[JohnHorton]

I really like the idea of a launched minibot, as opposed to one running under its own power. A section of PVC that could fit around the pole (1.75" internal diameter, 6 in long) is about 105g. Say, with some form of hinging and latching system to secure it around the pole (split in half, with hinges on one side and magnets on the other, maybe?), it could weigh in at 120g. That wouldn't take much to produce the 4N or so at impact to trigger the target. Several thousandths of a joule or so.