Diangle expansion

So a friend just asked if the expansion was

  1. Just front and back or right and left
    Or
    2 would include expanding included 36 inches front and back as well as 36 right and left which would allow him to expand diagonally.

36 inches in every horizontal direction, not just one or two.

The 36" rule refers to the bot being within a 36" diameter cylinder

This is not correct. The rule is if the bot has a horizontal measurement is within 36 inches, not just be in a cylinder. This being said, you will almost always fit in a cylinder too.

You will always fit inside of a 36 inch diameter cylinder, although I am not certain if the cylinder must be completely vertical (as in the top is not directly over the bottom).

No, @Carter is correct. The robot can be legal and not necessarily fit within a 36-inch diameter cylinder.

<SG2> b) Once the Match begins, Robots may expand, but no horizontal dimension can exceed 36” (914.4 mm) at any point during the Match.

In order to meet this rule, you would have to be able to draw a 36" circle on the ground and have no part of the bot extend beyond the circle. You would also have to be able to project that circle vertically perpendicular to the ground and still not intersect any part of the robot in any configuration (i.e. an arm moving in a vertical arc, etc.) The solid thus described is, my friends, a cylinder.

No, not quite.

Here is a quick example. Draw an equilateral triangle measuring 36" on a side. Draw a 36" diameter circle centered on the center of the triangle. Measure point-to-point anywhere on the triangle. You will see that it does not measure more than 36" in any dimension. At the same time, it won’t fit inside the 36" diameter circle.

There are more examples than that triangle, and even nearly such a perfect triangle won’t likely happen with VEX parts. I don’t remember the name of the shape that encompasses all of the shapes that don’t exceed 36" in any dimension. Someone posted it before. I’ll have to look it up.

You are talking about how big the robot itself can get, without any extending long arms.
I think we were talking about how far an arm can go out from the robot. Once you extend an arm from the side of your triangle robot (or other shape that works) it usually immediately becomes illegal.
So you could have a robot that is a triangle with 36" sides, but you could not extend any arms except for very short ones from the middle(ish) of each side of the triangle.

You could measure with a cylinder when the robot fits within the cylinder.

Also has anyone ever thought have having a robot that starts diagonally, and then once the match starts it retracts its support beam up and it becomes a tower on the robot?

No, I’m not. Not at all. I’m saying you are allowed to expand to shapes that do not fit inside a 36" diameter cylinder. Besides which, a triangular robot like that which hadn’t extended wouldn’t fit inside the starting box.

Sure, you could, but you have to be careful with the logic. You could use such a cylinder, and any robot fitting inside would be legal. But you could not determine if larger robots are legal or not this way. Here is the logical issue with if-then statements (ignoring height): If the robot fits inside a 36" diameter cylinder, it is legal. The converse is: If the robot is legal, it fits inside a 36" diameter cylinder. The former is true, but logical statements do not imply their converses. In this case, the converse is actually false.

I should have clarified that by extension I meant arms and stuff, I assumed that we were assuming that the robot had already expanded to its triangle (or whatever shape) as soon as the match had begun. My bad.

Hence I said you could measure robots that fit within cylinder with the cylinder. If I have a 10"x10" robot (assuming that it is not intended to expand into a shape that goes outside of the cylinder and remains legal) and it extends an arm, since the original robot fits within the cylinder now if it does not fit within the cylinder after the arm expansion then it is illegal.

After you pointing out the error of cylinder measurements I have decided that when using this technique for competitions the best thing to do is either notify the ref before your match of your robots capabilities, or to have a premade printed or digital argument to show the ref.

No, this is not true.

Of course, you can just use a tape measure to show trivially that the robot is legal. That’s much easier than presenting an argument. Though at the same time, doing so also definitively shows that this notion of having to fit inside the cylinder is false.

Alright if the robot is not going to expand into a shape that is able to legally be outside of the cylinder, and then it expands so that a piece is outside of the cylinder, how is what I said incorrect?

Alright cylinders are stupid

OK, can’t argue with geometry. Below is an image to clarify the point @callen is making. On the left are superimposed 36" circle and equilateral triangle. On the right the 1/6 of a pizza shape that also has no dimension over 36". Inside that is a robot-ish shape inside indicating how much you might gain by building with this understanding of a cylinder not being the real measure of rule SG2b. There is definitely a gain to be had, and it can definitely be greater than what is shown below… but the orthogonal nature of VEX structural parts is limiting.

To be clear, and i hope i am just misunderstanding some of the questions and statements, arms extending off of the robot are part of the robot, and also constrained to a 36" horizontal shape… If your robot base has extended to 36", there are no additional inches allowed for arms. If your robot is 18", then you still have 18" for arms (in that direction).

A robot can be built in such a way that it is legal but does not fit within a 36" cylinder. All 36" cylinders are legal, not all legal robots fit in that cylinder. If you have any question if your robot is legal, a yard stick across the two furthest points on the robot will tell you.

You can also use the expansion measuring tool. It gives you 36" like the regular sizing tool does 18". Just make sure you always hold it flat. :slight_smile:

I used it at our state inspection last year. I got lots of strange looks.

(I love inspecting robots. I wish that was my real job.)

@Doug Moyers what program did you use to create that drawing because it is beautiful.

Autocad