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Recommendations for uav can hub


(Peter Amond) #1

Dear All,

I’m designing a CAN HUB for UAV CAN. (Some thing similar to DJI CAN HUB like follow, Link >> http://www.helipal.com/dji-can-hub.html)

dji-can-hub-pd_large

My purpose is connecting many devices via CAN BUS. This is the initial circuit schematic diagram. I hope to connect 8 CAN devices to the same HUB. Can you see any problem with this design ? As well as 5V power input to HUB will give from outside.

Please give me your recommendations and ideas for this. Do you have any schematic or hardware design for this ?

Regards,
Peter.


(Pavel Kirienko) #2

Generally, star topologies are not recommended for CAN due to associated problems with signal reflections. This is not to say that it wouldn’t work but you should be ready to face signal integrity issues, especially with large high-speed networks. Consider connecting your nodes in a linear bus instead (like a daisy chain).


(Alexander Sysoev) #3

In fact UAVCAN hub kinda exists(though it is not recommended to use it)
Check this repo


(Peter Amond) #4

Hi Pavel,

Thank you for your prompt reply.

But in following documentation it is recommended to have star topology for CAN.
Link >> http://www.mindsensors.com/content/86-can-and-its-topology

Do you know any hardware design for UAV CAN HUB ?

Regards.


(Peter Amond) #5

Hi Alexander,

Many thanks. Why it is not recommended to use ? If we need to build a CAN HUB with UAV CAN like DJI CAN HUB what we can do ?

When I refer repo link I could see the schematics. What is the purpose of having 3.3V(From IC 3) and 5V (from GW1584) both inputs ?

And also why GND pins connect to ADC_IN1 via 19K resistors and 0.1uF C12 capacitor ?

Regards.


(Alexander Sysoev) #6

It is not recommended to use any kind of hubs on UAVCAN bus because it is supposed to be daisy-chained and all UAVCAN devices shoukd have 2 can connectors per bus(one for input and one for output). This will guarantee that wire stubs are minimal and the bus may be longer without signal degradation.

Also, speaking about the existing HUB, this device allows for 3 assembly variants.
And part GW1584(which is a cheap dc-dc module) is there to provide UAVCAN bus with 5V@3A power rail from VBAT(up to 6S). It is totally optional

All the MCU part may be there for CAN bus power consupmtion and voltage monitoring. This part is optional as well…


(Alexander Sysoev) #7

I have just understood what you were asking about.
R8 R9 R10 in the schematic have invalid values. These resistors should form a current shunt for UAVCAN bus consumption measurement(with ADC_IN1) and C12 is there for some basic filtering.
R8-R10 values should be somewhere in 1-10 ohms(we should use ohm’s law for that)