CANopen vs EtherCAT vs RS-485 | AGV Drive & Lifting Interfaces

Key takeaways

• CANopen is the pragmatic default for most AGVs: a handful of drives and actuators, moderate update rates, mature drive profiles (CiA 402) and simple wiring.
• EtherCAT is worth the extra cost when you need tightly synchronised multi-axis motion, short cycle times or many nodes on one network, and your vehicle controller already has an EtherCAT master.
• RS-485 is only a physical layer. It is cheap and robust for simple point-to-point or multi-drop control, usually with Modbus RTU, but it has no standard drive profile, so integration effort moves into your software.
• For lifting modules the bus speed rarely decides the choice. Position or speed commands, limit and fault feedback, brake control and compatibility with your vehicle controller matter more.

What does the vehicle really need from the bus?

On an AGV or AMR the fast control loops, current, torque and speed, run inside each drive. The fieldbus mostly carries setpoints (speed or position targets), status (actual speed, position, temperature, faults) and configuration. Update rates between roughly 1 and 10 ms are common for wheel speed commands. Three questions drive the interface choice:

1. How many nodes are on the vehicle: two traction drives, a steering motor, a lift, a battery management system?
2. Do any axes need to move in strict synchronisation, for example four steered wheels following one kinematic model?
3. Which interfaces does your vehicle controller or PLC already support?

The three options at a glance

CANopen in practice

CANopen standardises how devices describe themselves (the object dictionary), how process data is exchanged (PDOs), how configuration is read and written (SDOs) and how the network is monitored (NMT and heartbeat). The drive profile CiA 402 defines operating modes such as profile velocity, profile position and cyclic synchronous modes, so a vehicle controller can drive devices from different vendors with the same commands.

• Bit rate against length. Classical CAN is specified up to 1 Mbit/s, and the usable bus length falls as the bit rate rises. CiA guidance is roughly 25 m at 1 Mbit/s, 100 m at 500 kbit/s and 250 m at 250 kbit/s. Most vehicles are short enough for 500 kbit/s or 1 Mbit/s.
• Termination. A 120 Ω terminator at each end of the bus, and no long stubs.
• Frame size. A classical CAN frame carries up to 8 data bytes, enough for velocity or position setpoints plus a status word.
• Files to ask for. The EDS file and the list of supported CiA 402 modes. A device that speaks "CAN" but not CANopen will not work with a standard CANopen master.

EtherCAT in practice

In EtherCAT the master sends one frame that passes through every device. Each device reads its output data and inserts its input data while the frame passes through, so the whole network is updated in one pass. Distributed clocks synchronise the devices to better than a microsecond.

• When it pays off. Coordinated multi-axis motion, short cycle times (well below 1 ms is possible) and large numbers of nodes.
• What it needs. An EtherCAT master in the vehicle controller and shielded Ethernet cabling with connectors rated for vibration. The master software and tooling add cost and learning effort compared with CAN.
• Drive profile. Most servo drives expose CiA 402 over EtherCAT (CoE), so the application logic can be similar to CANopen.
• Files to ask for. The ESI file for the device.

RS-485 in practice

RS-485 describes differential signalling on a twisted pair. It is long-reaching (up to about 1,200 m at low speed) and noise-tolerant, and a multi-drop bus connects several devices. Most low-cost actuators use Modbus RTU over RS-485: the master polls one device at a time, so total latency grows with the number of nodes and the polling design becomes part of your software. There is no standard drive profile, so every vendor's registers differ.

RS-485 fits a single lifting actuator or a small, slow system. When a vehicle has several drives that must be commanded together, CANopen or EtherCAT scale better.

Lifting modules need a different checklist

Lifting is usually a slow, point-to-point motion with a defined stroke. For a lifting module such as the JY Robot ball screw lifting module, which offers RS-485, CANopen or EtherCAT interfaces, the important questions are:

• Is the command a target position, a speed, or a simple up/down? Does the controller need position feedback?
• How are limit switches and over-travel reported?
• Who controls the holding brake, and what happens to it on power loss?
• Which fault codes does the module report, and how are they cleared?
• Does lifting share a bus with traction? If so, check bus load and latency for the safety-relevant signals.

If a safety function must stop the lift, use a dedicated safety channel such as a hardwired STO input rather than a normal fieldbus command. See our guide to STO in AGV drive wheels.

Wiring and EMC on a moving vehicle

• Use shielded twisted pair for CAN and RS-485, and shielded Ethernet for EtherCAT.
• Terminate the shield consistently and keep signal cables away from motor and battery power cables.
• Use locking, vibration-rated connectors, for example M12.
• Plan for hot-swap and diagnostics: heartbeat or watchdog monitoring, and clear fault reporting to the vehicle controller.

A simple decision guide

1. Does your vehicle controller already have an EtherCAT master and do you need synchronised multi-axis motion? Choose EtherCAT.
2. Do you have several nodes and want vendor-neutral integration at moderate cost? Choose CANopen.
3. Do you have one or two simple devices and no need for a profile? RS-485 can be enough.
4. Are you unsure? Ask your supplier which interfaces are available on the actual part number, because options differ between variants.

FAQ

Is CANopen the same as CAN?

No. CAN defines the physical and data-link layers. CANopen is a higher-layer protocol on top of CAN that adds the object dictionary, PDOs, SDOs, network management and device profiles. A device with a proprietary CAN protocol is not automatically CANopen compatible.

Is EtherCAT much faster than CANopen for an AGV?

EtherCAT has far more bandwidth and much better synchronisation, but a typical wheel speed command loop at 1 to 10 ms does not need it. The advantage appears with many axes and tight synchronisation.

Can I mix interfaces on one vehicle?

Yes. Many vehicles use CANopen for drives and a separate interface for sensors or the battery management system. Plan the gateway or controller that connects them.

Which interfaces does my JY Robot product offer?

Interfaces depend on the product and variant. The ball screw lifting module offers RS-485, CANopen and an EtherCAT option. Send us the part number or your requirements and we will confirm.