Data Logging 4 PID Tuning

By Hugh Meyer

Red Alert Robotics FRC Team 1741

Center Grove High School

Greenwood Indiana

October 24, 2015

Compelling Reasons for Data Logging

Capture fast events Thoughtful evaluation process Verify repeatability

Compelling Reasons for Data Logging

Establish normal operating range Detect leading edge of failure before

disaster Verify design target

Different Approaches for Logging Data

Use built in logging feature of the driver station.

Located on the “Charts” tab Click “Launch Viewer” button for more

detail Windows on the left indicate the file and

location of the data files

Driver Station Charts

Charts tab give a continuous display of many useful attributes

If you click on the “Launch Viewer” button it opens the Log File Viewer

Log File Viewer

Different Approaches for Logging Data

The supplied Driver Station Log File Viewer is helpful, but you really need data that is specific to your robot to be helpful

I suggest you create your own logging system

You have several options

Different Approaches for Logging Data

Save the data on the driver station computer

Save the data on the RoboRIO Save the data on an external memory

card Save the data on an external computer

What you need for saving data on the RoboRIO

Code that reads the data

Writes the data to disk

Move data from RoboRIO to processing system

Code to open log file and write data

void Tshirt::WriteToLogFile(){

if (!logfile.is_open()) {logfile.open("logging.csv", ios_base::out);logfile << "SteerSetpoint,SteerActual,SteerOutput\n";

}

logfile << steer_control->GetSetpoint() << ',' << steer_encoder->GetDistance() << ',' << steer_control->Get() << "\n";

}

void Tshirt::DisabledPeriodic(){

if (logfile.is_open()) {logfile << flush; // Make sure any messages still

// in the buffer get written to "disk"logfile.close();

}}

void Tshirt::TeleopPeriodic(){...

WriteToLogFile();}

Moving Data from the RoboRIO

Use FTP to transfer the file back to the driver station after the match is concluded

We create a batch file that does this

This batch file is in the same folder destination where the data is to go

The batch file renames the file to include the date and time in the file name

Data Transfer Batch File

# ftpcmds.txt file

get logging.csvget config.txtbye

# GetLogging.bat file

cd C:\FIRSTrobotics\RA14_LogFileArchive\2014_HomeComingftp -A -s:ftpcmds.txt 10.17.44.2

for /f "tokens=1-3 delims=/- " %%a in ('date /t') do set XDate=%%a-%%b-%%cfor /f "tokens=1-2 delims=: " %%a in ('time /t') do set XTime=%%a.%%brename "config.txt" "config-%XDate%-%XTime%.txt"rename "logging.csv" "logging-%XDate%-%XTime%.csv"

Data Folder Example

Analyzing the Data

Import into a spread sheet program Create specialized evaluation program Moving data from capture device to

evaluation device Archiving data into a subversion

repository

The Data File an Example

SteerSetpoint,SteerActual,SteerOutput0,0,00.0866142,0,00.102362,0,0.04330710.11811,0,0.05118110.125984,0,0.05905510.133858,0,0.06299210.149606,0,0.06692910.165354,0,0.07480320.19685,0,0.08267720.228346,0,0.09842520.251969,0,0.1141730.291339,0.045,0.1047340.314961,0.115,0.08816930.346457,0.1,0.106230.377953,0.0975,0.1402260.401575,0.145,0.1282870.425197,0.2275,0.09884840.448819,0.26,0.08259840.503937,0.26,0.09440950.559055,0.255,0.1244690.598425,0.28,0.1592130.661417,0.44,0.1132090.692913,0.65,0.006958660.748031,0.7225,0.01276570.787402,0.745,0.02120080.818898,0.745,0.03694880.858268,0.745,0.05663390.889764,0.745,0.05663390.944882,0.745,0.0999410.984252,0.745,0.1196260.992126,0.75,0.1210631,0.765,0.11751,0.78,0.11

Open Data in OpenOffice Calc

Text Import to OpenOffice Calc

??? Questions ???

These are the steps to getting the data from the robot to a graph.

Are there any questions about this process before we move on?

PID Tuning Process

Need method to command a step response

Easy ability to change PID gain values

Step Response

One must be able to command an immediate change to a different value

This should be done in a very controlled and precise manner

Essentially the command to the system should be a few cycles of square wave

This can be as simple as a button for the user to press, or as complex as an automation sequence

Step Response

We usually just add a button for testing and have the user command the change

logging-Thu-09-18-09.12.csv

Easy Method to change PID gain values

Setup a configuration file on the RoboRIO

Include in that configuration file the 3 gain values

Develop a simple procedure to apply a changed configuration file to the system

Configuration Code

Config.h

Config.cpp

config.txt

putconfig.bat

ftpcmds.txt

Config File Initialization

void Tshirt::RobotInit()

{

//Start robot

cout << "Starting up..." << endl;

cout<<"Loading Config File..... "<<endl;

Config::LoadFromFile("config.txt");

cout<<"Done!"<<endl;

Using Config function to initialize PID values

cout << "Initializing PID control...";steer_control = new PIDController(

Config::GetSetting("steer_p", 1),Config::GetSetting("steer_i", 0),Config::GetSetting("steer_d", 0),steer_encoder,axle,Config::GetSetting("steer_period", 0.010 ));

steer_control->SetInputRange( - MAX_RANGE_OF_STEER, MAX_RANGE_OF_STEER); // in revolutions, just for testing

steer_control->SetOutputRange(-1, 1);steer_control->SetSetpoint(0);steer_control->Enable();

cout << "PID enabled!" << endl;

Reset code to reload new PID values

void Tshirt::ResetPID(){

Config::LoadFromFile("config.txt");steer_control->SetPID(

Config::GetSetting("steer_p", 1),Config::GetSetting("steer_i", 0),Config::GetSetting("steer_d", 0)

);steer_control->Reset();

cout << "PID:" << endl;cout << "P: " << steer_control->GetP() << endl;cout << "I: " << steer_control->GetI() << endl;cout << "D: " << steer_control->GetD() << endl;

}

Config File Example

# .d8888b. .d88888b. 888b 888 8888888888 8888888 .d8888b. #d88P Y88b d88P" "Y88b 8888b 888 888 888 d88P Y88b #888 888 888 888 88888b 888 888 888 888 888 #888 888 888 888Y88b 888 8888888 888 888 #888 888 888 888 Y88b888 888 888 888 88888 #888 888 888 888 888 Y88888 888 888 888 888 #Y88b d88P Y88b. .d88P 888 Y8888 888 888 Y88b d88P # "Y8888P" "Y88888P" 888 Y888 888 8888888 "Y8888P88

#8888888888 8888888 888 8888888888 #888 888 888 888 #888 888 888 888 #8888888 888 888 8888888 #888 888 888 888 #888 888 888 888 #888 888 888 888 #888 8888888 88888888 8888888888

# This is the config file

steer_p = 0.220steer_i = 0.005steer_d = 0.300

steer_period = 0.010

FTP Transfer System

# putconfig.bat

cd C:/WindRiver/workspace/Tshirtftp -A -s:ftpcmds.txt 10.17.44.2pause

# ftpcmds.txt

asciisend config.txtbye

Questions

We now have in place all we need to be able to easily change the PID gain variables

Are there any questions at this point?

PID Tuning Strategies

Iteration by experience

Ziegler-Nichols and other tuning strategies

Several are mentioned on Chief Delphi http://www.chiefdelphi.com/forums/portal.php

PID without a PhD by Tim Wescott

Iteration by Experience

After doing this for a while you will get to recognize different patterns and what will correct them

P will make slower oscillations

D will make fast high frequency oscillations

I helps reach the target

Not very scientific

Can take really long time to find a solution

Start with P Tuning ProcessFor small, low torque motors with little or no gearing, one procedure you can use to

get a good baseline tune is to probe it’s response to a disturbance.

To tune a PID use the following steps:

1. Set all gains to zero.

2. Increase the P gain until the response to a disturbance is a steady oscillation.

3. Increase the D gain until the oscillations go away (i.e. it’s critically damped).

4. Repeat steps 2 and 3 until increasing the D gain does not stop the oscillations.

5. Set P and D to the last stable values.

6. Increase the I gain until it brings you to the set point with the number of oscillations desired (normally zero but a quicker response can be had if you don’t mind a couple oscillations of overshoot)

What disturbance you use depends on the mechanism the control is attached to. Normally moving the mechanism by hand away from the set point and letting go is enough. If the oscillations grow bigger and bigger then you need to reduce the P gain.

If you set the D gain too high the system will begin to chatter (vibrate at a higher frequency than the P gain oscillations). If this happens, reduce the D gain until it stops.

Start with D Tuning Process

To tune a PID use the following steps:

1. Set all gains to 0.

2. Increase Kd until the system oscillates.

3. Reduce Kd by a factor of 2-4.

4. Set Kp to about 1% of Kd.

5. Increase Kp until oscillations start.

6. Decrease Kp by a factor of 2-4.

7. Set Ki to about 1% of Kp.

8. Increase Ki until oscillations start.

9. Decrease Ki by a factor of 2-4.

Ziegler-Nichols & Other Tuning Strategies

Set one of the variables to where the system just oscillates

Measure the time period of the oscillation

Calculate the PID values from some formula or look up table based on these measurements

Ziegler-Nichols

The Ziegler–Nichols tuning method is a heuristic method of tuning a PID controller. It was developed by John G. Ziegler and Nathaniel B. Nichols.

It is performed by setting the I (integral) and D (derivative) gains to zero. The "P" (proportional) gain, KP is then increased (from zero) until it reaches the ultimate gain KU , at which the output of the control loop oscillates with a constant amplitude.

KU and the oscillation period TU are used to set the P, I, and D gains depending on the type of controller used.

Use the table to determine the final gains.

Ziegler-Nichols

Ziegler-Nichols & Others – Links

1. Ziegler-Nichols Method http://en.wikipedia.org/wiki/Ziegler%E2%80%93Nichols_method

2. Tyreus-Luyben Tuning http://www.chem.mtu.edu/~tbco/cm416/zn.html

3. Comparison of PID Controller Tuning Methods by Mohammad Shahrokhi and Alireza Zomorrodi

Questions?

Are there any questions regarding tuning methods?

Steering System Example

Position control for an Ackermann steering mechanism

http://en.wikipedia.org/wiki/Ackermann_steering_geometry

Servo style motor control Joystick position translates to steer

angle

Ackermann Steering Example

Ackermann Steering Example

First Pass at Tuning

113

2537

4961

7385

97109

121133

145157

169181

193205

217229

241253

265277

289301

313325

337349

361373

385397

409421

433

-8

-6

-4

-2

0

2

4

6

8

SteerSetpoint

SteerActual

SteerOutput

P = .125I = .001D = .00125

Second Pass at Tuning

222

4262

82102

122142

162182

202222

242262

282302

322342

362382

402422

442462

482502

522542

562582

602622

642662

682702

722

-8

-6

-4

-2

0

2

4

6

8

SteerSetpoint

SteerActual

SteerOutput

P = .220I = .005D = .320

Third Pass at Tuning

224

4668

90112

134156

178200

222244

266288

310332

354376

398420

442464

486508

530552

574596

618640

662684

706728

750

-8

-6

-4

-2

0

2

4

6

8

SteerSetpoint

SteerActual

SteerOutput

P = .220I = .005D = .300

Launching Mechanism Example

Position control for a Leonardo Da Vinci cam mechanism

Reflective index sensor for homing each cycle

Schmitt trigger (7414) for optical sensor http://www.digikey.com/product-detail/en/SN7414N/296-33604-5-ND/1575159

http://www.ti.com/lit/ds/symlink/sn7414.pdf

De Vinci CamRed Alert Cam

De Vinci Cam

First Pass at Tuning

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

ShooterMotorLeftPositionSetpointShooterMotorPositionActualShooterMotorLeftDemand

# CAM PIDcam_p = .06cam_i = .003cam_d = .003

logging-Wed-02-26-07.37.csv

Next Pass at Tuning

-20

0

20

40

60

80

100

0 1 2 3 4 5 6 7

ShooterMotorLeftPos itionSetpoint

ShooterMotorPos itionActual

ShooterMotorLeftDemand

logging-Mon-02-24-08.13.csv

# CAM PIDcam_p = .75cam_i = 0cam_d = 0

Better But Still Oscillatinglogging-Mon-02-24-08.19.csv

-10

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8

ShooterM otorLeftPos itionSetpoint

ShooterM otorPos itionActual

ShooterM otorLeftDem and

# CAM PIDcam_p = .1cam_i = 0cam_d = 0

Another Pass Tuning

-10

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50

ShooterMotorLeftPos itionSetpoint

ShooterMotorPos itionActual

ShooterMotorLeftDemand

logging-Mon-02-24-08.22.csv

# CAM PIDcam_p = .01cam_i = 0cam_d = 0

Nearing Final Solutionlogging-Mon-02-10-10.44.csv

-20

0

20

40

60

80

100

120

1 224 447 670 893 1116 1339 1562 1785 2008 2231 2454 2677 2900 3123 3346

ShooterMotorLeftPos itionSetpointShooterMotorPos itionActualShooterMotorLeftDemand

# CAM PIDcam_p = 0.017cam_i = 0.0005cam_d = 0.00

Wind Up Detail

Launch Detail

Sequence of Several Launches

Speed Control for Frisbee Launcher Example

Velocity control for drive wheels

Frisbee Launcher

Shooter Testing - March 11, 2012

0

200

400

600

800

1000

1200

1400

1600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Time - 50 Millisecond Steps

RP

M

-20

-10

0

10

20

30

40

50

60

70

80

Cu

rren

t &

Vo

ltag

e

BottomShooter RPM Target Bottom Shooter RPM Actual BottomShooter Voltage BottomShooter Current

Drive Base Example

Mecanum Drive

Drive Wheel PID Tuning

-6000

-4000

-2000

0

2000

4000

6000

1 78 155 232 309 386 463 540 617 694 771 848 925 1002 1079

Front Left Target

Front Left Actual

Front Left Voltage

M:\FirstRobotics\RA12_LogFileArchive\20120307_PIDTuning\Logging-Wed-03-07-07.52.csv

Drive Wheel PID Tuning

-6000

-4000

-2000

0

2000

4000

6000

1 83 165 247 329 411 493 575 657 739 821 903 985 1067 1149 1231 1313

Front Left Target

Front Left Actual

Front Left Voltage

M:\FirstRobotics\RA12_LogFileArchive\20120307_PIDTuning\Logging-Wed-03-07-08.43.csv

Conclusion

Log as much data as you can Build your code as modular as possible

so you can reuse it Implement a config file for your robot Save your config file with the log data

file

Questions

Any questions?

Contact Information

Find this presentation at http://hughmeyer.com/workshops

Hugh Meyer Phone: 317 786-9214 Email: hmeyer@redalert1741.org