06 - Using IMU Integration with VB3iS
Instead of using its own internal IMU, VB3iS can be integrated with an external IMU04. An external IMU04 performs the same functions as the internal IMU, however it could be beneficial in certain circumstances, e.g. if an IMU04 is already mounted on the test car or the VB3iS is unable to be firmly mounted within the vehicle.
An external IMU04 can either be roof mounted on top of the vehicle or in-vehicle mounted. More information on mounting methods is available here.
When using the IMU roof mount, the user has the option to translate the data from the roof to another point on the vehicle. By default, when the roof mount is enabled, a 1 m Z offset is added, translating the filtered speed down in to the vehicle, towards the centre of gravity.
If the Kalman Filter data is required relative to an alternate or more precise location on the vehicle, then measurements should be made from the centre of the IMU to the desired location. As the IMU is housed within the enclosure, precise measurements are not easy to make. So a Z measurement can be taken from the centre of the GPS antenna, provided 3 cm is subtracted from the physical measurement. Translation measurements need to be made in all 3 axis, X, Y and Z.
Required Equipment
| VB3iS |
| IMU04 |
| RLCAB129 - VB3iS Braking Cable or RLCAB130 - VB3iS ADAS Interface Cable |
| RLCAB131 - External IMU Interface Cable |
| RLACS216 - Magnetic roof mount or RLACS256 - Suction roof mount or RLACS212 - Mounting arm or Mechanical fixings |
| RLCAB131 - External IMU Interface Cable |
| VBOX Setup Software (optional) |
| VBOX Manager (optional) |
Setup
Hardware
IMPORTANT - IMU04 must be connected to VB3iS before power is applied to ensure data is correctly synchronised.
- Fit VB3iS into the test vehicle, and mount the IMU as described here.
- Connect the antenna to the VB3iS.
- Use the RLCAB131 cable to connect the left hand 'CAN/KF' port on the IMU to the 'EXT.IMU' lead of the RLCAB129 or RLCAB130 loom connected to the VB3iS.
- Measure Antenna to Ref/IMU Offsets, more information on this is available here.
- Using Roof Mount: If required, take data translation measurements in X, Y and Z axis from centre of IMU. Set as 1 m directly beneath the IMU by default when Roof Mount is 'Enabled'.
- In vehicle mounted: Measure the relative position from the top centre of the GNSS antenna to the top centre of the IMU. Measurements need to be made in all 3-axis, X, Y and Z.
- After IMU04 is connected, apply power to VB3iS.
- Enable External IMU Integration and enter the Antenna to Ref/IMU Offsets using either the VBOX Setup Software, the Front Panel of the unit or using the VBOX Manager.
Configuration
External IMU Integration can be configured via the VBOX Setup Software, the Front Panel of the unit or using the VBOX Manager.
VBOX Setup Software
- Connect IMU04 to VB3iS, ensuring the unit is powered.
- Connect VB3iS to a computer using the supplied loom, connect an RLCAB001 cable to the 'CONFIG' lead and connect the serial plug to the computers serial port – this can be done via a serial > USB convertor if required.
- Open VBOX Setup and connect to VB3iS by selecting the correct COM Port.
- Select the 'IMU' menu and then the 'Settings' tab.
- Ensure IMU integration is 'Enabled' and set the Location to 'External'.
- If you are using an external roof mount, tick the box below 'Roof mount' to Enable, if you are mounting the IMU within the vehicle, leave the box unticked.
- Enter the measured ahead/behind, right/left and above/below offset values within the 'Antenna to reference offset' options. More information on this is available here.
Note: The options will be labelled 'Antenna to IMU offset' if being used without a Roof mount.
- Select 'Write to unit' to save the settings.
- Perform initialisation and full calibration procedure before commencing testing.
Front Panel
- Connect IMU04 to VB3iS and then power the unit.
- Press the 'OK' button to enter the menu, navigate to 'IMU' using the 'Down' arrow and then press the 'OK' button.
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- If IMU Integration is 'Disabled', press the 'OK' button and then use the 'Up' arrow to select 'Enable'.
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- Press the 'OK' button, once the confirmation screen has cleared, 'Enabled' will be displayed.
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- Navigate to 'IMU Location' using the 'Down' arrow and press the 'OK' button.
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- Use the 'Down' arrow to select 'External' and press the 'OK' button again to confirm.
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- Navigate to 'Roof Mount' using the 'Down' arrow. It will display whichever mode has been previously set.
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- If you would like to change the setting, press the 'OK' button then select the desired option using the 'Up' and 'Down' arrows.
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- Press the 'OK' button again to confirm.
- Navigate to 'Ant to IMU Offset' using the 'Down' arrow, press the 'OK' button to enter the menu.
Note: This menu is labelled 'Ant to Ref. Offset' if an External IMU is being used in conjunction with a Roof Mount.
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- Use a combination of the 'Up' and 'Down' arrows and the 'OK' button to enter the measured ahead/behind, right/left and above/below offset values. More information on this is available here.
Note: This menu is labelled 'The reference point is' if an External IMU is being used in conjunction with a Roof Mount.
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- Selecting the 'OK' button will move along digits and selecting past the final digit will store the value.
- Perform initialisation and full calibration procedure before commencing testing.
- If IMU04 is placed on a non-flat surface, the 'Pitch/Roll Offset' action should be used to compensate the IMU attitude angle channels (pitch angle, roll angle).
This will zero the Pitch_imu and Roll_imu channels. Angle offsets calibration must be performed after the IMU Kalman Filter calibration has been completed, and the vehicle is static on a level surface.
- Navigate to 'Pitch/Roll Offset' using the 'Down' arrow, press the 'OK' button to enter the menu.
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- Press the 'OK' button again to auto level the pitch and roll offset.
Be aware that when mounting the IMU04 on an angle, the raw accelerometer and gyro data will be incorrect as the channels are not pitch compensated.
Important Note
- The IMU04 must be in a Racelogic CAN mode to be used for IMU Kalman Filter.
Initialisation
When using IMU integration, an initialisation phase is required when the IMU is first connected to the VBOX after being set up. This will be run through automatically after the VBOX has successfully gained satellite lock. When the initialisation process is complete, 'Stationary Initialisation Complete' for will display on the front panel for 2 seconds before displaying 'Waiting For Movement'.
IMU04 LED Indicators
| IMU04 LED Colour | Power | Coms |
|---|---|---|
| Red | Initial boot up phase | No coms |
| Orange | Temperature checks. If temperature outside optimum operation range, LED will remain orange. | Using IMU integration, inertial data being sent to host VBOX via RS232. |
| Green | Fully operational. | Inertial data being sent to host system via CAN. |