Helios

This bot, despite having no sensors, avoids shadows and stays in the warm sunlight.

I used no complicated electronics in this build - but you could improve it by adding a photo-popper circuit.

How it works

The trick is simple: Left solar cell powers right motor, and vice versa.

Here’s an illustration of the movement:

Here’s also a very old video of it:

Materials used

• Solar cells in series (2 per motor - the more, the better)
• Two motors from CD-ROM drives (or any other)
• A piece aluminium, aluminium foil for the chassis, some plastic to encase the cells.

Here’s a detail from the front:

(There used to be a rubber tubing on the axes, I must’ve lost it somehow)