[Tristan Lall]

The key point in my reasoning is Natchez's stipulation that "only one mechanism is on Redabot at a time" (i.e. a situation where both were attached would be physically impossible). It wouldn't be a "possible configuration" of the robot to have both modules installed. (In the situation where both modules might be attached at once, the rule is unambiguous.)

The fact that a drill motor is a common part to both assemblies means that it shouldn't matter in which position a drill is installed. I would suggest that Al's statement that it is not a "fully assembled attachment" is an ad hoc ruling, and one that is not explicitly stated in, or even supported by the official rules. While it may be a reasonable ruling, it is not the only possible interpretation of the rules as written. For the purposes of inspection, I would expect that the robot have only one drill motor attached, and therefore would come in underweight.

For the purposes of having your assembly ready for competition, the later installation of the second motor is equivalent to switching the drill for a fresh one while you change assemblies, unless, of course, FIRST was really trying to disallow the time savings involved. I don't see how that could be construed as a sensible motivation.

To further clarify my position, consider the following: you have a device which can accept an M12, 50 mm bolt in any of 24 positions. Only one M12 bolt is to be installed at a time, during competition. By the same sort of reasoning which requires a team to install both drill motors for weigh-in, the team is also required to install 24 M12 bolts, because a provision for attaching such a component exists. I'm reasonably sure that nobody would have insisted upon this absurd situation, even if it would have resulted in an overweight robot; but perhaps because of the "high profile" of the drill motor, we're granting it special treatment in this regard.