Is it legal to make a custom slip ring?

[TheModMaster8]

I was wondering if it is against First's rules to make a custom slip ring commonly used for swerve modules if you all have any insight to this, it would be welcomed :)

[asid61]

Not legal for power lines according to last year's game manual; you are not allowed to use CUSTOM CIRCUITS there. This has been a rule for several years.
I'm not entirely clear what the rules are for signal wires, however, it's definitely in the manual where it talks about custom circuits.

[InFlight]

R55 wouldn't permit a custom circuit in the motor power wire path.

COTS slip rings are permitted, non Mercury. There are some inexpensive wind turbine ones in the 30 Amp range. I never found any 40 Amp ones that would be legal for a CIM that were reasonably priced.

[marshall]

R55 wouldn't permit a custom circuit in the motor power wire path.

COTS slip rings are permitted, non Mercury. There are some inexpensive wind turbine ones in the 30 Amp range. I never found any 40 Amp ones that would be legal for a CIM that were reasonably priced.

Got links to the ones you did find?

[InFlight]

Got links to the ones you did find?

Most the ones sold on Amazon and elsewhere are Moflon MW series. (www.moflon.com)
The 30 Amp ones are realively cheap and a nice size.
They then step to 60 Amp which are quite large to package and too expensive for a Swerve drive.

[Jon Stratis]

It looks like you can get the MW1430 for around $55. It has 4 contacts, each rated for 30A... what about running the contacts in parallel? This is something I would want to ask the GDC before implementing, but running 12 gauge wire up to the slip ring, splitting each wire across two connectors in the slip ring, then combining them again when you go into the CIM motor. It would be an interesting way to get around the 30A limitation! Not really convinced the GDC would think it legal, though.

[asid61]

It looks like you can get the MW1430 for around $55. It has 4 contacts, each rated for 30A... what about running the contacts in parallel? This is something I would want to ask the GDC before implementing, but running 12 gauge wire up to the slip ring, splitting each wire across two connectors in the slip ring, then combining them again when you go into the CIM motor. It would be an interesting way to get around the 30A limitation! Not really convinced the GDC would think it legal, though.

Probably not the GDC's cup of tea, I would imagine, but for something like a turreted shooter that would be really handy.

EDIT: As a side note, to date I have not found a non-coaxial or coaxial design lighter or more compact than 1323's coaxial design this year last year. It integrates many parts together that cannot be integrated on a non-coaxial, so it saves a lot of weight and space. The only issue with it is how to add encoders, and that can easily be solved by using an AMT-103 on the CIM shaft or a gear tooth sensor on the CIM pinion.

[InFlight]

It looks like you can get the MW1430 for around $55. It has 4 contacts, each rated for 30A... what about running the contacts in parallel? This is something I would want to ask the GDC before implementing, but running 12 gauge wire up to the slip ring, splitting each wire across two connectors in the slip ring, then combining them again when you go into the CIM motor. It would be an interesting way to get around the 30A limitation! Not really convinced the GDC would think it legal, though.

R50 Branch circuits may include intermediate elements such as COTS connectors, splices, COTS flexible/rolling/sliding contacts, and COTS slip rings, as long as the entire electrical pathway is via appropriately gauged/rated elements.

Seems like it would be legal with 12 AWG elsewhere. The downside is there would be no contacts available for any kind of speed measurement for a motor on pivot swerve.

I spent sometime looking at these, and decided a coaxial swerve was a simpler approach from my viewpoint.

[Jon Stratis]

R50 Branch circuits may include intermediate elements such as COTS connectors, splices, COTS flexible/rolling/sliding contacts, and COTS slip rings, as long as the entire electrical pathway is via appropriately gauged/rated elements.

Seems like it would be legal with 12 AWG elsewhere. The downside is there would be no contacts available for any kind of speed measurement for a motor on pivot swerve.

I spent sometime looking at these, and decided a coaxial swerve was a simpler approach from my viewpoint.

The question is... Are two connectors each rated for 30A, placed in parallel, gauged correctly for a 40A branch circuit? I could make an argument in either direction. It really would need a GDC ruling on it through the Q&A.

[efoote868]

The question is... Are two connectors each rated for 30A, placed in parallel, gauged correctly for a 40A branch circuit? I could make an argument in either direction. It really would need a GDC ruling on it through the Q&A.

And next year's rules around the electrical side could very well be different. :p

[InFlight]

The question is... Are two connectors each rated for 30A, placed in parallel, gauged correctly for a 40A branch circuit? I could make an argument in either direction. It really would need a GDC ruling on it through the Q&A.

It would be good to see an official Q&A ruling.

I would suggest a reference to NEC sections 310.10H and 310.15(B)(3)(a) as guidance to amperage rating of using parallel conductors in a slip ring module.

For a Four Conductor Module you should be approved for 80% of the conductor amperage rating of each individual wire pair, provided they are same overall length.

Thus with two + two of the four conductors in parallel, the Rating should be = 2*30A*0.8=48 amps

[jvriezen]

The question is... Are two connectors each rated for 30A, placed in parallel, gauged correctly for a 40A branch circuit? I could make an argument in either direction. It really would need a GDC ruling on it through the Q&A.

There is a safety concern in using two connectors. In normal motor circuits, if a wire comes lose, current stops flowing (until the loose wire shorts to the other side of the circuit and trips the breaker). If a connection breaks loose to one of the slip ring connectors, you now have 40A going through the 30A remaining ring -- and things start to heat up -- the slip ring conductor is your breaker, and not a very good one :(

I'd think that overloading a circuit due to losing half the conductor might have more danger than the lower risk of suddenly shorting something and blowing a breaker immediately.

Disclaimer: I am not an electrical engineer nor an electrician. I occasionally play one on CD. And when inspecting robots, sort of...

[InFlight]

There is a safety concern in using two connectors. In normal motor circuits, if a wire comes lose, current stops flowing (until the loose wire shorts to the other side of the circuit and trips the breaker). If a connection breaks loose to one of the slip ring connectors, you now have 40A going through the 30A remaining ring -- and things start to heat up -- the slip ring conductor is your breaker, and not a very good one :(

I'd think that overloading a circuit due to losing half the conductor might have more danger than the lower risk of suddenly shorting something and blowing a breaker immediately.

Disclaimer: I am not an electrical engineer nor an electrician. I occasionally play one on CD. And when inspecting robots, sort of...

The specified current carrying capability of wires is highly derated vs. their actual capability at room temperature conditions. (Likely 2x or more). The National Electric Code is very conservative, and it permits parallel power feeds.

The CIM motor is wound with magnet wire that is a very small fraction of the circular mills of either a 30 or 40 amp wire. The internal brush connections are not that large either. If you provided a constant 40+ amp load to a CIM motor with 30 amp wiring, the CIM motor would in all likelihood be the first source of failure. It simply can't reject the heat fast enough.

[DonRotolo]

Could you power such a CIM through a 30A breaker and thus be fully compliant?

[InFlight]

Could you power such a CIM through a 30A breaker and thus be fully compliant?

R48 allows Motor Controllers with "Up to 40A" Circuit Breakers. Thus a 30Amp breaker would be compliant when paired with a 30A rated slip ring.

The problem is a 30 amp breaker has much less margin when you get into a pushing match and are monetarily drawing high current. Same could happen running into an obstacle during autonomous. The stall current of a CIM Motor is rated at 131 Amps.

Might be fine depending on the game; but I have no experience running a CIM with anything but a 40A breaker.

[pwnageNick]

Jon brings up an interesting point, and it would definitely have to go to Q&A to get a definitive answer. However based on past rulings my guess is they probably wouldn't be huge fans. Also the 4-channel one still gets quite bulky and thus probably not worthwhile.

If they were to ever allow custom slip rings, our team has worked on a design in the past.

You can reference this thread (http://www.chiefdelphi.com/media/photos/38268) to see the original version we actually built using the CIM brush assemblies from inside the motor.

We later refined the design using the brush assemblies from BAG motors, which made for a much lower weight per module, and much smaller footprint (2" dia. x 2" height). It also integrated an absolute encoder mount for the steering onto the slip ring which was convenient.

Here is the link to the CD thread for that: here (http://www.chiefdelphi.com/forums/showthread.php?t=130637)

And here is a direct link to an imgur gallery of it: here (http://imgur.com/a/o5s4d)

While I wish that someday FIRST could make safe custom electrical applications legal, I don't see it happening any time soon.