Let's Make Robots!

xi, the cross-eyed phototropic robot

Heads towards brightest light source it can see.
circuit diagram2.48 KB
Just after it was built46.3 KB
xi_side.png205.01 KB
xi-front.png199.48 KB
xi-top.png208.18 KB
xi-under.png193.96 KB

I named the robot "xi" - pronounced "cross-eye" for reasons which may be a bit embarrassing. Having completed my phototropic robot and went to test it I discovered that the robot would run away from the light as the two motors were supposed to be connected on opposite sides of the IC, instead of re-wiring the project I twisted the photodiodes so they cross each other, giving the appearance of crossed eyes.

The robot consists of: two photodiodes (pulled from a VCR), a 7404 IC (Hex Inverter), two transistors (BC548), two diodes (scavenged from some PCB or another) and a Ni-MH battery pack from an old mobile phone. The chassis was made by soldering copper wire to the motors and provides a simple, flexible base for the bot. Two wheels made from balsa wood finish the robot. As all the parts were scavenged or found (exception of the transistors which were bought in a set) the build didn't cost anything, which was a key factor in the design as I didn't have any money for buying parts when I made this back in 2004 (poor student and all that).

Circuit Diagram

Thanks to the folks who commented on this I was spurred into taking a few photos.

xi - frontxi - underxi - topxi - side

09/09/12 - Added video I made today. Sorry it took so long to get round to making it.

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I can't tell from the photo if there is a piece of copper wire in the back keeping it "standing", or if there is a small wheel back there.

correct with your first guess. at the tail of the robot a single loop of copper is soldered in place to prove a small point of contact to skid along upon.

I would like to see that little dude in action ;) video please?

Dusted off xi and charging the batteries just now.

Better late than never I hope.

Cool video. It was worth the wait :-)

That little guy looks cool and I can see the two Cross-Eyed Photo diodes, it really looks like a Cross-Eyed Robot and nice name, I like it "xi" :)

The little devil is really cool. I like that it moves so smoothly.