https://github.com/ctu-vras/gazebo_ros_battery

Battery plugin (open-circuit model) for any kinds of robot simulations in Gazebo.

https://github.com/ctu-vras/gazebo_ros_battery

Repository

Battery plugin (open-circuit model) for any kinds of robot simulations in Gazebo.

https://github.com/ctu-vras/gazebo_ros_battery/blob/master/

# Gazebo ROS Battery plugin

## Functionality
This is a Gazebo classic plugin that simulates an open-circuit battery model. This is a fairly extensible and reusable battery plugin for any kind of Gazebo compatible robots.
The base of this plugin was primarily developed for the challenge problem 1 (CP1) of the BRASS Project at CMU and substantially extended by Czech Technical University in Prague.

This power model simulates the power consumption of a robot. The amount of power consumed by each component of the robot depends on its usage. The state of charge of the battery is updated after each iteration considering `dt`, the power loads of all components in the robot that consume energy and voltage of the battery (which behaves according to the open circuit voltage model).

If wanted, the plugin can also model dynamic temperature and internal resistance of the battery.

## Support
This plugin is tested for ROS Melodic/Gazebo 9 and ROS Noetic/Gazebo 11.

## Build
This is a standard catkin package. Just add it to your workspace, install dependencies via rosdep, and build it.

Compiling will result in a shared library `$WORKSPACE/devel/lib/libgazebo_ros_battery_discharge.so` that can be inserted in a Gazebo simulation (and other libraries for consumers).

## Usage

See `example/battery_demo.world` file for an example on how to integrate the plugin in your model.

You can run the example world using:

```bash
rosrun gazebo_ros gazebo --verbose $WORKSPACE/src/gazebo_ros_battery/examples/battery_demo.world
```

## libgazebo_ros_battery_discharge.so

This is the main plugin that represents the discharging process of a battery.

### Topics

The plugin reports its state on the following ROS topics:

- `/battery_state` (`sensor_msgs/BatteryState`): General characteristics of the battery state.
- `/charge_level_wh` (`std_msgs/Float64`): Watt-hours estimate of the battery charge level.

In addition, these Gazebo topics are published:

- `///discharge_power` (`gazebo.msgs.Any` with type `DOUBLE` and a double value): Total actual power discharging the battery (in Watts).
- `///charge_power` (`gazebo.msgs.Any` with type `DOUBLE` and a double value): Total actual power charging the battery (in Watts).

### Configuration

The plugin accepts the following configuration XML tags:

- `` (string, default ''): If nonempty, this value prefixes the ROS topics created by the plugin.
- `` (string): Name of the link the battery is attached to.
- `` (string): Name of the battery (has to correspond to the `` tag in the SDF).
- `` (bool, default `true`): Whether the battery can charge ("consume" negative power).
- `` (string, default `~//allow_charging`, relative to world name): The Gazebo topic to subscribe which allows/forbids charging. The topic is expected to have type `gazebo.msgs.Any` with type BOOLEAN and bool data. Set to empty string to disable subscribing to the topic.
- `` (float, default 1.0 Hz): Rate at which the state topics will be published.
- `` (float): Constant parameter of the open circuit model. This is the highest voltage the battery can have.
- `` (float): The linear parameter of the open circuit model. This value should be negative. ` + 1 * ` should give the minimum voltage of the battery.
- `` (float): Initial charge of the battery in Ah.
- `` (float): Capacity of the battery in Ah.
- `` (float): Capacity of the battery when it was new in Ah.
- `` (bool, default `false`): Switches between static temperature model and a thermal development model based on power loss due to internal resistance and heat dissipation into environment.
  - Static model (selected by `false`):
    - `` (float, default `NaN`): The reported battery temperature.
  - Thermal development model (selected by `true`):
    - `` (float): Initial temperature of the battery.
    - `` (float, default 1 J/K): Thermal capacity of the battery in J/K. It can be computed as `specific heat` * `mass of heated material`.
    - `` (float, default 0 W/K): Rate of heat dissipation in J/(K.s) or W/K. It can be computed as `heat transfer coefficient` * `cooling area`.
    - An ambient temperature model is required. It can either be static or read from a topic.
      - `` (float, default 25 deg C): The initial ambient temperature in degrees Celsius. If no topics are specified, this temperature is treated as static.
      - `` (string, optional): If specified, the plugin will subscribe to the given ROS topic to update the ambient temperature. The topic is expected to have type `sensor_msgs/Temperature`.
      - `` (string, optional): If specified, the plugin will subscribe to the given Gazebo topic to update the ambient temperature. The topic is expected to have type `gazebo.msgs.Any` with `DOUBLE` type and double value.
- `` (bool, default `false`): Switches between static internal resistance model and a temperature-based one.
  - Static model (selected by `false`):
    - `` (float): Internal resistance of the battery in Ohms. It affects how large is the influence of power load to voltage drop.
  - Temperature-based model (selected by `true`) can only be used if temperature is specified (i.e. either static and non-NaN, or computed via model):
    - `` (list of float): Coefficients $`c_i`$ of the polynomial $`\sum_i{c_i \ast T^i}`$, where $`T`$ is current temperature of the battery. This field expects multiple float values separated by either `,` or `;`. Article https://www.sciencedirect.com/science/article/pii/S2352152X21010689 gives a 3-rd order polynomial for Li-Ion batteries.
- `` (float): Parameter of a low-pass filter that filters the power load measurements. Should be between 0 and 1.
- `` (string, default ``): The frame ID used in ROS messages.
- `` (string, default ''): Value of the `location` field in the ROS messages.
- `` (string, default ''): Value of the `serial_number` field in the ROS messages.
- `` (string, default ''): Value of the `power_supply_technology` field in the ROS messages. Can be one of `''`, `NIMH`, `LION`, `LIPO`, `LIFE`, `NICD`, `LIMN`.
- `` (int, default 0): If non-zero, the published message will contain `cell_voltage` and `cell_temperature` arrays filled with either `NaN`s or actual values. If it is zero, the arrays will be empty.
- `` (bool, default `false`): If `true`, the `cell_voltage` array will contain total battery voltage divided by number of cells. If `false`, the array will contain `NaN`s.
- `` (bool, default `false`): If `true`, the `cell_temperature` array will contain temperature values. If `false`, the array will contain `NaN`s.

## Provided consumer plugins

The following consumer plugins are provided by this plugin (and more plugins can be implemented by extending class `BatteryConsumerBase`).

### Topics

Each consumer plugin publishes its power load to ROS topic `//power_load` (type `cras_msgs/PowerStamped`) unless disabled by `` set to `false`.

Each consumer plugin publishes its power load to Gazebo topic `///power_load` (type `gazebo.msgs.Any` with `DOUBLE` type).

Each consumer also publishes its consumer ID to Gazebo topic `///consumer_id` (type `gazebo.msgs.Int`). When subscribing, make sure you use a latched subscriber - the value is only published once.

Each consumer subscribes Gazebo topic `///enable` (type `gazebo.msgs.Any` with type `BOOLEAN` and bool value). Messages on this topic can enable and disable the consumer.

### Configuration

Each consumer plugin has these XML configuration options (and some other specific to the plugin):

- `` (string, default ''): If nonempty, this value prefixes the ROS topics created by the plugin.
- `` (string): Name of the link the battery is attached to.
- `` (string): Name of the battery (has to correspond to the `` tag in the SDF).
- `` (string, defaults to the `name` attribute of the plugin): Name of the consumer (will be used as prefix for the `power_load` topic and others).
- `` (bool, defaults to `true`): Whether the `power_load` ROS topic should be published.
- `` (bool, defaults to `true`): Whether the consumer is enabled. Disabled consumers do not consume any energy. The consumer can be "woken up" using a topic.

### libgazebo_ros_battery_consumer.so

Constant load consumer that just applies the given load all the time.

The applied load can be changed by messages published to ROS topic `//power_load_cmd` (type `cras_msgs/Power`)
or Gazebo topic `///power_load_cmd` (type `gazebo.msgs.Any` with `DOUBLE` type).
The load can also be negative, which means charging.

The following configuration options are available:

- `` (float): The initial power load in Watts.
- `` (bool, defaults to `true`): Whether the `power_load_cmd` ROS topic should be subscribed.

### libgazebo_ros_cmd_vel_battery_consumer.so

Consumes battery based on the values published to a `cmd_vel` topic.

The following configuration options are available:

- `` (float, default 0.0): Linear coefficient of `Twist.linear.x` of the messages that converts it to power load in Watts.
- `` (float, default 0.0): Linear coefficient of `Twist.linear.y` of the messages that converts it to power load in Watts.
- `` (float, default 0.0): Linear coefficient of `Twist.linear.z` of the messages that converts it to power load in Watts.
- `` (float, default 0.0): Linear coefficient of `Twist.angular.x` of the messages that converts it to power load in Watts.
- `` (float, default 0.0): Linear coefficient of `Twist.angular.y` of the messages that converts it to power load in Watts.
- `` (float, default 0.0): Linear coefficient of `Twist.angular.z` of the messages that converts it to power load in Watts.
- `` (float): Minimum power consumed by the consumer (in Watts).
- `` (float, default 0.1 s): How long is each `cmd_vel` command effective. The load will only be counted for this long.
- `` (string, default ''): If nonempty, the plugin watches this Gazebo topic for velocity commands in the form of `msgs::Pose` messages.
- `` (string, default ''): If nonempty, the plugin watches this Gazebo topic for velocity commands in the form of `msgs::Twist` messages.
- `` (string, default ''): If nonempty, the plugin watches this ROS topic for velocity commands in the form of `geometry_msgs/Twist` messages.

### libgazebo_ros_motor_battery_consumer.so

Consumes battery based on the effort of a joint reported on a `joint_states` topic (type `sensor_msgs/JointStates`).

The following configuration options are available:

- `` (float, default 1.0): Ratio between required mechanical power and the consumed electrical charge. It should be a number between 0 and 1.
- `` (float): Minimum power consumed by the consumer (in Watts).
- `` (string, multiple tags allowed): Names of the joints this plugin handles. It reads the `` messages and if it finds any of the joints in the message, it calculates the power load of all the handled joints. All handled joints must come together in a single message.
- `` (string, default `joint_states`): Name of the ROS topic to subscribe.

### libgazebo_ros_mechanical_energy_battery_consumer.so

Consumes battery according to the changes in the robot's kinetic and potential energy. This plugin is useful if you don't know what force is applied by the locomotion system of the robot, but you know it has to correspond to the change in the robot's energy.

The following configuration options are available:

- `` (float, default 1.0): Ratio between required mechanical power and the consumed electrical charge. It should be a number between 0 and 1.
- `` (float, default 0.0): Ratio of kinetic energy that will be counted as additional power load. This allows drawing power even in case the robot doesn't accelerate, but has non-zero velocity.
- `` (float): Minimum power consumed by the consumer (in Watts).
- `` (float, default 1.0 s): A few first seconds after simulation start can be ignored by the plugin, so that it doesn't consume energy e.g. when the robot is falling and settling on the terrain.

## Notes about conversions
For converting capacity and charge rate (in `Ah`) to power (`mWh`) which is consumed by the robot, the formula is `(Ah)*(V) = (Wh)`. For example, if you have a `3 Ah` battery rated at `5 V`, the power is `3 Ah * 5 V = 15 Wh` or `15000 mWh`.
For converting `Watts` to `Watt-hours`, we do `Watt * hour`, e.g., `6 Watts / 3600 (Wh)` per seconds. 

## Acknowledgements
CMU authors used/inspired by existing theory of open circuit battery model. This battery discharge/charge plugin uses the Gazebo `Battery` class which is shipped by the default simulator.

Further references: [r1](http://security.livewatch.com/forum-ref/ohms-law-calculator), [r2](http://batteriesbyfisher.com/determining-charge-time), [r3](https://electronics.stackexchange.com/questions/24160/how-to-calculate-the-time-of-charging-and-discharging-of-battery).

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