How to "Real-Time" and Quickly Update Speed During Rotation of A6-RS Series Servo Motors Using 485 Control?
Communication protocols such as Modbus over 485 were originally designed for industrial monitoring and data acquisition, emphasizing stability and reliability rather than real-time performance. Each command involves a complete cycle of "send-receive-process-respond," which inherently introduces unavoidable time delays.
There are two main reasons why we do not recommend modifying speed via 485 commands during operation:
- Safety Concerns: In practical scenarios, abruptly changing speed may lead to accidents.
- Communication Limitations: When multiple commands are issued, modifying speed during operation may result in command loss, slow responses, and other issues. Therefore, we advise against real-time speed adjustments via the 485 protocol during operation.
The above refers to continuously sending 485 commands. If you only need to send a single command to change speed for testing purposes, this is acceptable.
If you need to adjust speed in real-time while the motor is running, the following two solutions are recommended:
Option 1: Use Pulse Control
Pulse control is the best choice for real-time speed adjustment with the A6-RS series servo motors.
- Working Principle: Motor speed is directly controlled by varying the pulse frequency.
- Control Method: Real-time changes in pulse frequency immediately adjust the speed.
- Advantage: True real-time control with fast response.
Option 2: Use the Multi-Speed Function
If your application only requires switching between a few fixed speeds, this option may be suitable.
- Working Principle: Pre-set several fixed speeds in the driver. By modifying the run time settings for each speed segment (highlighted in the following code example), you can achieve faster speed updates.
- Control Method: Adjust acceleration/deceleration rates, speed, and run time for each segment to modify speed. However, this only allows changes to preset speeds and requires fixed run times. The figure below illustrates a specific example of multi-speed operation.
Code | Description |
|---|---|
01 06 00 00 00 01 CRC CRC | Set drive control mode to speed mode: C00.00=1 |
01 06 03 20 00 03 CRC CRC | Set to use internal planned speed command: C03.20=3 |
01 06 12 00 00 01 CRC CRC | Set speed planning mode to 1-cycle operation: C12.00=1 |
01 06 12 01 00 01 CRC CRC | Set speed planning start group number to Group 1: C12.01=1 |
01 06 12 02 00 02 CRC CRC | Set speed planning end group number to Group 2: C12.02=2 |
01 06 12 06 00 64 CRC CRC | Set first group speed to 100 RPM: C12.06=100 |
01 10 12 08 00 02 04 00 64 00 00 CRC CRC | Set first group running time to 15000 ms: C12.08=15000 |
01 10 12 0A 00 02 04 00 64 00 00 CRC CRC | Set first group acceleration time to 100 ms: C12.0A=100 |
01 10 12 0C 00 02 04 00 64 00 00 CRC CRC | Set first group deceleration time to 100 ms: C12.0C=100 |
01 06 12 10 00 05 CRC CRC | Set second group speed to 5 RPM: C12.10=5 |
01 10 12 12 00 02 04 00 64 00 00 CRC CRC | Set second group running time to 15000 ms: C12.12=15000 |
01 10 12 14 00 02 04 00 64 00 00 CRC CRC | Set second group acceleration time to 100 ms: C12.14=100 |
01 10 12 16 00 02 04 00 64 00 00 CRC CRC | Set second group deceleration time to 100 ms: C12.16=100 |
01 06 04 11 00 01 CRC CRC | Enable motor to trigger operation: C04.11=1 |
01 06 04 11 00 00 CRC CRC | Emergency stop command, motor disables: C04.11=0 |
Note: If you encounter situations where the motor suddenly stops and starts, we recommend adding a braking resistor, as back electromotive force (EMF) generated during braking may damage the motor.
Furthermore, faster speed updates can be achieved by adjusting the interval time between each segment command in the serial port software.
Advantage: The control system is simple and does not require real-time operation.
Updated on: 30/01/2026
Thank you!