Game piece inflation
 

At the Michigan Center Line District event the game pieces were so inflated they were actually squarish. We asked about it and the officials said they had inflated it to the specification of the field reset guide. We designed our robot to pick up 25" (+/- 1") balls as were explained by the GDC. We even underinflated and what we considered to be overinflated some ball in practice. But many of the robots at our event had significant difficulty picking up the balls cleanly. I was surprised that there isn't a sizing box!

Were they like that everywhere?

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They were fine at Palmetto.

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They were also exceptionally inflated at GSD

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GTRW's balls were also overinflated as far as many of the teams were concerned. Many robots spent the portion of Friday that wasn't waiting for the field to work trying to adjust their intakes to deal with the crazy over inflation.

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Due to the weather and the temperatures inside the Avanti Dome at the Central IL Regional, at the beginning of the day(40 degrees indoor temp), the game pieces were perfectly inflated but as the indoor temperature rose with robot interaction and increasing outdoor temperatures, the game pieces looked like they were going to burst. We had to drop our 3.5" roller for two 4" wheels spaced about twelve inches apart and we had to change our reduction on that collector to adjust the geometry of our shooter so we could continue to shoot.

The event staff adjusted the game pieces by Friday, however. Teams mentioned the issue to event staff and they did everything they could to improve it! :)

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I'll keep an eye on this at N/E Groton & N/E Southington.

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They were very much over inflated at Alamo on Thursday, and after many complaints, the balls were slightly deflated during lunch and they were fine throughout the event.

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GTRW had a ball sizing ring. It was 25" in diameter and came with the field. I'm assuming other regionals had one as well. Was it being used?

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If there was a ring to be used, why wasn't its size shared with teams weeks ago such that we could test robots accordingly? The inflation level of the balls completely changes how they fly from some shooter designs and changes the intakes too.

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Officially, the balls are inflated to the point where they look about right and thats it.

Although I agree there should be a sizing box 100%, this is the first I'm hearing of it being actually used.

+1 GTRW Crew

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The problem though, is that many teams at GTRW had to rework their intakes and shooters as the balls at GTRW seemed to be overinflated by the official inflation method provided to teams at kickoff.

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There was a sizing box used for Logomotion . Unfortunately it didn't help because people were still inflating the tubes until they were overflowing from the box and were bigger than most teams expected.

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The sizing ring had a hole exactly 25" in diameter. When a few teams at GTRW complained about the ball sizes, they were checked and a few were found to be oversized. Those ones were deflated.

Some teams cam by and used the sizing ring on their practice balls as well.

The ring went in the robot inspectors case.

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Does anyone else think that a sizing box is not the way to go here? We have no idea the tolerances that these balls are designed at. If the balls are +/- .5in a sizing box would lead to over and under inflated balls, and then everyone would be complaining about that.

I think there is a bunch of confusion here.
Having all balls the same size in diameter would lead to different levels of inflation.
Having all balls inflated to the same PSI would lead to different sizes, in diameter.

Simply put the tolerances on there balls are not +/-.0000000001 There is no way to have all these balls be the same size and same pressure.

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The rules state nothing about ball pressure, but they do state an approximate size. And assuming that all of the covers are approximately the same size the balls should be inflated to around the same size according to the inflation guide. So there is no argument backing pressures since the rules state nothing about it.

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We really should not have a problem putting a ball in a box and pumping it up till it touches the sides.

I don't see why you can't just pump them up in the morning and check them at lunch each day and be done. Or even just once a day (I'm assuming they may lose some air getting hit and squished all day).

The rules say approximately 2ft diameter. Excuse me for designing for 23"-25".

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Has this actually been tried out tho? Its all speculation until you see the actual results.

I don't think anyone is asking for 10 decimal places of tolerance on the diameter.... However a single decimal place or 2 would certainly be welcome.

Honestly I would take one or the other if it helps consistency in an event and event to event. Right now, we don't have either besides a general 'look' and 'feel'.

-Brando

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Remember this video was to address this concern. http://youtu.be/Azc8AKzgEwE

The sportogo makes them as 25" balls, AndyMark sells them as 2' balls.

They must loose an inch in Indiana air. :)

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None of the balls at Palmetto looked even close to the example in the video, some where stretching the stiches at the seams.

By saturday about 1/2 the balls on the field had been corrected. but most where still oversized.

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The actual result can be seem using chemistry.
What does our result show? Well the Smaller diameter ball is at a greater pressure. Meaning that it is firmer.
If you try to instead control the pressure you'll see that you get stuck with a different ball diameter.

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As the field supervisor for the Center Line district, with the exception of maybe 1 or 2 balls all weekend the game pieces were actually not overinflated. They were filled to the specifications in the field manual, and when we received complaints about overinflated balls we began seeing where the issue was. We double checked the field manual, measured their circumference with string, and had a piece of plywood made with a 25" cutout. All of these methods checked out, aside from 1 or 2 that were corrected, the game pieces were all between 24" and 25" in diameter. We were not supplied an official box or ring from FIRST, but from all of the methods we had at our disposal, the balls came out within the tolerances specified in the game manual.

Upon feel, however, I believe that regardless of size, the balls were firmer than the one supplied in our KoP. I cannot confirm this, as I don't have a side-by-side comparison, but it did at least feel that way. This could easily be mistaken for overinflation, as a firm ball would not compress like a soft ball.

The event staff did our best to make the balls playable, but we could not deflate them below the size specifications in the game manual.

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We in the PNW district did not receive any sizing rings with our fields. I was there in the process of unloading all the stuff we received to inventory it and test it before repacking and loading on the truck. We never saw any such rings.

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Thanks for the data point Brandon!

So the 25" was maintained, but they may have been firmer than what we got in our KOP.

In the kick off Video they say about 25", but the indicator was zipper functioning, and seems not bursting. I would say that both of these indicators are Pressure based.

Now we are at week 1, and the control is now sized based, it will be close to 25" ring, string, or hole in plywood.

This seems to be a significant change in the criteria for a "playable" game piece.

As there really is no governing body of the game piece, (i.e. official size and weight, like baseball, basketball, etc.) Sportogo publishes no tolerance specs on their ball, we should anticipate game piece variance in our design, that is part of the challenge.

We purchased 2 additional game balls, and did size and weight measurements on the 3 balls we had access too. We also contacted sportogo and asked about their ISO quality system, and what determines a sellable ball vs. an unsellable ball. This was never responded too, but review of the website, showed no mention of a ISO standards or a quality system, so we determined that the design should expect deal with large variance in ball diameter.

We also under inflated and over inflated our balls during testing, based on the video.

What we did not do, and what is being done at the events, is to do whatever it takes to get the ball to be 25".

That is what I think is happening, so a cover that is slightly under sized, is now being "overinflated" (by video terms) to meet a 25" size. The pressure of this ball is significantly higher, which will greatly impact the ability of may intake systems to function as designed.

As another side note, and I did not see which event I was watching at the time, but I noticed that none of the balls had the FIRST logo on them, like the KOP balls we received.

Did anyone else notice that?

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When we unloaded our truck late Wed evening at Palmetto (A big thanks to the volunteers at Palmetto for waiting for us) Our rather chilly practice ball was noticeably under inflated. The next day it had magically refilled itself to what I consider to be its normal size. I did not notice any difference between it & the practice field balls. Non of them was perfectly round, but all were close. I never got close enough to the competition field balls to have an opinion.

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You think that's bad? We had the garage door to our shop open for about 15 minutes when loading up the trailer for a week-0 event and the ball shrunk down at least 6 inches in diameter from where it was!

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Fun fact: when we were practicing scoring goals outside, we lost 2 feet (in height) on our shot after 15 minutes outside in 20 degree weather. After coming back inside, the shot was normal again after about 10 minutes of 8th graders hugging the ball

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I believe this to be the actual problem. I did not notice this much on Saturday (so perhaps it was fixed) but on Friday at Centerline I noticed that some of the game pieces looked like eggs more than balls. We noticed that our robot sometimes got the ball stuck in the arm one way and picked it up fine another way. So perhaps more than just a circle cutout needs to be used because a sphere and a cylinder can both fit into a circular hole. The suggested box idea would probably meet this criteria.

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I did wonder if temperature shift might have been why the GTRWest balls seemed overinflated, especially early on Friday.

Crescent's fieldhouse, being essentially a big tent with hockey-arena style infrared heating, might have been colder when the balls were being filled in preparation for the event, and then as the arena warmed up (because the heaters had been on and we added 900 people to the mix), the balls might have expanded.

It would be interesting to see how much temperature affects the ball diameter at different pressures. I wonder how static the temperature has to be to maintain a relatively consistent ball diameter.

The fieldhouse was experiencing fairly large swings in air temperature because of the nature of its heating, I wonder if that would have been enough to change diameter of the balls significantly while we were playing.

EDIT:

I think this would be covered under ideal gas law too.

PV = nRT

n, and R are constant since we're not adding or subtracting any air from the ball. I don't know that P is constant, but assuming it is:

V1 = 8181.23in^3 (the volume of a 25" sphere)
T1 = 20degC (293.15K)
T2 = 21degC (294.15K)

(V1/T1) = (V2/T2)

(8181.23/293.15) = V2/294.15
294.15*(8181.23/293.15) = 8209.138in^3

8209.138 = (4/3)pi * (r^3)
8209.138 /((4/3)*pi) = r^3
1959.787336 = r^3
1959.787336^(1/3) = r
12.514in = r

Changing air temp from 20C to 21C would add 0.028" to the diameter of a ball. (If T1 = 15C and T2 = 22C, the ball changes 0.200" in diameter)

Did I do that right? It doesn't seem right to me. I think changing temperature will also change P.

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Hmm sounds like different events are using different methods (or even no methods at all) to ensure some semblance of ball consistency from event to event....or even day to day within an event.

Numerous teams at Crossroads suggested the balls on Saturday were smaller/had vastly different shot characteristics between Thursday/Friday and Saturday. I know they weren't flying the same on our bot, and that observation held true even when we swapped out our shooter/claw. We will adjust accordingly; however, this type of reality seriously calls into question whether this game holds up to the definition of "professional" when measured against the policies professional sports leagues apply to game piece consistency. This is supposed to be the highest level of professional robot competition, is it not? Do the NFL/NBA/MLB require their teams to play with vastly different specifications of game balls? If you want to be pro, then establish and enforce the rules that merit that label.

Can the GDC PLEASE generate, communicate, and mandate some kind of DAILY check for ball consistency at events, such that teams have SOMETHING concrete to take to volunteers if a sudden change in gamepiece characteristics is noticed by a great many teams in attendance?

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So in the manual, they state 24" ball (2ft). In the video, they say 25" ball. In the manufacturer specs, it says 25" ball, and andymark sells it as 2ft ball.

The video tells us literally to inflate it till it looks 'just right'

So which is it, GDC? Why is this such a hard question to answer?

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After reading this I tried to inflate ours to 25". It would not get any bigger then 24" no matter how much air i put in. (almost to the point of bursting). Are the balls supplied by the field different than the ones supplied in the KOP? I sure hope not.

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You did it correctly assuming that pressure remains constant. If pressure remains the same then your volume will increase as temperature increase and vice versa. Unfortunately this doesn't translate perfectly to the real world since the balls would most likely increase in both pressure and volume. If you had the measurement of one of those two factors (before and after of volume or pressure) you could find the other one fairly easily.

Our team has also noticed a large variability due to temperature of the ball. When prototyping our shooter and performing initial testing with it mounted on our robot we tested outside. We noticed a significant difference after moving our testing into an abandoned Sears building (free rent since it's soon to be demolished) and the temperature was a good 40* warmer.

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That's what I'd thought, was that it would change in pressure and volume together (and thus the volume would change). I looked around hoping some kind of formula exists to model that relationship, but was unable to find one. I suppose it would depend partially on the pressure vessel, as a compliant vessel like our balls would be able to expand more in volume than a steel tank.

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I can assure you, inflated balls happened from time to time. But every instance where we noticed it we just asked for a different ball and we were very gracious to receive one.

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They were extremely inflated at teh Glacier Peak PNW regional as well. So inflated in fact, that it started to continuously stall our motor and wouldn't allow us to gather the balls at all. We want to put some slop in our pneumatic mounts to our arm to try to fix this problem, any other teams done things to help this problem?

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This thread can go on and on, but the one thing to remember is that according to the Filed manual, the balls should be inflated to the point where the zipper is not touching itself, nor stretched into a football shape. They are to be inflated where the zipper is slight pulled apart where the inflating plug can be inserted. The zipper should be able to be pulled closed with some slight resistance. I did not receive any complaints at the Groton District event. I checked all balls often & they were consistent. We did have 2 balls checked at the beginning of the Eliminations & found to be slightly over-inflated by a volunteer who was just trying to keep up & was pumping them up rapidly. After that they seemed to be consistent. They will be scrutinized at the Southington District Event to be properly inflated.

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we noticed that the balls were more inflated than we expected at auburn mountain view during week 1 and upon further testing found problems similar to the ones you describe. We then altered our intake by moving the roller up about an inch to decrease ball compression and avoided problems at glacier peak. Though the balls may be over inflated they have been consistent at PNW event

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Has anybody out there actually measured the difference in pressure between a properly inflated ball and a slightly over-inflated (and under-inflated) one?

Is it a large enough difference that it could be reliably measured with a relatively inexpensive gauge at the events?

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Last week, 4183 lengthened their pickup arms an inch to allow the more-inflated balls to fit without stalling the motor.

Measuring the pressure would require a special fitting or gauge, although it wouldn't be too hard to make something to do it. 1/4" pneumatic tubing fits into the inflation hole in the ball.

The extent of wrinkling at the seams of the ball gives an indication of how full it is...until the wrinkles go away entirely, then who knows?

The balls aren't exactly round, either...they're sort of cube shaped.

I think this is a game where you need to take a lot of effort to make sure your robot will work with the game pieces, whatever they end up being like at the competitions. If you didn't, you're going to have problems. The low goal is a good option if you can't shoot into the high goal reliably.