Re: Looking for slip rings and distributors
 

That's why I qualified it with knowingly. The tense you used I thought meant to imply that teams may do it in the future after parts are (possibly) declared illegal.

I also will give you that cheating might be a strong word to use there. I play a lot of Magic the Gathering, and at competitive levels doing something knowingly illegal is classified officially as Cheating :)

Re: Looking for slip rings and distributors
 

I know of at least one team that used them and DID disclose their use to inspectors.

Re: Looking for slip rings and distributors
 

Message received.

I do not think a team that used these in the past was cheating. They read the rules one way or didn't consider the interpretation I am making in this thread. This is quite common with parts that are not used on a lot of robots. Inspectors who don't know an item on sight alone may or may not ask for identification or description. FRC teams make some great robots so it follows that those teams will try and find an advantage in using a COTS part that someone hasn't thought of using. Even inspectors with a fair amount of industrial experience may not have seen some of these items. Inspectors with little experience may not recognize some of the things LRIs are trained to look for.
For an interesting story...A few years ago at an LRI training weekend in NH, we asked teams to supply a few robots for our training purposes. One of the group activities was to walk through a typical inspection process with me. I showed them how I interact with the team, how i use the Inspection Checklist to work through the robot and how I attack individual systems separately so that I get a look inside the robot for several different items (mechanical, electrical and pneumatic). As I was "working the list" I looked down and noticed an illegal item on the robot. I asked if anyone saw a problem and only one of the LRIs in training caught it. It was a good training day for that reason.

Re: Looking for slip rings and distributors
 

I didn't say you couldn't spill mercury by breaking these. I said that there probably wasn't much to spill. (In other words, it's a question of the magnitude of the hazard, rather than the existence of the hazard.)

I'd previously referred to that documentation, and I don't believe it explained that difference. Can you elaborate on why these are in one category, but not the other?

If a fluorescent light above the field were to shatter, surely the amount of mercury released and its state would be considered when choosing corrective actions. Why is this different?

In terms of assessing risks, even if a prohibition exists, inspections won't catch everything, and force majeure is still a possibility, so event staff may still be in the position to decide whether a chemical hazard justifies (for example) suspending the event. It's fine to set zero mercury contamination as a target, but it's unreasonable to suppose that contamination is inherently unacceptable, irrespective of degree.


I think the best action is definitely to communicate it to FIRST, so that they can decide what risks are acceptable and codify prohibitions and procedures accordingly. It's crucial to do so in a way that educates FIRST about the hazards without sensationalizing them, because there are important considerations other than safety which must be weighed realistically. If we expected to be completely safe, we probably wouldn't attend competitions where robots fling balls around—so perhaps the thresholds of risk due to chemical exposure should be evaluated against that sort of benchmark.

Re: Looking for slip rings and distributors
 

If this has already been mentioned in this thread, please forgive me, I didn't see it.

Funny timing here. Sparkfun just announced yesterday that it was introducing slip rings into it's product offerings. They are offering 3 versions: 12 wire (2 A), 6 wire (2 A), and 3 wire (15 A).

While none of these carry enough current for drive-train motors, they do provide serious potential for some very interesting mechanisms.

Re: Looking for slip rings and distributors
 

Tristan,
Mercury wetted contacts have mercury droplets in them that pull together when the contact is closed. They do not form the only conducting surface in the contact but they do make the resistance of the contact low and are especially useful in very low current applications where surface contaminants prevent good contact. These often are in the form of a relay and require specific mounting attitudes to work. These were common in low power microwave applications and in video switching prior to reliable electronic switching.
In mercury contacts, the mercury is used as the contact. Mercury bulbs in thermostats are this type. In these applications, all current flows through the mercury. Such is the case with the rotating device under discussion. The temperature of the mercury is proportional to the current flowing through, much the same as in wire. Arcing within the medium also raises the temperature (significantly) which is true of the switched load used with PWM speed controllers feeding brushed motors.
In comparing the amounts of mercury in these contacts to that in a fluorescent bulb, I believe there is no comparison. The contact will have far more. In the case of the bulb, mostly in a gaseous form.

Bilbo,
The transformers you link are the type that have been used for years on video recorders to link the record and playback heads on rotating disks to the electronics. A good application for these would be sensors and perhaps PWM signals. Please be advised that these carry specific RPM limitations and a finite life. Exceed the RPM and the contacts become intermittent. The brush assemblies are often multiple (3-5) pieces of fine wire in contact with the rotating mechanism. As the RPM increases, the wires become air born and cease to conduct. Low RPM applications are ideal. The lifespan is dependent on the wear of the wires. VTR manufacturers made these assemblies a repairable/replaceable item.

Re: Looking for slip rings and distributors
 

For 2015, it's in the manual, and illegal.

Re: Looking for slip rings and distributors
 

I'm very appreciative that FIRST and the GDC eliminated this ambiguity. This is a great example of them listening to community feedback.

Re: Looking for slip rings and distributors
 

I couldn't agree more. Reading through the manual this year, it looks like they really listened to the community about problems (like this ambiguity), but also opening up motors to unlimited quantities, and overall giving more flexibility. I don't read any of the rules and ask "but why?!?" I think they're all very reasonable rules.

Re: Looking for slip rings and distributors
 

A piece of equipment I service used to use the Mercotac connectors, had one blow during a fault. The plant's Hazmat team got to put their mercury cleanup procedure to use.

Had that been at an event somebody would probably have gotten a bill for cleanup.