My model of  K-9;  Dr Who's mechanical dog. 

I built this out of  Balsa wood,  from plans I found on the Internet (thanks to whomever produced those plans, let me know and I'll credit you). To download right click and 'Save Target As'.

Here are some pictures:

The wheeled base comes from an old toy train chassis that takes a single AA battery. I use a linkage to a rotating cam to move the ears...... not brilliant but affective. The 'eyes' are made from the translucent red casing of an old  pen.
There is a LED that lights when he hits an obstacle, taken from an old Scalextric car.

I think I will get a small remote control car and use the chassis.................................