The good thing about this weight class being new-ish is that there is no established 'best setup' yet and weapons that wouldn't normally work or be effective in other weight classes have more of a chance of doing something.

I never got round to building a second beetle for the Wales event but if I had, I was toying with the idea of a spinning drill bit (somewhere around 6-10mm) that would go in and out of the robot. It's a wee bit old school and probably not hugely effective but would've been fun.

Using a cordless drill motor/gearbox for a weapon will eat up a lot of weight but it's doable. You can also use smaller scale motors and methods such as friction drive (a wheel rubbing against something to spin a weapon, possibly a flail if you're bored of the usual type of spinners) will be more effective and/or easier to implement at this level. Just keep bashing away at it, inspiration will hit eventually - probably when you're on the toilet or in the shower - then you'll be all set