PDP branch circuits - connecting stuff other than motor controllers

We read the robot construction rules for power distribution. Being a rookie team we’ve got a few questions.

REV Servo Power Module - This obviously would connect to a PDP branch circuit but no specified breaker rating so we’ll just select appropriately based on servos in use.

Our robot has a LimeLight camera. It’s considered a custom circuit right thus PDP branch circuit?

Could the servo power module be connected to the same PDP branch circuit as the LimeLight?

Can we make a custom circuit that has additional fusing for each sub-branch load? That makes sense electrically.

Answering your questions in order:

  1. The tech specs for the REV servo power module list the max current for all channels as 15 Amps, so I would use at least that size breaker. If you want to use higher than that, that’s up to you. Just make sure you use the right size wire for the breaker you choose.
  2. Yes. The Limelight, and any other cameras or sensors are custom circuits. They can be powered from a PDP branch circuit, a VRM output, or a COTS battery pack (depending on your definition of “computing device”)
  3. Thanks to Q281 you are explicitly allowed to connect multiple individual components with separate tasks as a single custom circuit. Therefore, they can both be powered from the same PDP branch circuit. Just make sure you only have one wire going into the PDP sport itself to comply with R56.
  4. You’re allowed to add whatever fusing you want to inside your custom circuit. How you do that is completely up to you; there’s no rules requiring fuses inside custom circuits. Even if you have additional fuses inside the custom circuit, all of the power wires will still have to be the proper size based on the fuse in the PDP slot.

Your looking for a “12V Fused Distribution Block”, commonly used in some car audio applications. We used one once for an of over the top Robot Bling Display. It easily passed inspection. Just Keep all the wiring nice and neat, and labeled.

Thanks for the helpful answers. I think we’ll add an additional fuse block mostly to allow sensible wire gauge reduction. Good to know Q281.

Doesn’t R54 / R55 mean you can only have 1 VRM module? And once you’ve used the 12V 2A output there’s not a lot of juice remaining to run a LimeLight camera?

By my reading of the rules, the minimum required wire gauge is based on the size of the fuse in the PDP. Any subsequent fuses in the custom circuit don’t affect the allowable minimum size. That might be a question worth asking the Q&A.

While I wouldn’t recommend it because of the increased risk to radio power failures, plenty of teams connect other things to the other ports on their VRM. I don’t know the input power specs for the Limelight, but in theory it can be powered from there if the required voltage/current matches one the VRM can provide.

If you reread R54/55, you’ll find they’re carefully worded to allow for multiple VRMs. The VRM that powers the radio must be plugged into the VRM slot on the PDP (R55) and can only power the radio from the 12V/2A port (R54). There’s no rule against using a second VRM as part of a custom circuit, or powering a custom circuit from a second VRM. In fact, R59 specifically lists the maximum breaker size required for powering additional VRMs from a PDP branch circuit.

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I read this in the contrary sense, that internal fusing would enable use of smaller wires. The phrasing of R60 indicates that protection is a continuum (e.g. 31A of protection is a case worthy of consideration). Also, specific protection for the standard devices is called out in rows three and further down. It’s not explicit either way, but it certainly seems implied that the breakers and fuses in the PDP are not the only protection available.

Update: Oh, yes - the blue box in R59 supports this even more strongly. Emphasis mine:

R59 does not prohibit the use of smaller value breakers in the PDP or any fuses or breakers within CUSTOM CIRCUITS for additional protection.