Breaker placement: What does accessible mean?

In our attempt to optimize our battery to PDH pipeline we want to place our breaker in the center of our robot to reduce the total length from the robot side SB120 to the PDH. R612 states that the placement needs to allow for quick and safe accessibility but we’re not sure how to evaluate whether our breaker position is accessible?

For example, this is where we currently have it in order to make it “accessible.”


I’m not even sure if this counts as being accessible but this position isn’t preferred because of the extra wire length needed to put the breaker here.

What would instead be preferred is if we could put the breaker like this (the gray box is the general area of where we would want to put it).


It would significantly reduce the wire length but we are afraid this isn’t considered to be “quickly and safely accessible.” You would have a clear shot from the back to close this without any moving parts getting in the way but it’s inside of the robot.

So to generalize my question, what do RIs consider to be quickly and safely accessible? Reducing robot side SB120 to PDH distance aids us in reducing the amount of resistance in the system so we’re highkey tryna put it in the center but it’s lowkey not the move to go to a competition and get finessed for our breaker position. Are there concrete guidelines that we can follow to ensure we don’t get finessed for putting our breaker in a position that doesn’t meet this criteria?

Here’s our full system sketch if it helps.

I can ask 30 RI’s and get 30 different answers. This has always been a varying ambiguity among inspection experiences. I’ve had the requirements change on me more times than I can count. Some say you have to be able to hit it with a falling 2x4 (wide side), some say the same but thin side is okay, some say you shouldn’t need to reach your hand inside the bot, some say it can be upside down, some say it can’t.

You’re gonna get a lot of answers here - some of them are probably gonna be good advice, but unless your specific inspector comments on this thread and tells you what they’re looking for, you’re probably going to be left just as clueless as the rest of us.

4 Likes

I’d definitely say no but I’m not a RI.

I’d move it to an L bracket here. Maybe also make a guard so the belt is harder to touch.

We have placed our breaker in a similar position and passed inspection before.

Do I need to reach inside of/under/through a moving mechanism? Do I need to reach around something with exposed moving parts, like a gearbox?

You’ll find that “accessible” isn’t well defined anywhere, so it becomes a bit of a subjective decision. The real question you should be asking yourself - if the worst happens on the field, would you prefer the volunteers be able to turn your robot off quickly and easily, or sit back and watch it tear itself apart?

From the pictures, I would say it’s probably not the best location, but also not the worst I’ve seen. Something as simple as rotating it 90 degrees and raising it up a few inches would likely make it much more accessible.

3 Likes

slight caution on that. Even though extending into someone else’s frame perimeter isn’t encouraged, that makes for an easy “off button” that might get smacked while in some heavy defense.

I’d also mount some polycarb nearby to prevent accidental shut-offs, and/or roll the dice and keep it a bit more buried in the bellypan.

In our experience, as long as it can be easily reached by a human (IE, doesn’t require removing panels), and is clearly labeled, it takes a really crotchety robot inspector to not pass inspection.

Fair enough. Revised a bit. Just make a square stand off with a smallish hole cut out to turn it off. Buried where it is just seems inconvenient all around. So something like this.

1 Like

Much easier to use a 120A Breaker Shield - just download and print it!

2 Likes

Our plan is to use these to protect the breaker from game pieces/external factors.

This makes sense. Ultimately, I’m curious as to how we can use the rules to ensure that we don’t fail inspection because of something like this? The surefire way is to place it on the side or something but that’s even more unideal in terms of reducing system resistance. There’s a balance somewhere–I’m just not sure what it is and how to ensure that we don’t fail an inspection in the process of pushing the limits of what the rules allow.

Correct me if I’m wrong but I thought the Emergency Stop button was used to stop the robot? I understand the difference between powering off the robot and stopping it but I can’t imagine a single breaker configuration that a volunteer could use to power off if say the robot spinning around like crazy. What are some possible reasons as to why manual power offs happen?

2 Likes

Failure redundancy. What if the e-stop doesn’t work for some reason? What if there’s an electrical short that needs to be cut off (as your robot sits there on fire)? It’s not like the emergency-off situation happens very often, but when it does happen, you really want it to happen quickly in most situations. I’ve seen big clouds of magic smoke come from a robot before, and we’re going to make sure power is cut before anything else happens with that robot!

1 Like

in theory is the critical modifier to use.

E-STOP relies heavily on the FMS itself, plus the wifi communication, plus some assumptions on the robot side to fully work. Even when activated, it only issues software-driven commands to stop motors, it won’t eliminate electrical faults which are (potentially) starting fires.

So, you’re not wrong, but there’s more aspects to “safely shut down the robot” than the FMS E-STOP.

2 Likes

330 got away with some of the most absurd main breaker placements a few times. I think this was mostly due to inspectors not fully thinking through the scenarios where the breaker might need to be accessed, and assuming we knew what we were doing.

We never got called for any of these afaik (never had to move them anyway), though ymmv ofc. I would advise against doing this; usually we were optimizing for total battery wire length, especially any that counted against robot weight.

2016:


Robot arm falls on human arm

2018:


Wrist sprocket crushes your hand. This honestly might be the safest spot short of running up to the side of the elevator, as all other sides of the robot are more dangerous to stick your hand in.

2019:


Wrist sprocket crushes your hand again.

These are all “accessible” in the sense that the powered off robot can be easily manipulated to get to the breaker quickly. Powered on with the arm/elevator being actively driven down? No dice.

My advise is be prepared to move it, but don’t let the inspector know that. If you put a good-faith effort into careful breaker placement don’t worry about it too much.

3 Likes

As other have said, this is an area where you get a wide range of opinions between RIs/LRIs. Rule R612 says that the main breaker “must be quickly and safely accessible from the exterior of the ROBOT”. For me, there are four criteria:

  • I can find the breaker quickly. Stickers with arrows or a brightly-coloured surround would help with this.
  • The breaker is accessible without removing any access panels.
  • I can see the breaker clearly in order to press it. This means that a breaker mounted on an interior surface that I have to feel for and press blindly (or stick my head inside the robot) would not qualify.
  • I can press the breaker without putting my hand near moving parts (e.g. a climber or an intake).

In particular, it is not necessary that the breaker be easily pressed by accident. I encourage teams to use shrouds.

I would like to provide a little guidance here for both teams and RIs/LRIs that may be reading this thread.

First off the main breaker needs to be ACCESSABLE but should not be VULNERABLE. That is it needs to be placed in a location that someone unfamiliar with the robot (field staff) can quickly locate and shutoff the robot in case of an emergency. It should not be placed so accessible that it gets shutoff accidentally during the course of regular game play by a flying/falling game piece or regular interaction with other robots.

Questions to ask yourself when placing the main breaker:

  • If I was a stranger to the robot (not someone on the team intimately familiar with it) would I be able to quickly locate the breaker? The more obvious you can make it the better.

  • Is the breaker located where someone has to stick their hand in/through/around/under/near moving mechanisms (arms/gearboxes/chains/etc.) to access it?

  • Is there excess wire runs that could be reduced while also accomplishing safely accessible while not exposing it to being vulnerable to being accidentally tripped?

This is how Al and I train the LRIs and expect them to train their RIs. I don’t know where the reference to 2x4’s came from above but that is certainly not part of the training nor any sort of official “accessibility” standard. We have considered all sorts of alternate wording of R612 but the reality is every robot is different so the rule is subjective. It would be impossible to define a standard main breaker mounting criteria without restricting other aspects and I don’t think anyone wants FIRST specifying exactly where the main breaker needs to be on every robot. So it is left to the judgement of the teams and inspectors. This requires a balance. Somewhere between “don’t burry your main breaker deep inside the robot where someone unfamiliar with your robot can’t readily locate it and access it” and “don’t put it so open on the perimeter of your robot that it gets accidentally tripped by game pieces or other robots or driving into field elements”. Obviously, no matter where it is people shouldn’t have to stick their hand into/through/around/under/etc. parts of your robot that might cause injury. Keep safety first but don’t restrict your placement to somewhere that will cause performance issues with long wire runs or accidentally trips. Both the team and the inspectors need to be reasonable and prudent here. I wish I could provide a non-subjective cut and dry answer but, again, the reality is every situation (robot) is different so every breaker placement needs to be evaluated individually.

As others have noted, there are numerous downloadable 3D printable solutions to breaker covers out there that I highly encourage teams to utilize. Printing one of those in a nice bright color can aid in making the breaker easily locatable to someone unfamiliar with the robot as well. Of course, big red “Main Breaker” labels, red arrows, etc. are also welcomed and encouraged.

Keep in mind that is field staff need to quickly locate your main breaker and shut your robot off it will by default be in an emergency situation, likely due to a fire. As has been mentioned, the E-Stop should, theory, disable an out of control robot and jumping on a wildly spinning robot to find the main breaker is not something likely to occur at an event. So the main purpose of good breaker placement is for fire. Trust me, you would much prefer the FTA to press the button on your main breaker before a fire gets too big than break out the fire extinguisher on your robot and the field.

5 Likes

When I was an RI for FTC every team was given (and expected to use) a sticker to identify their “main breaker”. Seems something like this wouldn’t go amiss as a future FRC KOP item.

VEX used to include a sticker pack in the KoP, one of which was a Main Breaker sticker

This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.