Nice! I had to give up on the chuck and interchangeable weapon. I found loads of tasty tools/bits I could fit, but the original drill motor and assembly was too heavy and using an arbor, adapters, chuck etc would also add too much mass. I want some spare capacity for some decent armour. I may return to the pure drill concept in a Featherweight, possibly multiple interchangeable weapons.
I personally liked core cutters and forstner bits as weapons, but these would look awesome! graduated hole cutter

The shape I chose is deliberately 'square edged' as I like the idea that they could flip as well as cut into opponents. I'd aim to get the tip to be as close to the ground as possible to get at wheels, or under the other bots. Through the use of skid plates I should be able to adjust the angle of the robot depending on the condition of the arena floor. If I was able to get the prongs fabricated from something tough say 3+mm Titanium or Hardox my hope is in this class they should be able to take most of what is thrown at them. Perhaps need to get the calculator out and do some calculations. Deformation and sheer I suppose I could calculate, but I'll have to do some research.

The motor powering the weapon will be this one from RobotShop which has 42kg-cm stall torque but is only spinning at around 100rpm. For me that seems plenty, unless I pin something to a wall I am never cutting/boring through it. I want to basically smack things about and if I come across something with weak armour I could in theory spike it and chew/spin it up. Not much in a 1.5kg class will stop that weapon moving with a radius of 3.5cm it will still flip or push/punch anything with ease (I hope). But I do have concerns about a fast spinner.

As a complete novice this is all based on estimates, instinct and supposition. Only building it and then competing will tell.