My problem is right now that the sign up for Manchester went up a couple of days ago,
Eh? When (and where) did this happen?

Should I buy a 24v scooter motor and run it at 18v?
When you say scooter motor.... do you mean the MY1020 variants? If so, I am quite happy to lend you one of Kaizen's drive motors, they are 500w with a gearbox attached but I will need it back. Comes with the "out of the box" gear sprocket on it.

Ultimately, even if you don't get the weapon going, I'd still go if only for the experience and "stress testing" of your drive.