Legality of Jaguar closed-loop control modes

[rrossbach]

Originally Posted by Al Skierkiewicz

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.

Originally Posted by EricVanWyk

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.