Re: Pneumatic Restrictions & Improvments
 

The off board compressor must use the same system as an onboard compressor. So you'll never fill past the shutoff limit anyway.

Re: Pneumatic Restrictions & Improvments
 

Hey Al-
I don't have an issue with the rule, and the intent of the rule- as has been outlined by yourself/Q&A. However, the phrasing of this rule was taken to extreme limits at the Groton District Event this year. We were forced to remove our 1 gallon air compressor used for our pneumatic tools from the pit citing this exact rule.

I took this ruling to mean we were basically not to be trusted for even having a shop compressor in our pit. The rule does not say you can't have spares, it doesn't say you can't have a shop compressor in your pit- it says you can only fill your robot with one compressor.

Just wanted to provide that feedback, as this particular interpretation of the rules is not only completely wrong, it is insulting to a team as you are essentially calling them untrustworthy.

-Brando

Re: Pneumatic Restrictions & Improvments
 

This won't change through allowing the use of an off-board compressor to pre-charge the tanks while still having an on-board one. You would still need to use a pressure switch and have it controlled through the control system...

Re: Pneumatic Restrictions & Improvments
 

Brandon - In general we don't like shop compressors in the pits at all, for a couple of reasons. First, the high-current they require at start up can often overwhelm the pit power supply. Doing so can trip breakers and shut down power to a group of pits, not just your own, in many venues (especially when running in high schools for district events). Second, when you have a shop compressor in a pit, there's no way for us, as inspectors, to know 100% that you aren't using it to charge your robot.

What pneumatic tools do you use that can't easily be swapped out for a motor-driven equivalent? In my experience working on these robots, there's nothing we can do with a pneumatic tool that we can't do with a motor-based tool.

Re: Pneumatic Restrictions & Improvments
 

Jon-
The biggest reason we bring it is for our pneumatic rivet guns. Many of our modular sub assemblies are mounted purely with rivets, and popping 100+ steel 3/16" rivets with a pneumatic rivet gun is MUCH faster than doing it by hand (and comes out higher quality).

We obviously make do with the manual tools, as we've been forced to remove this compressor in the past. However the preference will always be to have it IF we are allowed to.

Just to add perspective, this is not a large shop compressor. Its a 1 gallon harbor freight job that would be something akin to what's in the trunk of your car to fix a flat.


Regarding not knowing if a team is using to fill their robot- you're 100% right. However, how do you know a team isn't using a spare legal robot compressor to fill their robot? Or breaking one of many other rules? We trust teams and give them the benefit of the doubt on so many levels, it just seems odd that this is the item that pushes us over the edge to where we say a team cannot be trusted. And just to bring this full circle, if a team does need to remove a compressor for one of the reasons you outlined- we shouldn't quote the rule being discussed in this thread- its simply not right.

-Brando

Re: Pneumatic Restrictions & Improvments
 

It seems strange to mince words. Air is air. It makes sense to limit what compressors are available in the onboard system, since this governs availability of air during a match. But if we are allowed to start with our tanks charged, what difference does it make where this air comes from, or how quickly we are able to charge before the match? As long as the compressor/system being used is safe and doesn't knock out venue utilities.

It is legal to charge up other stored energy systems however we like (R34 from 2014 - of course, presuming it's safe), for example winding up a spring mechanism with a motor powered by any battery, or even with work directly from a person. So why limit how we charge up the pneumatic stored energy system before a match? What difference does it make if Team A filled up in 2 minutes and Team B filled up in 1 if they are otherwise identical at the start of the match?

Re: Pneumatic Restrictions & Improvments
 

Presumably the reason to require the offboard compressors be controlled by the robot is to ensure that all safety systems are functioning anytime air is being loaded into the system. Otherwise I could over pressure my pneumatic system to 150psi and nothing would stop me. This is a dangerous situation.

However, I agree with the sentiment that offboard compressors should not be limited in the rate they can fill. If it can be powered and controlled by the robot it should be legal off board. Why? Because filling in 2 minutes and filling in 1 minute are identical from the perspective of on field performance.

Re: Pneumatic Restrictions & Improvments
 

The on board relief valve will limit you to 125 psi or so. If the team is going to readjust that after inspection then they are willing to cheat in other ways as well? Typically one of the things the robot inspectors are looking at in queue is the storage & working pressures.

Since you are not limited (2014 at least) in storage volume, the difference between an unregulated air source & legal source could be 15 -20 minutes in extreme cases. Personally I would prefer they limit on board storage volume, but that would be harder to inspect for.

Re: Pneumatic Restrictions & Improvments
 

Stuff we have already. We have pneumatic shears that are really awesome when cutting lots of lexan, but we don't want to spend $300 on new electric ones.

The main reason we bring a compressor is to use a nozzle and clear off chips and stuff like that.

Also, we use a pneumatic ratchet to allow us to get loosen/tighten bolts that are in tight spots. We've had some that we couldn't get with any other tool.

A few more-
pneumatic riveter, nail gun (wooden robots!), pneumatic cut-off tools (only $8 at harbor freight!). We use pneumatic drills sometimes to test mechanisms instead of a normal drill because they spin much quicker.

Re: Pneumatic Restrictions & Improvments
 

I was for limiting on board storage in the past, but when you compare the energy density of the tanks to the batteries, it's just not a big deal in my mind.

a 44 cubic inch tank at 120 psi stores .7 KJ of energy if released adiabaticly, teams won't effectively ustilize all .7 kJ of this for various reasons (losses in the system before it even gets to cylinders, as well as not operating down to 0 psi). So let's call this .35 Kj.

I'm going to be lazy and approximate the FRC battery in the average bot as supplying 100 Amps at 10 V for 2 minutes, this is 60KJ/min for 120 KJ total.

If a team precharges 20 44 in^3 tanks... you'd have ~ 7 kJ of usable energy versus ~120 KJ.

Numbers are admittedly fudged here for quick calculation, but the trend is valid. The amount of air you can store in terms of energy is not much compared to the battery, so in the name of an even playing field in terms of energy use across teams, it really isn't a big deal.

Now, limiting storage for safety reasons is another argument....

Re: Pneumatic Restrictions & Improvments
 

They did it in the past... For example, 2010 R72A:
I remember people rejoicing when this rule disappeared a few years back. To ensure safety from exploding tanks, though, it wouldn't surprise me if we saw something similar to this appear in the future... although it would probably just list legal storage tanks and not put a limit on them. Kind of like we have a list of legal batteries.

Re: Pneumatic Restrictions & Improvments
 

Using compressed air to blow out metal chips and shavings is fairly dangerous, and if I saw it occurring I would personally get the lead safety adviser over there to talk with the team. When you blow those chips, they go everywhere, which could very easily include into the face and behind the safety glasses of someone on the other side of the robot or in the next pit over.

Edit: Check OSHA 29 CFR 1910.242(b). It requires that compressed air used for cleaning purposes must be reduced to less than 30 psig (pounds per square inch gauge, 204 kPa). Compressed air used for cleaning must only be permitted with effective chip guarding and personal protective equipment to protect the operator and other employees from the hazards of the release of compressed air and flying debris.

Re: Pneumatic Restrictions & Improvments
 

We use a "safety" nozzle limited to 30 psi and we've always done it in some type of enclosure, like our pit's side area, which has walls over a trash can. If you end up doing serious machining at the event, it's really nice to have. We actually checked with pit safety people at the beginning of the event (as we often offer our pit resources to other teams), and they said they would be okay with it. Next competition, we'll be sure to check again, just to be safe.

I don't like limiting the storage volume. It doesn't make too much sense to me, as I don't think quantity of air is the big danger factor of FRC pneumatics.

I do agree that we should have a list of legal tanks, and I wouldn't be too upset if plastic tanks were banned.

Re: Pneumatic Restrictions & Improvments
 

Who is we? Are you speaking for your regional? Are you being the voice of all inspectors? Is this just you?

Re: Pneumatic Restrictions & Improvments
 

Not speaking for John... At Peachtree (Atlanta) the use of shop compressors where discouraged. I got the impression from the LRI that that was a source higher than him. As stated earlier power required for a shop compressors can be an issue.

We use a small shop vacuum for cleaning. You can also use it for blowing if the situation calls for it.