Further to my previous post on this. Pin headers are now soldered on to the motor board, and the project is rebuilt. This works much better. A bit of re-wiring was needed but it is complete and does find objects and turns to avoid them.
The code probably needs a little more refining. I am now hoping to demonstrate this at the tech jam. However also in schools. When I find a suitable box that can house this, then I can transport it round without it getting bashed about.
Also note that I have replaced the cheap Poundland batteries with decent Duracell batteries. These have much more power so the motors now turn properly rather than struggling like they were before.