I’ve heard of/seen robots that weigh up to 40 pounds. However, the density of steel (which I’m assuming is the densest vex legal material) is .2843 lbs/in^3, meaning that the theoretical upper bound of weight is 1658 pounds. The heaviest vex legal robot would obviously be lighter, as it would have to have a cortex, but how heavy could a functional, vex legal robot get?
For the purposes of this thread, I’ll define “functional” as able to move translationally i.e. a pushbot.
The robots tend to sink into the foam field tiles after 60ish pounds which means if you’re using wheels you need clearance for you chassis to not drag on the ground the wheels will sink in but should be able to drive as long as it has the torque to move out of the hole it’s sunk into and pretty much every robot has drive wheels. So in terms of how heavy a competition robot can be it’s really about how much weight can you’re chassis dig out of the field tiles.
I’m pretty sure Gladstone Robosavages team 2W for Gateway was the heaviest VEX robot I’ve seen. It was geared for something like .6 feet per second, and weighed in the neighborhood of 60 pounds. They were the critical robot on the World Champion alliance that year. Here is a video (they are the far robot on the blue alliance.)
It is the Mother of all wallbots.
At my team’s most recent competition, we were paired with a pushbot (464Z) in eliminations that weighed about 50 pounds. They put about 20 steel plates on the robot to give them more traction. The extra weight actually ended up helping a lot because they got into pushing battles with a nearly identical, but lighter, pushbot in finals and won almost all of them.