If IMU Integration has been Enabled, it is important to perform the full calibration procedure before meaningful testing commences. The calibration procedure is a series of specific manoeuvres that should be performed to help the Kalman Filter characterise the outputs from the IMU.
If the calibration procedure is not performed, the Kalman Filter will still function, but may not produce the high level of accuracy until dynamic manouevres in the X and Y plane have been performed (i.e. left and right hand turns, braking and accelerating). This should occur after a few minutes of driving.
- Park the vehicle in an open area, where the GNSS antenna has a clear view of the sky. Remain static and wait for the VB3iS/external IMU to complete the 30 second stationary initialization. The process is indicated on the Front Panel. If the vehicle moves before initialisation finishes, the 30 second process will restart once stationary again.
- When the front panel states 'Waiting for Movement', drive forward to complete initialisation of the IMU. Continue to an open area to perform calibration procedure.
- Drive in a ‘figure of eight’ at least twice. These can be as little as 5 m in radius (almost full-lock in some vehicles), but 10 m is better. The vehicle should be travelling above 15 km/h during this procedure in order to generate sufficient forces for the calibration process.
- Accelerate hard from standstill to 50 km/h or above, perform two brake stops with a deceleration force of at least 0.5 g.
When is the calibration required?
When carrying out high dynamic tests such as braking and ESC testing, this recommended process calibrates the Kalman Filter as quickly as possible. When carrying out low dynamic tests such as driving on urban routes, or doing long term data collection, then this calibration is not as critical.
Re-running the calibration
The Kalman Filter is constantly adapting its calibration depending on the information received from GNSS receiver and the IMU. Therefore, if the vehicle is left stationary for a long time, or if an External IMU is moved from its mounting position, then the calibration procedure should be repeated if further high dynamic testing is to be carried out.
The calibration should also be repeated after anything which causes the communication to break between VB3iS and External IMU, such as:
- Power cycle to either VB3iS or External IMU.
- VB3iS IMU settings are changed using either VBOX Setup Software, the Front Panel of the unit or using the VBOX Manager.
- VBOX Setup Software is used to read the VB3iS settings.
- VBOX Setup Software is used to read the External IMU settings.
- A GNSS Coldstart is performed.
What happens if this isn’t done?
If this procedure cannot be carried out as above then the speed accuracy will be reduced, especially for the first few minutes until the Kalman Filter is able to calibrate itself. We strongly recommend that the Kalman Filter is calibrated when carrying out high dynamic tests.