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#1
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Jaguar Communication
Hi everyone this year my team is looking into new and more efficient ways of doing things with our robot. one of the questions that came up is what is the best way to communicate with the Jaguars. We were wondering what the advantages and disadvantages are to using PWM, CAN, or Ethernet.
Thanks in advance. |
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#2
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Re: Jaguar Communication
1 - It's either PWM or CAN; there is no Ethernet.
2 - Please use the search function. Although the bulk of the threads regarding Jaguars primarily discuss the advantages of Jaguars over Victors, they do summarize what Jaguars can do under what conditions. 3 - CAN allows you to access the finer functions of Jaguars, specifically closed-loop control using sensor input. See http://www.ti.com/lit/ug/spmu131b/spmu131b.pdf for more details. |
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#3
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Re: Jaguar Communication
Strictly speaking, Jags can't communicate with actual Ethernet. Andymark's 2CAN is a device which acts as a bridge between Ethernet (from the wireless bridge) and CAN to the Jags. If you have at least one Black Jag, it is possible to use it as a serial-to-CAN bridge, albeit at a slower speed than straight CAN. That said, the advantages of CAN are easier wiring (daisy chaining), potential for feedback, and more control options (for example, speed or position control with built in PID loop, which is specifically permitted by <R52>). The disadvantages are expense (if using the 2CAN, about $200), more complex, and potentially less reliable (several teams had CAN-related software problems last year, although I have heard those have been fixed by now).
DISCLAIMER: My team has never actually used CAN on a robot, but I have experimented with it personally. (It feels great to get Black Jags in the mail.) |
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#4
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Re: Jaguar Communication
Check out the CAN tutorial on my team's site:
http://team2168.org/index.php/resour...10-can-jaguars The video and instructions on the site should answer most of your questions, If you have any remaining questions, let us know and we'll work to update our guide. Also check out our other tutorials by discipline: Electrical Mechanical Programming Scouting |
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#5
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Re: Jaguar Communication
One point that I forgot to mention earlier was that using Jaguars on PWM is largely the same thing as using Victors (excepting the fact that Jaguars have a much higher refresh rate; they operate at ~15 kHz, as opposed to Victors' 480 Hz, if memory serves correctly). Jaguars on CAN require firmware updates (which can be found on TI's site), which is still bug-ridden despite all that's been done to fix them. For some teams, the firmware will work fine and CAN will function with no problems; others will experience disastrous firmware malfunctions that shut down their robot, and yet others will find that some Jaguars don't like firmware.
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#6
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Re: Jaguar Communication
thank you all...i had searched the forums already and read many threads about the jags; some of them had some small references to some of the advantages and disadvantages of the CAN and PWM so i was looking for a consolidated list on these. Thank you very much for providing this.
What method do your teams use/prefer? |
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#7
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Re: Jaguar Communication
Every year since Jaguars were released, we've experimented with using Jaguars. Each year, many, if not all of them, failed horribly to factors outside of our control - we had one release blue sparks last year, quite memorably; when I took a tan one out of its box and set it up on an electronics board last week, it released magic smoke. We also ran into countless firmware issues that refused to reconcile themselves, and probably did more than 50% of our debugging, if not all, in week 6 last year due to innumerable problems with Jaguars themselves. Our first shipment in 2011 had an out-of-box failure rate of something on the order of 70% (i.e. could not be configured right after it was taken out of the antistatic bag).
Needless to say, we hate Jaguars. That being said, there are teams out there who swear by them and have never seen one explode, and we have managed to access Jaguars' advanced features, though we've never before had an application where they were necessary. |
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#8
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Re: Jaguar Communication
My recommendation, if your team is tight on resources or time, don't learn how to use CAN in season. That being said, we did exactly what I'm recommending you not do...
Jags have a bad reputation with FRC teams. For the most part failures I've seen have been do to wiring or hardware problems and not necessarily with the Jags themselves or with CAN. So for this reason I feel obligated to report that we used only Jags last year, all of which were controlled over CAN (using LabVIEW). In the off season we did the same using Java. There is risk associated with trying something new, do your research and things should work out well. That said, there are a lot of places to mess things up in wiring and software. So test along the way and always have a fallback plan. |
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