For the impatient, skip down to the section titled "Cloning Instructions" or "Flight Mode Switch setup" (not recommended).
LibrePilot has ported Tau Labs / dRonin "Autotune" into a coming version of the LibrePilot firmware.
First some precautions. Tuning carries a risk of oscillation and for LibrePilot firmware, oscillation tends to effectively move the throttle toward 50%. If your copter requires more than 50% power to hover, then oscillation will make it descend. If your copter needs less than 50% to hover, then obviously 50% will have it climbing. In extreme cases any throttle above 0% will effectively be 50%. Remember that zero throttle stick will stop the motors. Don't make any changes to this important "motor off" safety feature. Tuning is known to fail in some cases. Testing has shown that these same cases fail dRonin Autotune as well. Be prepared.
Oscillation generally comes in 3 forms.
Normal oscillation is a rhythmic motion that is generally visible and audible. It is usually caused by PIDs being too high.
Jerkiness is random, and is not actually an oscillation. It is usually caused by too much vibration. Replace or straighten bent shafts, balance and track your props, and if that is not enough and the tuning doesn't fly right, try increasing (doubling) GCS -> Configuration -> Stabilization -> Expert -> Gyro Noise Filtering.
Invisible oscillation generally cannot be seen or heard. The way you know you have it is that all throttle stick positions act as if they were closer to the middle. Motors tend to run hotter and batteries don't last as long as they should. Powerful copters (those that require less than 50% power to hover) will take off with much less throttle than expected. Weak copters (those that require more than 50% power to hover) will need more power than expected to take off, or will not take off even at full power. Try increasing (doubling) GCS -> Configuration -> Stabilization -> Expert -> Gyro Noise Filtering, but realize that this will make AutoTune create very slow smooth PIDs.
Oscillation can cause AutoTune to fail. If AutoTune internal sanity checks fail, it won't write PIDs. It's also possible to get PIDs that don't fly well. If you have a problem with oscillation, it must be corrected before running AutoTune. This is especially true of invisible oscillations.
This version of AutoTune puts the copter into a special version of Attitude flight mode that shakes the copter and measures the motions. As a pilot, you should be able to confidently fly in Attitude mode because it will be a bit more difficult than normal to maintain control. Tuning also needs a larger area than simple hovering. As a point of reference, a good pilot should be able to do a tuning in a single car garage stall.
Multicopters fly better if they have "Light Damping (BLHeli)" or "COMP_PWM + MOTOR_BRAKE (SimonK)". Without these, when there is a lot of stick control (or oscillation) happening, the copter tends to climb because the motors speed up more quickly than they slow down. With slow ESCs you may notice this when AutoTune mode starts shaking the copter.
AutoTune is not currently supported on CC3D. Also, there will be a GCS GUI for all this at some time, but it was designed to make it possible to set it up at home and be run at the flying field without requiring use of the GCS.
Currently you must be able to compile LibrePilot software / firmware yourself to be able to use this. The pre-release source code can be found at: https://bitbucket.org/TheOtherCliff/librepilot/branch/theothercliff/LP-76_Port_Autotune_from_dRonin
Before you uninstall or overwrite your old software / firmware you should run the old GCS, plug the FC (flight controller) into USB, and do a "File → Export UAV Settings" to save your old settings in case you want to know how it was set up. You should also do screen captures (print screen) on all the setup pages you have used (and thus have non-default values). These could be valuable later on.
Cloning Instructions (tested on Linux):
It is assumed that you have a working development environment:
git clone https://bitbucket.org/TheOtherCliff/librepilot.git autotune
cd autotune
git checkout theothercliff/LP-76_Port_Autotune_from_dRonin
git checkout theothercliff/LP-340_AutoTune_fix_some_time_measurement_issues_in_original_code
ln -s ../downloads ../tools . (or whatever you need to do for downloads and tools)
nice -n15 make -j4 gcs revolution revonano (the 4 is however many real CPU cores you have to keep all of them busy, it still works even if it is wrong) (gcs might take 30 minutes to build) (or remove 'nice -n15' which says to run it at low priority in case you want to do something else with the computer while it is making the software)
./build/librepilot-gcs_release/bin/librepilot-gcs (runs the GCS that you just built) (in Linux that is ./b <tab> l (lower case L) <tab> b <tab> <tab>)
With GCS running and firmware built, go to the Firmware page, press Halt. Wait about 15 seconds for the Flash button to appear. Also, it should automatically select firmware that matches your flight controller. Press Flash. You will also have to erase settings and run the setup wizard again. With that complete, you need to do your calibrations before anything else.
Flight Mode Switch setup:
Note that when AutoTune is complete, it writes the calculated PIDs into the destination stabilization (PID) bank which by default is configured to be bank 2. The standard procedure has you flying the AutoTune mode on bank 1 and writing the new PIDs to bank 2.
The recommended setup for running AutoTune uses a 3 position Flight Mode Switch. With this, you can take off and fly Attitude mode with default PIDs, run AutoTune with default PIDs and fly Attitude mode with new PIDs, all without using the GCS:
Pos#1 - Attitude mode using bank 1
Pos#2 - AutoTune using bank 1 with SystemIdentSettings.DestinationPidBank set to 2 (that is the default)
Pos#3 - Attitude mode using bank 2 (bank 2 is where the tuned PIDs are written by default)
This setup can all be done at home, and everything else can be done at the flying field, without using the GCS.
With this FMS (Flight Mode Switch) setup, you always have Pos#1 to fall back on. Use Pos#1 to recover from any bad situation or to start over and run AutoTune again.
Remove anything that is expensive or fragile (e.g. cameras and antennas, but understand that transmitters must remain unpowered any time they don't have an antenna attached) from the multicopter if this is your first experience with AutoTune on this multicopter.
Arm and take off in Pos#1 which is Attitude mode with default (or other known-good) PIDs. These PIDs must not oscillate for the tuning to work. Switch to Pos#2 which is AutoTune mode which is also configured to use default (or other known-good) PIDs. After a few seconds the copter begins to shake. Fly it smoothly. Don't let the copter touch anything (such as the ground) while tuning is running. 60 seconds after that, the shaking stops and the tuning is complete. The PIDs have already been written to the destination PID bank, but are only stored in RAM memory at this point. The standard procedure is to land and disarm which writes the PIDs to permanent storage. The PIDs will be written to permanent settings if you disarm before powering off. The PIDs will be discarded if the copter is powered off without disarming it.
That covers the basics of AutoTune. Many people will be satisfied with using and knowing only what has already been described. Enhanced functionality, further tweaks, and safety issues are discussed below.
Further Information follows:
Any time after tuning is complete, you can switch to Pos#3 which is Attitude mode using the tuned PIDs to test them. Use caution! It's recommended that when tuning completes you land and disarm, but if you were to switch to Pos#3, even without landing, you would be flying the new PIDs. If you have time and access to a GCS at this point and understand what reasonable PID values look like, you could examine the new PIDs before you fly them.
To test fly your new PIDs, switch to Pos#3 (Attitude with tuned PIDs), arm, and cautiously take off. Beginners beware: a slow increase in motor power for takeoff is not recommended as it causes PID windup. It is best to start with motors off and immediately jump up the smallest amount you can to barely get off the ground and stay off. You can learn the correct amount of throttle by starting with small blips and giving bigger and bigger blips until you learn how much throttle it takes to take off. Before you take off, mentally prepare yourself to immediately apply zero throttle if something doesn't feel right. A fall from 3 feet / 1 meter generally causes little or no damage.
You can simply retune by running AutoTune again if you want to. The use of Attitude mode when testing the new PIDs is recommended (but not required), even for experts. AutoTune mode itself is a modified form of Attitude mode and it doesn't matter what other modes you have as far as the tune is concerned.
In the worst case scenario where you don't have your FMS set up as recommended, oscillation may cause it to climb, and the only way to get down is to cut power for short periods and let if fall. Automatic leveling in that case is very desirable. This isn't an issue if you have the FMS set up as recommended. In that case, just switch to Pos#1.
Tricopters are a special issue. They may or may not tune correctly. An assumption is made that the control delay is the same for roll pitch and yaw. This is not true for tricopters which use a servo for yaw and motor thrust for roll / pitch.
It won't arm:
It won't arm if you
- try to arm it in AutoTune mode
- have put SystemIdent stabilization on Thrust on any FMS switch position
- use GPS Assist with AutoTune
- enable it on a vehicle that is not a multicopter
SmoothQuick:
There is a virtual slider called SmoothQuick, and the PIDs you get by default are in the middle of the slider. At one end of the virtual slider are smooth PIDs which may be preferred for photography. At the other end are quick PIDs which may be preferred for racing. Once you have run the tuning, the FC will always remember the tuning and allow you to change PIDs along this sliding scale at any time in the future. Starting the AutoTune process by staying in AutoTune mode for over 2 seconds while armed will erase the old settings and start a new tuning. If you accidentally start an unwanted new tuning you can just power it off without disarming and it will forget the new tuning rather than making it permanent. To use the SmoothQuick virtual slider, you need to attach a real slider (or knob or FMS 3x toggle) to it. SmoothQuick works in real time, even while you are flying the tuned/destination PID bank if you want.
SystemIdentSettings -> SmoothQuickSource is where you attach a real slider. SmoothQuickSource = 0 disables SmoothQuick entirely. The default of 25 says to access the next of a set of 5 equally spaced points on the slider by toggling the Flight Mode Switch (starting outside of AutoTune) into AutoTune and back out, 3 times, in less than 2 seconds, but only if armed. If you think of the SmoothQuick slider as a scale from 0 to 100, with smoothest being 0 and quickest being 100, then you start out at 50. The first time you do the fast FMS 3x double toggle it will move you to 75 on the slider, then 100, then 0, then 25, then back to 50, etc. If you do the fast FMS 3x toggle while disarmed, it will always set it to 50. 23, 25, and 27 give you 3, 5, and 7 equally spaced stops on the SmoothQuick slider. 25 is the default. You get 25 without any extra setup.
You can also set SmoothQuickSource to be a number from 10 to 13 which corresponds to using Accessory0 to Accessory3 to directly adjust the slider. This requires that you have an available knob or slider on your transmitter, that you already have your transmitter configured to send it out as a separate channel, that the FC has been configured to attach that RC channel to one of the four FC Accessory channels, and that that FC Accessory is not being used by another FC function.
AutoTune / SmoothQuick 'data' is stored permanently. Once you have run AutoTune once, you can use it any time in the future. You don't have to run AutoTune again, but you may want to if you change something, like props or weight.
Using SmoothQuick semi-permanently:
If you enable the AutoTune module manually then it will always be running, even if there is no AutoTune flight mode or SystemIdent stabilization mode in your FMS. In that case your SmoothQuick Accessory knob is always active for the destination PID bank (default 2) and you can adjust PIDs from smooth to quick any time you need it.
AutoTune data:
The settings used by SmoothQuick are all stored permanently in SystemIdentSettings. They are Tau and the 3 Beta values. 'Complete' must also be True. You can copy these by hand from another FC or from a previous tuning session. Then while disarmed and depending on which kind of SmoothQuick input you have enabled, you should do the SmoothQuick FMS 3x double toggle or move (important) and center your SmoothQuick Accessory channel with everything powered up (e.g. flight battery plugged in for the receiver and transmitter switched on). This last bit will guarantee that you start out with PIDs in the middle of the SmoothQuick range.
AutoTune tries to produce results that make the tuning flight correctly tuned. That does not take into account the non-linearity of thrust response. To remove high thrust oscillations (or increase stability during descent), use TPS to decrease PIDs at high thrust (and if necessary, increase PIDs at low thrust). Typically you want the TPS curve/line to cross the horizontal axis at the point (thrust value) where the copter hovers. Examine SystemIdentState -> HoverThrottle after tuning and before you power off (not saved) to see what your hover thrust is. Beware of throttle bloom that happens when slow responding ESC's make a copter climb just because of the fast RPY controls.
SystemIdent stabilization mode:
AutoTune is a flight mode that can directly go on the FMS. SystemIdent is a stabilization mode that can be put in a Stabilized1-6 flight mode. There is no reason to use SystemIdent stabilization mode. What you will get is a mode that acts a lot like the shaking part of AutoTune, but the shakes may be bigger or smaller.
Field descriptions:
System.SystemIdentSettings are stored permanently but do not show up in logs. DataObjects.SystemIdentState shows up in logs but is not stored permanently. Read the source if you need to know more of the technical aspects of their fields.
System.SystemIdentSettings:
- Is stored permanently
- Is not logged
- Is reset to default values if you stay in AutoTune mode until the shaking starts (about 2.5 seconds). As with other data changes, this is not stored permanently until you disarm. If you power off without disarming, the reset values are not stored permanently.
- Tau, Beta (3 values), and Complete are the only fields filled in by AutoTune. Other fields are used by SmoothQuick to convert Tau and the Betas into PIDs and check and limit the PIDs.
- DampMin, DampRate, DampMax affect the control damping. Decrease damping to make your aircraft response more rapidly.
- NoiseMin, NoiseRate, NoiseMax affect control sensitivity. Increasing noise (sensitivity) will make your aircraft respond more rapidly, but will cause twitches due to noise
- These Damp and Noise values together form the dual virtual slider SmoothQuick
- The smooth end of SmoothQuick uses DampMax and NoiseMin
- The quick end of SmoothQuick uses DampMin and NoiseMax
- The center of the SmoothQuick slider uses DampRate and NoiseRate
- CalculateYaw can be False,TrueLimitToRatio,TrueIgnoreLimit default is TrueLimitToRatio
- YawToRollPitchPIDRatioMin is enabled with CalculateYaw default is 1.0
- YawToRollPitchPIDRatioMax is enabled with CalculateYaw default is 2.5
- DestinationPidBank default is 2
- TuningDuration is 60 seconds
- SmoothQuickSource default is 25
- DisableSanityChecks disables certain checks that stop the PIDs from being written default is false
- Complete is set true after a successful AutoTune run. It must be true for PIDs to be written to DestinationPidBank
DataObjects.SystemIdentState
- Is logged
- Is not stored permanently
- Goes away when power is removed
- HoverThrottle is the average throttle used during tuning. It is a good value to use in Settings.AltitudeHoldSettings.ThrustLimits.Neutral although it is usually a little smaller than it should be due to throttle bloom during shaking.
- The 3 values in Noise tell you how much vibration you have on the 3 axes. Normal values range from about 100 to about 1000. For high values, or jittery response to the PIDs created, you may want to increase Settings.StabilizationSettings.GyroTau (found in the GCS GUI at Configuration -> Stabilization -> Expert -> GyroNoiseFiltering) and retune. Now you know how much vibration you actually have.
- Contains fields that may be useful if debugging problems with AutoTune
- Contains copies of some fields from System.SystemIdentSettings