Re: Al's Annual Inspection Thread
 

I personally do not trust any sort of "aircraft cable" to prevent explosive disassembly in a robot mechanism. We all know that mechanical engineers are allowed to tinker with the robot after inspection, and there is no sort of control in place to prevent the removal of aircraft cable, either intentionally or accidentally.

One characteristic of a "robot" is that it's a system where, if the software fails, hardware will break.

Of course, if the software works, it'll probably break then too, we just won't know who to blame.

Re: Al's Annual Inspection Thread
 

The mechanism for this is reinspections. Any time a team makes changes (which incldues removing components), they are supposed to ask for reinspection, and reinspections can happen at any point in time. I know that I always have my inspectors watching the field and chatting with teams in the queue after we're doing with inspections Thursday morning... this is to give inspectors a chance to notice something dangerous on the robots and then perform an inspector-initiated reinspection.

Re: Al's Annual Inspection Thread
 

Am I missing something here? Our catapult is applying 150lbs over 1/4 sec or so. I assume many people are doing something similar. It does NOT matter all that much whether the 2.75 pound ball is there or not - I think. Why is a "dry fire" all that different from a "wet fire"? The mechanism that stops the motion has to work all the time.

So why not demo a dry fire for the inspector to let him/her see the robot does not fly apart? Ours has a ratchet to prevent back drive and if the motors are disabled it would be difficult to accidentally fire. I don't even get the necessity for a "ball present" sensor - the driver can see it well enough.

Re: Al's Annual Inspection Thread
 

Al,

Thanks again for this annual thread.
I just passed the VIMS RI "test" this morning as I will be a Inspector this year at Davis.

This is the first time I have filled this roll. Reading through this thread always helps a team, as well as Inspectors, prepare for competition.

Re: Al's Annual Inspection Thread
 

Most shooters are going to need the ball to be settled in a specific spot, if that ball is not settle before they try to shoot its not going to go where they want.

Re: Al's Annual Inspection Thread
 

That is for shooters that store energy in some sort of spring. our uses 6 cims in a similar manner to the way Team Boom Done's shooter worked. we fired ours into our hard stop and it did stop it-- it also bent the shooter shaft and took a chunk out of our stop. that is where I have a problem with this. It does not say in the rules your shooter has to be capable of dry firing either.

Re: Al's Annual Inspection Thread
 

Agreed - but that is not a safety issue. And it is hard to understand how it would be visibly "unsettled".

Re: Al's Annual Inspection Thread
 

Many catapult systems will fire a lot slower with the load of the ball at the end of the lever. Thus 'dry' firing will be a lot faster.

Since F=M*V(squared) if you double the speed of the catapult, you get 4X the forces on it. Some catapults will triple (9x forces) or even quadruple (16x forces) their speed when 'dry' fired vs. the standard 'live' fire.

Re: Al's Annual Inspection Thread
 

Wow - something is not right about the design, sounds scary. Perhaps you could add a spring-loaded bumper or something to keep the shooter from destroying the stop. Or maybe a spring that engages just after the soft stop?

Good luck!

Re: Al's Annual Inspection Thread
 

OK,
This will be brief as I am already very late. Dry firing a shooter mechanism that is suspect has been part of FRC inspections as far back as I can remember, perhaps 1998. I know and you should know that students make mistakes driving and shooting. I know that just at the wrong time, the ball comes out and bang, a shooter dry fires. I have seen hundreds of wiring errors, software glitches and damaged latches fail in competition. I know that regardless of your software or hardware, an unsafe mechanism is still unsafe. I and all other inspectors, field volunteers, Safety Advisors and Refs are tasked with keeping the participants safe. I am not going to take your word that your shooter won't harm anyone, I want/need to prove it to myself. You only have to see one near miss to know you never want to relive that experience again.
So here is the only answer I can give you. If an inspector believes your shooter or anything on your robot violates...
R8
ROBOT parts shall not be made from hazardous materials, be unsafe, cause an unsafe condition, or interfere with the operation of other ROBOTS.
and you disagree, then you will be asked to prove it. It is the third item in the Inspection Checklist under the mechanical section.

Re: Al's Annual Inspection Thread
 

Are code safeties enough to pass a dry fire inspection? Our shooter has issues dry firing, but we do have a reliable safety mechanism to guarantee no shots without a ball in place.

Re: Al's Annual Inspection Thread
 

I believe the request for a "Dry Fire" has less to do with software or mechanical safeties, but has wholly to do with mechanical robustness.
In other words, and as Al has stated, will the shooter catastrophically self destruct, endangering ..... you name it.

Re: Al's Annual Inspection Thread
 

I can remember being asked to dry-fire more than once over the years. We account for that in the design to avoid self-destruction.

As a RI, I'd only ask for a dry-fire if it looked like something could be flung from the robot and off the field.

It is feasible to add some mechanism to help mitigate the destructiveness of a dry fire in your system?

Re: Al's Annual Inspection Thread
 

Al,

On our robot we currently have a end of a piston protruding 0.2 in outside of the frame perimeter in it's default position and are wondering if this counts as an minor protrusion?

This is less than the 0.25 in shaft collars that we have that are deemed acceptable.

Re: Al's Annual Inspection Thread
 

After 3 pages of "Dry firing" discussion, I'd like to underline the excellent point Jon made earlier. In my visits with a few teams I can see this being very relevant and I'm going to be asking teams to show me some type of mechanical interlock if they intent to load up their mechanism prior to placing it on the field and demonstrate a safe way to unload it or lock it up prior to removal from the field. Hopefully most have already thought of this but it reminds me of the wheel guards we had everyone add last year. I don't want teams to be caught by surprise by such an obvious safety precaution.

Good luck!