The Shooter (and Kicker) Saftey Thread

[Matt H.]

Now that teams have decided on their general strategies and are starting to prototype/design it's probably time to discuss how to make a safe mechanism.
My comments are based on my experiences while a member of team 1726 and are intended to spark a discussion of safe practices. I would also deeply appreciate comments on safety from the numerous professions on this forum.

Note you may be able to make a safe robot while violating some of the below comments there is always some room for discretionary judgments

Also in the below stored energy does not refer to energy stored in the battery or in pneumatic tanks. It refers to energy stored in latched pneumatic cylinders/springs/other elastic deformations/flywheels etc.

General Comments:
--Efficient systems are often safe systems. Using the minimum energy required to complete a task requires less stored energy and produces less thermal energy (smoking motors).

--Be sure to consider how your shooter/kicker performs if it fires without a soccer ball. In this case the energy normally transferred to the soccer ball will need to be dissipated elsewhere.

--Both mechanical and software based fail safes are prone to failure. Be sure to consider what will happen when your robot is turned off.

--Consider how your system will perform after being fire 100 times or even 1000 times? Set clear criteria for when parts should be replaced.

Regarding Stored Energy Systems:
--Mechanisms which store energy in pneumatic cylinders, elastic deformations, and fly wheels tend to be more dangerous than systems which do not. If you can kick the ball without storing energy, kudos to you.

--Systems should be charged/compressed/rotating only when necessary. Robots should not have to drive around the field with "loaded" systems for the entire match. I prefer systems which charge and release in one fluid motion (for example using off center circles).

--If a stored energy system is not in use the energy should bleed off rather quickly. You don't want to end a match with springs/cylinders compressed.

--Warning systems are wonderful. Lights/danger signs which appear when your robot is storing energy should be a priority. Make sure your systems is clear to everyone.

Regarding Latches:
--I tend to be afraid of systems which use latches to hold back pistons or springs. Using a latch invites accidental releases.

--If using a latch use one designed to handle what ever load your mechanism will place on it. I've notice many teams using fence latches to hold back ~300lb loads: this is unsafe. Look into industrial quick releases designed to hold load. Be very careful when modifying latches (something which teams are also prone to do) this could have unexpected consequences later.

--Consider carefully the default state of your latches. Could a referee touching your robot at the end of the match cause the kicker to fire?

--What kind of warning system to do you have when the latch is engaged? How do other teams know?

--Do you have procedure or backup if the latch become jammed?


Well that's all that I can think of right now. Remember be safe and have fun!

[the man]

Good idea safe shooters

[Rob]

I think it is a very good idea to have this discussion. There will be lots of kicker devices that have components modified or used in ways other than they were designed for. In most safety situations you can use PPE or read the instructions and if used properly you can avoid unsafe situations.

When you modify things or use them outside of their design scope AND you are putting them under great stress there is a huge potential for bad things to happen.

Another area to watch out for not mentioned above is what your kicker is going to do after it impacts the ball. It will likely be going very fast and will have to stop abruptly to avoid extending over 2" outside the frame. Some kind of spring device to slow it down after ball impact could make it safer as well as lengthen it's lifespan. Imagine pounding into a hard stop 100-200 times over the course of the season! We have made several wooden prototypes that battered themselves apart after 30-40 shots.

let's all have a safe 2010 FRC season!

Rob

[Matt382]

Thanks for the ideas about safe practices, I will pass this on to my team.

[falconmaster]

Originally Posted by Matt382

Thanks for the ideas about safe practices, I will pass this on to my team.

Thanks for bringing this up, we will have to seriously look at how we can make our bot safe for the refs and other teams...

[DonRotolo]

Great idea, specifically the warning system to indicate a "loaded" mechanism. We have a microswitch that tells the software when the latch is latched; we'll also use that to turn on a light or indicator of some type.

Our kicker does not extend beyond the frame perimeter (if nothing breaks! ); we intend to make it so it's difficult to get a hand anywhere near the moving parts. We also will fabricate a "safety latch" that our drivers and pit crew will carry with them - if the mechanism is armed, the safety bar is installed as a secondary way of preventing accidental firing.

I also like the idea of driving around with the mechanism disarmed - our arming system takes just over 1 second, I can see us re-arming only just before taking a shot, not just after. Not sure about that though.

I also want to consider a way of firing the mechanism just before the match ends (with a ball or dry, no matter) so it's safer after the match. Need to think on that.