Maybe not most knowledgeable, but the will to make the effort and take the time to share this knowledge even to such noobs as me is a really big plus

And actually i was thinking of making the tube (almost) the diameter of the discs, so it would work as a drum with teeth only on the outside. But yeah.. making it smaller and possibly just use that as the pulley also sounds great, have to do the math on it.

On another route i was redesigning the weapon end completely to put the motor on one side, have slightly angled side/front armor and two 1cm thick aluminium bulkheads to put weapon axis as well as motor and pulley on to, and only having a ~10cm long (maybe a bit more, but have to make better scetches before i can say that) and 25cm diameter place for the weapon to fill.

Don't ask me how i did that, should do some recalculations, but somehow i ended up with adding a lot of Ali and a longer circumference (if i only count those places with side armor) and still somehow saved 1.7kg o.0
So if i didn't miscalculated the needed screws (i'll need a few more now), too, that leaves me with over 6.5kg for the weapon and pulleys left. That doesn't seem to be right. Would really have to upgrade to a bigger motor with that, i fear.
There must be a mistake somehow, going to try and put it into CAD today/tomorrow to prove me wrong somewhere. Only if "C" will be Cardboard or Computer i have to decide. possibly both.

Anyway, looks a lot more like the picture you posted earlier, nick. Just not exactly 45° corners, and still more like... up to 25cm of the bot lenght is weapon/bulkhead, and the Battery, ESCs, drive system and wedge only take up a combined 17cm of length.