As far as the minibot / tower problems, there are 4 bolts hanging out the bottom of the sensor which are firmly attached to the top plate of the tower, so hitting them wont trigger the plate. These are in the field drawings (Page 37, 38, and 69, the bottom-left drawing on page 37 is upside-down, the collar should be on top), and a reminder was sent out in TU18 that these bolts will not trigger the sensor. Also discussed to great length in this thread:
http://www.chiefdelphi.com/forums/sh...ad.php?t=93650
The bolts themselves have a pretty significant weight, if they were attached to the bottom plate (and thus would trigger the sensor), the mass of the bolts and plate would take much more force to move (probably double, maybe more)
A number of teams who had problems with the bolts came up with some pretty innovative solutions, including one I saw today at North Star which added a piece of surgical tubing to the top, inside of the bolt radius, that would trigger the sensor and then collapse, so their switch would still turn the bot off, even through their switch (The original point of contact) may hit a bolt.