stopping behavior it is recommended to set Rudder Servo centering position in the following way:

1. Enable Subtrim (Tuning)
2. Verify that Rudder Servo Arm is exactly at the middle position.
3. If it is'nt in the center, use Subtrim in the Spirit Settings software to center it.

Only after a proper centering change Tail push rod length to achieve correct neutral position of the Tail Mechanics. For the best performance make sure that there is a slight pitch between tail blades - approximately 3-4°. Tail slider should be usually closer to the tail boom. If you wish to verify tail centering you can use Gyro Rate mode - Set Stabi/Function to Disabled and use a Negative Gyro gain.

Only after these two adjustments set Rudder End-points in the Spirit Settings software - Limits tab. Left and right values should not necessarily be similar but it is recommended there is not too big difference. If values are over 150 it is sign tail mechanics has too low mechanical gain. It is recommended to use Longer rudder servo arm. This could not only improve Tail performance but also stopping behavior.

For some helicopters it is possible to set one limit much bigger which usually result in pitch near 45°. This is too big and is highly recommended to use lower limit.

In case that stopping is still not good, make sure that Pirouette Consistency and Rudder Dynamics parameters (Advanced tab) are not way too high. Usage of too high Revomix value (over 4) or Rudder Delay (over 20) can also result in degraded performance of Tail Stopping. It is recommended to start tuning with Revomix at 0 and Rudder Delay set according our Servo List table.

3.5 Main rotor check

If you can observe that the model is pitching up when moving collective pitch or there is excess elevator bounce back do the following check:

1. Enable Servo/Subtrim (tuning) menu. All servo arms MUST be at the center position. If not, use Subtrims in the software to fix this.
2. After adjusting subtrims and servo arms are at the center, make sure the swashplate is perfectly level by using Cyclic Leveler tool. Using eye only will not reach to desired point.
3. Make sure that axial bearings in the main rotor hub are properly oriented. The most models require correct I/O direction. Note that even after 30 flights the axial bearings could be damaged completely. Rotor grips must move with no steps. If there are steps they must be replaced for new.
4. Make sure that a Ball reamer was used to all push rods. When you disconnect servo arms from the servos, the swashplate must move on its own depending on how you tilt the model. If swashplate will remain at the same position this will result in decreased cyclic performance. Strong and fast cyclic servos can overcome this issue in the most cases but it is always better to build the model properly.
5. Make sure you used Spirit double sided tape. Otherwise a strange bobbing or oscillations could occur - especially when using a soft tapes.