Game piece inflation

[jman4747]

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".

[Brandon Holley]

Originally Posted by Patrick Flynn

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.

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

[tr6scott]

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.

[Bochek]

Originally Posted by tr6scott

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.

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.

[Patrick Flynn]

Originally Posted by Brandon Holley

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

The actual result can be seem using chemistry.

Lets say we have a 25'' Sportlogo ball, and a 24'' AndyMark ball, I know their the same ball
R1=12.5in
R2=12in
V1=(4/3)pi(r^3)
V1=8181.23in^3
V2=7238.23in^3

Ideal Gas Law, PV=nrT
Assume (nrT) is constant between two balls.
We have have (P1)(V1)=(P2)(V2)
From above (P1)(8181.23)=(P2)(7238)
Notice the two pressures cannot be the same.
Lets say we inflate one ball to P1=7.5PSI, NCAA Basketball recommendation pressure
Now we see that P2= 8.477PSI

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.

[Agentarrow]

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.

[Mr V]

Originally Posted by Jim Wilks

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?

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.

[tr6scott]

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?

[FrankJ]

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.

[Jon Stratis]

Originally Posted by FrankJ

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.

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!

[Rynocorn]

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

[Squeakypig]

Originally Posted by FrankJ

Non of them was perfectly round, but all were close.

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.

[Racer26]

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.

[Travis Hoffman]

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?

[Brandon_L]

Originally Posted by tr6scott

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.

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?