If you have enabled IMU Integration, you must perform the full calibration procedure before you can start to produce meaningful test results. The calibration procedure is a series of specific manoeuvres that you should perform to help the Kalman Filter characterise the outputs from the IMU.
If you do not perform the calibration procedure, the Kalman Filter will still function. It may, however, not produce a high level of accuracy until after you have performed dynamic manoeuvres in the X and Y plane (i.e. left and right-hand turns, braking and accelerating) which could take several 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 IMU to complete the 30-second stationary initialization. The process is indicated on the front panel of the unit. If the vehicle moves before the initialisation finishes, the 30-second process will restart when the vehicle is stationary again.
- When the front panel states 'Waiting for Movement', drive forward to complete the initialisation of the IMU. Continue to an open area to perform the calibration procedure.
- Drive in a ‘figure of eight’ at least twice. These can be as small as 5 m in radius (almost full-lock in some vehicles), but a 10 m radius is a better size. The vehicle should be travelling at a speed of more than 5 km/h during this procedure to generate sufficient force for the calibration process.
- Accelerate hard from a standstill to 50 km/h or above. Perform a brake stop with a deceleration force of at least 0.5 g. You must perform this step twice.
When is the calibration required?
When you are carrying out high-dynamic tests such as braking and ESC testing, this process will calibrate the Kalman Filter quickly and be ready for the tests. When you are carrying out low-dynamic tests such as driving on urban routes or doing long-term data collection, this calibration is not as critical.
Re-running the calibration
The Kalman Filter is constantly adapting its calibration depending on the information it receives from the 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, you should repeat the calibration procedure if you need to perform further high-dynamic testing.
The calibration should also be repeated if there has been a communication break between the VBOX unit and the External IMU, such as:
- You power cycle either the VBOX unit or the External IMU.
- You change the VBOX IMU settings through either the VBOX Setup Software, the Front Panel of the unit, or by using a VBOX Manager.
- You use the VBOX Setup Software to read the VBOX unit's settings.
- You use the VBOX Setup Software to read the External IMU settings.
- You perform a GNSS Coldstart.
What happens if you do not carry out this procedure?
If you cannot carry out this procedure as above, 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 you calibrate the Kalman Filter before you carry out high-dynamic tests.