Safe Mechanisms in 2014

Sanddrag brought this up in another thread, and I think it’s a discussion worth having. I feel this year has a significant potential for teams to show up at events with unsafe mechanisms. It takes a reasonably large amount of energy to launch the ball, and the more inefficient your mechanism is, the more energy it takes. I would wager there is also correlation between teams with inefficient mechanisms and teams likely to build less safe mechanisms. On top of that, this year there is no easy way out if your team wants to score truss points or in the high goal. In 2008 if you didn’t feel safe or comfortable launching the ball, you could build an elevator or arm. In 2010 if you didn’t want to kick, you could always push the ball into the goal. This year if you want to do the cool task, you’ve got to launch the ball.

Is there a precedence for ruling a robot ineligible if the lead robot inspector feels it is unsafe? Obviously the rules say that they can. In my years of FRC I’ve seen many teams be asked to install additional shields and safeguards, but I’ve never seen a team told they couldn’t play. If a LRI has to make that call, I do not envy them.

I like the suggestion, but I’m not sure if it’s possible to come up with a universal standard of safety as Sanddrag suggests. Some things just make you feel uncomfortable even if they meet the letter of the law, and it seems to me that those things should not be given the opportunity to injure people.

I totally agree that this needs to be a separate post by itself because it is an important topic that needs to be addressed.

I think one of the biggest issues will be with that of teams building inefficient robots that require a lot of power. This will cause teams to use much more motor power or larger springs or any of a number of things that will cause more stress and tension on the robot that can prove dangerous for the robot or anyone around it. I think the LRI will have to determine whether or not too much stress is being put onto a system for it to be safe, which can be difficult and most likely will not be done because trying to guess how the robot will be affected by stress over time is hard to judge and LRI’s will be hesitant to keep robots out of action on a hunch.

That being said I don’t think that teams have to be fully disqualified if their shooting mechanism is deemed unsafe. I just think it would mean that they would either have to provide some form of safe guard, lower the power in the system if possible, or disable that part of the robot and just be a straight passing a defensive bot which is a very viable option for this year.

Unfortunately, I have to agree with the first part, and disagree as well. My thought is that some inspector will raise the concern first, and the team won’t agree (trust me, I’ve seen that a few times on CD), thus forcing the LRI to get involved. Depending on the LRI’s best judgement is about the only thing available. We’re just going to have to hope and pray that their experience pays off here.

The second part I fully agree with–no team will be removed from competition unless their robot cannot be made both legal and safe. Refusal to make the robot legal, I’ve heard of in the past. Refusal to make it safe, or to disable a mechanism for a match so they can play and then work on a fix, I don’t think I’ve ever heard of.

I understand that they’ll be allowed to play minus the offending mechanism, it’s just going to be a very upsetting day for both the team and the inspectors if they have to disallow something. :frowning:

How many teams pass inspection really depends how the robot inspectors want to play it. I’m sure that given some adequately stupid “safety” requirements (ie, no injury sustained if team members hands are in the mechanism when it is dry fired), we’d see 90% of teams fail inspection. On the other hand, a more reasonable requirement (IE, that the mechanism can be dry fired without causing any damage, has a reasonably robust and reliable firing system, and that the thing looks strong enough not to self destruct in the first match) will result in all but the most flagrantly unsafe teams passing inspection.

IMO, the best standard would be this: there is a reasonable expectation that the mechanism will not fail catastrophically, and that the team has worked to mitigate injuries that could possibly be sustained from a mechanism that did fail catastrophically. For example, a spring just waiting to be shot into the crowd at high speeds from the smallest bump would be unsafe. A properly tied down spring which would be confined to the robot if it did fail would be considered safe, and pass inspection no matter how much energy it stored.

I can answer some of these concerns. Be aware that not all designs will fit all parts of this discussion and the event LRI still has the authority to rule something “unsafe” when they are examining the individual robot. As always, the Q&A is the final authority and the inspection staff will inspect as directed by the GDC and the official Q&A.
As far as launch mechanisms in general, a safe device will only launch the ball and nothing else, EVER! This is the basis for inspectors to see what happens in a dry fire situation. Often a launch mechanism unloaded acts much differently than when a ball is in place. We don’t want and cannot allow, a mechanism that appears as if it can launch pieces of itself into people standing near the field or in the stands. Additionally, we do not want to see launch mechanisms that can trigger accidentally anywhere in the competition venue. That holds true for the queue, near or on the playing field, the pit, or during inspection.
As to general areas that are under scrutiny every year…

  1. Surgical tubing needs to be securely fastened to the robot so as to not pull out under tension and cause harm to those close by.
  2. Springs are of concern under certain uses where shock is caused to the spring during the firing period. This shock may cause cracking or other metal fatigue. A common method in this case is to string aircraft cable through the spring. Should the spring fail, the broken parts will generally be restrained by the cable. COTS springs that are used without modification (i.e. are not cut, ground or heated, etc. by the team) are generally acceptable. A garage door spring (generally not appropriate), cut to length by the team for example, is suspect to fail.
  3. Pneumatics when used for launch mechanisms must conform to all pneumatic rules. That means any stored air pressure must be provided by the one and only one robot compressor. Should a system be capable of causing a rise in working pressure as a piston is moved, then the increase in pressure must escape through the required, pressure (Norgren regulator P/N: R07-100-RNEA recommended) relieving primary regulator. At the end of the match, all pressure on the robot must be relieved by the one and only one pressure vent plug valve.
  4. Other parts of the mechanism may be subject to considerable stresses during a firing sequence. As such, parts held together with unsuitable fasteners will be questioned.
  5. There has been some recent answers in the Q&A that relate to the above, please review and apply as needed in your design.
    I can tell you that inspectors are very excited about seeing some of these mechanisms actually play this year. This kind of game really brings out the creativity in design. We want to see you play but we are serious about safe play and operation. Please remember safety when testing your mechanisms at an event especially in the pit.

Seems like a sensible answer Al, and I think my own team will be in the clear, because we’ve done our homework on the calculations. My experience with the safety inspectors was actually very pleasant during the past two competition seasons. I’m looking forward to demonstrating that our device will not break itself, misfire, or harm anyone.

Al -
If there are safety devices built into the device, both hardware and software, that prevent firing unless there is a ball present, will the team still need to dry fire during inspection?

If there is a concern, I would expect that the inspector would like to see the test or at a minimum examine the safety measures.

I agree with everything that Al has said, and I would like to expand on this statement from Al. The LRI’s at the events are not just concerned about the safety of the robot on the field, though this is important. Generally, the field is a safe place due to the distances that the robots operate from the humans around it. The key areas that we are concerned about is when the robot is within close proximity to people, which is when it is in your pit, when it is being pushed around the venue, and when it is in queue. To help you out, here are some things that LRI’s will be concerned about:

  1. Make sure that the mechanism cannot unintentionally fire, while sitting still or when in transit.

The amount of force that is required to fire these balls and the possible size of the launching mechanisms will be a concern. An unintentional firing can cause serious damage to a person nearby, or inadvertently tip a robot possibly causing it to fall off a cart onto somebody nearby. Make sure that you have some sort of way to either release all stored energy, or safely contain it so that a single point failure will not cause an inadvertent firing, such as locking pins, straps, etc.

  1. Check the weak links within your system, and also have spares handy.

Due to the large forces that may be required to propel the ball, there could be a massive amount of stress experienced by the springs, surgical tubing, bungees, etc. that are powering the firing mechanism. First of all, never “modify” COTS springs. Even small defects in a modification could cause a catastrophic failure due to fatigue. Attachment points should also be looked at since those are sometimes the week link in the system. Make sure you have appropriately tied down, crimped, knotted your bungees or surgical tubing. Any springs, surgical tubing, bungees, etc. that are frayed, chewed up, noticeably kinked, etc. will also be looked at very hard throughout the event. If we see any damage that may be done to your firing mechanisms, we will ask you to fix it for your own safety and the safety of people around the robot. Also, it will make sure that the robot still works during the competition.

  1. Make sure that the stored energy is contained if the robot decides to “spontaneously disassemble”.

Even if the best attachment points are used, with new springs, surgical tubing, bungees, etc., bad things can happen. Manufacturing defects can cause catastrophic failures of these energy storage devices when they are under load. To make sure that your robot does not create any whips or missiles, take the time to try and make sure that a catastrophic “spontaneous disassembly” of your robot is contained to the robot. You can fish a safety wire down the center of a spring to make sure if it breaks it will not fly out of the robot. Make sure that surgical tubing or bungees are buried inside the robot, so if they break, they will rattle around in the robot and not whip outside the robot. Any stretched and fully exposed surgical tubing or bungees will be looked at for further consideration. The team may be asked to add a few structural members to make sure that if they snap they will not fling outside of the robot.

I am looking forward to seeing the awesome designs teams will be creating during this competition. Always be thinking about safety when you operator your robot, not just at the events, but also at home as well. We want to make sure to see everyone on your team at the events.