# Starling 2 px4 topic description document?

Source: https://forum.modalai.com/topic/5547/starling-2-px4-topic-description-document
Category: Development Drones (https://forum.modalai.com/category/44/development-drones)
Posted: 2026-11-11 20:41:00 UTC by kdeshmu2
Replies: 1 · Views: 27

## kdeshmu2 · 2026-11-11 20:41:00 UTC

**Hardware:** Model - D0012, Flight controller - M0154

**Software version:** VOXL 2

**What I am trying to do:**
I want a document containing a detailed description of the topics/messages recorded by the px4 in the ulog file.
For e.g. What information is contained by the actuator_outputs, actuator_motors datasets.

**What actually happens:** (error messages, behavior)
I have the message description available in the .msg file; but it contains information about what should be the datatype of the message rather than what the data represents or which signal it is logging.

**Logs / pictures:** Below is the description of actuator_outputs dataset, as present in the actuator_outputs.msg file:

uint64 timestamp				# time since system start (microseconds)
uint8 NUM_ACTUATOR_OUTPUTS		= 16
uint8 NUM_ACTUATOR_OUTPUT_GROUPS	= 4	# for sanity checking
uint32 noutputs				# valid outputs
float32[16] output				# output data, in natural output units

## Reply by tom (ModalAI staff) · 2026-11-11 21:33:39 UTC

Hi @kdeshmu2, the PX4 uORB message reference has a page per message with field descriptions and units where PX4 defines them: https://docs.px4.io/v1.18/en/msg_docs/

For the motor topics on Starling 2 (VOXL ESC), we added a table here: https://docs.modalai.com/voxl-px4-files/#logged-topic-contents

In short:
- actuator_motors: motor commands from the control allocator, normalized 0 to 1
- actuator_outputs: the same commands scaled by the voxl_esc driver to RPM, between VOXL_ESC_RPM_MIN and VOXL_ESC_RPM_MAX
- esc_status: ESC feedback per motor (measured RPM, voltage, current, temperature, power)

The voxl_esc driver source is here if you want to see exactly how the outputs are produced: https://github.com/modalai/px4-firmware/tree/voxl-dev/src/drivers/actuators/voxl_esc