Transmitter Based Tuning

You can perform extensive parameter tuning in flight using your R/C transmitter. This is meant for advanced users who are unable to use the autotune features or wish to do fine tuning with full manual tuning control of each parameter

Overview

Transmitter based tuning allows you to tune a single parameter or a set of parameters while flying. The basic idea is to link the tuning value of a parameter to a knob or slider on your transmitter then to adjust the parameter in flight by moving the knob.

Key features of transmitter based tuning are:

  • Tune either a single parameter or a whole set of related parameters in a single flight
  • Re-scale the range of the parameter value linked to the tuning knob using a “selector switch”
  • Switch between parameters to tune while flying using a selector switch
  • Save the new parameters in flight
  • Receive audible feedback from the flight board buzzer and the GCS on tuning progress

Concepts

The two key controls for transmitter based tuning are:

  • A “tuning knob”, setup on your transmitter to a convenient knob or slider and linked to a RC channel that your board receives
  • An optional “selector switch” for controlling advanced features of the tune. This should be linked to a two position switch mapped to a RC channel that your board receives. A spring loaded switch (such as the trainer switch) works particularly well.

In addition to those input controls the following concepts are useful in understanding the tuning process:

  • A “parameter set” is a group of related parameters that can be tuned one after the other in a single flight
  • The “mid-point” is point on the tuning knobs range where it produces a PWM value half way between minimum and maximum

Setting up for tuning

To setup your vehicle for tuning you need to set the following parameters:

  • TUNE_CHAN: the RC input channel associated with your chosen tuning knob
  • TUNE_CHAN_MIN: the minimum PWM values produced on TUNE_CHAN
  • TUNE_CHAN_MAX: the maximum PWM values produced on TUNE_CHAN
  • TUNE_PARAM: the parameter or set of parameters you will be tuning
  • TUNE_SELECTOR: the RC input channel associated with your chosen selector switch (optional)
  • TUNE_RANGE: the scaling range which the tuning knob covers

The TUNE_PARAM parameter selects the parameter or set of parameters you will be tuning. Values of TUNE_PARAM less than 100 correspond to individual tunable parameters whereas values of 101 or higher correspond to sets of related parameters that can be tuned one after the other in a flight.

Use your ground stations parameter interface to see see the full list of tunable parameters and parameter sets available for TUNE_PARAM. For APM:Plane most of the parameters are associated with tuning the QuadPlane VTOL motors as those are the most difficult to tune. You can also tune some fixed wing parameters, although most people find the automatic tuning with AUTOTUNE mode is the best option for fixed wing flight.

If you want to tune a set of parameters (by choosing a TUNE_PARAM value over 100) you must have a selector switch configured with the TUNE_SELECTOR parameter.

Using the tuning knob

The basic operation of the tuning knob is very simple. If the tuning knob is at the bottom of its range then the parameter being tuned is set to the initial value divided by the TUNE_RANGE. If the tuning knob is at the top of its range then the parameter being tuned will be set to the initial value multiplied by TUNE_RANGE.

So with a default value for TUNE_RANGE of 2 you will be able to change the parameter in a range from half its initial value to 2x the initial value. This is a good range for many tuning tasks.

Activating the tuning knob

When you first start tuning a parameter you will find the tuning knob is not yet active. This is because the knob does not activate until it passes the “mid-point value”, defined as half way between TUNE_CHAN_MIN and TUNE_CHAN_MAX. Activating the tuning knob in this way ensures that you don’t accidentially take off with a large change in tuning value. You are guaranteed to start the tune with a value very close to your current value for the parameter.

When the tuning knob activates by reaching the mid-point the buzzer on the flight board will give a quick “bup-bip” sound to indicate that tuning has been activated.

Re-centering the tuning knob

It is quite common to find that the TUNE_RANGE is not wide enough to move the tuning value to the ideal point for your vehicle. For example, you may have started the tune with a P gain for some axis of 0.7, and when you move the tuning knob up all the way the vehicle still hasn’t started oscillating. In that case the tuning value will have reached 1.4 and you need some more range.

To get more range you can use the selector switch to re-center the tuning knob around the current value. Toggle the selector switch briefly high then low and the center-value will change to whatever the tubing knob is set to. When you re-center the tuning knob will de-activate again until you move it to the mid-point position. This prevents you getting a jump in the tuning value when you re-center.

Tuning multiple parameters

You can tune multiple parameters in one flight by setting TUNE_PARAM to one of the “tuning set” parameters. For example, if you set TUNE_PARAM to 101 then you will have 4 different stages to your tune:

  • RATE_RLL_D
  • RATE_RLL_PI
  • RATE_PITCH_D
  • RATE_PITCH_PI

notice that RATE_RLL_PI is actually two parameters in one, controlling both the P gain and the I gain for roll. This follows the normal advice for MultiCopters that you should keep the P and I values equal when doing a manual tune.

When you choose a tuning set with TUNE_PARAM then you will initially be tuning the first parameter in the set. Once you have adjusted that parameter as much as you need to you can move to the next parameter in the set by holding the selector switch for more than 2 seconds. It is suggested that you count to 3 to ensure you are over 2 seconds.

Holding the selector switch for more than 2 seconds will switch you to the next parameter and will also change the tuning knob back to its “wait for mid-point” state on the new parameter. The buzzer on the board will give a loud BEEP sequence to indicate which parameter in the set you have changed to. For the first parameter in the set you will get one loud BEEP. For the second parameter you will get two loud BEEPs and so on.

When you have cycled through all of the parameters in the tuning set you have chosen it will wrap back around to the first parameter in the set.

Saving the tuning results

When you are happy with the tune you can save the result by holding the selector switch for more than 5 seconds. After 5 seconds the board will make a rapid bup-bip-bup-bip sound to indicate that the save is complete. If you leave the selector switch in the high position then tuning will remain disabled after the save.

Reverting the tune

If you are not happy with your tuning results or the vehicle becomes unstable you should change flight mode. Any change of flight mode will immediately revert all of the parameters you are tuning to the last saved value.

The tuning process

The tuning system is designed to make it easy to quickly get a reasonable manual tune on a vehicle in one flight. The most common use for this type of tuning will be in adjusting the rate roll and pitch PID gains. The tuning procedure outlined below is for that particular case.

Setting up

To setup for tuning your rate PIDs you should set TUNE_CHAN to your tuning channel, TUNE_SELECTOR to your selector switch and TUNE_PARAM to 101 (which is the “rate roll and pitch PIDs tuning set”).

Then takeoff and switch the vehicle to a comfortable flight mode for rate tuning. ALT_HOLD or LOITER in copters works well. For a quadplane QHOVER or QLOITER are the best choices.

The first parameter you will be tuning will be RateRollD. To tune that parameter (and the other parameters in the rate roll/pitch set) you should follow this process:

  • move the tuning knob to the mid-point to active the knob. You will hear a rapid bup-bip from the board to indicate the tuning knob is activated.
  • start raising the tuning knob slowly, stopping immediately if the vehicle starts to oscillate. While you raise the gain you should give some small roll inputs on the sticks.
  • if you get to the top of the tuning knob range and the vehicle has not yet started to oscillate then use the selector switch to re-center the range, then move the tuning knob to the mid-point to reactivate the tuning knob
  • as soon as you see oscillation you should immediately lower the tuning knob to the point where the oscillation just stops
  • once the oscillation stops then re-center the tuning knob using the selector switch, then move it to the mid-point to activate it, and then lower the tuning knob all the way down. That will move the tuning value to half of the value that just stopped the oscillation (assuming a TUNE_RANGE of 2). Moving to half of that value will give you enough margin in your tune to ensure your vehicle can handle a wide range of flight conditions.

Once you have completed the above process for the first parameter then you can move to the 2nd parameter by holding the selector switch for a count of 3. You will hear a BEEP BEEP sound from the vehicle indicating that you have moved to parameter 2, which is the RateRollPI parameters. You should then repeat exactly the same tuning process with that parameter.

Keep tuning each parameter in turn using the above process until you are happy with all of them and then save your new tuning parameters by holding the selector switch for more than five seconds. You will know the 5 seconds is up when you hear the distinctive rapid bup-bip-bup-bip sound from the buzzer.

At that point you can land the vehicle, or just enjoy flying it.

The first time you do a full tune in this way it will probably take about five minutes of flight time to do a tune. With some practice you can do a full tune in a bit over a minute.