I'm assuming the spinner is 15 to 25kg.

Nice idea but a few things that jump out at me as issues,

- Ring spinners are a nightmare as your bearing supports have to be incredibly well machined (see MR speed square) to take the knocks. Not sure I understand what you mean by 170mm by 25mm ball bearings?

- You will not get anywhere near a 2s spin up with friction drive. It's a method that is limited to the small contact area between the wheel and ring. Whereas belts and chains have contact right around the pulleys and cogs and transfer it far more efficiently.

- What grade of ali?

- Omni wheels are a nightmare as well. Each one of those pins has to contend with potential forces that will bend 20mm axles. Tried a couple of custom made ones in typhoon 2. They were binned after the qualifying match for series 7.

Honestly, I'd junk the omni wheels and just go for 3 standard wheels with big axles set at 120 deg then use one of these to control it,

http://www.robotmarketplace.com/products/0-OMX4.html

No point re-inventing the wheel when it's easy enough to order up. The arena floor is slippy enough that 3 regular wheels should do the job fine. Driving with brushless is still very experimental. Here is where dragons lie.

Oh and I think you will struggle to fit it all in a 70cm diameter shell. Typhoon 2 was 1 metre in diameter and it was tight on space. At 70cm diameter and 15 to 25kg I suspect you are only going for around 15mm thick steel? Might want to up that to 20mm plus at least.