# IMU stream rate fixed at 10Hz (PX4)

Source: https://forum.modalai.com/topic/4235/imu-stream-rate-fixed-at-10hz-px4
Category: VOXL SDK and Software (https://forum.modalai.com/category/47/voxl-sdk-and-software)
Tags: ros
Posted: 2025-03-05 16:26:44 UTC by Judoor 0
Replies: 10 · Views: 7081

## Judoor 0 · 2025-03-05 16:26:44 UTC

Hello,
I'm using an IMU with PX4 firmware. I attempted to change the stream rate of the IMU data to at least 50Hz, instead of the default 10Hz. However, when I use rosservice /mavros/set_stream_rate or rosservice /mavros/set_message_interval, there is no change.
Could this be related to MPA, PX4, or another factor?
Thanks in advance.

## Reply by Eric Katzfey (ModalAI staff) · 2025-03-05 19:39:49 UTC

@Judoor-0 What flight controller are you running this on?

## Reply by Judoor 0 · 2025-03-06 08:07:53 UTC (in reply to Eric Katzfey)

@Eric-Katzfey I'm using integrated IMU with VOXL2

## Reply by Eric Katzfey (ModalAI staff) · 2025-03-06 16:26:58 UTC (in reply to Judoor 0)

@Judoor-0 I'm not sure what those mavros commands are trying to do. But you can change the rate at which mavlink messages are streamed out of PX4. Take a look at the PX4 startup file `/usr/bin/voxl-px4-start` and look for the lines like: `mavlink stream -u 14556 -s HIGHRES_IMU -r 10`. Adding lines like that or modifying the existing ones can change the rates.

## Reply by KLindgren · 2025-09-04 14:56:52 UTC (in reply to Eric Katzfey)

@Eric-Katzfey hoping you can share some more insights here.

I have edited the `HIGHRES_IMU` line in `/usr/bin/voxl-px4-start` to set the rate at 500 but the `/imu_mavlink` rostopic from `voxl-mpa-to-ros` shows a publish rate of ~137hz. Collected data with voxl logger shows the timing issue is not related to ROS -- do you know what may be causing the dropped imu messages in the mpa pipe?
![e88acd2d-6cc3-4e96-a944-5ec4e5f28870-image.png](https://forum.modalai.com/assets/uploads/files/1756997129903-e88acd2d-6cc3-4e96-a944-5ec4e5f28870-image.png) 

`voxl-version`
```
────────────────────────────────────────────────────────────────────────────────
system-image: 1.8.04-M0104-14.1a-perf
kernel:       #1 SMP PREEMPT Mon Mar 24 21:03:36 UTC 2025 4.19.125
────────────────────────────────────────────────────────────────────────────────
hw platform:  M0104
mach.var:     2.0.2
SKU:          MCCA-M0104-C22-T0-M0-X0-E1
────────────────────────────────────────────────────────────────────────────────
voxl-suite:   1.5.0
────────────────────────────────────────────────────────────────────────────────
```

voxl-px4-start
```
#!/bin/sh
# PX4 commands need the 'px4-' prefix in bash.
# (px4-alias.sh is expected to be in the PATH)
. px4-alias.sh

echo -e "\n*************************"
echo "AIRFRAME: $AIRFRAME"
echo "GPS: $GPS"
echo "RC: $RC"
echo "ESC: $ESC"
echo "POWER MANAGER: $POWER_MANAGER"
echo "AIRSPEED SENSOR: $AIRSPEED_SENSOR"
echo "DISTANCE SENSOR: $DISTANCE_SENSOR"
echo "OSD: $OSD"
echo "ARTIFACT_MODE: $ARTIFACT_MODE"
echo "EXTRA STEPS:"
for i in "${EXTRA_STEPS[@]}"
do
	echo -e "\t$i"
done
echo -e "*************************\n"

# In order to just exit after starting the uorb / muorb modules define
# the environment variable MINIMAL_PX4. (e.g. export MINIMAL_PX4=1)
# This is useful for testing / debug where you may want to start drivers
# and modules manually from the px4 command shell
if [ ! -z $MINIMAL_PX4 ]; then
    /bin/echo "Running minimal script"
    exit 0
fi

# Figure out what platform we are running on.
PLATFORM=`/usr/bin/voxl-platform 2> /dev/null`
RETURNCODE=$?
if [ $RETURNCODE -ne 0 ]; then
    # If we couldn't get the platform from the voxl-platform utility then check
    # /etc/version to see if there is an M0052 substring in the version string. If so,
    # then we assume that we are on M0052.
    VERSIONSTRING=$(</etc/version)
    M0052SUBSTRING="M0052"
    if [[ "$VERSIONSTRING" == *"$M0052SUBSTRING"* ]]; then
        PLATFORM="M0052"
    fi
fi

# We can only run on M0052, M0054, or M0104 so exit with error if that is not the case
if [ $PLATFORM = "M0052" ]; then
    /bin/echo "Running on M0052"
elif [ $PLATFORM = "M0054" ]; then
    /bin/echo "Running on M0054"
elif [ $PLATFORM = "M0104" ]; then
    /bin/echo "Running on M0104"
else
    /bin/echo "Error, cannot determine platform!"
    exit 0
fi

# Sleep a little here. A lot happens when the uorb and muorb start
# and we need to make sure that it all completes successfully to avoid
# any possible race conditions.
/bin/sleep 1

param select /data/px4/param/parameters

# Load in all of the parameters that have been saved in the file
param load

# IMU (accelerometer / gyroscope)
if [ "$PLATFORM" == "M0104" ]; then
    /bin/echo "Starting IMU driver with rotation 12"
    qshell icm42688p start -s -R 12
else
    /bin/echo "Starting IMU driver with no rotation"
    qshell icm42688p start -s
fi

# Start Invensense ICP 101xx barometer built on to VOXL 2
qshell icp101xx start -I -b 5

qshell temperature_compensation start

# Auto detect the magnetometer. If one or both of these devices
# are not connected it will fail but not cause any harm.
# Rotation 10 = ROLL_180_YAW_90
/bin/echo "Looking for qmc5883l magnetometer"
qshell qmc5883l start -R 10 -X -b 1
/bin/echo "Looking for ist8310 magnetometer"
qshell ist8310 start -R 10 -X -b 1
/bin/echo "Looking for ist8308 magnetometer"
# Rotation 12 = PITCH_180
qshell ist8308 start -R 12 -X -b 1

# GPS and magnetometer
if [ "$GPS" != "NONE" ]; then
	# On M0052 the GPS driver runs on the apps processor
	if [ $PLATFORM = "M0052" ]; then
	    gps start -d /dev/ttyHS2
	# On M0054 and M0104 the GPS driver runs on SLPI DSP
	else
	    qshell gps start
	fi
fi

# Auto detect an ncp5623c i2c RGB LED. If one isn't connected this will
# fail but not cause any harm.
/bin/echo "Looking for ncp5623c RGB LED"
qshell rgbled_ncp5623c start -X -b 1 -f 400 -a 56

# We do not change the following parameters but QGC will complain if they aren't
# being reported as "used" by px4. "Touching" them accomplishes that.
param touch SYS_AUTOCONFIG
param touch SDLOG_MODE

# ESC driver
if [ "$ESC" == "VOXL_ESC" ]; then
    /bin/echo "Starting VOXL ESC driver"
	qshell voxl_esc start
elif [ "$ESC" == "VOXL2_IO_PWM_ESC" ]; then
	if [ "$RC" == "M0065_SBUS" ]; then
		/bin/echo "Starting VOXL IO for PWM ESC with SBUS RC"
		qshell voxl2_io start
	else
		/bin/echo "Starting VOXL IO for PWM ESC without SBUS RC"
		qshell voxl2_io start -e
	fi
else
	/bin/echo "No ESC type specified, not starting an ESC driver"
fi

# RC driver
if [ "$RC" == "FAKE_RC_INPUT" ]; then
    /bin/echo "Starting fake RC driver"
    qshell rc_controller start
elif [ "$RC" == "CRSF_RAW" ]; then
    /bin/echo "Starting CRSF RC driver"
    qshell crsf_rc start -d 7
elif [ "$RC" == "CRSF_MAV" ]; then
    /bin/echo "Starting TBS crossfire RC - MAV Mode"
    qshell mavlink_rc_in start -m -p 7 -b 115200
elif [ "$RC" == "SPEKTRUM" ]; then
    /bin/echo "Starting Spektrum RC"
	# On M0052 the RC driver runs on the apps processor
	if [ $PLATFORM = "M0052" ]; then
        rc_input start -d /dev/ttyHS1
	# On M0054 and M0104 the RC driver runs on SLPI DSP
	else
        qshell spektrum_rc start
	fi
elif [ "$RC" == "GHST" ]; then
    /bin/echo "Starting GHST RC driver"
    qshell ghst_rc start -d 7
elif [ "$RC" == "M0065_SBUS" ]; then
	if [ $PLATFORM = "M0052" ]; then
		apps_sbus start
	elif [ "$ESC" != "VOXL2_IO_PWM_ESC" ]; then
    	/bin/echo "Attempting to start M0065 SBUS RC driver for original M0065 FW"
    	qshell dsp_sbus start
		retVal=$?
		if [ $retVal -ne 0 ]; then
	    	/bin/echo "Starting M0065 SBUS RC driver for original M0065 FW failed"
	    	/bin/echo "Attempting to start M0065 SBUS RC driver for new M0065 FW"
			qshell voxl2_io start -d -p 7
		fi
	else
    	/bin/echo "M0065 SBUS RC driver already started with PWM ESC start"
	fi
fi

if [ "$DISTANCE_SENSOR" == "LIGHTWARE_SF000" ]; then
	# Make sure to set the parameter SENS_EN_SF0X to 8 for sf000/b sensor
	qshell lightware_laser_serial start -d 7
fi

if [ "$POWER_MANAGER" == "VOXLPM" ]; then
	# APM power monitor
	qshell voxlpm start -X -b 2
fi

if [ "$AIRSPEED_SENSOR" == "MS4525DO" ]; then
	qshell ms4525do start -X -b 4
fi

# Optional distance sensor on spare i2c
# qshell vl53l0x start -X -b 4
# qshell vl53l1x start -X -b 4

# Start all of the processing modules on DSP
qshell sensors start
qshell ekf2 start

if [ "$AIRFRAME" == "FIXED_WING" ]; then
	qshell fw_pos_control start
	qshell fw_att_control start
	qshell fw_rate_control start
	qshell airspeed_selector start
	qshell fw_autotune_attitude_control start
	qshell land_detector start fixedwing
elif [ $AIRFRAME = "MULTICOPTER" ]; then
	qshell mc_pos_control start
	qshell mc_att_control start
	qshell mc_rate_control start
	qshell mc_hover_thrust_estimator start
	qshell mc_autotune_attitude_control start
	qshell land_detector start multicopter
fi

qshell manual_control start
qshell control_allocator start
qshell load_mon start

# Only start the rc_update module if an actual RC driver
# is publishing input_rc topics. Otherwise for external RC
# over Mavlink this isn't needed.
if [ "$RC" != "EXTERNAL" ]; then
	qshell rc_update start
fi

qshell commander start

# This is needed for altitude and position hold modes
qshell flight_mode_manager start

# Start all of the processing modules on the applications processor
dataman start
navigator start
load_mon start

# Start microdds_client for ros2 offboard messages from agent over localhost
microdds_client start -t udp -h 127.0.0.1 -p 8888

# On M0052 there is only one IMU. So, PX4 needs to
# publish IMU samples externally for VIO to use.
if [ $PLATFORM = "M0052" ]; then
	imu_server start
fi

# start the onboard fast link to connect to voxl-mavlink-server
mavlink start -x -u 14556 -o 14557 -r 100000 -n lo -m onboard

# slow down some of the fastest streams
mavlink stream -u 14556 -s HIGHRES_IMU -r 500
mavlink stream -u 14556 -s ATTITUDE -r 100
mavlink stream -u 14556 -s ATTITUDE_QUATERNION -r 100
mavlink stream -u 14556 -s GLOBAL_POSITION_INT -r 30
mavlink stream -u 14556 -s SCALED_PRESSURE -r 10

# Increase heartbeat rate so VFC can get faster mode updates
mavlink stream -u 14556 -s HEARTBEAT -r 100

# start the slow normal mode for voxl-mavlink-server to forward to GCS
mavlink start -x -u 14558 -o 14559 -r 100000 -n lo

mavlink boot_complete

# Optional MSP OSD driver for DJI or HDZero goggles
# This is only supported on M0054 (with M0125 accessory board)
if [ "$OSD" == "ENABLE" ] || [ "$OSD" == "DJI" ]; then
    /bin/echo "Starting DJI OSD driver"
    msp_osd start -d /dev/ttyHS1
elif [ "$PLATFORM" == "M0054" ] && [ "$OSD" == "HDZERO" ] || [ "$OSD" == "DJI_MSP_DP" ]; then 
    /bin/echo "Starting $OSD OSD driver for $PLATFORM"
    msp_dp_osd start -d /dev/ttyHS1
elif [ "$PLATFORM" == "M0104" ] && [ "$OSD" == "HDZERO" ] || [ "$OSD" == "DJI_MSP_DP" ] ; then
	/bin/echo "Starting $OSD OSD driver for $PLATFORM"
	msp_dp_osd start -d /dev/ttyHS0
fi

# Start optional EXTRA_STEPS
for i in "${EXTRA_STEPS[@]}"
do
	$i
done

if [ "$ARTIFACT_MODE" == "ENABLE" ]; then
	# Do not start the logger module if we are in artifact mode. Logging
	# produces a log artifact. If there are currently any saved logs make
	# sure to delete them now.
	# Also remove the data manager file that may have saved GPS waypoint information
	# in it.
	# Use shred to remove all files so that they cannot be recovered.
	# shred should be effective on the /data partition since it has this configuration:
	# /dev/sda8 /data ext4 rw,nosuid,nodev,noatime,discard,noauto_da_alloc,data=ordered 0 0
	/usr/bin/find /data/px4/log -name "*.ulg" -exec /usr/bin/shred -u -n 7 {} \;
	/bin/rm -fR /data/px4/log
	/usr/bin/shred -u -n 7 /data/px4/dataman
    /bin/echo "Artifact mode has been enabled"
else
	# Start logging and use timestamps for log files when possible.
	# Add the "-e" option to start logging immediately. Default is
	# to log only when armed. Caution must be used with the "-e" option
	# because if power is removed without stopping the logger gracefully then
	# the log file may be corrupted.
	# This is done as the last step because any topics marked as optional will only
	# be logged if they have been advertised when this is started. By starting it last it
	# makes sure to see those advertisements as the other modules are starting before it.
	logger start -t
fi
```

## Reply by Eric Katzfey (ModalAI staff) · 2025-09-17 03:52:18 UTC (in reply to KLindgren)

@KLindgren Why do you think there are dropped messages? That is just the rate that the data is being produced within PX4. The Mavlink HIGHRES_IMU message is constructed based on the internal vehicle_imu topic which publishes at that rate. It is slower than the rate that IMU samples are being generated by the IMU driver.

## Reply by Alex Kushleyev (ModalAI staff) · 2025-09-17 04:30:28 UTC (in reply to Eric Katzfey)

Just FYI, It is possible that messages are also getting dropped on the ROS side as well due to the fact that the publisher only has a queue size of 1 : https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-mpa-to-ros/-/blob/master/catkin_ws/src/src/interfaces/imu_interface.cpp?ref_type=heads#L74.

This has been an issue before (other users reported), but we never updated this. The fix for that should be to increase the queue size (to 10 or so).

@KLindgren , I know you said that the issue seems to be present in the output of voxl-logger, but there could be another issue with the ROS publisher queue size.

From the plot, it looks like the base rate of the IMU messages is 200hz (5ms dt), but there are a lot of drops, resulting in dt's > 5ms. I am not sure why, just an observation based on the plot. @Eric-Katzfey , perhaps that's due to limited buffer / bandwidth sending data from the DSP?

Alex

## Reply by Eric Katzfey (ModalAI staff) · 2025-09-17 15:05:11 UTC (in reply to Alex Kushleyev)

@Alex-Kushleyev If I log the vehicle_imu topic within PX4 at full rate I see exactly the same distribution of timestamps.

## Reply by KLindgren · 2025-09-18 18:44:28 UTC (in reply to Eric Katzfey)

@Alex-Kushleyev, we thankfully came across the ROS publisher queue size limit when debugging IMU1 timing and have since increased the queue size to 25.

@Eric-Katzfey, is it possible to get a clean ~200 Hz sampling of data from the px4 imu/imu_mavlink? Even setting HIGHRES_IMU to the low value of 100 produces the distribution of timestamp deltas below. 
![d8d27dfd-2c71-47ab-af2d-3edf957f8281-image.png](https://forum.modalai.com/assets/uploads/files/1758220950122-d8d27dfd-2c71-47ab-af2d-3edf957f8281-image.png) 

![1a2151c3-e47e-4234-8d88-0b1620fc1b3c-image.png](https://forum.modalai.com/assets/uploads/files/1758221049891-1a2151c3-e47e-4234-8d88-0b1620fc1b3c-image.png)

## Reply by Eric Katzfey (ModalAI staff) · 2025-09-18 21:34:50 UTC (in reply to KLindgren)

@KLindgren The problem is that px4 does not generate that data at a constant rate. You can see the code here: https://github.com/modalai/px4-firmware/blob/8147a6476d78a4745058a002857aae8f1fd3b7ef/src/modules/sensors/vehicle_imu/VehicleIMU.cpp#L237. Our fork is based off of an older version of PX4. The latest PX4 code has changed in this area so it's possible it no longer does this.

## Reply by KLindgren · 2025-09-24 13:20:29 UTC (in reply to Eric Katzfey)

@Eric-Katzfey got it, thank you for the info.