Sprockets
The sprockets need modifying before they can be driven by the motors
First remove the hub from the back of the sprocket, use a drill and drill down the center of the hub and then cleanup the surface so that's smooth and flat.
Place a washer in the centre hole of the sprocket then insert the center screw from the new hub
Now screw the new hub onto the screw sticking up, this will clamp the new hub on the sprocket and allow you to drill the holes for the mounting bolts (my bolt holes are already drilled in the photo's)
Makesure the hub is central before drilling bolt holes, using the hub as an jig
It should look like this when you have finished, I used M2 brass bolts to mount the hub.
The outer sprocket is held on by the central screw.
The hubs are HUB-06 from www.activerobots.com but they have a 4mm center hole and must be drilled out to 6mm - don't drill right through because you need the threaded center hole.
To help with track alignment over the sprockets grind the drive teeth off as per these pictures, on both sides.
Finished sprockets