7 tetras will not exceed any restrictions in an arena. Consider last years field: we had a 10’ tall bar in the middle and many teams exceeded that by a foot. To get one of the eight shorter goals that high would require 10 tetras to be stacked on it. I am not sure how much taller the center goal is, but I am pretty sure that you should be able to get 7 tetras on it before getting 11’ in the air. And the 11’ is just based off last years field. I am sure that you are allowed to extend past that (until it becomes a safety hazard). I do however think that 5-6 may be the tallest stack we see.
What part of the rules is that restriction in? I can’t find it anywhere…
Just a little side note: Team MOE had a 30 ft tower inside of their pit at one of last year’s competitions…
I’m sorry, but anyone who thinks that any single robot will be able to stack 7 or more tetras has obviously run no tests. Either that, or they have done completely inaccurate tests.
My team ran some tests.
In a best case scenario, it takes 8 seconds for a robot to load a tetra from the human player loading zone and return to such a position as it is able to reload another one.
It takes closer to 20 to stack a single tetra at the closest goal, using a reasonable time frame for stacking.
I think we’re looking at a much lower scoring game–where the vision tetra is much more important–than anything else we’ve predicted, folks. The autonomous loading station isn’t going to be significantly faster, because your robot still has to load tetras and leave/re-enter the loading dock.
–Petey
It is going to be vital to stack more than one at once.
Think of all the time you spend in transit between goals. If you can even store more than one tetra on your robot, that saves you 10-20 seconds, or a good 20th to 10th of the game.
–Petey
This is true if, and only if, your tests reflect the timing characteristics of every possible way to stack tetras. Never underestimate the ability of truly creative imaginations to find ways to challenge your presumptions! 
-dave
Of course.
I will try to scrounge up the data we got. I will be truly impressed to see if a team can find reliably more efficient way to stack tetras quickly than anything we tried.
I won’t be unduly surprised if they do…but I will be surprised.
–Petey
I don’t know how many times my former teammates and I sat down and tried to logically figure out what an average number of scored objects might be, and what would be an unbelievable amount. I recall a team (maybe 95?) that looked like a popcorn popper (in 2002, I think) that was able to pretty much suck up every single ball on the field, when my team thought something like 1/4 of the balls would pretty much be the max. As soon as you start to put a limit on the scoring, you’ve made an assumption.
Of course, optimum scoring isn’t just adding tetras, but adding them to the best places and ending up in your end zone.
Still, as soon as you put out a number, someone will top it (not that the highest number of tets scored will win, but never say it can’t be done)