Re: R3 20" rule
 

If I understand correctly, you want to extend into the corner such that, looking downward on a rectangular robot, the furthest point is 20 inches in both the X and Y dimensions from a corner of the robot, leaving it 28" from the corner itself, measured on the diagonal.

Again,

Figure 4-2 also clearly shows rounded corners for the 20" - you can NOT extend 28" into the corner, only 20" from the nearest point on the frame perimeter.

Re: R3 20" rule
 

How does this figure, taken from the manual, not answer most of the questions in this thread? This rule seemed pretty cut and dry to me.

Re: R3 20" rule
 

The technique I saw being used for checking this at the LaCrosse WI week 0 event may be helpful.

Hold a plumb bob* so that it touches the furthest reaching (or suspect) point of the extension. If the horizontal distance from the string to the frame perimeter (where the bumpers attach) is > 20" you have a problem.

The plumb bob is also useful to assure that the starting configuration is legal and that everything is inside the frame perimeter

* a free hanging weight attached to a string to produce a vertical line

Re: R3 20" rule
 

It's pretty simple. If you were to draw an outline of your frame perimeter, then you would draw another profile around it offset 20" from your frame. If you had a square frame, the corners of this outer profile would be rounded with a 20" radius. You may fill up this entire outer profile with extensions if you want, but you can't go past it.
For example:
Attachment 16308

Re: R3 20" rule
 

The only issue I have with that image is that it's nowhere near to scale. 20" means you can almost double the short dimension of the kit frame in both directions.