Re: Looking for slip rings and distributors
 

These type of connectors were explicitly allowed in 2006

Re: Looking for slip rings and distributors
 

Perhaps you may want to consider changing your mechanical design then. You can still have 2-speed swerve modules without having the CIM or the servo rotate with the module, and thus avoid the slip ring problem all together (along with other benefits). Look at how many previous teams have implemented co-axial swerve modules (1717, 148 in 2008, 973's "emperor swerve", 118 in 2007, etc.).

Re: Looking for slip rings and distributors
 

Regarding Mercotac "slip rings":

They passed inspection in 2008 without any concerns being communicated to our team by any inspectors, and even contributed to the TechnoKats' being awarded the Industrial Design Award at the Boilermaker Regional.

I rarely disagree with Al, but in this case I think his objection is too strong. In my opinion, the hazard of contained mercury-wetted contacts is akin to the hazard of sealed lead-acid batteries. Of course, it's his opinion that counts when determining legality of components, not mine.

Re: Looking for slip rings and distributors
 

Kevin,
I think the GDC changed their mind on that issue later in the season. Alan, I am not aware of the Technokats using those.

Re: Looking for slip rings and distributors
 

We used the Mercotac slip rings all season without issue, including long practice sessions with CIM motors getting extremely hot. We first saw them on Bombsquad's 2013 bot. I saw them on Bombsquad's 2014 bot at the St Louis offseason event, and I saw them on Pwnage's bot at the Rockford offseason event.

We included a mercury cleanup kit in our safety kit. But I see practically no risk of it being released, even in the event of severe mechanical damage.

I was under the impression that mercury was not disallowed by the FRC rules. FTC rules however have specifically disallowed mercury for a number of years (in the same rule as lead is disallowed).

Re: Looking for slip rings and distributors
 

For reference, we did not use the Mercotac slip rings during the season but did test them post season. I also contacted Mercotac years ago and came to the conclusion that we would be running them above their specifications. Mercotac has multichannel units and we could have run multiple circuits in parallel but those get big, heavy and expensive. Ultimately we read the rules to say mercury was not legal and didn't want to hinge a design on that risk. Once we found that Bomb Squad ran the 230's all season with no issues we decided to test them ourselves post season. If First specifically disallows the Mercotac slip rings and lifted the COTS slip ring rule we feel that we have a good alternative in the two designs we've posted on CD. These could be 3d printed by the teams and assembled or if Andy has his ears on... There are also windmill slip rings on Ebay that we have evaluated and would handle the current no problem but they are big and heavy.

Re: Looking for slip rings and distributors
 

I had a look at the documentation for the Mercotac slip rings, and judging by the external design and description, I suspect they have very little mercury inside. Given how catastrophically mercury corrodes aluminum (like the housings), they're presumably designed to resist that failure mode—and the simplest way to do that would be to use just enough mercury to wet two closely spaced parallel plates with concentric traces, and then fill the housing with an insulating oil. (The aluminum housings are anodized, which helps, but likely not enough.) The amount of mercury needed to go around the circumferential contact would likely be on the order of microlitres. Judging by voltage ratings on the larger ones (maybe the small ones don't have oil?), that seems like a plausible method of construction.

If that's the case (and contact with their applications engineers ought to confirm/repudiate it), then we're probably looking at a level of hazard comparable to lead in batteries and soldered components, or hexavalent chromium and cadmium on plated components. While not ideal, there hasn't been a blanket prohibition on other components that contain metals that exhibit toxicity when ingested, and with form factors that permit accidental exposure to the metal.

As for the implications of a spill, I think that would depend a lot on how much information was immediately available about the quantity and toxicity of the substances released, and the stringency of the applicable regulations (as interpreted by the people in charge). If cleanup is necessary, it could be a fairly onerous process requiring external assistance.


As for the contact ratings, check with Mercotac's applications engineers if they are willing to publicly provide duration vs. current ratings, because typically, the failure mode is due to temperature rise. If they compare favourably to the trip performance of the circuit breakers, they may be usable for brief periods in excess of their constant current rating. Similarly, if they can provide ratings that presuppose a reduction in the expected life of the device, but won't cause catastrophic failure, perhaps you could get away with more current. In any of the above circumstances, you'd want an engineer's input to have documentation for the inspectors as to why the figures in the published datasheet are not applicable.

Re: Looking for slip rings and distributors
 

Tristan,
You must have missed my earlier post. I did check with Mercotac engineering, earlier this year. Their response was that mercury spills were a reality when the maximum current or the mechanical specifications (specifically misalignment of the two rotating bodies and excessive vibration) are exceeded. There is a difference between "mercury wetted contacts" and using mercury as a contact. These fit into the latter category. For more info please refer to their literature... http://www.mercotac.com/html/literature.html
All of these documents discuss the need to correctly dispose (must be recycled) of these contacts due to the mercury they contain. In almost every paragraph of the two application sheets, connector failure is mentioned as a danger. In the case of a mercury spills on an FRC field does the amount or cleanup procedure really matter? Any is too much!

Re: Looking for slip rings and distributors
 

Al,

I think the underlying theme of this thread is that the FRC rules have been unclear, at best. It looks like your opinion is clear so please help reduce an obvious Q & A question and use your influence to get the 2015 FRC rules to be clear on this issue.

Paul

Re: Looking for slip rings and distributors
 

In today's regulator environment, Mercury should be avoided period. All of the products that I install have had the mercury removed for a couple years now. My company would not purchase and install any product containing mercury. We go to great lengths to identify products that are removed and replaced that contain mercury. After, removal they are sent to a approved recycler. One must be "compliant". After, the above statement I can't help thinking about the amalgam fillings in my mouth and I made tuna fish salad this week. Ate 4 sandwiches. How can I still be alive?

Re: Looking for slip rings and distributors
 

I emailed the EH&S gurus at my place of business, UTAS, a division of UTC, and they sent me these two links: http://www.epa.gov/mercury/exposure.htm
http://www.epa.gov/mercury/schools.htm

We go through great pains to make sure mercury is NOT in any of the equipment we make for NASA and being used for life support on ISS.

I did take a look at them, I didn't read everything, but ANY product containing mercury being used in FIRST should not be deemed legal. IMHO.

Re: Looking for slip rings and distributors
 

Agreed about the ambiguity. Here's what I've gathered from this thread.

1. The GDC never ruled about these slip rings in 2014, either via Q&A or manual.
2. Some LRI's, who have final authority at the events, have come out and said these slip rings are illegal in this thread.
3. Other LRI's (or RI's) have ruled these slip rings to be legal, as seen by the teams who were allowed to use them throughout the 2014 season.

This is not a good combination, especially when there are safety concerns about a part. There needs to be a uniform ruling on this going forward. We can't have a situation where a key robot part's legality is determined by which Robot Inspector sees it. This leads to a situation where teams who err on the side of safety end and don't use a risky part, end up giving up a competitive advantage to the team who takes the risk and decides to use the part.

Re: Looking for slip rings and distributors
 

Part of the issue is that teams may not necessarily disclose the use of them to inspectors.

Re: Looking for slip rings and distributors
 

Then they are cheating (if they are knowingly breaking the rules)?

Like a lot of things, we already use the honor system on so many things like Bag and Tag, I'm not really sure what you could propose to enforce "disclosure" besides what they write on the BOM and tell the inspector about.

Re: Looking for slip rings and distributors
 

I think "cheating" is a bit of a strong term, in terms of how you apply it. Since these were specifically allowed in previous years, they may not even know they aren't allowed. This is compounded when an LRI acknowledges a team's use of it and passed them.