For my next robot I plan to make a wall (defensive) bot. We are curious however as to what a wall-bot would actually do in sack attack. We were especially concerned since the robots would be separated by troughs at the outset of a match
Especially in the case of a defensive robot, the robot should be designed with a very specific purpose in mind. Just as there are offensive objectives in the game (intaking sacks, outtaking sacks, trough vs. high goal, etc.) there are a different set of defensive objectives.
A discussion about the relative importance of these defensive objectives will give you an idea of what your robot should and shouldn’t do. For example, the defensive objectives intrinsic to the generic “wall bot” would be either goal starvation or object starvation (or are there more?). Looking at defense in Gateway as a precedent, wall bots did this best with horizontal expansion and high power drives. Achieving goal starvation by creating a situation where the opposing alliance didn’t have enough goals to use all the objects on their side of the field.
Questions for thought:
-Is it feasible for a wall bot to block off the full 12 feet before a robot blocks the expansion/gets past?
-Is there a problem with blocking off half the field to your alliance partner?
-Is it necessary for a wall bot to block off the full 12 feet?
-Could you hoard sacks?
-The floor goals seem hard to cut the opponents off from, how will you deal with this?
-What would theoretically happen if you played a robot identical to yours?
Your post was very open ended, so I gave an open ended response. By your forum tag, I noticed that you were from Exothermic. Hope to see you at Jumpstart and good luck to you.
I’d say have it go to the other side of the field and just block the other teams. It needs an intake system too, though. If you can’t pick up the sacks, it’ll be pretty worthless since it’ll be so easy to get around it unless you can somehow manage to get the robot all the way across the field before either of the opposing alliance robots pass it. A wallbot this year should really only be used to annoy the other team and make it harder for them to score/descore. Actually stopping them from getting anywhere like in Gateway would be near impossible.
If you really want to make a wallbot, here’s how I’d go about it. Basically a “son of 575” design.
Make a 12’ elastic powered pneumatic-latched wall on the front of the robot. This is the difficult part, and it’s going to be very heavy.
Put all the motors you can on drive.
In autonomous, shoot under the trough and expand, blocking off 3/4 of the field from the opposing robots.
Try not to get pushed.
I never did see the 575 bot. EDWARDZAHHH, 16807, 575Haiku: Got any pictures/ video?
I think the 575 robot may have broken down or not worked as planned, however they did end up winning the innovate award.
http://sphotos.xx.fbcdn.net/hphotos-ash4/s720x720/398881_319061218165941_100001861978366_753653_1461146138_n.jpg
I remember that they were not working properly in one match, but i did see the coach holding the robot on the way to the pit, and it looked like it was at least 4, if not 5 feet tall. (when tilted) 
Uh, well, there are no pictures/video of it working in a match because it never did…
Basically, the idea was to have an immobile base extend a wall down the center of the field, defending our partner and hoarding all of the pyramid objects. It would have been mathematically impossible to beat us if it worked. Unfortunately, our bot got messed up on the plane, new sliders needed to be changed to old ones because the plastic inserts started breaking, and a host of other problems cropped up during worlds. We had some other neat features, like a super stacker (developed simultaneously with 1107B’s, we didn’t copy them) and a doubler preventer, but we were too busy fixing wall to get the others mounted for matches.
A word of the wise, don’t try to make a super extending robot. The tension you need to extend 6’ instantaneously, let alone 12’, strains VEX parts and is inherently dangerous. Stopping your opponents from reaching the troughs or the high goal is a guaranteed way to win, but you can’t bank on your ability to drive far enough through the troughs to prevent scoring and then extend before another robot can get by you.
One of the major anti-pushing ideas from last year was just to make the wallbot really heavy. I guess this year, if you have a wallbot with a simple intake, it can make itself heavy by taking in objects.
I think “son of 2W” will be more feasible for this game 
Having built 4886c, which is what brought on the term “wallie” using just VEX sliders will not work for this game. I say this because the sliders on my wallbot were unstable past a certain point.
I think that a defensive bot shouldn’t automatically be a wall bot. With the relatively open field layout, trying to block off a portion of the field to prevent scoring does not seem quite as feasible, or at least as easy, as some other possible defensive solutions. It worked for Round Up and Gateway, but it might not be quite as good for Sack Attack.
Defensively, you’re trying to prevent them from scoring as much as your alliance can score. Physically blocking off the goals might work, but it just seems really hard. The other option is to make it impossible for them to access any sacks to score with, although there’s quite a lot of them all over the field, so it would be pretty hard to do that too.
Actually, I’m not entirely sure that making a purely defensive bot is that viable this year. Defensive actions, yes, but maybe not a robot that is purely designed around preventing opponents from manipulating game objects and moving them to a scored area for their team. Might as well work on the other half of the game (manipulating game objects into your own scoring zones).