6kw - it will probably get to that if you were to stall the motors but I have a feeling that the wheels will spin on the arena floor before that happens.

In terms of boring out the sprockets, I would recommend doing it on a lathe. If you arent in a rush and the sprockets are small enough I could do it for you. Although my lathe is a small model makers lathe and I am currently busily getting both a feather and heavyweight ready.

Email me at gary.cairns at strath.ac.uk if you want to chat about it.