How can I set up a chained DAQ system with small off the shelve boards?
So you have 2 legs times 3 joints = 6 CAN nodes, each needing to send 500 bytes at a sample rate of 200Hz.

Each CAN message can contain up to 8 bytes data, and given that you pick 11 bit CAN identifiers, each CAN message has an overhead of 47 bits (including end of frame and intermission). The number of messages = 500/8 = 62.5, round up to 63 messages needed.  

The total number of bits to send per node will then be:

Total bits = total data bits + number of messages * overhead bits

Total bits = 500*8 + 63*47 = 6961 bits

You need a sample rate of 200Hz, meaning 6961 bits has to be sent each 1/200 = 5th millisecond. 6961 / (5*10^-3) = 1.39 Mbit/s, assuming continuous transmission on the bus with 100% bus load. Max recommended data speed for a CAN bus is 1 Mbit/s.

And that's just the need for one node. Multiply this by 6 and you get a total need of 8.35 Mbit/s.

So CAN bus will not work. Not even if you would use 6 parallel CAN buses, which would also in turn force you to use some unorthodox automotive MCU with 6+ CAN controllers on board. Or alternatively, create some nightmare solution with an array of 6 external CAN controllers...



Also of interest: your "master" CPU will have to be able to process 500*6 = 3000 bytes of data each 5th millisecond = 600k bytes/second. Unless the data is of trivial nature, you are in need of a powerful CPU to handle that. 

So the sensible solution here is to go check those 500 bytes and see if you really need that many:


Are integers 32 bit resolution and if so, why do you need that? 
What is the actual resolution on the DACs and ADCs? 
Is there floating point data? Replace with integers.
Are there ASCII strings or other forms of non-compact data that could be replaced by index numbers?
Is there some kind of identifier or priority among the data which you can replace with the CAN identifier? 
Does the data have a checksum and if so, do you really need one, given that a CAN message comes with built-in 15 bit CRC? 
And so on.