VJ-03-CAN: Robot Joint with CAN Bus

VJ-03-CAN is the CAN bus version of the VJ-03 joint: the same motor, harmonic gear and torque range, controlled over CAN 2.0A at 1 Mbit/s and built into a fully enclosed housing with screw-locking M12 connectors. Any master with a CAN port – an STM32 board, a PLC or a PC with a USB-CAN adapter – can read position and command position or speed with a handful of simple messages. No EtherCAT master or real-time PC is needed. It suits custom robots, mobile robots, OEM machines and research or teaching labs. Designed and built by Robot3T in Vietnam.

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Typical applications

• Custom robots and OEM machines: multi-axis arms, gantry wrists and rotary tool heads driven from an STM32 or a PLC with a CAN port.
• Mobile and service robots: arms on AMRs and pan-tilt heads; CAN keeps wiring short and noise-tolerant.
• Research and education: students read position and current and command position or speed using a USB-CAN adapter and Python.
• Rotary axes and positioners: indexing tables and camera or sensor gimbals that need high torque and absolute position.

Why VJ-03-CAN

• All-in-one, fully enclosed – motor, harmonic gear, driver, absolute encoder and brake in one sealed unit, with screw-locking M12 connectors.
• Simple CANopen-style protocol – 16 commands, standard 11-bit IDs; each joint has its own command and reply IDs, so the master can query several joints at once.
• Keeps absolute position through power loss – 20-bit single-turn and multi-turn encoder backed by a 3.6 V battery; no homing at every start-up.
• Safe by design – electromagnetic brake that closes when control is lost, command watchdog, broadcast E-STOP and protection against over-current, over-voltage, over-temperature and encoder faults.
• Two ways to move – stream setpoints every 1–2 ms like EtherCAT, or send a target once and let the joint generate its own acceleration profile.

Specifications

Torque and speed are listed for ratios 50 / 80 / 100. Max. motor shaft speed ≈ 2,400 rpm at 48 VDC (2,000 rpm at 30 VDC).

VJ-03-CAN vs. VJ-03 (EtherCAT)

Same motor, harmonic gear, 20-bit encoder and torque range.

CAN interface – bus parameters

Identifiers (COB-ID), N = joint ID

Example for joint N = 2: send commands to 0x602, receive replies on 0x582. Every command gets a reply, even when rejected; replies to SET_POSITION and SET_SPEED can be turned off to reduce bus load.

Command set

Result codes: 00 OK · 01 unknown command · 02 missing bytes · 03 invalid value · 04 wrong state. Encoder reset, brake release and remote restart require the A5 confirmation byte.

Modes and configuration

• Mode 1 – position: stream setpoints every 1–2 ms (level 0), or send a target once (levels 1..15) for a built-in trapezoidal profile
• Mode 2 – speed: zero speed holds position without drift
• Mode 3 – hand guiding: reduced stiffness for teaching by hand
• Jerk-free enable: holds the current position, releases the brake after 200 ms
• Heartbeat: configurable period, sent immediately on error change
• Cyclic feedback: position and current, from 1 ms period
• Command watchdog: joint decelerates and brakes if the master or cable is lost
• Profile speed and acceleration: set with SET_CONFIG, effective immediately
• Absolute or relative position: selected with parameter 7
• Service: RS232 debug port, 115,200 bps

Example: move joint N = 2 to 100,000 counts

Emergency stop for all joints: send 02 00 to ID 0x000. You can test quickly with any USB-CAN tool (PCAN-View, ECANTools, SavvyCAN): 1000 kbit/s, Standard frames.

CAN bus wiring

• Daisy-chain topology: master → joint 1 → joint 2 → … → last joint; no star wiring, stubs no longer than 0.3 m.
• Termination: two 120 Ω resistors at the two far ends of the bus. With power off, CANH–CANL should read about 60 Ω.
• Cable: 120 Ω twisted-pair CANH/CANL, 0.2–0.35 mm², shielded near power wiring; up to about 40 m at 1 Mbit/s, under 25 m recommended on a robot.
• Ground: connect signal ground between the master and every joint.

Supplied with the joint

• Full CAN integration manual: wiring, command set, operating sequence, error codes and troubleshooting.
• Sample code: reading position and status, position and speed moves, safe stop.
• Options: USB-CAN adapter, M12 cables, 48 VDC power supply, training fixtures.

Video

FAQ

What do I need to control the joint?
A 24–48 VDC supply and any device with a 1 Mbit/s CAN 2.0 port: an STM32 microcontroller, a PLC with a CAN module, or a PC with a USB-CAN adapter. The driver is built into the joint.

Is it standard CANopen CiA 402?
Not fully. The joint uses CANopen-style ID assignment (0x600 + N, 0x580 + N, 0x700 + N, 0x180 + N) with a compact command set of its own, so you can program it quickly without a CANopen stack. If your project requires CiA 402 or 29-bit IDs, contact us about a custom firmware version.

How many joints can one bus run?
Up to 127 joint addresses. A 6-joint arm at a 2 ms cycle uses about 35–65 % of the bus, depending on whether replies are enabled.

Will it lose position after a power cut?
No. The multi-turn absolute encoder is backed by a 3.6 V battery, and the joint reports the battery voltage so you can replace it before it runs low (below 3.0 V).

VJ-03-CAN or VJ-03 EtherCAT?
Choose CAN for your own controller, mobile robots or teaching. Choose EtherCAT for multi-axis cobots that need very short synchronized cycles.