This is the reveal for the wallbot we brought to Worlds. As far as we know, this is the largest robot in VEX history. Sadly we do not have any footage of it, but you can check out the livestream archives from worlds if you’d like to see. Our final match was Q195 in the Engineering division. Pictures are here: https://www.flickr.com/photos/123583170@N08/sets/72157644089099400/
This robot was built in about two months. We worked on it in the background while we competed with our offensive bot to get qualified for worlds. The goal of the wallbot was to block the opponents from the cylinders, but given the way the robot came out a lot had to be done to make that actually help our team.
At the start of the autonomous period, the two long linear expansions expand from 18" to a length of about 12 feet in the space of about one second. Yes, ONE second. This was an extremely fast expansion requiring four pistons to release and nearly 200 rubber bands by the end of worlds to actually expand fully. Those 200 rubber bands needed to be replaced before every single match, because they wore out with just a single expansion. Additionally, standard #32 rubber bands did not stretch to 17.5" without breaking, so we had to pre-stretch every single one of the 2000 rubber bands we used at worlds.
Additionally, our “minibot” drives off the top into the goal zone and our “microbot” drives into the middle zone at the start of auto as well.
We did not want to make the entire robot move forward so that our partner could pass through from the hanging zone to the goal zone because we knew the robot would be very unreliable that way, so we had to improvise. We built an entire side roller robot capable of playing buckies and big balls with 8 motors. It was only 10.5" tall and could still reach the cylinders. This was connected through the C channel “umbilical cord” seen in the photos. The goal was for the partner to pass us objects over the main “wall” base, then we would score them with the “minibot.”
We felt that we needed to protect our partner from the opponents so that they would not get defensed, though we did reconsider this during worlds. However, as you can see the robot shoots two linear “spears” out at the start of the match. The one on the hanging zone side is shorter, and there is a double piston assembly on the front/bottom that pushes it out and into the wall to make the geometry work out on the field.
What an average onlooker might not realize is that when this robot plays red and blue, the hanging zone expansion and goal zone expansion would have to switch places. Thus, even though only the hanging zone side needs to “pop” out to the side while expanding, and even though the hanging zone expansion needs to be shorter but also more powerful to get over the bump, the two linear slide racks on this robot are actually exactly the same.
A system of mechanical stops that could be switched between matches was created such that we could choose which spear would be for the hanging zone and which would “pop” out to the side while expanding. Other things that had to be switched for sides include the ENTIRE umbilical cord for the minibot as well as the direction of the chute the partners pass the balls over. The color switch usually took about 20 minutes between matches.
The “microbot” was created because we knew we really only needed 8 motors for the minibot and we wanted to try to make a difference with the last 2 of our 10. We built a small, agile robot with those two motors and deployed it into the middle zone with another umbilical cord behind it. Its goal was to do just about anything, wreak as much havoc as possible, etc. We never really expected it to be a game changer, but we figured anything this little guy could buy us would definitely be worth it, so we built it. Problem was, since the Cortex was on the minibot, this microbot was separated from the brain by about 30 feet of wire. Turns out, if you try to run a motor about 30 feet away from the Cortex, it doesn’t work very well. We solved this problem by installing the power expander inside the tiny microbot, meaning the only thing that had to go 30 feet was the signal. The power for the motors only had to travel from the power expander to the motors. This solution worked very well. The microbot was definitely silly and we appreciated that.
We had some issues at the beginning of the event. The expansions did not always deploy all the way right at the start, and a couple of teams managed to drive over our expansions which was one of the last things we worried would happen. Obviously this was not ideal, but we worked hard to get it fixed. The expansions got tuned up relatively quickly. We added more rubber bands and got the pneumatic pins that released them working better. We completely de-greased and re-greased our entire slide racks each night.
We got it fixed by Saturday morning and added in some hardware that actually made it impossible for anyone to drive over the walls in our last two matches but it was too late to show what our robot could do. We had several matches near the end where our robot deployed perfectly, scored autonomous points, and blocked the goal zone off.
The hanging zone wall was there to keep the opponents from 2v1 defending our partner. That being said, by alliance selection we had decided that we would be willing to leave that wall in and allow a strong alliance partner to have free reign of the field because we believed they would probably be capable of holding their own against the opponents.
We were not picked, probably because we had some bad matches near the beginning and hadn’t shown a strong enough case for our robot’s strength. This was a rushed 6 week build with no cad and several hiccups building the 26 sections of the linear slides. We fabricated nearly 200 brackets out of steel plate on a vise with two bends in each finding the perfect design for the front and back stops for our slides and the rubber band holders. We also went through about 2,000 rubber bands at worlds- every one of which had been prestretched ahead of time to be able to stretch to the 18" length of our slides without snapping. We used an entire tube of grease redoing our slides each night before the next day and spent over $500 on linear slides building this robot.
This robot was a massive engineering challenge, but we wanted to see if we could do it. I am very proud of the team and of this robot and I’m glad we chose to build something unique.
We may not have won that many matches, but I think the robot excited a lot of people and drew crowds to our booth almost constantly throughout worlds. People came to see our matches just because we built three robots in one and they wanted to see it. It was a great experience, definitely a lot more fun than the scoring robot we built last year. We won the engineering division Create Award and made Karthik appear speechless at our match, and that’s enough to satisfy us for this trip to worlds. 
We will be in college next year, but this was our third year building a wallbot and it won’t be our last. We built a scoring wallbot for gateway, a 12 foot double trough blocker that opened in 8 seconds for sack attack, and then this ridiculous robot that took about a second to open and expand thirteen feet. I have no idea how we will raise the bar for ourselves again 
Thanks for all the compliments we received on our robot at worlds
Any questions or comments would be much appreciated.
Pics https://www.flickr.com/photos/123583170@N08/sets/72157644089099400/
