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162 lines
13 KiB
Markdown
162 lines
13 KiB
Markdown
# Drive Modes (Ackermann Rover)
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Flight modes (or more accurately "Drive modes" for ground vehicles) provide autopilot support to make it easier to manually drive the vehicle or to execute autonomous missions.
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This section outlines all supported drive modes for [Ackermann rovers](../frames_rover/ackermann.md).
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For information on mapping RC control switches to specific modes see: [Basic Configuration > Flight Modes](../config/flight_mode.md).
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:::warning
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Selecting any other mode than those listed below will either stop the rover or can lead to undefined behaviour.
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:::
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## Manual Modes
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Manual modes require stick inputs from the user to drive the vehicle.
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The sticks provide the same "high level" control effects over direction and rate of movement in all manual modes:
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- `Left stick up/down`: Drive the rover forwards/backwards (controlling speed)
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- `Right stick left/right`: Make a left/right turn (controlling steering angle ([Manual mode](#manual-mode)) or yaw rate ([Acro](#acro-mode) and [Position](#position-mode))).
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The manual modes provide progressively increasing levels of autopilot support for maintaining a course, speed, and rate of turn, compensating for external factors such as slopes or uneven terrain.
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| Mode | 특징 |
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| -------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| [Manual](#manual-mode) | No autopilot support. User is responsible for keeping the rover on the desired course and maintaining speed and rate of turn. |
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| [Acro](#acro-mode) | + Maintains the yaw rate (This makes it feel more like driving a car than manual mode). <br>+ Allows maximum yaw rate to be limited (Protects against roll over). |
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| [Position](#position-mode) | + Maintains the course (Best mode for driving a straight line).<br>+ Maintains speed against disturbances, e.g. when driving up a hill.<br>+ Allows maximum speed to be limited. |
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:::details
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Overview mode mapping to control effect
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| Mode | Forward/backwards speed | Steering angle/yaw rate | Required measurements |
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| -------------------------- | ---------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------- |
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| [Manual](#manual-mode) | Directly map stick input to motor command. | Directly map stick input to steering angle. | None. |
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| [Acro](#acro-mode) | Directly map stick input to motor command. | Stick input creates a yaw rate setpoint for the control system to regulate. | yaw rate. |
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| [Position](#position-mode) | Stick input creates a speed setpoint for the control system to regulate. | Stick input creates a yaw rate setpoint for the control system to regulate. If this setpoint is zero (stick is centered) the control system will keep the rover driving in a straight line. | yaw rate, yaw, speed and global position (GPS). |
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:::
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### 수동 모드
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In this mode the stick inputs are directly mapped to motor commands.
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The rover does not attempt to maintain a specific orientation or compensate for external factors like slopes or uneven terrain!
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The user is responsible for making the necessary adjustments to the stick inputs to keep the rover on the desired course.
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| Stick | Effect |
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| ---------------------- | ---------------------------------------------------------- |
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| Left stick up/down | Drive the rover forwards/backwards. |
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| Right stick left/right | Move the steering angle to the left/right. |
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For the configuration/tuning of this mode see [Manual mode](../config_rover/ackermann.md#manual-mode).
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### Acro Mode
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:::info
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This mode requires a yaw rate measurement.
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:::
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In this mode the vehicle regulates its yaw rate to a setpoint (but does not stabilize heading or regulate speed).
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Yaw rate can be directly mapped to a steering input based on the forward speed of the rover:
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<!-- prettier-ignore -->
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$$\delta = \arctan(\frac{w_b \cdot \dot{\psi}}{v})$$
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with
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- $w_b:$ Wheel base,
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- $\delta:$ Steering angle,
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- $\dot{\psi}:$ Yaw rate
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- $v:$ Forward speed.
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For driving this means that the same right hand stick input will cause a different steering angle based on how fast you are driving.
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By limiting the maximum yaw rate, we can restrict the steering angle based on the speed, which can prevent the rover from rolling over.
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This mode will feel more like "driving a car" than [Manual mode](#manual-mode).
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:::info
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The yaw rate is only close loop controlled when driving forwards.
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When driving backwards the yaw rate setpoint is directly mapped to a steering angle using the equation above.
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This is due to the fact that rear wheel steering (driving a car with front-wheel steering backwards) is non-minimum-phase w.r.t to the yaw rate which leads to instabilities when doing closed loop control.
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:::
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| Stick | Effect |
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| ---------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| Left stick up/down | Drive the rover forwards/backwards. |
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| Right stick left/right | Create a yaw rate setpoint for the control system to regulate. If this input is zero the control system will attempt to maintain a zero yaw rate (minimal disturbance rejection) |
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For the configuration/tuning of this mode see [Acro mode](../config_rover/ackermann.md#acro-mode).
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### Stabilized Mode
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:::info
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This mode requires a yaw rate and yaw estimate.
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:::
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In this mode the vehicle regulates its yaw rate to a setpoint and will maintain its heading if this setpoint is zero (but does not regulate speed).
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Compared to [Acro mode](#acro-mode), this mode is much better at driving in a straight line as it can more effectively reject disturbances.
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| Stick | Effect |
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| ---------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| Left stick up/down | Drive the rover forwards/backwards. |
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| Right stick left/right | Create a yaw rate setpoint for the control system to regulate. If this input is zero the control system will maintain the current yaw. |
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For the configuration/tuning of this mode see [Stabilized mode](../config_rover/ackermann.md#stabilized-mode).
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### Position Mode
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:::info
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This mode requires a yaw rate, yaw, speed and global position estimate.
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:::
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This is the manual mode with the most autopilot support.
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The vehicle regulates its yaw rate and speed to a setpoint.
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If the yaw rate setpoint is zero, the controller will remember the GPS coordinates and yaw (heading) of the vehicle and use those to construct a line that the rover will then follow (course control).
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This offers the highest amount of disturbance rejection, which leads to the best straight line driving behavior.
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| Stick | Effect |
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| ---------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
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| Left stick up/down | Stick position sets a forward/back speed setpoint. The vehicle attempts to maintain this speed on slopes etc. |
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| Right stick left/right | Create a yaw rate setpoint for the control system to regulate. If this input is zero the control system will maintain the course of the rover. |
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For the configuration/tuning of this mode see [Position mode](../config_rover/ackermann.md#position-mode).
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## Auto Modes
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In auto modes the autopilot takes over control of the vehicle to run missions, return to launch, or perform other autonomous navigation tasks.
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For the tuning process see the configuration for [Auto modes](../config_rover/ackermann.md#auto-modes).
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### Mission Mode
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_Mission mode_ is an automatic mode that causes the vehicle to execute a predefined autonomous [mission plan](../flying/missions.md) that has been uploaded to the flight controller.
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The mission is typically created and uploaded with a Ground Control Station (GCS) application, such as [QGroundControl](https://docs.qgroundcontrol.com/master/en/).
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#### Mission commands
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The following commands can be used in missions at time of writing (`main`/planned for `PX4 v1.16+`):
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| QGC mission item | 통신 | 설명 |
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| ------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------ | ----------------------------------------------------------------- |
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| Mission start | [MAV_CMD_MISSION_START](MAV_CMD_MISSION_START) | Starts the mission. |
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| Waypoint | [MAV_CMD_NAV_WAYPOINT](MAV_CMD_NAV_WAYPOINT) | Navigate to waypoint. |
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| Return to launch | [MAV\_CMD\_NAV\_RETURN\_TO\_LAUNCH][MAV_CMD_NAV_RETURN_TO_LAUNCH] | Return to the launch location. |
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| Change speed | [MAV\_CMD\_DO\_CHANGE\_SPEED][MAV_CMD_DO_CHANGE_SPEED] | Change the speed setpoint |
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| Set launch location | [MAV_CMD_DO_SET_HOME](MAV_CMD_DO_SET_HOME) | Changes launch location to specified coordinates. |
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| Jump to item (all) | [MAV\_CMD\_DO\_JUMP][MAV_CMD_DO_JUMP] (and other jump commands) | Jump to specified mission item. |
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[MAV_CMD_MISSION_START]: https://mavlink.io/en/messages/common.html#MAV_CMD_MISSION_START
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[MAV_CMD_NAV_WAYPOINT]: https://mavlink.io/en/messages/common.html#MAV_CMD_NAV_WAYPOINT
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[MAV_CMD_NAV_RETURN_TO_LAUNCH]: https://mavlink.io/en/messages/common.html#MAV_CMD_NAV_RETURN_TO_LAUNCH
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[MAV_CMD_DO_CHANGE_SPEED]: https://mavlink.io/en/messages/common.html#MAV_CMD_DO_CHANGE_SPEED
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[MAV_CMD_DO_SET_HOME]: https://mavlink.io/en/messages/common.html#MAV_CMD_DO_SET_HOME
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[MAV_CMD_DO_JUMP]: https://mavlink.io/en/messages/common.html#MAV_CMD_DO_JUMP
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### Return Mode
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This mode uses the [pure pursuit guidance logic](../config_rover/ackermann.md#pure-pursuit-guidance-logic) with the launch position as goal.
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Return mode can be activated through the respective [mission command](#mission-commands) or through the ground station UI.
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