To form a group of Tripods:

My group so far (Building toward 18 tripods:)

1  Dominator
1  Veteran Tripod
6  Assault Tripod
3  Scout Tripod
2  Reaper
1  Grenadier
1 Royal Scientist
1 Harvester

My plan is to have a Dominator and two Assault tripods
                           a Veteran and 2 Assault Tripods
                           a Royal Scientist, a reaper and a scout
                           a Harvester a reaper and a scout
                           a grenadier a scout and an Assault
                           An Assault tripod is not used.  Two slots are remaining.

I may add an Assault instead of a /scout tripod with the Royal Scientist.  The scout allows me to "call in" the support of a Grenadier, and more speed to catch strays that the reaper digs out.  The Assault is a more robust bodyguard.

I have 16 tripods and I want to build to 18 tripods, and I am undecided on which two to get.  A second Grenadier and a constructor are my picks, but so far, no constructor.

I do have a small coven of drones.