Using CAN BUS in UAVs

March 26, 2021

A Controller Area Network (CAN) is a serial network technology that was originally designed for the automotive industry but has also become a popular bus in industrial automation as well as other applications. The CAN is a bus-based system that can be used in embedded systems to provide fast communication among microcontrollers in intelligent devices without the help of a hosting device. 
CAN is an International Standardization Organization (ISO) defined serial communications bus. It is a message-based protocol allowing individual systems, devices, and controllers within a network to communicate. 

A key motivation in the automotive industry was to replace the complex and heavier wiring harness and the developers selected a two-wire (parallel) bus. The specification calls for high immunity to electrical interference and the ability to self-diagnose and repair data errors. The greatest advantage of CAN lies in the reduced amount of wiring combined with ingenious prevention of message collision (meaning no data will be lost during message transmission). 

Devices and controllers connected to the CAN Bus can transmit data to the bus and receive data from the bus. A message transmitted by one unit is received by all the units connected to the bus. A data message is transmitted as a frame. In each frame, the message is labeled by an identifier that is unique throughout the network. Each unit will have a filter to accept the message relevant to it. 

CAN is an open standard so it can be used without a license. The current version is CAN 2.0B and can be obtained online. CAN was standardized in 1993 by the International Organization for Standardization (ISO) released the CAN standard ISO 11898 which was later restructured into two parts; ISO 11898-1 which covers the data link layer, and ISO 11898-2 which covers the CAN physical layer for high-speed CAN. ISO 11898-3 was released later and covers the CAN physical layer for low-speed, fault-tolerant CAN. CAN status messages are generated by the power management unit which converts the AC power from the starter-generator and converts it to DC at the appropriate voltage level(s). An intelligent PMU has a processor so it can connect to a CAN bus.  

The PMU can generate a range of messages covering: 

  • Device Information
  • Input & Output Connection Status
  • Event-Based Alerts
  • Real-Time Data Monitoring (RTDM) Functionality
  • Electric Engine Starter (EES) Functionality
  • Acknowledgement of Transmitted Messages 

As UAVs become more prevalent in a wide range of industries, mission profiles and the associated payloads are becoming more diverse and complex. Power systems are essential to ensure the success of these missions. It is critical to mission success that operators have complete information about the performance of the aircraft including the power system.