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imu_config.md

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Onboard IMU Configuration

This page describes the steps required to configure the onboard IMUs. We use the 3DM-CV7-AHRS (product specs) IMU from MicroStrain.

3DM-CV7-AHRS

Configuration steps for a new device.

  1. Get a brand-new IMU and an FTDI serial device (SparkFun FTDI Basic Breakout - 5V). Connect the IMU to a Windows PC. To do so, plug the IMU into a Hamilton board and plug in the FTDI cable (or use a breakout board provided by Microstrain).

  2. Open the SensorConnect app and go to the Device tab on top left. Click on "+Add Device" button on the bottom left. The connection should be via "Serial", at a COM port that is available (corresponding to the FTDI device port) and (initially) at a baud rate 115200 bps. Hit "Add Device" and you should see the device added on the left pane. 3DMCV7-AHRS Clicking on the device name will bring up the dashboard shown:

    dashboard

  3. [Optional] Update the IMU firmware. The 3DM-CV7-AHRS firmware has a bug that causes the quaternions to sporadically return NaNs. If you encounter this issue, contact Microstrain for updated firmware.

  4. Click on "UART baud rate" and change baud rate to 921600.

    baud_rate

  5. Save the current settings on to the device by clicking "Save/Load Settings", and then "Save as Startup Settings". save_as_startup_settings

    Make sure that the "Stream Data on Startup" button is unticked. This prevents the IMU from streaming data immediately on startup (data stream will be initiated by the NUC during normal operation).

    uncheck_startup_stream

  6. At this point it is helpful to re-add the device following step 2, this time configured at the new 921600 baud rate. If the change in baud rate is not saved and the device not re-added immediately, the baud rate can revert to 115200.

  7. On the new device, click on "configure" and select "Enable North Compensation" tickbox under Complementary Filter Settings. Apply the configuration. north_compensation

  8. Repeat step 4 to save the current settings on to the device by clicking "Save/Load Settings", and then "Save as Startup Settings". "Stream Data on Startup" should again be unticked.

  9. Check that the IMU is working properly. Click on "Sampling" and in the IMU Channel field, add "Accelerometer vector" and "Gyroscope vector" fields. if there is an error message in red, hit "Fix". Hit "Start on the lower right as shown:

    test_sampling

  10. Go to the "Data" tab in the top left. In the "Channels" pane, the active device should have a green dot next to it indicating that it is streaming data. Click "Add Widget" on the top of the right pane and select "time series".

    add_widget

  11. Select a few active channels on the left (with a green dot) to add to the widget. The widget should be displaying those channels now. Shake and tap on the IMU to see the change in the signals. Hopefully nothing looks odd.

    check_data