Shared Wires on Rev Pneumatics Hub

We are mounting several solenoids away from our control system, and are trying to save on wire count. Does anyone know if the Rev Pneumatics Hub switches on the positive or ground side? I saw some older posts about the CTRE PCM switching the ground side, but couldn’t find this in the specs on Rev’s website.

I believe this would be prohibited by R504 and R625

Would combining multiple common solenoid control lines (the common + or -) be considered a custom circuit? The definition in the rules is ‘Any active electrical item’, I wouldn’t think that landing multiple wires together would be considered an active item

R504 states one solenoid per channel.
R625 could also apply because something not wired to the FRC SOP may be considered a CUSTOM CIRCUIT. (the solenoid is an active component)

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If you have to ask rather than just pulling out a DMM and checking, you reeeeeally shouldn’t be messing with it, not to mention the whole robot manual.

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Unfortunately this was the last test before we left late Saturday night, but I was planning to put a meter on the outputs tomorrow at the meeting to check which side is switching. I just wanted to ask the community if anyone else has knowledge or experience with this.

We’re not trying to control more than one solenoid per output, nor are we trying to get around any rules. If we’re not able to reduce wire count, then we’ll obviously revert to running one pair of wires per solenoid to the ones mounted remotely on the robot

One thing we have done to save on wiring is use four wire like Spectrum recommends in their wiring guide. This way, you can run one cable for each solenoid. The cable is also relatively affordable.

The actual cable above does not have prime shipping (at least as far as expedited delivery) for us, but you should be able to find some similar that you could aquire in short order.

As stated above, R504 specifies only one solenoid valve per output on the PCM or PH.

I’d actually argue that rule depends on what you define output as. Do you define output as just the switching signal terminal, or the pair of terminals? If it’s just the switching signal, that rule wouldn’t stop you from wiring all the common signals together, or even getting them from another source entirely.

A similar thing on the PD boards as well. Does each load have to be connected to it’s pairing ground, or could it be on another ground output? As long as you’re legal with splices, there’s nothing explicitly in the rules requiring the power and ground of an output to be a matched pair. nevermind, R-610 specifies PD outputs are a pair.

Also, any explicit definitions here need to be carefully thought out if rule changes are made. For instance a quadrature encoder, since it requires 2 Dio signals, it should be legal to get the 5v from 1 header, and the ground from another. A mess up in this definition would make that illegal.

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R504 Table 9-2
Electrical Load - Pneumatic Solenoid Valves
Motor Controller - No
Relay Module - Yes (multiple)
Pneumatics Controller - Yes (1 per channel)

Only one Pneumatic Solenoid Valve per channel on the Pneumatics controller

But is channel defined as switched side or the pair?

Note I’m not saying it shouldn’t be defined (it probably should for safety reasons), I’m just saying as it sits right now it’s unclear, and because of how all the commons are likely all traced together, I’d probably define a channel as switched side, without an explicit ruling like R610 for the PD devices.

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What you have described is commonly done in industrial electronic/electrical systems. It is also how all the lights in most cars are wired. So yes, it would be good to get a clarification on whether the channel is only the switched signal or does it include the common hot or return line.

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Not exactly, when discussing car electronics, some designs use the frame of the vehicle for a common return some do not. In this case I think the definition is both terminals are considered a channel. You do want your pneumatic design to operate as you intend and not be influenced by current in other parts. The added second wire is a minuscule part of your design and adds little weight to the overall robot. It also prevents a single point failure for your pneumatics.

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From Q&A110 (which I assume started from this thread):

No. A single channel includes the pair of red/black terminals and is denoted with numbers 0-15 on the Pneumatic Hub.

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If all the solenoids are active at once, the sum of the currents would flow in the shared wire. At a minimum, you’d have to show that you had this covered according the the wiring “code” for FRC (the rules). But I think this has been answered – not legal in any case.

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Correct, I asked the question this morning for the official ruling and fortunately got a quick response from GDC. I do appreciate the input from folks on the thread, and am happy that FIRST gave a definitive answer we can design around.