Quote:
Originally Posted by JefferMC
I would think the reason someone would want to run a star topology vs. a single end-to-end would be a desire to retain some control in the event of a failure of a single point of the CAN wiring.
With a daisy chain arrangement with end terminators, the CAN bus cannot survive any physical failure at any point.
With a star arrangement, e.g. with discrete PWM cables, any single PWM cable can be lost and not affect the ability to control any other PWM.
I'm not saying it is possible to run CAN in a star topology. But I observe the move of Ethernet from a single coax bus arrangement with end termination to the current star topology and one of the reasons behind it is robustness.
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It may be possible (and probably difficult) to tweak the stub lengths and the termination values to get a star configuration to work reliably. If you then have wiring failure in one of the stubs, your CAN network would likely stop working correctly anyways. A short would kill the signal throughout the network. An open would change the reflections and ringing experienced at each node in the network causing the Signal-to-noise ratio to degrade, making it likely that some or all of the nodes fail to function correctly.
Yes, the daisy-chain configuration is vulnerable to a single wire connection failing. So is much of the rest of your control system. How many robots have sat dead on the field because the power jack popped out of the radio? The proper response to such a vulnerability to take very seriously the task of improving the quality of the construction so that the probability of a failure is acceptably low (longer MTBF). Treat the wiring as seriously as any repairs to the brakes on your car. It is not that hard to and there are people who can help you learn how to do it properly. It would be much easier than forcing a CAN network to work with acceptable reliably in a star configuration.