Frame Perimeter Tolerance
 

Let me start by saying I did search first so I know there is another thread here with a similar topic however since that thread was started prior to the new sizing rules I thought it would be better to just start a new one. My question is what is the tolerance on the frame perimeter at inspection? My team is making our frame 28"x28" - which is the max frame perimeter (we did it last year with no problem so that is not our concern). What we were wondering is if we were to powdercoat the frame, thus adding a few thousandths of an inch to each side, would that be a problem? I wouldn't think it would be but I wanted to see if any other teams had experience with this. Thanks,
Jesse

Re: Frame Perimeter Tolerance
 

Why would you build to the nominal max limit?

Re: Frame Perimeter Tolerance
 

Well, in my experience, the inspector won't pull out a giant 30" caliper to measure your perimeter, but I'd caution against building to the very max. I'd leave at least a quarter-inch, if you still have the chance.

Re: Frame Perimeter Tolerance
 

28" inches is 28" regardless of whats on it, however they do say things that protrude out like nut ans bolts < than 1/4" are ok so I would bet it would be ok, but thats just my bet. I would think that if you asked they would say what I said in my first sentence.

I dont think they measure to the nearest 1/16 - .0625, and I cant imagine your coat being much ticker than that? Ifs its an 1/8 thats a different story. Depend on the inspector.

Last year we used 1/4 coper tube from our compressor because of heat. We were failed even though it was not in the rules. Another team got inspected with coper and passed. We brought this to their attention and they revoked the other teams inspection cert and made them change it.(we felt bad) My point is ruels are interperted differently by different inspectors.

Re: Frame Perimeter Tolerance
 

If the inspection procedure is the same as last year, the inspector will be using a tailor-style measuring tape to check the frame perimeter. They will wrap it around the frame in the bumper zone across features that would define a "frame perimeter" per the rules (see the diagrams about gaps, etc). If that end tab is past the 112" mark, you're no good. So, it's up to you to decide the tolerance of the tape, but I'd say it is well under 1/16".

Regarding your powdercoat, that will be more than just a couple thousandths in thickness. I would put it into the tens of thousandths overall. So, if you gain 0.020 (0.005 per side), you're approaching the point where an inspector's tape will reflect the difference.

Re: Frame Perimeter Tolerance
 

All I can really say is good luck. Building up right against the limit in itself is asking for a bad time.

Re: Frame Perimeter Tolerance
 

This procedure is not consistent across events. We were never inspected this way.

Re: Frame Perimeter Tolerance
 

No margin? If you design something to be 28 inches square, there's a 50-50 chance it will be under and a 50-50 chance it will be over after fabrication. If the inspectors see a lot of robots close to the limit they may improve their measurement accuracy, in which case, even a 1/64 inch overage will be out of limits. The rules give no tolerance on the limit.

Re: Frame Perimeter Tolerance
 

Must be a Texas thing then. Lubbock, San Antonio, and Houston used the tailor's measuring tape to check the frame perimeter.

I stand corrected.

Re: Frame Perimeter Tolerance
 

There is no tolerance on the frame perimeter measurement. It is either 112.0 inches or less, or it is out of compliance with the rules.

Re: Frame Perimeter Tolerance
 

Please, please, please DO NOT BUILD YOUR FRAME 28 x 28!!!!

Let's assume you get your robot together perfectly, with absolutely no extra width or length, you pass your inspection, and play all your matches. Then, you go to pass inspection, and you robot is suddenly 112.5" in frame perimeter. How? When you got the corner of your frame smushed in because you drove into a wall and were hit by another robot, the frame perimeter changed, and you got too big. It's happened to us before, and the last thing an inspector wants to tell you is that your frame is 0.5" too big, and the last thing you want to do is make your frame smaller. It's really, really hard. Trust me....

Re: Frame Perimeter Tolerance
 

Thank you all for the input, most likely will not be powdercoating the frame then. As far as the frame perimeter goes, it's a little late to change now (parts already out for mfg) but we should be fine - last year we built to 28x28 doing our entire frame by hand, this year we are doing sheet metal (lasered and bent), so theoretically much tighter tolerance there. I will keep that advice in mind in the future though.

Re: Frame Perimeter Tolerance
 

[quote=amesmich;1331369]28" inches is 28" regardless of whats on it, however they do say things that protrude out like nut ans bolts < than 1/4" are ok so I would bet it would be ok, but thats just my bet. I would think that if you asked they would say what I said in my first sentence.
/QUOTE]

In regards to this, previously, I've had the "issue"(ie. it wasn't really an issue) where the LRI further clarified that that rule is simply there in respect to your own FP-ie. if you're 27.5x27.5, those protrusions are okay, but if you're 28x28, they would NOT be okay, because (as said in other posts) 112 inches is 112 inches, so no matter what you still need to fit under the 112 inches-including protrusions.

Keep in mind, this was just one LRI's interpretation, but I assume it'd be fairly consistent across the board.

Re: Frame Perimeter Tolerance
 

That's an interesting interpretation of the rules. R2 says that minor protrusions (such as bolt heads) less than 1/4" are not considered part of the frame perimeter doesn't mention anything about those allowances being related to the rest of the perimeter. I guess in certain situations the lead robot inspector just has to make a call but that would be a situation when I would definitely want to have a copy of the rules on hand.

Re: Frame Perimeter Tolerance
 

[quote=DevenStonow;1331383]Well, that inspector is wrong. The rule says "Minor protrusions no greater than ¼ in. such as bolt heads, fastener ends, and rivets are not considered part of the FRAME PERIMETER." It's very clear.

Re: Frame Perimeter Tolerance
 

That's an *ahem* interesting interpretation of the rules.

Regardless... seriously, good luck to the OP. Also:

Re: Frame Perimeter Tolerance
 

I was at an event a few years ago in which the team across from us failed inspection due to their frame being half an inch too wide. They only had 5 students on their whole team, so I sent a few of our students (and some of our tools) over to help them remake a whole lot of their robot. Very frustrating for that team (but I admired how they accepted and handled the situation).

If you have any possible way to take a quarter inch out now, I'd highly recommend it. Much better than going to your first regional with a 50% chance of failing. Maybe you can round off the corners a bit? But be careful about bumper rules...

Re: Frame Perimeter Tolerance
 

The recommendation from experienced (OK Old) mentors is to build to 1/4" under in every dimension. Tolerances in bending are finite and they could be too big. Whatever way the Inspection team decides to measure the Frame Perimeter, it better be less than 112". The guideline is using a 112" string wrapped around the robot frame. Boltheads, welds minor protrusions are different than a misplaced bend, angle stock in the corner or a transmission that stick outs from the frame. We call this practice "playing with fire".

Re: Frame Perimeter Tolerance
 

Instead of asking Chief Delphi, which is as official as asking a pet goldfish, ask the question on the OFFICIAL Q&A, where you'll get an answer who know is correct: https://frc-qa.usfirst.org/Questions.php

Re: Frame Perimeter Tolerance
 

Albeit a very well informed and intelligent pet goldfish.

Stil, it's true: FIRST Q&A is the only place you'll be getting an official answer.

Re: Frame Perimeter Tolerance
 

I'd recommend you take the advice from this thread now, not on the Thursday of your competition when you'll need to do it anyway.

http://www.chiefdelphi.com/forums/sh...ighlight=frame

Re: Frame Perimeter Tolerance
 

I hope it never comes to this, but remember that the pits (especially the ones at Championship) can be rather toasty. Aluminum expands 12.3E-6 inches for every extra degree Fahrenheit. If your build space is rather cold like ours is (~60° F), and the pits are ~76° F, a 28x28 inch robot could gain 0.0220416 inches in its perimeter. That could cause you to fail inspection. Build smaller on purpose!

(The calculations in this post are intended as a thought exercise and are not intended to be scientific.)

Re: Frame Perimeter Tolerance
 

If you're going to build your robot so close to the max dimensions that you're worried about tolerance, I highly recommend bringing a big bag of candy to bribe your inspector with before he/she starts the measurement! I recommend Godiva chocolates.

Re: Frame Perimeter Tolerance
 

Like I said, at this point we're a little committed to our frame - I don't mean this to sound like I am ignoring people's advice. Once we have the drive assembled I will double and triple (probably even quadruple) check the frame perimeter to make sure we are legal and if needed, we can modify it.

Re: Frame Perimeter Tolerance
 

[quote=DevenStonow;1331383]Was this issue when they still had the sizing box and the size limit of 28"x38"? Because back then that was the correct interpretation.

Re: Frame Perimeter Tolerance
 

[quote=kevin.li.rit;1331449]Yes, this was 2012. So yeah, maybe since then that is a different interpretation (I didn't read into the exact wordings in the past manuals)

Re: Frame Perimeter Tolerance
 

There technically is a tolerance but it's asymmetrical; it's 112.0 +0.0 / -112.0

Re: Frame Perimeter Tolerance
 

I think Chesapeake and DC used it as well?

Re: Frame Perimeter Tolerance
 

Last year at one of the MAR qualifiers the inspector used a metal measuring tape with the bow in it to keep it extended. When he wrapped it around our bot naturally it was way over because of the bow, so I asked him to pull it a bit tighter and jokingly said it was 112 in the CAD. after pulling It tight it was pretty hard to tell the exact size, but the tape still wasn't conforming to the frame properly so he just gave it to us.
My advice (if there is really no way to change it) would be to bring a cloth tape and pull it out if they give you any trouble after trying a metal one, no guaranty they will accept it but but be nice about it and maybe they will pass you.

Re: Frame Perimeter Tolerance
 

And FRC is a little committed to the rule book. ;)

Jason

Re: Frame Perimeter Tolerance
 

At every event I attended last year, a number of cloth measuring tapes were included in the supplies designated for robot inspectors.

If you haven't put your frame together yet, it would be easier to shorten it now rather than wait until it's assembled.

Re: Frame Perimeter Tolerance
 

Its better to go safe than being sorry. For design aim to be 4 inches less than frame perimeter. If needed this will allow the robot flexible later.:cool:

Re: Frame Perimeter Tolerance
 

At QCR last year, we had a piece of rope with 2 knots tied in it at 112". Unfortunately, it was rather difficult to measure exactly 112" because it stretched up to .25" or so. I was surprised we didn't use a soft measuring tape.

Re: Frame Perimeter Tolerance
 

When we used the sizing box, the robot had to fit, bolt heads and all. Now that bolt heads are not considered, this should be easier.