Hi folks,
just happened to stumble across this video where Ronin disassembles a CAN hub. Turns out it does not contain any electronics (one resistor…), but is just connected sockets (no real surprise if you look on how CAN bus works). What I find telling is however that Snapmaker sets you back 59 bucks for this simplistic device… Says something about Snapmaker pricing policy.
Yes, it’s a naked truth.
But that’s the only option if you need to connect more devices (in an elegant way).
Such dedicated sockets are not available on the market.
That’s a passive electronic component, but still electronic. It’s needed for impedance matching the transmission lines in the CAN cable.
I think there is no resistor at all - if you look closely at this PCB, there is only a dedicated place
but there is no physical component. This would be confirmed by the diagram made by @Ronin and shown in this film.
By the way - the CAN bus needs a terminator at the beginning and end of the line. The use of a hub device in the CAN network with a linear structure makes a tree structure - it differs a bit from the rules of the CAN bus . The use of resistors in the middle of the CAN network would not make sense in my opinion.
Haven’t looked at the video.
But a resistor is still required for impedance matching. The theory is beyond the scope of this forum. Here’s something that came up quickly for me in a search that’s enough to get started, if so interested: Wilkinson Power Splitters.
If they designed in a place for a resistor but it’s not there (for what? cost savings?), it says a lot about the basic competency of SM engineering management.
The CAN Bus has a 120Ohm resistor on both ends ususally, as they dont know whats plugged in so you either have to many or to few termination resistors, it has a 60Ohm resistor only in the Mainhub, thats it. there are two networks in the Hub, one for the toolhead and rails and one for the expansions.
According to Wikipedia in some scenarios star topology is allowed: CAN bus - Wikipedia. See the section about ISO 11898-3 - termination seems to be a bit vague here.
Yes - for low speeds (up to 125 kbit/s) the star topology in the CAN bus is acceptable.
But the speeds of both CAN buses in the Snapmaker are 500 kbit/s. 
In this case, the bus should be as linear as possible. However, practice shows that it still works somehow 
Daisy chain is for devices that are far apart from each other.
In rs485 (and also CAN according to this document) if you have devices next to each other you can have stubs but is not necessarily a ‘star’ configuration.