uavcan esc: translate temperature field from Kelvin to Celsius

[MaEtUgR]

Solved Problem

When looking at a log that was captured on a drone with Holybro Kotleta20 ESCs attached through CAN I found that the reported temperatures are unreasonably high:

Then I realized the temperature field definitions of UAVCAN:
float16 temperature # Kelvin
and uORB:
float32 esc_temperature # Temperature measured from current ESC [degC] - if supported

but there's no conversion:

PX4-Autopilot/src/drivers/uavcan/actuators/esc.cpp

Line 143 in 134ee7b

ref.esc_temperature = msg.temperature;

Solution

Add a conversion from degree Kelvin to Celsius.

Changelog Entry

Fix temperature conversion from UAVCAN to uORB ESC status

Test coverage

I did not test this yet.

[sfuhrer]

Good catch.

[MaEtUgR]

I replaced the hardcoded value with the already existing constant.