I have made three versions- The first using a 540 size car motor with a 1:3 reduction ratio- This worked VERY well- the battery would last for ages.
The second was a direct drive onto a 540 dustbuster motor- but this really did not have enough torque- even on 9.6V to start my V.A 049 reliably, and it chewed through the batterys.

The last version uses a motor from a makita cordless drill- which is bigger and has much more torque than the 540 motor-it probablyis not as good a solution as the geared 540 as it uses quite a bit of juice too- but i does start my V.A and norvel .074 and it was easy to bang a few wires on it and an adapter!

J.M