I worked out I’d need about 20 N*cm torque to drag my camera about - the motor came from Ebay, and runs on 4 AA batteries.
I wanted this to be light and strong. I sourced 1 metre long aluminium U-tubes from Homebase. The edge pieces are aluminium trim, also from Homebase.
An aluminium sheet did the job here, allowing me to mount the motor securely. More of the aluminium U tubes made up the connection to the rails. I didn’t use any wheels as I wanted the platform to stop quickly after each movement.
A cheap one from Jessops did the job, it’s a basic ball mount for a tripod. I'll probably upgrade this at some point.