Question about imu emplacement

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thank you i will try it , but abut the tf i thought that when i'm using the ekf package i's publishing tf and no need to publish tf from imu

If you're using robot_localization for your ekf, it doesn't publish base_link -> imu_link (this is a static transform). R_l will typically publish odom->base_link or map->base_link. You need to make sure you're publishing base_link -> imu_link so that r_l ekf can use the imu.

stevejp, I am about to add IMU to robot that uses wheel-chair motors in tank steer. My experience with IMU on a smaller robot is that it couldn't be made to work as it would lose calibration as soon as the motors came on. Any feel for how far the IMU needs to be from motor? On a 3 foot pole?

@billy Hard to give accurate numbers - 3 feet probably excessive though. My general advice for debugging magnetometers is to take the time properly understand sources of interference and why calibration not working. I would start by validating calibration process off the robot with no interference.

Then once you're confident in your calibration process, move the imu onto the robot and repeat. If your robot is too large to rotate around, you can rotate the imu in place as close to mounting point as possible. Also, no reason you can't calibrate with motors turned on.