The Thomson Electrac HD is a heavy-duty electric linear actuator designed for industrial and mobile applications that demand precise motion control under harsh conditions. One of its notable features is the ability to communicate via CAN Bus, with support for both CANopen and SAE J1939 protocols. While CANopen is well-known for its rich feature set and standardization, it often requires a full software stack and deeper protocol integration. In contrast, SAE J1939 offers a more streamlined approach, which is ideal for users seeking straightforward, low-level CAN messaging without the need to implement a complete protocol layer.
The appeal of SAE J1939 lies in its simplicity. Messages are sent using 29-bit identifiers and a small data payload, which allows for precise yet efficient communication with minimal overhead. The Thomson Electrac HD can be controlled directly by transmitting specific CAN messages that adhere to the actuator’s J1939 message structure. This method allows for quick integration into embedded systems, particularly those with limited processing capabilities or strict timing requirements.
One of the most useful aspects of the Electrac HD’s CAN Bus interface is the ability to control actuator motion through position and speed commands. However, the control is not entirely linear. The actuator uses pulse-width modulation (PWM) to regulate motor speed, but there is a hardware limitation: the actuator will not function below a 20% PWM threshold. That means the effective usable speed range begins at 20% and increases in steps of 5%, offering approximately sixteen discrete speed levels. It is also important to note that initiating movement often requires a higher-than-minimum PWM setting. Due to mechanical factors such as gear resistance or wear, a command issued at the lowest possible speed might not be sufficient to start motion, even if it would maintain motion once begun. Developers must therefore build a threshold check into their control code to ensure reliable actuation.
The actuator’s stroke range also requires consideration. Although the product specifications may state a stroke of 4000 mm, the actual usable range tends to fall slightly short on both ends. Developers should expect to lose about 10 mm at each extreme of the stroke, resulting in a real-world range of roughly 20 mm to 3980 mm. When precision at either end of the stroke is critical, it is advisable to select a slightly longer actuator and adjust your end-position calculations accordingly.
This application note focusses on the Thomson Electrac HD series of linear actuators. They support two higher-layer protocols based on Controller Area Network (CAN): CANopen, and SAE J1939. You can control the actuators merely with hardware switches (Start, Stop, Forward Motion, Backward Motion), but, in addition, both CAN protocols allow to regulate the linear speed.
If your application requires mere motion control (Start, Stop, Forward Motion, Backward Motion, Speed Control), you are better off with SAE J1939 because you don’t need to install the protocol stack. The Electrac actuator supports some SAE J1939 protocol features (e.g., the address claim procedure), but you can ignore the protocol requirements and control the linear motion with mere CAN Bus data frames (using a 29-Bit message identifier). Thus, “CAN Bus communication” describes the operation mode more accurately.
The CAN/J1939 approach will shorten the development cycle tremendously, which is why the focus is on SAE J1939 and not CANopen.
In some systems, it may be desirable to operate multiple Electrac HD actuators on the same CAN bus. However, this introduces challenges related to bus traffic and power management. Each actuator transmits periodic messages for position feedback, status, and diagnostics. When multiple units are broadcasting simultaneously, the network can become congested, which prevents the system—and the actuators themselves—from entering low-power or sleep states. This is particularly problematic in mobile or battery-powered systems. A practical solution is to connect each actuator to its own dedicated, galvanically isolated CAN port. This isolation ensures cleaner bus traffic and better power efficiency without sacrificing real-time control.
Wilfried Voss’s application note provides two sample implementations using an Arduino Due with a dual CAN interface. The first example demonstrates basic functionality, allowing control over movement direction and speed using a potentiometer as input. The second, more advanced version adds feedback monitoring, soft-start mechanisms, and diagnostic handling. Both examples highlight how the actuator’s motion control messages (known as Actuator Command Messages, or ACMs) can be constructed to drive movement, and how Actuator Feedback Messages (AFMs) can be interpreted to monitor position, detect overloads, and identify fault conditions.
Engineers working with the Electrac HD must also address a few hardware-level considerations. Proper CAN Bus termination is essential for reliable communication, particularly over longer cable distances or in electrically noisy environments. Fault flags such as motor overload or thermal shutdown must be interpreted correctly, especially since they can appear even under normal startup conditions. Furthermore, the actuator’s bus behavior must be accounted for during initialization, ensuring that devices are not attempting to communicate simultaneously at startup in a way that clogs the bus or triggers error states.
Ultimately, the Thomson Electrac HD, when paired with a simple and direct SAE J1939 interface, provides a powerful, cost-effective solution for embedded motion control. Developers gain access to real-time control, speed regulation, and feedback monitoring with minimal software overhead. With proper planning—particularly in managing startup behavior, power thresholds, and CAN traffic—the actuator can be deployed in a wide variety of industrial and vehicular applications. The VisualSizer examples offer a practical and accessible starting point, and with a modest investment in setup, developers can build highly reliable actuator control systems using low-cost microcontrollers and a robust communication standard.
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