Quote:
Originally Posted by Hugh Meyer
<snip> 2CAN device which is a bridge between Ethernet and CAN.
<snip> try the serial interface, mainly to save money. <snip> we discovered that the system couldn’t keep up. Switching to the 2CAN increased throughput by at least a factor of 10. Even with the 2CAN we could still take longer to transfer what we wanted than our periodic loop in the main code would support.
As a work around we changed our periodic loop to 100 msec and multiplexed the logging data. As I recall we divided up the requests for data from the Jaguars into 2. One pass through our main loop we request data from half of the Jaguars, and the next time through we get the other half.
<snip>
-Hugh
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This is from a few days ago, but now I finally have enough clarity of thought to ask questions about it.
2CAN:
$200 from AndyMark. I am not saying it is overpriced, but it is a lot of money. Is this the device of choice? Are there other possible choices?
100msec loop time:
Is that you MAIN loop time? 10Hz seems pretty slow to me. At 10fps the robot covers 1ft per loop. That seems a bit too slow for my blood. I suppose that if you had your Jaguars all in feedback mode, the robot behaved fine but what did your drivers think? I think it may be okay because my main motivation in this is not to make high speed better behaved but to make fine motions at low speeds better behaved.
I may even consider modifying the gains of my PID loop based on the robot configuation -- the robot in a compact position may need different gains from the robot with its arm reaching over some field obstacle -- it would be great if the driver didn't see a difference in behavior.
Data logging:
What sort of data were you logging and where we you logging it?
This part of the 2CAN documentation seems interesting:
The 2CAN also provides a web host dashboard that reports
information on all of the Jaguars on the CAN bus. Information
such as voltage, current, temperature, faults, etc… are displayed
in an easy to read webpage accessible to any laptop connected to
the Ethernet bus. This allows teams to perform quick diagnostics
on their motor controllers and also debug hardware issues
If this is true, then I think that the logging could all be done back on the Win7 PC via some Java code that scrapes the data off the 2CAN's web host dashboard.
Did you try this?
I don't know if it is true but I have heard that there is some magic (magic in fast and easy to implement) method to get data between the cRio and the Win7PC. If so, then there is yet another twist in the plot to consider.
More questions but my message is too long already.
Joe J.