Team 1058 studies Squishimetrics..and Needs Your Help!

FIRST General Forum
#1

During our shooter tests over the last week, we have noticed that one of the biggest variables in our ball shooter performance has been the density of the foam balls. In addition to the three balls in the KOP, we purchased two from Andy Mark. The balls seem to vary both in overall density and, much less significantly, in density throughout the ball due to being injection molded.

In order to test our theory, we realized we needed a squishometer. Unfortunately, we were unable to find any on eBay… Undeterred, we built one out of a small level, a robot battery, and a ruler (the squishigraph). To operate the squishometer, the robot battery was held level on top of the ball (right side up to simulate a wheel) and the deformation was recorded. Pictures of our test setup, operated by our Squishographer, Dan, can be found here:

https://plus.google.com/u/0/photos/104095061824420435375/albums/5701056105735114065

(let me know if you can see them)

We noticed a substantial range of 6.1875" to 6.625"!! Clearly, this was causing much of the variability in our shooter performance (we have verified this by using the same ball). This, however, creates a problem for the competitions as we cannot predict the densities we will encounter.

In order to benefit all teams, we are calling on everyone to build their own squishometers and develop a good global estimate of the range of ball stiffnesses.

To standardize the results, all teams should use a NEW robot battery. We noticed that the battery weights differed by specific part number…and possibly charge level :smiley:

Please report your results first in your post…followed by a line of asterisks to make it easier to visually parse.

Thanks Teams!! Happy Squishographing.

#2

Great idea! This is going to be a very variable problem for many teams if no answers are provided soon. I know for sure that the top teams will find a way to overcome this, but for us middle-teams, this will just give us some more math to do (I’m not mad about that. ;)).

Thanks for the post! I’m sure many teams will find this infinitely useful. Now what’s the difference between a new ball, and a well-used ball?

#3

The answer is build a robust mechanism or choose a robust strategy so that the density of the ball doesn’t matter. Very large tolerances have been part of FIRST for quite some time, and I don’t think it’s a bad thing. As Gene Kranz said, “I don’t care what it was designed to do… I care what it can do!” Picking up a deflated inner tube or scoring a broken moonrock might not be quite as glorious as returning three astronauts from deep space, but it is often a difference maker in close matches.

I’m curious what kind of math you plan on using to combat density differences? Will you weight each ball and adjust your mechanism accordingly? It has been my experience in FIRST that if you have to fiddle with it extensively to get it to work, you’re probably better off with a more direct approach.

#4

We were going to get an average ball weight by weighing every ball we come in contact with. Not for our design, where density doesn’t matter, but for other things, one example of which is our human players being able to pass balls over the middle bump when returning balls to the field. If we can find a ball with similar weight to the average weight, then we can use that to train our human players, and for other…secret uses our team has been working out. :slight_smile:

#5

As a point of clarification, when we used the term density, we were referencing the density of the foam matrix and its effect on the ball’s stiffness. This has a direct impact on the behavior of the ball in most pitching machine style shooters. We didn’t weigh them, but it stands to reason that the balls with a denser foam might weigh more.

For our purposes, and most teams with a rotary shooter, the stiffness changes will produce a greater variation than will the mass changes as it can be thought of as a change in the interference between the ball and the rotating mechanism. From our test, we discovered that the variations in density could be equivalent to a nearly half inch change in our wheel spacing!

We also agree that FIRST demands robust design, and these variables add to the fun! However, to appropriately design a solution, one must first have a solid grasp of the problem. In this case, we are hoping teams can help develop an idea for how the stiffnesses of the balls could vary at the competition.

#6