This general analysis of using a swarm focuses on the physical constraints imposed by the competition. Specifically, I'll look at swarms where one or two robots provide one function and the remainder of the swarm provides another function . (See Swarm or Solitare.)
The rules clearly allow for a swarm in rule R20 although the term used is "spawn". The rules consider a swarm as the robot. Generally, any physical restriction on the robot apply to the entirety of the swarm.
The following apply overall to the swarm:
Weight of 80 kg
Size of a 1.5 meter cube
An interesting restriction is created by the emergency stop (e-stop) and start switch requirement that these switches be .75 meter above the ground. If one were to envision somehow stacking swarm units, say a two layers of 5 robots, this switch arrangement, sticking up from each robot, would be an interesting challenge. Since the second layer's switches would be outside the 1.5 meter cube restriction, stacking is probably not feasible.
Just to obtain a sense of scale, if we put 10 robots in 2 rows of 5 (one layer!), the size of the robots is 0.3 m x 0.75 m (i.e, for my meter impaired brain about 12 in x 30 in). Thinking off the wall consider 12 robots in 3 rows of 4 which makes the robots 0.5 m x 0.375 m (20 in x 15 in). This latter sizing is probably a good starting point for a swarm robot design even if fewer than 12 were used. It would be possible to get a reasonable quantity of well sized robots.
For weight, ten robots would be 8 kg (17.6 lbs) and 12 robots 6.6 kg (14.5 lbs). The weights seem light for robots that have to run for 2 hours on battery power.
Update 10/25/2012
Continuing the thinking on swarms, what if there were 7 robots? Two are used for searching and five used for picking up samples and returning them to the starting platform. The starting point for consideration is that two searching robots can more easily cover the competition area within the time limits, especially if they do not need to stop to collect samples. Having five robots collecting samples means there is more time to go to a sample and return to the starting platform.
The weight of the robots could be 11.4 kg (24.5 lbs). The seven positioned side-by-side could be 0.21 m x 1.5 m (or 8.2 in x 39 in) which is a bit narrow. Five in a row with two on the back row back-to-back would be 0.3 m x 1.2 m in the front row and 0.3 m x 0.75 m in the back row (12 in x 47 in and 19 in x 30 in). Interestingly, these dimensions work out nicely for the Dagu Wild Thumper 6WD I mentioned in my blog a couple days ago (16.5" x 12" x 5"). The Thumper's weight is 6 lbs and can carry 11 lbs for a total weight of 17 lbs. The 7 robots would weigh 119 lbs, well under the weight limit. (The width at 12" may be tight but the dimensional drawings show the width at 297 mm or 11.7 in.) The height is not an issue.
Another layout is 4 x 3. The resulting dimensions are 0.38 m x 0.5 m (14.76 in x 19.69 in). That is with the back row robots back-to-back. Putting the back row side-by-side results in the same dimensions because the rows are both 0.75 m and the front row width remains a 0.38 m. A possible issue with the side-by-side back row is that these robots would be trapped by front row robots that failed to move when started.
At least based on dimensions and weight a swarm of seven robots, having the same sizes, is feasible. It would also be possible to increase the width of the back row robots since the front row has over 1.13 m in depth which could be shortened.