Q&A response - new interpretation of R16

[The Lucas]

Originally Posted by squirrel

It's called a "tram gage", and you can buy them

http://www.chassisliner.com/Product_Measuring_All.shtml

I wasn't going for practicality, I was kidding about building giant Motor Trend Car of the Year style outside calipers. Sort of a Geek Chic thing like MIT's Giant Slide Rule, but enough threadjacking for me. I just couldn't get the image of a team of Robot Inspectors wielding giant calipers out of my head.

[jgannon]

Originally Posted by dlavery

Eric's definition is much too permissive. If the explanation had been "must fit in an 80-inch square in every orientation" then I might buy it. But not as written.

Mea culpa. Your definition is unambiguous. Thank you, Dave.

[Tristan Lall]

I just wanted to point this out: the equilateral triangle isn't really the limiting case for a 3-sided figure. It's actually the curvilinear triangle with a width of 80 in. It has more area, for a given width.

Also, the triangle isn't the only figure for which this works: see here for an applet that demonstrates the principle for odd numbers of sides, from 3 to 21.

So, who's going to build a robot that fits a curvilinear pentagon, just to annoy the officials?

[MrForbes]

Originally Posted by The Lucas

I wasn't going for practicality, I was kidding about building giant Motor Trend Car of the Year style outside calipers.

You may have been kidding, but it might be helpful to make your own giant outside calipers, set at 80", from whatever is handy...say an 8 foot long by 4" wide strip of plywood and two shorter strips screwed onto the ends at right angles, with exactly 80" open space between them. Then you can check yourself to see if there is any place around your robot that you can't fit within the 80" limit.

[StevenB]

I just wanted to point this out: the equilateral triangle isn't really the limiting case for a 3-sided figure. It's actually the curvilinear triangle with a width of 80 in. It has more area, for a given width.

I realized that after about 24 hours of thrashing around thinking about this problem. I'm still trying to figure out how much a difference this makes, and how to shape the robot so as to get the maximum useful area. Thanks, FIRST, for providing sleepless nights even when I don't meet with the team.

[Kims Robot]

Originally Posted by Tristan Lall

So, who's going to build a robot that fits a curvilinear pentagon, just to annoy the officials?

I guarantee someone will need something other than an equilateral triangle or a circle to fit (heck my team may even try it to make our programmers lives easier - last year we made them take an 86" jointed arm and contstrain it to 72" at all times through feedback on our sensors!!).

But what I want to know is is this going to be in the referee training... keep your Q&A and rulebooks on hand if you really want to nitpick this rule!!

[Gdeaver]

This is a bad rule. Even with a Q and A response it's still gray to teams. On the field with a fast moving wide open game this year , refs will have a difficult time enforcing the rule. I predict many teams will violate it and get away with it. There is still time for the rule to be modified so that teams can more easily comply and make the refee's job easier.

[EricH]

Originally Posted by Gdeaver

This is a bad rule. Even with a Q and A response it's still gray to teams. On the field with a fast moving wide open game this year , refs will have a difficult time enforcing the rule. I predict many teams will violate it and get away with it. There is still time for the rule to be modified so that teams can more easily comply and make the refee's job easier.

Remember the similar rule from last year? How do you determine whether a team is in the box? There were infractions last year that apparently weren't called, even on the diagonal part. This year at least means that the refs don't have to call on diagonals. They have one standard size. So some teams slide through. It's part of the game. I've seen soccer games where the ref saw a hand ball and didn't call it. As long as the rules are applied evenly to all teams at the event (and, ideally, all events), I don't really care.

[AdamC]

Checking that article about curvilinear triangles (please don't harangue me for steering away from the original topic), does anybody know of a company that sells a curvilinear drill bit? It would be useful for drilling holes and then mounting a square locking pin as opposed to cutting notches and then mounting the pieces together (which changes the size of the bar stock). I suppose if they don't exist, I'll try and make one myself.

[jgannon]

Originally Posted by AdamC

Checking that article about curvilinear triangles (please don't harangue me for steering away from the original topic), does anybody know of a company that sells a curvilinear drill bit? It would be useful for drilling holes and then mounting a square locking pin as opposed to cutting notches and then mounting the pieces together (which changes the size of the bar stock). I suppose if they don't exist, I'll try and make one myself.

I don't totally understand the geometry behind it, but the second sentence in the linked article was "No - you can't drill square holes", so I'm guessing there's some reason that doesn't work.

[MrForbes]

look at what happens when you start drilling a hole in a piece of metal, with a relatively large drill bit, like 1/2", using a handheld drill. Often the hole will start out with 3 curved sides, even though the bit has only two cutting sides. I think this is sort of what you're thinking of?

so try a 3 sided bit to make a square hole.

[ay2b]

Originally Posted by Gdeaver

This is a bad rule. Even with a Q and A response it's still gray to teams.

I think this is a GREAT rule. In the past the rule was that robots had to fit inside a certain box. There was all sorts of confusion about orientation of the robot inside the box, and how the box shifted, etc. It lead to lots of diagrams and complex measurements.

Now the rule is simple - if any two points on the robot, measured parallel to the ground, are more than 80" apart, the robot is too big.

[DPTeam270Driver]

if the rule says a CYLINDER, then why is there talk of squares and triangles
we cant do anything by complaining. its just one of the thing that we have to design around. its part of engineering.

but.......
the way my team figured it out was that if the up right arm is 5 ft, and another arm(52 in) to extend out and reach up w/ claws ( at least 20 in it grab ball) to clear the front of the bot and bumpers, it will extend past the 80 in. theres almost no way that any bot would be able to pick the ball up and put it on the rack.

this was just my team, and we put it 2gether this morning, and found out it was 31 in too long when we had to grab the ball.

-team 270

[jgannon]

Originally Posted by DPTeam270Driver

if the rule says a CYLINDER, then why is there talk of squares and triangles

Please reread the Q&A response that this thread is about. The rule itself is not about a cylinder... that is provided only as an example. As it turns out, there are degenerate cases that satisfy the rule without fitting in the cylinder. One such case is an 80" equilateral triangle. The actual way the rule will be interpreted is that no two points on your robot can be more than 80" apart. If it's too confusing, forget about the cylinder entirely.

[Gdeaver]

The 80" rule is very restrictive. So far our team has worked out the bottom part of the arm geometry and extend out a maximum of 76". To get the top part to be with in is the hard part. If we get it right it should be about 79". To get to this point has given our team lots of problems. So much to do and so little time.