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Unread 17-01-2011, 01:29
EricVanWyk EricVanWyk is offline
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Re: Legality of Jaguar closed-loop control modes

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There is no rule that prohibits the Jaguars from reading the values from the encoders, however note that Rule R49 requires that the ROBOT must be controlled by the cRIO. In other words, commands may not originate in the Jaguar or any other controller, they must originate in the cRIO.
The commands for the various control moods do originate in the cRIO, it is just that the command is "Set your speed according to these parameters and the encoder".

The key word is command, not data.
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Unread 17-01-2011, 08:21
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by EricVanWyk View Post
The commands for the various control moods do originate in the cRIO, it is just that the command is "Set your speed according to these parameters and the encoder".

The key word is command, not data.
I believe you are right, but then why did GDC find it necessary to say "commands may not originate in the Jaguar" ? In what meaningful sense would this even be possible?



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Unread 17-01-2011, 09:51
EricVanWyk EricVanWyk is offline
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by Ether View Post
I believe you are right, but then why did GDC find it necessary to say "commands may not originate in the Jaguar" ? In what meaningful sense would this even be possible?


I think that half of the response is unrelated. I don't know why they bothered to type it.

A "bad" student could reprogram the Jaguars with entirely new firmware, but this would break several other rules. There would be no doubt that they were doing something illegal though, so I don't know why they bothered to mention it here.
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Unread 17-01-2011, 12:12
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by Al Skierkiewicz View Post
Ron,
I was under the impression that the heartbeat is to insure that something has not interrupted the CAN connection and therefore allow the Jaguar to continue to execute the last command received. This is something different than a disable command generated by the Crio either through internal firmware for a fault or as received from the FMS. Is this correct?
I'd have to let jhersh and/or dyanoshak provide the authoritative answer....but IIRC when the robot is disabled the cRIO stops sending out the FRC "trusted heartbeat" to the Jags, which causes the FRC-specific firmware on the Jag to disable the motor output - not unlike what the standard Jag firmware does when it doesn't see any CAN messages.

Since this "trusted heartbeat" is completely protected from interference - intentional or unintentional - from team software, it's this handshake between the protected FRC software on the cRIO and the FRC-specific firmware on the Jags that provides the required safety, allowing the driver station (or FMS when connected) to disable the Jag motor output, effectively negating any motor output "commands" that come from the team software on the cRIO or the internal control loops on the Jag. That's why the Jags require the special firmware when using CAN in order to be competition-legal.

Quote:
Originally Posted by EricVanWyk View Post
Quote:
Originally Posted by Ether View Post
I believe you are right, but then why did GDC find it necessary to say "commands may not originate in the Jaguar" ? In what meaningful sense would this even be possible?
I think that half of the response is unrelated. I don't know why they bothered to type it.
I see the ambiguity as coming from the terms "reading the values", "command" and "control". Even ignoring the second part of the response, the first sentence is also unclear IMHO.

To quote, adding my own emphasis:
"There is no rule that prohibits the Jaguars from reading the values from the encoders, however note that Rule R49 requires that the ROBOT must be controlled by the cRIO."

Here's a very plausible paraphrase (which is hopefully NOT what the GDC intends):

"There is no rule that prohibits the Jaguars from reading the values from the encoders, however the Jaguars are only permitted to provide the values to the cRIO and all control calculations must be performed on the cRIO."

Seems like we all agree it'd be non-sensical for the GDC to intend this - but it's unclear enough that we had visions of robots being wrongly declared illegal based on different inspectors' opinions.
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Unread 17-01-2011, 13:58
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Re: Legality of Jaguar closed-loop control modes

ok so if we interpret this the strictest way possible ( where the jag cant independently make a decision about its output ) wouldn't the current/voltage protection( a jag will shut itself off if it over amps or the voltage gets under 6v) built in to the Jags break this rule?

I dont think that this interpretation is correct ( or will remain correct ).
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Unread 20-01-2011, 22:13
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Re: Legality of Jaguar closed-loop control modes

The GDC has spoken, no closed loop control from the jaguar.
http://forums.usfirst.org/showthread.php?t=16326
Quote:
Originally Posted by FRC GDC
No closed-loop control modes are permitted within the Jaguar per <R62>.
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Unread 20-01-2011, 23:50
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by biojae View Post
The GDC has spoken, no closed loop control from the jaguar.
http://forums.usfirst.org/showthread.php?t=16326
Geez. This is a really unfortunate answer from the GDC. It greatly complicates the cabling and increases the complexity of closed-loop control.

Can someone ask on the First forum (it won't let me post) if this means that speed, current and position modes of the Jaguar are prohibited? If so, then there's no reason to use CAN bus. We might as well stay with PWM and the Victors.

Heavy sigh...

Last edited by taichichuan : 20-01-2011 at 23:56.
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Unread 21-01-2011, 00:02
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by taichichuan View Post
Geez. This is a really unfortunate answer from the GDC. It greatly complicates the cabling and increases the complexity of closed-loop control. Now, we're going to have to run another set of cabling... Sigh.
Can't the encoders still be connected to the Jaguar?
The only rule restriction is that commands must come from the cRio.

The cRio can read the position (or speed) from the jaguar.
PID (or other closed loop control) can be calculated on the cRio.
Then the calculated voltage can be sent to the jaguar.

Quote:
Originally Posted by FRC GDC
There is no rule that prohibits the Jaguars from reading the values from the encoders, however note that Rule R49 requires that the ROBOT must be controlled by the cRIO. In other words, commands may not originate in the Jaguar or any other controller, they must originate in the cRIO.
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Unread 21-01-2011, 00:14
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by biojae View Post
Can't the encoders still be connected to the Jaguar?
The only rule restriction is that commands must come from the cRio.

The cRio can read the position (or speed) from the jaguar.
PID (or other closed loop control) can be calculated on the cRio.
Then the calculated voltage can be sent to the jaguar.
In order to use the Jaguars in one of the closed loop modes, you have to load PID values to the Jag. That would appear to be prohibited by the GDC's ruling.
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Unread 21-01-2011, 00:26
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by taichichuan View Post
In order to use the Jaguars in one of the closed loop modes, you have to load PID values to the Jag. That would appear to be prohibited by the GDC's ruling.
The jaguar would be in Voltage control mode.
The position (or speed) values can be read through the CAN bus (after the correct settings are loaded into the jaguar, SpeedReference for example).
The voltage to send to the jaguar can then be calculated on the cRio.

This does not use any of the Jaguar closed-loop modes, and so it seems legal.
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Unread 21-01-2011, 00:42
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by biojae View Post
The jaguar would be in Voltage control mode.
The position (or speed) values can be read through the CAN bus (after the correct settings are loaded into the jaguar, SpeedReference for example).
The voltage to send to the jaguar can then be calculated on the cRio.

This does not use any of the Jaguar closed-loop modes, and so it seems legal.
While it is possible to run PID on the controller successfully, there are substantial advantages of running it on the motor controllers themselves. In particular there is less need to consider timing jitter in control loops or message bandwidth limits if using the Black Jaguar serial to CAN convertor.

But mostly this is a poor decision due to the reason Eric stated above.
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Unread 21-01-2011, 00:49
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Re: Legality of Jaguar closed-loop control modes

ok so what about the attached limit switches on the JAGS. by default ( and I don't think there is a way of turning this off) in both the PWM and CAN mode you can attach 2 limit switched to the Jag to stop the motor at both its low and high points . . am I to understand that these ports are off limits as well?

I get the desire to minimize “unanticipated surprises”, but we have had these devices for 3 seasons, CAN for 2 ( I would like to know if any one used the closed loop modes last year),and a whole range of beta tests ( not to mention the inclusion of the closed loop modes in the custom FRC Labview and Jag firmware builds).

it just seams a little weird
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Unread 21-01-2011, 01:06
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Re: Legality of Jaguar closed-loop control modes

Personally I'm fine with that decision (strange as that decision may seem). It's one thing to use closed-loop control. It's another to implement it in your own code, especially if you're using PID control. I'd much rather have my team know how the stuff works, than just be able to hook it up and see it do its magic.

After all, that's pretty much what FIRST is all about.
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Unread 21-01-2011, 01:49
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by jtechau View Post
Personally I'm fine with that decision (strange as that decision may seem). It's one thing to use closed-loop control. It's another to implement it in your own code, especially if you're using PID control. I'd much rather have my team know how the stuff works, than just be able to hook it up and see it do its magic.

After all, that's pretty much what FIRST is all about.
While I agree with the sentiment. I disagree with the argument.

a few years ago Dean talked about the idea that technology is something that is new to the generation. for his grandfathers generation the car was technology, for his generation the internet is technology, for this generation . . well we dont know. The point is each time we progress, the wild and amazing things of the past become base and mundane ( I would say transparent). When I was in high school ( circa 2004) it was all 15 pin analog ports and limit switches. if we wanted to do channel mixing that was like 2 weeks worth of coding, and trig for getting relitive positioning of the field, forget it!( I often wonder if those doing FIRST in 1994 would take a look at what I did in 2004 and say "well all the hard stuff is done for him what is he learning"). But now channel mixing and trig functions are mundane they are transparent, we talk about the underlying principals drop in the VI and move on. does this make the season any less hard? No work will always rise to its own level. This just pushes us to find something else thats new and interesting and exciting (technology).
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Unread 21-01-2011, 11:50
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Re: Legality of Jaguar closed-loop control modes

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Originally Posted by jtechau View Post
Personally I'm fine with that decision (strange as that decision may seem). It's one thing to use closed-loop control. It's another to implement it in your own code, especially if you're using PID control. I'd much rather have my team know how the stuff works, than just be able to hook it up and see it do its magic.

After all, that's pretty much what FIRST is all about.
I don't understand this argument. Even if you are using the Jaguar closed-loop control the PID values still have to be tuned, and you can't reasonably perform that tuning unless you understand the control algorithm. If the PID controller is implemented on the cRio there are some code structural issues to deal with but otherwise it's the same tuning problem, requiring the same level of algorithmic understanding.

The first programming language I learned was Z80 assembly, but I don't believe that I understood more when myopically concerned with register use than I do now when using WPIlib and can concentrate on higher-level design.
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