I cannot get acceleration data from /hedge_imu_fusion topic

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kazu
Posts: 4
Joined: Wed Feb 03, 2021 9:23 pm

I cannot get acceleration data from /hedge_imu_fusion topic

Post by kazu »

Hello,
We are trying to get acceleration data from /hedge_imu_fusion topic (using ros_marvelmind_package), but all acceleration data and velocity data we got were 0.
We could only get quarternion data and timestamp.

The result of

Code: Select all

rostopic echo /hedge_imu_fusion
is like

Code: Select all

timestamp_ms: 7952609
x_m: 0.0
y_m: 0.0
z_m: 0.0
qw: 0.526
qx: -0.0637
qy: 0.1364
qz: -0.837
vx: 0.0
vy: 0.0
vz: 0.0
ax: 0.0
ay: 0.0
az: 0.0
We did accelerometer calibration by Dashboard, enabled Processed IMU data, and enabled some other column seemed to be related with IMU,
but the results were the same.
I would appreciate it if you could tell me what to do or check nextly.

smoker77
Posts: 350
Joined: Sat Feb 06, 2016 4:03 pm

Re: I cannot get acceleration data from /hedge_imu_fusion topic

Post by smoker77 »

Hello,
I current software version for Mini-Rx, Super-Beacons and Industrial Super-Beacons you can get raw IMU data, including acceleration. In IMU fusion data we currently provide quaternion (orientation) data. Fused acceleration, speed and location will be provided in future versions.

kazu
Posts: 4
Joined: Wed Feb 03, 2021 9:23 pm

Re: I cannot get acceleration data from /hedge_imu_fusion topic

Post by kazu »

Thanks for your reply.
Do you mean that we can get acceleration data from /hedge_imu_raw topic?
/hedge_imu_raw topic has not been published yet, but do we need some setting from dashboard to publish the topic?

smoker77
Posts: 350
Joined: Sat Feb 06, 2016 4:03 pm

Re: I cannot get acceleration data from /hedge_imu_fusion topic

Post by smoker77 »

Hello,

Yes, you should enable 'Raw inertial sensors data' option for mobile beacon in dashboard as shown on the screenshot.
Attachments
raw_imu_enable.png
raw_imu_enable.png (10 KiB) Viewed 368 times

kazu
Posts: 4
Joined: Wed Feb 03, 2021 9:23 pm

Re: I cannot get acceleration data from /hedge_imu_fusion topic

Post by kazu »

Hello,

Thanks for your support.
We could get /hedge_imu_raw topic and acceleration data.
May I ask you another question about the unit?

When we did $rostopic echo /hedge_imu_raw ,
the outputs were like below.

Code: Select all

timestamp_ms: 63177
acc_x: -121
acc_y: -3
acc_z: 1216
gyro_x: 4325
gyro_y: -2248
gyro_z: 1664
compass_x: 0
compass_y: 0
compass_z: 0
---
I suppose the unit of acceleration z would be 12.16[m/s^2] in this case.
Using the same scale factor, I believe acc_x would be -1.21[m/s^2] and acc_y would be -0.03[m/s^2] but is this correct?
About gyros, I have no idea with the units but how is it like?
Maybe 43.25[degree/sec] for gyro_x?

smoker77
Posts: 350
Joined: Sat Feb 06, 2016 4:03 pm

Re: I cannot get acceleration data from /hedge_imu_fusion topic

Post by smoker77 »

Hello,

The unit of accelerometer data in /hedge_imu_raw topic is mg, so value 1000 means 1 g.
Note the data not calibrated, so you can have raw gravity value more than 1 g.

Resolution of LSB for gyro data is 0.0175 dps, so value 1000 means 17.5 degrees per second.

You can find these units in the section 1.3 of the protocol:
https://marvelmind.com/pics/marvelmind_ ... rfaces.pdf

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