Optimal Wiring Configuration for Multiple CAN-Connected Stepper/Servo Motors
This document outlines common issues, precautions, and standardization protocols for CAN communication motor wiring to ensure system stability and reliability. As a multi-master serial communication bus, the Controller Area Network (CAN) is widely implemented in industrial automation. Proper wiring design is critical for maintaining communication integrity in motor control applications.
Employ Dedicated T-Junction Cables: When connecting multiple motors to the bus, use purpose-built T-junction cables to minimize branch lines and reduce wiring complexity, thereby enhancing communication stability.
I. Excessive Bus Branch Length
Symptom Description:
Environmental constraints and device form factors may result in extended or excessive bus branches. In one documented servo system, extending a node's branch beyond specifications caused system errors and node failures.
Root Causes:
-
Signal Step Distortion (Terracing Effect):
- Extended branches cause rising/falling edges to develop terracing
- Terrace points near logic threshold (≈0.9V) induce bit-width distortion → reception errors
-
Impedance Mismatch:
- Excessive branch length disrupts impedance matching (Z0=120Ω)
- Resultant signal reflections cause waveform distortion
II. Branch-to-Trunk Length Principles
1. High-Speed CAN (ISO 11898-1/2)
| Parameter | Specification |
| Baud Rate | 1 Mbps |
| Max Branch Length | ≤ 0.3 m |
2. Vendor-Specific Protocols
For other baud rates, observe:
- Σ(Branch Length) + Trunk Length ≤ 70% max bus length
- Σ(Branch Length) ≤ 30% total bus length
3. Optimal Length Guidelines
Refer to Fig. 3.1 for motor-specific branch/trunk length limitations at various baud rates. Field implementations require environmental adaptation.
Conclusion
CAN motor wiring design is paramount for communication reliability. Critical practices include:
- Preventing excessive branching using T-junction cables
- Complying with ISO 11898-1/2 specifications
- Adhering to vendor length ratios (70/30 principle)
Effective implementation reduces error rates by ≤0.001% and increases MTBF by ≥40%, ensuring dependable motor control system operation.
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