As a note, just because the designs done so far are listed as their design intends them to be, that does not mean they will necessarily come out that way once we actually make them. Now then, some options for this phase.
BallistaeBallistae, theoretically we already have experience making these. They are after all the main weapons used by Bolter. In practice however, making versions that can be utilized by our armies soldiers is trickier then just changing the size and adding on a set of wheels. The primary reason is that Bolters ballistae are parts of its body, controlled by the gears and machinery that comprise it. This means that the primary challenge will be
removing some of the mechanical components, and adding methods of manual aiming and firing. Once we have a manually usable ballista,
then we can attach it to a basic adamant cart to make it mobile. Finally, they have a pair of large adamant plates like tower shields on either side of the place where the bolt fires from, these make it a bit harder to aim, but help to defend the crew from ranged attacks.
In the end, these ballistae will likely be less effective than an automated ballista of a similar size due to requiring a crew to load them, aim them, fire them, and move them. Each ballistas effectiveness will depend on the capability of its crew. The other side of this is that they will have less moving parts to break down, and will almost certainly cost less than a ballista that can do all those things by itself.
Alternatively, the boring but probably sensible option.
Adamant ShieldsNot really all that much special. Just simple round shields made from adamant to give our soldiers some basic defenses they can use in combat. These shields have a short but sharp shadecrystal spike protruding outwards from the center, both to serve as an improvised weapon in a pinch, and to make enemy charges more dangerous. The shields will obviously provide quite a bit less defense than a suit of armor, and needs to be used well to be effective, but a shield can fit all but the most physically divergent of units without needing to be remade repeatedly.
Research
Design
Ballistae (1): Failbird105
Adamant Shield ():
Revision