R67B expressly forbids controlling multiple Jaguars from a single PWM port on the digital sidecar.
Interestingly, I can’t find anything that forbids multiple Victors or Talons from being controlled by the same PWM port [depending on whether “corresponding”, in R66 implies “unique”]
Where in that does it “expressly” forbid using a Jaguar with a PWM-Y cable?
While I’m inclined to say this this is allowed, my only reservation is with R67. It’s specific to Jaguars. Item B states:
PWM configuration: If the Jaguar motor controller is controlled via PWM communications, the PWM port on the Jaguar motor controller must be connected directly to a PWM port on the Digital Sidecar with a PWM cable. No other device may be connected to these PWM ports. No other device may be connected to any other port on the Jaguar motor controller with the exception of connection to the coast/brake port or the limit switch ports.
The “directly” bit has me confused. I’m not sure what they are trying to prevent from happening here. Further, this rule only applies to Jaguars, so it would seem there’s a specific concern with them. I would be surprised if they were actually trying to prevent PWM Y cables from being used as you have described.
It might be worth asking a question on the Q&A, as I wouldn’t expect the use of PWM Y cables to be prohibited with any of the motor controllers.
FWIW Section 4 of wpilib screensteps live shows them being used with Jags…
I don’t read R67B that way, necessarily, though I do see how you could draw that conclusion.
B. PWM configuration: If the Jaguar motor controller is controlled via PWM communications, the PWM port on the Jaguar motor controller must be connected directly to a PWM port on the Digital Sidecar with a PWM cable.
Translation: Jaguar connected to PWM port–theoretically, using the Y-cable would be legal here, especially if the other end of the Y wasn’t connected.
No other device may be connected to these PWM ports.
Can’t connect anything else–including another Jaguar that’s powering a motor in the same gearbox? That’s a ruling that would be pretty dumb, at least on the surface. I can see not having a Victor or Talon on the Jag ports, but not having two Jags? Also, having the Talons and Victors allowed to Y-cable but not the Jags doesn’t make sense.
I’d say to ask Q&A whether R67B prohibits connecting Jags to the same PWM port via Y-cable, and if it does, what the reasoning is behind that, given that R66 seems to allow Talons, Victors, and Spikes to share PWM ports via Y-cable.
Of course, if you wanted to use CAN capability, you’d have no trouble connecting all the Jags you wanted in line…
It is saying that if there is one jaguar connected to a PWM port, then nothing else (including a second jaguar) can be connected to the same PWM port. You are right, you can use a PWM Y-cable, if there is only one jaguar attached.
I agree. I would also like to know what their intentions are, and if indeed, we can use a single PWM port for multiple talons, spikes or victors.
Here’s a possible interpretation which makes more sense: Perhaps the pronoun “these” in the sentence “No other device may be connected to these PWM ports” refers to the Jaguar PWM port, so the rule is intended to mean:
"No other device, such as an arduino, may be connected to the Jaguar’s PWM input port".
In the event this is determined to be within the rules, the question becomes one of the DSC PWM output being able to drive enough current to power the optoisolators on three Jags. The spec on the DSC says 15mA, so up to 5mA for each of the three Jags.
The spec for the Jag says 5mA typical current, but up to 25mA maximum current. Note that 25mA is over 15mA, so this maximum is a theoretical issue in any case.
Bottom line is that this should work electrically, but if you have the extra PWM outputs, just using these avoids any question, so long as you couple them in S/W.