Electronic – How to select the most appropriate (serial) bus for controller

There are standard RS422/RS485 transceiver ICs available

Here you'' find many pages of RS485 related ICs at Digikey

You can use standard asynchronous serial data using RS485 if desired. "Rolling your own" multistation code should not be too hard [tm], but it's an oft invented wheel - there will be many people already offering software (much for free) that does this.

The CAN bus lives on top of RS485, but is probably overkill for what you want.

Superb application note

AN-218 Implementing a RS-485 Multi-drop Network

This is targeted at ZBASIC but is liable to be of direct relevance to your application.

• This application note describes how to interface ZX devices with a RS-485 multi-drop network. RS-485 networks are used by many industrial applications including process control, building automation and even the control of lights at a concert. A RS-485 header board and example hookup is provided to explain the simple hardware required to get started with networking ZX devices. The software included with this application note gives a sample application and a reusable set of APIs to send and receive messages on a RS-485 network. Here is a table of contents to help with document navigation.

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Here you find ...

RS485 Multidrop Wiring Diagram & RS232 - RS485 comparison

They say -

• RS485 is sometimes termed as RS485 Multidrop LAN since it can connect several devices in a LAN network environment. These devices are all connected to a single pair wire. Transmit and receive share the same two wires.

• Officially the RS485 specification allows only 32 nodes (devices) on the LAN. However, I.C. manufacturers have developed RS485 drivers capable of allowing 128 to 255 nodes on an RS485 LAN. We use these next generation RS485 drivers in our products. This means that you can use our Converters and Remote I/O devices in more expansive situations.

Useful tutorial Wikipedia - RS485

Lots of ideas here from G's image search

You would have a CAN backbone of the typical layout, as shown in this Wikipedia-provided image:

You'll want to define how this backbone will be routed in your robot. The resistors will go at each end of the backbone. "T" or "Y" connectors and/or splices are commonly done. CAN "Y" connectors are a reliable way to do it but will be expensive and consume space. Splices are cheap and small but make sure they are reliable.

Given your dimensions, you are well within tolerances for backbone total length and stub lengths.

If each controller drop on the bus has an optional 120 ohm CAN resistor, make sure it is taken off in the drops in the middle and left on in the nodes at the end, such that there are only two 120 ohm resistors in the circuit. As per some CAN specs (J1939) you aren't supposed to put the resistors inside a node, but many (most?) products put them into nodes because it is far cheaper that way. To make sure you did a good job, put a multimeter between CAN High and Low and you should see close to 60 ohms (which is what you get with two 120 ohm resistors in parallel).

For your robot, try to twist the CAN High and Low wires together as they make their run through the robot. For your application I wouldn't worry too much about the number of twists per inch, and frankly it would probably work without twisting, but it gives it some EMI resistance which is probably why you are using CAN.

If you are making your own harness, try to use yellow wire for CAN High and green wire for CAN Low. Those are the standard colors.

Bonus if you get a UTP or STP (unshielded/shielded twisted pair) cable to do your install. If you use shielded, you will need to connect the shield to negative battery. For your application, I suspect you won't need shielded cable and can get away with unshielded cable or unshielded wires twisted together.

You may also check out the DB9 CAN standard - might be useful, or maybe not.