Servo tuning problems

Something definitely is/was broken

This config was set up using PNCconfig.

and the hal file has this line in it:
net x-vel-fb <= hm2_5i25.0.encoder.00.velocity

commenting out this line fixed the D (made it work) and things are working much better.

Any ideas why this line was made, or what it should be instead, or am I just better off without it.

Sorry I said the wrong line that I commented out

net x-vel-fb => pid.x.command-deriv

is the line I disabled that is making it work better.

The D sign can only be wrong if the P sign is wrong as well (which would cause an instant runaway)

It should be there to connect the encoder velocity to the PID loop so that the PID component uses the cleaner encoder velocity instead of the noisier DP/DT thet the PID comp calculates but maybe something is broken in the HAL so it has the wrong polarity. Just checked here, encoder velocity has the correct sign (and I have used this connection and it functions correctly)

Can you post your HAL file here?

# Generated by PNCconf at Wed Aug 8 15:36:09 2012
# If you make changes to this file, they will be
# overwritten when you run PNCconf again

loadrt trivkins
loadrt [EMCMOT]EMCMOT servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[TRAJ]AXES
#loadrt probe_parport
loadrt hostmot2
loadrt hm2_pci config=" num_encoders=4 num_pwmgens=0 num_3pwmgens=0 num_stepgens=0 sserial_port_0=000xxxxx "
setp hm2_5i25.0.watchdog.timeout_ns 5000000
#loadrt at_pid
loadrt pid names=pid.x,pid.y,pid.z,pid.w

addf hm2_5i25.0.read servo-thread
addf motion-command-handler servo-thread
addf motion-controller servo-thread
addf pid.x.do-pid-calcs servo-thread
addf pid.y.do-pid-calcs servo-thread
addf pid.z.do-pid-calcs servo-thread
addf pid.w.do-pid-calcs servo-thread
addf hm2_5i25.0.write servo-thread
addf hm2_5i25.0.pet_watchdog servo-thread

# external output signals


# --- Z_SPINDLE_ON ---
net Z_Spindle_ON hm2_5i25.0.7i77.0.0.output-00

# --- W_SPINDLE_ON ---
net W_Spindle_ON hm2_5i25.0.7i77.0.0.output-01

# --- ESTOP-OUT ---
net estop-out hm2_5i25.0.7i77.0.0.output-02

# external input signals


# --- MIN-HOME-X ---
net min-home-x <= hm2_5i25.0.7i77.0.0.input-00

# --- MAX-X ---
net max-x <= hm2_5i25.0.7i77.0.0.input-01

# --- MAX-Y ---
net max-y <= hm2_5i25.0.7i77.0.0.input-03

# --- MIN-Z ---
net min-z <= hm2_5i25.0.7i77.0.0.input-04

# --- MAX-HOME-Z ---
net max-home-z <= hm2_5i25.0.7i77.0.0.input-05

# --- MIN-W ---
net min-w <= hm2_5i25.0.7i77.0.0.input-06

# --- X_READY ---
net X_Ready <= hm2_5i25.0.7i77.0.0.input-08

# --- Y_READY ---
net Y_Ready <= hm2_5i25.0.7i77.0.0.input-09

# --- Z_READY ---
net Z_Ready <= hm2_5i25.0.7i77.0.0.input-10

# --- W_READY ---
net W_Ready <= hm2_5i25.0.7i77.0.0.input-11

# --- Z_SPINDLE_RUNNING ---
net Z_Spindle_running <= hm2_5i25.0.7i77.0.0.input-12

# --- W_SPINDLE_RUNNING ---
net W_Spindle_running <= hm2_5i25.0.7i77.0.0.input-13

# --- ESTOP-EXT ---
net estop-ext <= hm2_5i25.0.7i77.0.0.input-14

#*******************
# AXIS X
#*******************

setp pid.x.Pgain [AXIS_0]P
setp pid.x.Igain [AXIS_0]I
setp pid.x.Dgain [AXIS_0]D
setp pid.x.bias [AXIS_0]BIAS
setp pid.x.FF0 [AXIS_0]FF0
setp pid.x.FF1 [AXIS_0]FF1
setp pid.x.FF2 [AXIS_0]FF2
setp pid.x.deadband [AXIS_0]DEADBAND
setp pid.x.maxoutput [AXIS_0]MAX_OUTPUT

net x-index-enable <=> pid.x.index-enable
net x-enable => pid.x.enable
net x-output => pid.x.output
net x-pos-cmd => pid.x.command
#net x-vel-fb => pid.x.command-deriv
net x-pos-fb => pid.x.feedback

# ---PWM Generator signals/setup---

setp hm2_5i25.0.7i77.0.1.analogout0-scalemax [AXIS_0]OUTPUT_SCALE
setp hm2_5i25.0.7i77.0.1.analogout0-minlim [AXIS_0]OUTPUT_MIN_LIMIT
setp hm2_5i25.0.7i77.0.1.analogout0-maxlim [AXIS_0]OUTPUT_MAX_LIMIT

net x-output => hm2_5i25.0.7i77.0.1.analogout0
net x-pos-cmd axis.0.motor-pos-cmd
net x-enable axis.0.amp-enable-out
# enable _all_ sserial pwmgens
net x-enable hm2_5i25.0.7i77.0.1.analogena

# ---Encoder feedback signals/setup---

setp hm2_5i25.0.encoder.00.counter-mode 0
setp hm2_5i25.0.encoder.00.filter 1
setp hm2_5i25.0.encoder.00.index-invert 0
setp hm2_5i25.0.encoder.00.index-mask 0
setp hm2_5i25.0.encoder.00.index-mask-invert 0
setp hm2_5i25.0.encoder.00.scale [AXIS_0]ENCODER_SCALE

net x-pos-fb <= hm2_5i25.0.encoder.00.position
net x-vel-fb <= hm2_5i25.0.encoder.00.velocity
net x-pos-fb => axis.0.motor-pos-fb
net x-index-enable axis.0.index-enable <=> hm2_5i25.0.encoder.00.index-enable
net x-pos-rawcounts <= hm2_5i25.0.encoder.00.rawcounts

# ---setup home / limit switch signals---

net min-home-x => axis.0.home-sw-in
net min-home-x => axis.0.neg-lim-sw-in
net max-x => axis.0.pos-lim-sw-in

#*******************
# AXIS Y
#*******************

setp pid.y.Pgain [AXIS_1]P
setp pid.y.Igain [AXIS_1]I
setp pid.y.Dgain [AXIS_1]D
setp pid.y.bias [AXIS_1]BIAS
setp pid.y.FF0 [AXIS_1]FF0
setp pid.y.FF1 [AXIS_1]FF1
setp pid.y.FF2 [AXIS_1]FF2
setp pid.y.deadband [AXIS_1]DEADBAND
setp pid.y.maxoutput [AXIS_1]MAX_OUTPUT

net y-index-enable <=> pid.y.index-enable
net y-enable => pid.y.enable
net y-output => pid.y.output
net y-pos-cmd => pid.y.command
#net y-vel-fb => pid.y.command-deriv
net y-pos-fb => pid.y.feedback

# ---PWM Generator signals/setup---

setp hm2_5i25.0.7i77.0.1.analogout1-scalemax [AXIS_1]OUTPUT_SCALE
setp hm2_5i25.0.7i77.0.1.analogout1-minlim [AXIS_1]OUTPUT_MIN_LIMIT
setp hm2_5i25.0.7i77.0.1.analogout1-maxlim [AXIS_1]OUTPUT_MAX_LIMIT

net y-output => hm2_5i25.0.7i77.0.1.analogout1
net y-pos-cmd axis.1.motor-pos-cmd
net y-enable axis.1.amp-enable-out

# ---Encoder feedback signals/setup---

setp hm2_5i25.0.encoder.01.counter-mode 0
setp hm2_5i25.0.encoder.01.filter 1
setp hm2_5i25.0.encoder.01.index-invert 0
setp hm2_5i25.0.encoder.01.index-mask 0
setp hm2_5i25.0.encoder.01.index-mask-invert 0
setp hm2_5i25.0.encoder.01.scale [AXIS_1]ENCODER_SCALE

net y-pos-fb <= hm2_5i25.0.encoder.01.position
net y-vel-fb <= hm2_5i25.0.encoder.01.velocity
net y-pos-fb => axis.1.motor-pos-fb
net y-index-enable axis.1.index-enable <=> hm2_5i25.0.encoder.01.index-enable
net y-pos-rawcounts <= hm2_5i25.0.encoder.01.rawcounts

# ---setup home / limit switch signals---

net y-home-sw => axis.1.home-sw-in
net y-neg-limit => axis.1.neg-lim-sw-in
net max-y => axis.1.pos-lim-sw-in

#*******************
# AXIS Z
#*******************

setp pid.z.Pgain [AXIS_2]P
setp pid.z.Igain [AXIS_2]I
setp pid.z.Dgain [AXIS_2]D
setp pid.z.bias [AXIS_2]BIAS
setp pid.z.FF0 [AXIS_2]FF0
setp pid.z.FF1 [AXIS_2]FF1
setp pid.z.FF2 [AXIS_2]FF2
setp pid.z.deadband [AXIS_2]DEADBAND
setp pid.z.maxoutput [AXIS_2]MAX_OUTPUT

net z-index-enable <=> pid.z.index-enable
net z-enable => pid.z.enable
net z-output => pid.z.output
net z-pos-cmd => pid.z.command
#net z-vel-fb => pid.z.command-deriv
net z-pos-fb => pid.z.feedback

# ---PWM Generator signals/setup---

setp hm2_5i25.0.7i77.0.1.analogout2-scalemax [AXIS_2]OUTPUT_SCALE
setp hm2_5i25.0.7i77.0.1.analogout2-minlim [AXIS_2]OUTPUT_MIN_LIMIT
setp hm2_5i25.0.7i77.0.1.analogout2-maxlim [AXIS_2]OUTPUT_MAX_LIMIT

net z-output => hm2_5i25.0.7i77.0.1.analogout2
net z-pos-cmd axis.2.motor-pos-cmd
net z-enable axis.2.amp-enable-out

# ---Encoder feedback signals/setup---

setp hm2_5i25.0.encoder.02.counter-mode 0
setp hm2_5i25.0.encoder.02.filter 1
setp hm2_5i25.0.encoder.02.index-invert 0
setp hm2_5i25.0.encoder.02.index-mask 0
setp hm2_5i25.0.encoder.02.index-mask-invert 0
setp hm2_5i25.0.encoder.02.scale [AXIS_2]ENCODER_SCALE

net z-pos-fb <= hm2_5i25.0.encoder.02.position
net z-vel-fb <= hm2_5i25.0.encoder.02.velocity
net z-pos-fb => axis.2.motor-pos-fb
net z-index-enable axis.2.index-enable <=> hm2_5i25.0.encoder.02.index-enable
net z-pos-rawcounts <= hm2_5i25.0.encoder.02.rawcounts

# ---setup home / limit switch signals---

net max-home-z => axis.2.home-sw-in
net min-z => axis.2.neg-lim-sw-in
net max-home-z => axis.2.pos-lim-sw-in

#*******************
# AXIS W
#*******************

setp pid.w.Pgain [AXIS_8]P
setp pid.w.Igain [AXIS_8]I
setp pid.w.Dgain [AXIS_8]D
setp pid.w.bias [AXIS_8]BIAS
setp pid.w.FF0 [AXIS_8]FF0
setp pid.w.FF1 [AXIS_8]FF1
setp pid.w.FF2 [AXIS_8]FF2
setp pid.w.deadband [AXIS_8]DEADBAND
setp pid.w.maxoutput [AXIS_8]MAX_OUTPUT

net w-index-enable <=> pid.w.index-enable
net w-enable => pid.w.enable
net w-output => pid.w.output
net w-pos-cmd => pid.w.command
net w-vel-fb => pid.w.command-deriv
net w-pos-fb => pid.w.feedback

# ---PWM Generator signals/setup---

setp hm2_5i25.0.7i77.0.1.analogout3-scalemax [AXIS_8]OUTPUT_SCALE
setp hm2_5i25.0.7i77.0.1.analogout3-minlim [AXIS_8]OUTPUT_MIN_LIMIT
setp hm2_5i25.0.7i77.0.1.analogout3-maxlim [AXIS_8]OUTPUT_MAX_LIMIT

net w-output => hm2_5i25.0.7i77.0.1.analogout3
net w-pos-cmd axis.8.motor-pos-cmd
net w-enable axis.8.amp-enable-out

# ---Encoder feedback signals/setup---

setp hm2_5i25.0.encoder.03.counter-mode 0
setp hm2_5i25.0.encoder.03.filter 0
setp hm2_5i25.0.encoder.03.index-invert 0
setp hm2_5i25.0.encoder.03.index-mask 0
setp hm2_5i25.0.encoder.03.index-mask-invert 0
setp hm2_5i25.0.encoder.03.scale [AXIS_8]ENCODER_SCALE

net w-pos-fb <= hm2_5i25.0.encoder.03.position
#net w-vel-fb <= hm2_5i25.0.encoder.03.velocity
net w-pos-fb => axis.8.motor-pos-fb
net w-index-enable axis.8.index-enable <=> hm2_5i25.0.encoder.03.index-enable
net w-pos-rawcounts <= hm2_5i25.0.encoder.03.rawcounts

# ---setup home / limit switch signals---

net w-home-sw => axis.8.home-sw-in
net min-w => axis.8.neg-lim-sw-in
net w-pos-limit => axis.8.pos-lim-sw-in

#*******************
# SPINDLE S
#*******************

# ---setup spindle control signals---

net spindle-vel-cmd-rps <= motion.spindle-speed-out-rps
net spindle-vel-cmd <= motion.spindle-speed-out
net spindle-on <= motion.spindle-on
net spindle-cw <= motion.spindle-forward
net spindle-ccw <= motion.spindle-reverse
net spindle-brake <= motion.spindle-brake
net spindle-revs => motion.spindle-revs
net spindle-at-speed => motion.spindle-at-speed
net spindle-vel-fb => motion.spindle-speed-in
net spindle-index-enable <=> motion.spindle-index-enable

# ---Setup spindle at speed signals---

sets spindle-at-speed true


#******************************
# connect miscellaneous signals
#******************************

# ---HALUI signals---

net joint-select-a halui.joint.0.select
net x-is-homed halui.joint.0.is-homed
net jog-x-pos halui.jog.0.plus
net jog-x-neg halui.jog.0.minus
net jog-x-analog halui.jog.0.analog
net joint-select-b halui.joint.1.select
net y-is-homed halui.joint.1.is-homed
net jog-y-pos halui.jog.1.plus
net jog-y-neg halui.jog.1.minus
net jog-y-analog halui.jog.1.analog
net joint-select-c halui.joint.2.select
net z-is-homed halui.joint.2.is-homed
net jog-z-pos halui.jog.2.plus
net jog-z-neg halui.jog.2.minus
net jog-z-analog halui.jog.2.analog
net joint-select-d halui.joint.8.select
net w-is-homed halui.joint.8.is-homed
net jog-w-pos halui.jog.8.plus
net jog-w-neg halui.jog.8.minus
net jog-w-analog halui.jog.8.analog
net jog-selected-pos halui.jog.selected.plus
net jog-selected-neg halui.jog.selected.minus
net spindle-manual-cw halui.spindle.forward
net spindle-manual-ccw halui.spindle.reverse
net spindle-manual-stop halui.spindle.stop
net machine-is-on halui.machine.is-on
net jog-speed halui.jog-speed
net MDI-mode halui.mode.is-mdi

# ---coolant signals---

net coolant-mist <= iocontrol.0.coolant-mist
net coolant-flood <= iocontrol.0.coolant-flood

# ---probe signal---

net probe-in => motion.probe-input

# ---motion control signals---

net in-position <= motion.in-position
net machine-is-enabled <= motion.motion-enabled

# ---digital in / out signals---

# ---estop signals---

net estop-out <= iocontrol.0.user-enable-out
net estop-ext => iocontrol.0.emc-enable-in

# ---manual tool change signals---

loadusr -W hal_manualtoolchange
net tool-change-request iocontrol.0.tool-change => hal_manualtoolchange.change
net tool-change-confirmed iocontrol.0.tool-changed <= hal_manualtoolchange.changed
net tool-number iocontrol.0.tool-prep-number => hal_manualtoolchange.number
net tool-prepare-loopback iocontrol.0.tool-prepare => iocontrol.0.tool-prepared

could you post your .ini file as well?

I tried to duplicate this but see no problem (with LinuxCNC2.51)

That is with the PID comps DP/DT (feedback-deriv unconnected) or using the external feedback-deriv pin connected
to encoder velocity results in the same PID output at a given velocity

# Generated by PNCconf at Wed Aug 8 15:36:10 2012
# If you make changes to this file, they will be
# overwritten when you run PNCconf again

[EMC]
MACHINE = Digital_4
DEBUG = 0

[DISPLAY]
DISPLAY = axis
POSITION_OFFSET = RELATIVE
POSITION_FEEDBACK = ACTUAL
MAX_FEED_OVERRIDE = 2.000000
MAX_SPINDLE_OVERRIDE = 1.000000
MIN_SPINDLE_OVERRIDE = 0.500000
INTRO_GRAPHIC = linuxcnc.gif
INTRO_TIME = 5
PROGRAM_PREFIX = /home/digital4/linuxcnc/nc_files
INCREMENTS = 1.0in .1in .05in .01in .005in .001in .0001in
POSITION_OFFSET = RELATIVE
POSITION_FEEDBACK = ACTUAL
DEFAULT_LINEAR_VELOCITY = 2.000000
MAX_LINEAR_VELOCITY = 10.000000
MIN_LINEAR_VELOCITY = 0.010000
DEFAULT_ANGULAR_VELOCITY = 0.250000
MAX_ANGULAR_VELOCITY = 1.000000
MIN_ANGULAR_VELOCITY = 0.010000
EDITOR = gedit
GEOMETRY = xyzw

[FILTER]
PROGRAM_EXTENSION = .png,.gif,.jpg Greyscale Depth Image
PROGRAM_EXTENSION = .py Python Script
png = image-to-gcode
gif = image-to-gcode
jpg = image-to-gcode
py = python

[TASK]
TASK = milltask
CYCLE_TIME = 0.010

[RS274NGC]
PARAMETER_FILE = linuxcnc.var

[EMCMOT]
EMCMOT = motmod
COMM_TIMEOUT = 1.0
COMM_WAIT = 0.010
SERVO_PERIOD = 400000

[HOSTMOT2]
# **** This is for info only ****
# DRIVER0=hm2_pci
# BOARD0=5i25

[HAL]
HALUI = halui
HALFILE = Digital_4w.hal
HALFILE = custom.hal
POSTGUI_HALFILE = postgui_call_list.hal
SHUTDOWN = shutdown.hal

[HALUI]

[TRAJ]
AXES = 9
COORDINATES = X Y Z W
MAX_ANGULAR_VELOCITY = 1.67
DEFAULT_ANGULAR_VELOCITY = 0.17
LINEAR_UNITS = inch
ANGULAR_UNITS = degree
CYCLE_TIME = 0.010
DEFAULT_VELOCITY = 5.0
MAX_LINEAR_VELOCITY = 15

[EMCIO]
EMCIO = io
CYCLE_TIME = 0.100
TOOL_TABLE = tool.tbl

#********************
# Axis X
#********************
[AXIS_0]
TYPE = LINEAR
HOME = 0.0
FERROR = 10.0
MIN_FERROR = 10.0
MAX_VELOCITY = 10.0
MAX_ACCELERATION = 10.0
P = 1100
I = 0
D = 2.5
FF0 = 0
FF1 = 1.4
FF2 = 0.02
BIAS = 0
DEADBAND = 0
MAX_OUTPUT = 10
ENCODER_SCALE = 20371.83
OUTPUT_SCALE = 10
OUTPUT_MIN_LIMIT = -10
OUTPUT_MAX_LIMIT = 10
MIN_LIMIT = -0.001
MAX_LIMIT = 8.0
HOME_OFFSET = 0.000000
HOME_SEARCH_VEL = -0.050000
HOME_LATCH_VEL = -0.016667
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = YES
HOME_IGNORE_LIMITS = YES

#********************
# Axis Y
#********************
[AXIS_1]
TYPE = LINEAR
HOME = 0.0
FERROR = 10.0
MIN_FERROR = 10.0
MAX_VELOCITY = 10.0
MAX_ACCELERATION = 10.0
P = 1100
I = 0
D = 2.5
FF0 = 0
FF1 = 1.4
FF2 = 0.02
BIAS = 0
DEADBAND = 0
MAX_OUTPUT = 10
ENCODER_SCALE = 20371.83
OUTPUT_SCALE = 10
OUTPUT_MIN_LIMIT = -10
OUTPUT_MAX_LIMIT = 10
MIN_LIMIT = -0.001
MAX_LIMIT = 8.0
HOME_OFFSET = 0.000000
HOME_SEARCH_VEL = -0.050000
HOME_LATCH_VEL = -0.016667
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = YES
HOME_IGNORE_LIMITS = YES

#********************
# Axis Z
#********************
[AXIS_2]
TYPE = LINEAR
HOME = 0.0
FERROR = 10.005
MIN_FERROR = 10.0005
MAX_VELOCITY = 10.0
MAX_ACCELERATION = 10.0
P = 1100
I = 0
D = 2.5
FF0 = 0
FF1 = 1.4
FF2 = 0.02
BIAS = 0
DEADBAND = 0
MAX_OUTPUT = 10
ENCODER_SCALE = 40000
OUTPUT_SCALE = 10
OUTPUT_MIN_LIMIT = -10
OUTPUT_MAX_LIMIT = 10
MIN_LIMIT = -0.001
MAX_LIMIT = 8.0
HOME_OFFSET = 0.000000
HOME_SEARCH_VEL = -0.050000
HOME_LATCH_VEL = -0.016667
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = YES
HOME_IGNORE_LIMITS = YES

[AXIS_3]
[AXIS_4]
[AXIS_5]
[AXIS_6]
[AXIS_7]

#********************
# Axis W
#********************
[AXIS_8]
YPE = LINEAR
HOME = 0.0
FERROR = 10.005
MIN_FERROR = 10.0005
MAX_VELOCITY = 10.0
MAX_ACCELERATION = 10.0
P = 1100
I = 0
D = 2.5
FF0 = 0
FF1 = 1.4
FF2 = 0.02
BIAS = 0
DEADBAND = 0
MAX_OUTPUT = 10
ENCODER_SCALE = -40000
OUTPUT_SCALE = -10
OUTPUT_MIN_LIMIT = -10
OUTPUT_MAX_LIMIT = 10
MIN_LIMIT = -0.001
MAX_LIMIT = 8.0
HOME_OFFSET = 0.000000
HOME_SEARCH_VEL = -0.050000
HOME_LATCH_VEL = -0.016667
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = YES
HOME_IGNORE_LIMITS = YES

Looking at some other sample servo configs, I think maybe the line:
net x-vel-fb => pid.x.command-deriv
should be:
net x-vel-fb => pid.x.feedback-deriv

Yep that looks like a pncconf bug
I must apologize for not catching that, I'm afraid my eyes
glazed over on the fine print...

That's OK seems like something that would be easy to miss. Glad we can straighten it out. Kind of surprised it would not have been caught by now though. Must not really be that many people using PnConf with the 7i77 yet. Since my problem has turned into less a tuning issue and more a PnConf problem. Maybe someone should move this thread to the PnConf area.