Its the second bot I have made . It's using a phototropic bicore and 2 phototransistors instead of the normally used photodiodes. The bicore take me a lot of time to do because the space was very small on the pcb. The circuit and idea came from Ray Diaz website. I have used littles dc motors that came from a 1$ shop (originaly a ventilator ) If you decide to build yours , you should take others motors because these ones did not offer good performance (they are draining my battery very fast) For the real circuit look at Ray Diaz website on the links page.Click on the pictures to see them full size