Canburglar Safety

FIRST General Forum
#1

As noted by Frank in his recent blog entry canburglars have the potential to be dangerous. We need to make sure to reduce or eliminate the danger of these devices.

We insert a steel pin into the linkage that drives our burglars when the robot is on the cart, and the pins are tied to the cart so they can’t be forgotten before a match. We also unplug the motors when we know we won’t be using them for a while, in case somebody forgets to put in the pins.

What is your team doing to make your canburglars safer?

Has anyone had an inspector bring up a canburglar safety issue yet?

#2

I’d like to address the elephant in the room…
Many teams are now competing quietly, in the background, to build the world’s fastest canburglar.

We all know that the guy next of us is trying to go faster. So we go faster. We know that he knows that we know he’s trying to go faster… so we go even faster. We know that he also knows this…

We all know the solution at a certain point comes down to energy. How much energy? More. More, and more, and more.

Are these high energy, super fast canburglars safe?
Depends who you ask. Safe is not quantifiable. Safe is not defined in the manual. Safe is relative.

However… safe is required for legality.

G1 ROBOTS whose operation or design is dangerous or unsafe are not permitted.
VIOLATION: If before the MATCH, the offending ROBOT will not be allowed to participate in the MATCH. If during the MATCH,
the offending ROBOT will be DISABLED.

The blue box clarifies:

Examples include, but are not limited to:
A. Uncontrolled motion that cannot be stopped by the DRIVE TEAM
B. ROBOTS arms “flailing” off the FIELD
C. ROBOTS dragging their battery
D. ROBOTS that consistently extend outside the FIELD

All Canburglars must be “safe” to be allowed to compete, however “safety” is only loosely defined.

Who will determine which canburglars are safe?
How will this standard of safety be fairly and equally applied across all canburglars?
Will the World Championship be determined by an inspector’s subjective decision that 118’s canburglar is safe, but 254’s isn’t?

-John

#3

Our canburglar is held, when not in use, by two 60 lb pull neodymium magnets on each arm, plus a mechanical lock that engages once the arms are fully retracted. The motor is physically incapable of pulling the arms just off the magnets, much less off the magnets and out of the locking mechanism. We feel that, since it takes two people to even pull the canburglar from its rest position (and it has already been tested through the rigors of slamming repeatedly into an alliance wall to dislodge a stuck tote), it’s a near-impossibility for it to fall and injure someone out of the blue. The hooks also rest inside our frame perimeter, despite an optical illusion that makes them appear far outside it, so there are no similar concerns of people standing up into them.

The only concern is to keep phones, computers, and buttons away from the magnets! My driver button was attracted to them, pulling my shirt with it, from around five inches away and I was convinced I’d gotten myself hooked on something until I looked more closely.

#4

Safety is a very important aspect to always keep in mind, and each game has an aspect that is “dangerous”. In 2013 someone at MSC took a frisbee straight to the face from looking into his robot’s shooter.

2013 and 2014’s games seemed questionable to me in regards to safety. Shooting hard frisbees the entire length of the field? Robots high on a flimsy pyramid? Throwing a giant ball at average head height? Those all came to mind, and unfortunately some people were injured.

When it comes to canburglars, the goal is to slam a small hook into the opening (or reach around the back), and drive forwards as fast as you can.

As an inspector, I’ll be looking for ways to safely secure and disarm your canburglar. You don’t want them to accidentally fire right onto a team member.

Another thing that’s been a staple for robot design is to make sure none of your appendages have a pointy or sharp element to them, usually less than 1 square inch in area.

Finally, I would reccomend designing a “fail point” in your arms so if they do interlock with another team, they can safely break rather than exploding pieces into the crowd or other robots. Having a controlled failure is always better than an uncontolled burst of parts.

A piece of advise I would give to drive teams setting up is that if you know your robot and an opposing robot are going for cans, and there’s a chance that you’ll interlock, try to go for a different set. The earlier video on CD was a glimpse of what’s to come for future can battles.

#5

Chris,
Thank you for proving my point.
Are you the person in charge of judging whether canburglars are legal in STL this year?

Are we using the “Loose Screw” standard of canburglar safety? Or is there a different standard?

#6

So you made your arms safer by instead introducing a pinch point that would destroy whatever appendage happens to get caught between them?

#7

Not at all. This will be my first time inspecting actually. Your point stands strong; safety is relative. I think the head refs should take a good look at these mechanisms, but it ultimately relies on teams’ judgement when designing. If you build a mechanism that moves at high speeds with sharp hooks without at least 2 safety latches, don’t be mad when the inspectors fail you.

I like the single hook grabbers the best because they can be built with easy failure points. That and there’s less to get tangled with compared to a bar-behind-RC grabber.

#8

I’d say that 99.9% of launchers last year were more dangerous in terms of serious injury than most can grabbers we will see at champs this year.

What if the system is powered by a motor? A disabled or unpowered robot wouldn’t need safety latches in my opinion.

#9

That is true. However, if there’s stored energy involved (surgical tubing, springs, ect), I would reccomend a safetly latch. That latch could be as simple as a zip-tie that you’ll cut after you’re on the field.

#10

Drivetrains tend to use motors, but safe teams put their robot on blocks in the pits (or integrate such blocks in their cart). None of your programmers have ever accidentally started the robot in practise mode and run auton without intending to?

I’ve never inspected or reffed, so I don’t feel comfortable categorically saying you should have a latch of some sort, but it’s just seems like good safety sense to include one if your mechanism is using that much energy.

#11

There have not been issues with pinching. If there is a finger or a hand in the way, the distance between the two magnets is enough to significantly diminish the attractive force between the two magnets. As one of the drivers who sets it up on the field, I did have the magnets attempt to pull together with my hand between them before I managed to set up our drop away. It was about the same amount of force as a gentle handshake. The force gets much stronger as the magnets get closer to each other, and equally decreases as the distance increases (I believe at a rate proportional to the cube of the distance, if memory serves me correctly). By the time the distance is great enough to fit a finger or hand between the magnets, the force is weak enough to be a non-issue. Just don’t try to be funny and put your earlobe between them or you’ll get a good pinch.

EDIT: A little research on the University of Illinois website appears to show that the strength of two magnets acting upon each other will fall off proportionally with the distance to the fourth power (read the second answer given). https://van.physics.illinois.edu/qa/listing.php?id=419

The reason the pin was attracted from a greater distance is because it’s quite light. I would agree with previous posters that robots from other years carried greater risks in terms of danger. My team’s robot from 2014 used four linear composite springs with 80 pounds of force each to propel the ball, and our 2013 robot climbed all the way to the third level of the tower. Both of those represent much greater potential for bodily harm than two properly managed magnets on our canburglar device to prevent it from breaking loose.

#12

On the software side of things, if we wanted the driver to control the canburglars we would have them press two buttons simultaneously to raise and lower them. This is so they can’t accidentally bump the button and have them triggered. It’s a bit safer than just one button, especially on the practice field when lots of people are around. Also before we enable we make sure we are in the right mode and people are clear of the mechanism.

#13

Extending that argument, then all motored system should have safety latches and/or pins.

I don’t think that’s a good solution.

#14

I think we are in a Canburglar Cold War right now. We know the other side is working on making nuclear weapons, so we have to make more nukes, and come up with better ways to deliver them.

The current trends in speeds make me think that pneumatics and motors will soon be, or are already, not going to be fast enough to win the Canburglar war. Stored energy in the form of springs is naturally the next thing to turn to. Unfortunately, I believe that these spring loaded designs are going to lead to much more dangerous situations.

Another thing that the cold war analogy brought up to me was the idea that cheesecaking=nuclear proliferation. If you are a third alliance member, you may have to choose if you want to put a potentially dangerous device on your robot.

I have already decided on the level of energy that I am comfortable with: if we miss the hole and our hook punches through the trash can lid, we have too much energy and have to dial it back a bit.

#15

He said “disabled or unpowered” - so why would the robot be moving? This is a distinctly different situation than what you’re describing, which is accidentally enabling in auton instead of teleop.

#16

One could quantify the safety of these mechanisms by measuring how much force they can produce…but you’re absolutely right. I’m waiting for teams to go back to winches like many shooters last year had, if they haven’t already. One could impose a limit to how much potential energy can be stored upon loading a robot onto the field maybe?

Oh lord, at an open house 2 years ago we were demoing our robot. Something happened and it started our vision assisted autonomous. The vision system tracked metal picture frame about 20 feet away, auto lined up to it and nailed it perfectly with all 3 shots, shattering the glass. The principle was more impressed than upset. There’s a video of it somewhere…

I think if there are no limitations to the amount of potential energy allowed while loading, teams will be able to at the start of autonomous release their winch design and start driving forward at the same time and still get them.

I anxious to see if there will be a gentleman’s agreement at the highest level in which each team gets two center bins, but that most likely won’t happen. Citrus Curcuits, 1114, 2056, 254, 118, and many other elite teams will allow for einstein teams to have 2 canburglar robots and a 3 tote autonomous robot.

#17

I think the danger is different this year: tip speeds are going to be much faster in general, because can burglars are usually long. From the videos I have analyzed, several canburglars go faster than 18 m/s ~40 miles per hour].

Canburglars also tend to reach out much farther from the robot that launchers did.

Last year our ball shooter used 4x 180N ~40lbf] constant force springs, but our motor powered can burglar still concerns me more because it deploys a somewhat sharp metal hook at high speeds about 1.8m ~6 feet] from the robot.

#18

Obviously it’s a matter of degrees. Most motored systems aren’t moving that quickly, don’t have that much kinetic energy. These canburglars honestly seems more dangerous to me than a robot driving full speed. Compare those to an actuating tote-grabbing mechanism. You don’t think the average inspector can tell the difference?

Show me a robot that has an ultrafast canburglar and is always disabled or unpowered when it isn’t on the field.

#19

What we are making inherently is not safe. If making robots was a safe thing to do then we wouldn’t have so many rules. In my opinion if your design is justified then safety in that situation is not only making the design as safe to handle as possible, but it also includes being around it. Securing springs, monitoring air pressure, safety isn’t just making things not hurt, its about stopping the situations that get people hurt.
This is from the experience of having a can burglar on our robot that straight up scares me and being in charge of field reset for our teams drive practice.

#20

Assuming you use one of those constant force springs: the torque would be 332.77 NM (that’s metre), or for Americans: 1.2652092 x 10^-13 ounce-lightyears (running joke at my university, "how many ounce lightyears is that?)