EscStatus: decrease message size by ttechnick · Pull Request #26520 · PX4/PX4-Autopilot

ttechnick · 2026-02-18T17:18:34Z

Solved Problem

This pull request updates the data types used for ESC (Electronic Speed Controller) telemetry fields to use smaller types. The main focus is on reducing memory usage.

Message and Data Structure Updates:

Changed
esc_errorcount from uint32 to uint16
esc_rpm from int32 to int16
esc_temperature from float32 to int16
in EscReport.msg to reduce memory usage and standardize data types.

hamishwillee · 2026-02-18T20:44:09Z

msg/EscReport.msg

+uint16 esc_errorcount					# Number of reported errors by ESC - if supported
+int16 esc_rpm						# Motor RPM, negative for reverse rotation [RPM] - if supported


Would be good to at least update the fields you touch to current docs standard https://docs.px4.io/main/en/uorb/uorb_documentation#uorb-documentation-standard

Also if you wouldn't mind a short description and long description up the top, though that is much more optional

Is the invalid value NaN as I have indicated?

Suggested change

uint16 esc_errorcount # Number of reported errors by ESC - if supported

int16 esc_rpm # Motor RPM, negative for reverse rotation [RPM] - if supported

uint16 esc_errorcount # [-] [@invalid NaN] Number of reported errors by ESC - if supported

int16 esc_rpm # [rpm] [@invalid NaN] Motor RPM, negative for reverse rotation - if supported

hamishwillee · 2026-02-18T20:44:57Z

msg/EscReport.msg

 float32 esc_voltage					# Voltage measured from current ESC [V] - if supported
 float32 esc_current					# Current measured from current ESC [A] - if supported
-float32 esc_temperature					# Temperature measured from current ESC [degC] - if supported
+int16 esc_temperature					# Temperature measured from current ESC [degC] - if supported


Suggested change

int16 esc_temperature # Temperature measured from current ESC [degC] - if supported

int16 esc_temperature # [degC] [@invalid NaN] Temperature measured from current ESC - if supported

mrpollo

Hey @ttechnick, thanks for working on this! I looked into this since the Cyphal builds are failing in CI and wanted to share some findings that might help.

CI build error: The Cyphal targets fail because src/drivers/cyphal/Actuators/EscClient.hpp:249 assigns NAN to esc_temperature, which can't be represented in int16_t:

EscClient.hpp:249:39: error: overflow in conversion from 'float' to 'int16_t' 
changes value from '+QNaNf' to '0' [-Werror=overflow]
  249 |                 ref.esc_temperature = NAN;

Are you still working through the remaining consumers of esc_temperature? In case it helps, here are the spots I found that still need updating:

Writers:

src/drivers/cyphal/Actuators/EscClient.hpp:249 — assigns NAN (the build failure)
src/drivers/uavcan/actuators/esc.cpp:117 — float arithmetic with -273.15f
src/drivers/actuators/vertiq_io/vertiq_telemetry_manager.cpp:123 — mcu_temp * 0.01 produces a float
src/modules/simulation/simulator_mavlink/SimulatorMavlink.cpp:160 — double expression
boards/modalai/voxl2-slpi/src/drivers/dsp_hitl/dsp_hitl.cpp:506 — same pattern

Readers:

src/modules/mavlink/streams/ESC_INFO.hpp:115 — multiplies by 100.f, so whatever sentinel replaces NAN would need to be handled here to avoid sending a bogus value over MAVLink
src/drivers/uavcannode/Publishers/ESCStatus.hpp:84 — copies to a UAVCAN float field

You'll also want to settle on a consistent sentinel value (looks like you're going with INT16_MAX based on the EscBattery.cpp change) and make sure all writers use it instead of NAN, and all readers check for it instead of PX4_ISFINITE().

One concern on esc_rpm: I did a pass through the drivers and int16 (max 32,767) might be too narrow for RPM. A few examples:

DShot — a 14-pole motor at ~2500 eRPM gives ~35,714 RPM (common real-world scenario)
UAVCAN/DroneCAN — source field is 18-bit, up to 131,071 RPM
HoTT — raw * 10, so anything above 3276 raw overflows
VOXL ESC — extended mode supports up to 65,530 RPM
Cyphal — 13-bit velocity field × 9.55 ≈ up to ~39,104 RPM

Only the simulators (max 6000) and TAP ESC (already int16 source) are safe. This would silently truncate/wrap on real hardware without any warning, which could be confusing for users checking telemetry. Might be worth keeping esc_rpm as int32 and focusing the size savings on the other fields?

Let me know if any of this is helpful or if you'd already spotted these.

dakejahl

Are you sure this captures all of the uses of EscStatus and EscReport?

dakejahl · 2026-02-19T05:27:12Z

msg/EscReport.msg

-uint32 esc_errorcount					# Number of reported errors by ESC - if supported
-int32 esc_rpm						# Motor RPM, negative for reverse rotation [RPM] - if supported
+uint16 esc_errorcount					# Number of reported errors by ESC - if supported
+int16 esc_rpm						# Motor RPM, negative for reverse rotation [RPM] - if supported


singed 16 bit has a max of 32767 - too low to cover all vehicle types. Also ESC_STATUS uses 32 bit.

dakejahl · 2026-02-19T05:29:40Z

src/drivers/dshot/DShot.cpp

 		esc_status.esc[telemetry_index].esc_voltage     = static_cast<float>(data.voltage) * 0.01f;
 		esc_status.esc[telemetry_index].esc_current     = static_cast<float>(data.current) * 0.01f;
-		esc_status.esc[telemetry_index].esc_temperature = static_cast<float>(data.temperature);
+		esc_status.esc[telemetry_index].esc_temperature = static_cast<int>(data.temperature);


Suggested change

esc_status.esc[telemetry_index].esc_temperature = static_cast<int>(data.temperature);

esc_status.esc[telemetry_index].esc_temperature = static_cast<int16_t>(data.temperature);

and throughout

dakejahl · 2026-02-19T05:32:24Z

src/modules/esc_battery/EscBattery.cpp

 				total_current_a += esc_status.esc[i].esc_current;

-				if (PX4_ISFINITE(esc_status.esc[i].esc_temperature)) {
+				if (esc_status.esc[i].esc_temperature != INT16_MAX) {


Did you check that ESC temp gets properly init to INT16_MAX?

Wait, why is EscBattery using the ESC temperature as battery temperature? This seems completely wrong.

dakejahl · 2026-02-19T05:33:03Z

src/modules/esc_battery/EscBattery.cpp

 		float average_voltage_v = 0.0f;
 		float total_current_a = 0.0f;
-		float average_temperature_c = 0.0f;
+		int average_temperature_c = 0;


you can keep as float, since Battery::updateTemperature(float temp) function signature has float param

ttechnick · 2026-02-20T15:52:29Z

Some context:
In another PR, it was pointed out to me that there is room for improvement, but I did not want to have too much scope creep, so i made a separate PR for this.

Question: How important is this? Is communication bandwidth an issue currently?
Considering the improvements will only be minor, I would like to avoid spending too much time on this, when its not even that big of a deal....
If it is, I`m happy to push it more;

ttechnick and others added 2 commits February 18, 2026 18:12

decrease EscStatus size

ef26617

Merge branch 'PX4:main' into pr-decrease_esc_status

a58bbd7

hamishwillee reviewed Feb 18, 2026

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mrpollo reviewed Feb 19, 2026

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dakejahl self-requested a review February 19, 2026 05:24

dakejahl reviewed Feb 19, 2026

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EscStatus: decrease message size#26520

EscStatus: decrease message size#26520
ttechnick wants to merge 2 commits intoPX4:mainfrom
ttechnick:pr-decrease_esc_status

ttechnick commented Feb 18, 2026

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		uint16 esc_errorcount # Number of reported errors by ESC - if supported
		int16 esc_rpm # Motor RPM, negative for reverse rotation [RPM] - if supported

	int16 esc_temperature # Temperature measured from current ESC [degC] - if supported
	int16 esc_temperature # [degC] [@invalid NaN] Temperature measured from current ESC - if supported

	esc_status.esc[telemetry_index].esc_temperature = static_cast<int>(data.temperature);
	esc_status.esc[telemetry_index].esc_temperature = static_cast<int16_t>(data.temperature);

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ttechnick commented Feb 18, 2026

Solved Problem

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