This should give you an idea of what the finished spinner will look like. Ignore the extra threaded rod sticking out to one side. I originally cut it to have eight nuts on each "blade"; running the energy calculations on the spreadsheet revealed four nuts per blade will actually work much better (and shaves precious weight -- bonus!).
The support for the blades is 1" steel bar (cut from the same piece I used for the motor mounts), center-drilled for 1/4" shaft, drilled-and-tapped for 3/8" (I think) threaded rod on either end. I jumped the gun and rounded the edges of the bar with an angle grinder, but in retrospect I should have left it square for better "catch" when it contacts another 'bot. I've got plenty of steel bar leftover so building another shouldn't be an issue.
The spinner is held onto 1/4" steel shaft via shaft collars. In the final version I'll JB Weld the collars to the spinner. A keyway would be far superior but I don't have the hundreds of dollars to buy a broach set and arbor press. :(
The timing pulley is bored out to 1/4" to fit the shaft. Again, some JB Weld may be in order.
The whole thing will be driven by a timing belt connected to the weapon motor.