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In-flight tuning¶ A single parameter’s value can be tuned in flight using the transmitter’s Ch6 tuning knob. A specific example for tuning the Rate Roll/Pitch P values can be found on the Rate Roll and Pitch P tuning. Note: On LeViteZer gimbals, the basic setup has been been performed and you just need to do the balancing of the gimbal when changing lens or camera and auto tuning + maybe adjusting the RC and Follow parameters for your specific needs. Gimbal introduction - introducing the LeViteZer prototype gimbal used on making these videos.

1. Pid Tuning Software
2. Pid Tuning Cheat Sheet
3. Auto Pid Tuning Apm Parts
4. Pid Tuning Explained

This article provides an overview of how to tune various Copter parameters.

Overview¶

The default PID gains are meant forthe 3DR IRIS although they work on a wide variety of frames. Still, to get optimalperformance you may need to adjust them which can be done through theMission Planner’s Config/Tuning Copter Pids screen. The screenshot below shows the most important parameters for Roll/Pitch (yellow),Yaw (orange), Altitude hold (green),Loiter (pink) andWaypoint navigation(blue).

The most important parameter to get right is the Rate Roll P (and bydefault Rate Pitch P is locked to the same value) as discussedhere.

Normally it’s best to start by tuning the Rate Roll/Pitch P in Stabilizemode then move onto tuning altitude hold in AltHold mode, then Loiter(which often needs no tuning) and finally the waypoint navigationperformance in Auto mode.

Note

Dave C’s AC2.8.1 tuning guidehas good information for tuning for rate roll and pitch but altitude hold,Loiter and navigation has changed dramatically since AC2.8.1 so thosesections are no longer valid.

Roll/Pitch tuning¶

The Stabilize Roll/Pitch and Rate Roll/Pitch parameters, highlighted inyellow in the screen shot above control the roll pitch response.

The Rate parameters which convert the desired rotation rate into a motoroutput are the most important. The Rate Roll and Pitch P tuning page has themost information on tuning them.

The Stabilize Roll/Pitch P converts the desired angle into a desiredrotation rate which is then fed to the Rate controller.

• A higher value will make the copter more responsive to roll/pitchinputs, a lower value will make it smoother
• If set too high, the copter will oscillate on the roll and/or pitchaxis
• If set too low the copter will become sluggish to inputs

More information on tuning the roll and pitch can be found on theStabilize mode page’s Tuning section.

An objective view of the overall Roll and Pitch performance can be seenby graphing the dataflash log’sATT message’s Roll-In vs Roll and Pitch-In vs Pitch. The “Roll” (i.e.actual roll) should closely follow the “Roll-In” while in Stabilize orAltHold modes. Pitch should similarly closely follow Pitch-In.

Alternatively you may wish to try tuning both the rate and stabilize(i.e. angular) parameters using the AutoTune feature.

Yaw tuning¶

The Stabilize Yaw and Rate Yaw parameters, highlighted in orange in thescreen shot above control the yaw response. It’s rare that the yawrequires much tuning.

Similar to roll and pitch if either Stabilize Yaw P or Rate Yaw P is toohigh the copter’s heading will oscillate. If they are too low the coptermay be unable to maintain it’s heading.

As mentioned on the Stabilize mode’s tuning section,the ACRO_YAW_P parameter controls how quickly copter rotates based ona pilot’s yaw input. The default of 4.5 commands a 200 deg/sec rate ofrotation when the yaw stick is held fully left or right. Higher valueswill make it rotate more quickly.

Altitude Tuning¶

The Altitude hold related tuning parameters are highlighted in green inthe screen shot above.

The Altitude Hold P is used to convert the altitude error (thedifference between the desired altitude and the actual altitude) to adesired climb or descent rate. A higher rate will make it moreaggressively attempt to maintain it’s altitude but if set too high leadsto a jerky throttle response.

The Throttle Rate (which normally requires no tuning) converts thedesired climb or descent rate into a desired acceleration up or down.

Pid Tuning Software

The Throttle Accel PID gains convert the acceleration error (i.e thedifference between the desired acceleration and the actual acceleration)into a motor output. The 1:2 ratio of P to I (i.e. I is twice the sizeof P) should be maintained if you modify these parameters. These valuesshould never be increased but for very powerful copters you may getbetter response by reducing both by 50% (i.e P to 0.5, I to 1.0).

See the Altitude Hold flight mode page for more information.

Loiter Tuning¶

Generally if Roll and Pitch are tuned correctly, theGPSand compassare set-up and performing well and vibration levelsare acceptable, Loiter does not require much tuning but please see theLoiter Mode page for more details on tunableparameters including the horizontal speed.

In-flight tuning¶

A single parameter’s value can be tuned in flight using thetransmitter’s Ch6 tuning knob. A specific example for tuning the RateRoll/Pitch P values can be found on the Rate Roll and Pitch P tuning wiki page.Please see the Ch6 Opt drop-down on the Mission Planner’sConfig/Tuning Copter Pids’s screen for a full list of parametersthat can be tuned.

After setting the Ch6 Opt value, the Min and Max should also be set toreasonable values (i.e. non-zero and also not unreasonably high) andthen the “Refresh screen” button should be pushed by tuning the Ch6 knobto ensure that the parameter is updating correctly.

Filter tuning¶

Copters are often affected by vibration and tuning the various software filters available is critical to achieving an overall tune.A guide on tuning the various notch filters available can be found on the Notch Filtering wiki page.

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Video introduction to PIDs¶

PIDs (Proportional - Integral - Derivative) are the method used by ourfirmware to continuously stabilize the vehicle

• Proportional = Immediate Correction: The further off you are thebigger the correction you make.
• Integral = Over time or steady state correction: If we are failing tomake progress add additional correction.
• Derivative = Take it Easy correction: Is the correction going tofast? if it is slow it down (dampen) it a bit to avoid overshoot.

PID tuning refers to the parameters adjustment of a proportional-integral-derivative control algorithm used in most repraps for hot ends and heated beds.

Pid Tuning Cheat Sheet

PID needs to have a P, I and D value defined to control the nozzle temperature. If the temperature ramps up quickly and slows as it approaches the target temperature, or if it swings by a few degrees either side of the target temperature, then the values are incorrect.

To run PID Autotune in Marlin and other firmwares, run the following G-code with the nozzle cold:

This will heat the first nozzle (E0), and cycle around the target temperature 8 times (C8) at the given temperature (S200) and return values for P I and D. An example from http://www.soliwiki.com/PID_tuning is:

For Marlin, these values indicate the counts of the soft-PWM power control (0 to PID_MAX) for each element of the control equation. The softPWM value regulates the duty cycle of the f=(FCPU/16/64/256/2) control signal for the associated heater. The proportional (P) constant Kp is in counts/C, representing the change in the softPWM output per each degree of error. The integral (I) constant Ki in counts/(C*s) represents the change per each unit of time-integrated error. The derivative (D) constant Kd in counts/(C/s) represents the change in output expected due to the current rate of change of the temperature. In the above example, the autotune routine has determined that to control for a temperature of 200C, the soft PWM should be biased to 92 + 19.56*error + 0.71 * (sum of errors*time) -134.26 * dError/dT. The 'sum of errors*time' value is limited to the range +/-PID_INTEGRAL_DRIVE_MAX as set in Configuration.h. Commercial PID controllers typically use time-based parameters, Ti=Kp/Ki and Td=Kd/Kp, to specify the integral and derivative parameters. In the example above: Ti=19.56/0.71=27.54s, meaning an adjustment to compensate for integrated error over about 28 seconds; Td=134.26/19.56=6.86s, meaning an adjustment to compensate for the projected temperature about 7 seconds in the future.

The Kp, Ki, and Kd values can be entered with:

In the case of multiple extruders (E0, E1, E2) these PID values are shared between the extruders, although the extruders may be controlled separately. If the EEPROM is enabled, save with M500. If it is not enabled, save these settings in Configuration.h.

Auto Pid Tuning Apm Parts

For the bed, use:

Pid Tuning Explained

and save bed settings with:

For manual adjustments:

• if it overshoots a lot and oscillates, either the integral gain needs to be increased or all gains should be reduced
• Too much overshoot? Increase D, decrease P.
• Response too damped? Increase P.
• Ramps up quickly to a value below target temperature (0-160 fast) and then slows down as it approaches target (160-170 slow, 170-180 really slow, etc) temperature? Try increasing the I constant.

See also Wikipedia's PID_controller and Zeigler-Nichols tuning method. Marlin autotuning (2014-01-20, https://github.com/ErikZalm/Marlin/blob/Marlin_v1/Marlin/temperature.cpp#L250 ) uses the Ziegler-Nichols 'Classic' method, which first finds a gain which maximizes the oscillations around the setpoint, and uses the amplitude and period of these oscillations to set the proportional, integral, and derivative terms.

Saving PID settings

You will need to commit your changes to EEPROM or your configuration.h file for them to be permanent.

To save to EEPROM use:M500

Modifying Marlin Autotune parameters

The default Marlin M303 calculates a set of Ziegler-Nichols 'Classic' parameters based on the Ku (Ultimate Gain) and the Pu (Ultimate Period), where the Ku and Pu are determined by searching for a biased BANG-BANG oscillation around an average power level that produces oscillations centered on the setpoint. (See https://github.com/ErikZalm/Marlin/blob/Marlin_v1/Marlin/temperature.cpp#L238 )

You can transform these 'Classic' parameters into the Zeigler-Nichols 'Some Overshoot' set with:

Or the Z-N 'No Overshoot' set:

Note that the multipliers for the autotuning parameters each have only one significant digit (implying 10% maximum precision), and that the other schemes differ by factors of 2 or 3. PID autotuning and tuning isn't terribly precise, and changes in the parameters by factors of 5 to 50% are perfectly reasonable.

In Marlin, the parameters that control and limit the PID controller can have more significant effects than the popular PID parameters. For example, PID_MAX and PID_FUNCTIONAL_RANGE, and PID_INTEGRAL_DRIVE_MAX can each have dramatic, unexpected effects on PID behavior. For instance, a too-large PID_MAX on a high-power heater can make autotuning impossible; a too-small PID_FUNCTIONAL_RANGE can cause odd reset behavior; a too large PID_FUNCTIONAL_RANGE can guarantee overshoot; and a too-small PID_INTEGRAL_DRIVE_MAX can cause droop.

PID Tuning by Commercial PID

If you have access to a PID controller unit and a compatible thermal probe that fits down into your hotend, you can use them to tune your PID and calibrate your thermistor.

Connection of the output of the PID to your heater varies depending on your electronics. (I used a 1K2:4K7 voltage divider to drop the 22V output of the PID to 5V for my bread-boarded VNP4904)

After the PID is connected you can use it to measure the nozzle temperature and correlate it with the thermistor readings and resistances.

Conversion from the commercial PID values of kP in %fullscale, Ti in seconds, and Td in seconds is as follows:

As an example, a $30 MYPIN TD4-SNR 1/16 DIN PID temperature controller and $10 type-K probe can hold a particular Wildseyed hotend with a 6.8ohm resistor at 185.0C+/-0.1C using 12V with about a 43.7% duty cycle, or 0.437*12*12/6.8=9.25W. Invoking the autotuning on the controller produces these parameters: P=0.8%/C, I=27s, D=6.7s. Converting these to Marlin PID values:

Differences between the results can be caused by physical differences in the systems, (e.g: the thermocouple is closer to the heater than the thermistor,) or by different choices of autotuning parameters (e.g.: the MYPIN TD4 autotuning process is a proprietary black box, while Marlin uses Zeigler-Nichols 'Classic' method.)

The Temperature/resistance table below was developed by using the PID+thermocouple system to set temperatures on a sample hotend by controlling the heater while measuring the thermistor resistance. These values can be used with Nophead's http://hydraraptor.blogspot.com/2012/11/more-accurate-thermistor-tables.html or Marlin's https://github.com/ErikZalm/Marlin/blob/Marlin_v1/Marlin/createTemperatureLookupMarlin.py to create calibrated thermistor tables. The PID column collects the autotuning values produced by the PID controller for the indicated temperature. The kP,Ki,Kd lists the converted parameters.