mirror of
https://gitee.com/mirrors_PX4/PX4-Autopilot.git
synced 2026-04-14 10:07:39 +08:00
8e0f223b3a
* Remove Zubax Orel - not available and no other presence * Fix up zubax product links * Snapdragon flight - delete as no longer relevant hardware * Delete intel aero docs * Brushless whoop - remove docs except for link to old version * Many link fixes
71 lines
4.0 KiB
Markdown
71 lines
4.0 KiB
Markdown
# Compass Power Compensation
|
|
|
|
Compasses (magnetometers) should be mounted as far as possible from cables that carry large currents, as these induce magnetic fields that may corrupt the compass readings.
|
|
|
|
This topic explains how to compensate for the induced magnetic fields in the cases where moving the compass is not realistic.
|
|
|
|
:::tip
|
|
Moving the compass away from power-carrying cables is the easiest and most effective way to fix this issue, because the strength of the magnetic fields decreases quadratically with the distance from the cable.
|
|
:::
|
|
|
|
::: info
|
|
The process is demonstrated for a multicopter, but is equally valid for other vehicle types.
|
|
:::
|
|
|
|
## When is Power Compensation Applicable?
|
|
|
|
Performing this power compensation is advisable only if all the following statements are true:
|
|
|
|
1. The compass cannot be moved away from the power-carrying cables.
|
|
1. There is a strong correlation between the compass readings and the thrust setpoint, and/or the battery current.
|
|
|
|
|
|
|
|
1. The drone cables are all fixed in place/do not move (calculated compensation parameters will be invalid if the current-carrying cables can move).
|
|
|
|
## How to Compensate the Compass
|
|
|
|
1. Make sure your drone runs a Firmware version supporting power compensation (current master, or releases from v.1.11.0).
|
|
1. Perform the [standard compass calibration](../config/compass.md#compass-calibration).
|
|
1. Set the parameter [SDLOG_MODE](../advanced_config/parameter_reference.md#SDLOG_MODE) to 2 to enable logging of data from boot.
|
|
1. Set the parameter [SDLOG_PROFILE](../advanced_config/parameter_reference.md#SDLOG_PROFILE) checkbox for _Sensor comparison_ (bit 6) to get more data points.
|
|
1. Secure the drone so that it cannot move, and attach the propellers (so the motors can draw the same current as in flight).
|
|
This example secures the vehicle using straps.
|
|
|
|
|
|
|
|
1. Power the vehicle and switch into [ACRO flight mode](../flight_modes_mc/acro.md) (using this mode ensures the vehicle won't attempt to compensate for movement resulting from the straps).
|
|
- Arm the vehicle and slowly raise the throttle to the maximum
|
|
- Slowly lower the throttle down to zero
|
|
- Disarm the vehicle
|
|
|
|
::: info
|
|
Perform the test carefully and closely monitor the vibrations.
|
|
:::
|
|
|
|
1. Retrieve the ulog and use the python script [mag_compensation.py](https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/sensors/vehicle_magnetometer/mag_compensation/python/mag_compensation.py) to identify the compensation parameters.
|
|
|
|
```sh
|
|
python mag_compensation.py ~/path/to/log/logfile.ulg <type> [--instance <number>]
|
|
```
|
|
|
|
where:
|
|
- `<type>`: `current` or `thrust` (power signal used for compensation)
|
|
- `--instance <number>` (optional): The number is `0` (default) or `1`, the instance of the current or thrust signal to use.
|
|
|
|
::: info
|
|
If your log does not contain battery current measurements, you will need to comment out the respective lines in the Python script, such that it does the calculation for thrust only.
|
|
:::
|
|
|
|
1. The script will return the parameter identification for thrust as well as for current and print them to the console.
|
|
The figures that pop up from the script show the "goodness of fit" for each compass instance, and how the data would look if compensated with the suggested values.
|
|
If a current measurement is available, using the current-compensation usually yields the better results.
|
|
Here is an example of a log, where the current fit is good, but the thrust parameters are unusable as the relationship is not linear.
|
|
|
|
|
|
|
|
1. Once the parameters are identified, the power compensation must be enabled by setting [CAL_MAG_COMP_TYP](../advanced_config/parameter_reference.md#CAL_MAG_COMP_TYP) to 1 (when using thrust parameters) or 2 (when using current parameters).
|
|
Additionally, the compensation parameters for each axis of each compass must be set.
|
|
|
|
|