Logging

The Crazyflie’s logging feature streams variables from the firmware to ROS 2. A log block groups variables that are published together at a chosen frequency. Available variables depend on the firmware and backend. See the firmware logging reference for variable names.

Creating and starting a log block

Connect a Crazyflie first, as described in Usage, and source install/setup.bash in each terminal. The examples below use Crazyflie ID 231; replace /cf231 with your Crazyflie’s namespace.

Both the hardware backend and the lightweight simulation provide these services:

/cf231/add_logging (crazyflie_interfaces/srv/AddLogging)
/cf231/remove_logging (crazyflie_interfaces/srv/RemoveLogging)

add_logging creates a block and starts publishing immediately. Its request is:

AddLogging.srv

string topic_name
int32 frequency
string[] vars
---
bool success

For example, log the battery voltage at 10 Hz:

ros2 service call /cf231/add_logging crazyflie_interfaces/srv/AddLogging \
  "{topic_name: 'pm_log', frequency: 10, vars: ['pm.vbat']}"

Check that the response contains success: true. The block publishes on /cf231/pm_log. topic_name is the block name relative to the Crazyflie namespace; use a unique name for each block and avoid built-in topics such as state. Values follow the order of vars.

frequency is an integer in Hz, rather than a period in 10 ms units. On hardware, the implementation converts it to a period in 10 ms steps, so some requested frequencies are rounded. Use a positive frequency; 1, 2, 5, 10, 20, 50, and 100 Hz map exactly to hardware periods. Never use zero, which causes division by zero in the current implementation.

Hardware blocks must fit within the firmware’s logging packet size and block limits. The size depends on the firmware types of the requested variables, not their ROS representation. Unknown variables and duplicate block names cause creation to fail; check the Crazyflie node’s output for details.

Receiving data

Read the block’s topic in another terminal:

ros2 topic echo /cf231/pm_log

The message type is crazyflie_interfaces/msg/LogDataGeneric:

LogDataGeneric.msg

std_msgs/Header header
uint32 timestamp
float64[] values

values contains the requested variables converted to float64, in the same order as vars. For the example above, values[0] is pm.vbat. timestamp represents the onboard timestamp in milliseconds when populated.

Note

Timestamp population currently differs between publishers. Custom hardware log blocks leave both timestamp fields at their default values. Custom lightweight simulation blocks populate header.stamp, but leave the onboard timestamp at zero. Do not assume both fields contain valid times.

Stopping and removing a log block

Remove the block with the same topic_name used to create it:

ros2 service call /cf231/remove_logging crazyflie_interfaces/srv/RemoveLogging \
  "{topic_name: 'pm_log'}"

A successful response contains success: true. This stops the block and removes its ROS publisher. Removing an unknown block returns success: false. To change the variables or frequency, remove the block and create it again. There are no separate start and stop topics in this interface.

Lightweight simulation

The lightweight simulation supports the same add/remove services, with a limited set of variables: pm.vbat, pm.chargeCurrent, pm.state, stateEstimate.x, stateEstimate.y, stateEstimate.z, stateEstimate.yaw, and stateEstimate.qx/qy/qz/qw. The last notation refers to four separate variables, such as stateEstimate.qx.

To print the available variables to the simulation node’s console:

ros2 topic pub --once /cf231/get_logging_toc_info std_msgs/msg/Empty '{}'

These instructions describe the hardware and lightweight simulation backends. The deprecated Webots backend may expose a different logging interface.

Built-in state and position logging

Hardware automatically publishes a state block at 2 Hz on /cf231/state with these values, in order:

The lightweight simulation also publishes /cf231/state at 2 Hz, with the first six values above. It does not include yaw in this built-in state message.

For hardware using internal position estimation (the default type), an additional block logs position and orientation at 20 Hz. These are published on /cf_positions as crazyflie_interfaces/msg/PoseNamedArray, rather than as a custom log topic. See Position Topics.