Let's Make Robots!

Phototropic BEAM vibrobot

Stays "alive" by navigating towards bright light sources

Updated 28/10/2009

Added a video of the bot in motion.


This is my first vibrobot. I've wanted to create a phototropic BEAM vibrobot for a long time but I was not sure how I was going to steer it to achieve the "phototropic" part. After seeing Evil Mad Scientist's Bristlebot I decided to try out a "catamaran-style" bot, essentially joining to Bristlebot's together and driving each side at different speeds to steer.

To control the bot's direction two LDRs are connected in parallel across the terminals of the motors (see below).


The LDR placed across the motor reduces the speed of the motor by reducing the voltage across it in bright light (more load on the output from the solar engine, the lower the voltage). The diodes allow the two LDR/motor circuits to operate independently. This configuration saves on using a transistor for controlling the motors' speed.

This configuration works quite well and the robot quite happily (erratically) drives toward the sun when left outside. The LDR's are on the same side as their motors so, for instance, bright light on the left side of the robot slows down the left motor, turning the bot to the left.

That's it for now, I will upload a video when I have consistent sunshine and my camera's battery decides to play nice :)

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Nice! I wonder if I could make a bristle bot out of my tooth brush. (it's a malibu bright toothbrush, the kind with a motor in it).  The motor is pretty powerful so I'm sure I could make something pretty wild with it.

Saw the video. Whoa he is fast! Neat little bot!

And I just threw out a toothbrush, too! Oh well. ; j

Cheers for the feedback guys, I will definitely post a video to show it actually tracking towards the sun as soon as I have a cloud-less day... :S
Why not make something like that controlled by a picaxe 08m? like instead of the logic alone, why not give it a light sensor and an SRFO5 to avoid obstacles?

Hi, I was going to use a picaxe initially, but I ran into a couple of problems.

My first attempt was with a 5v panel, but that was not constant enough in output and the current was too low (unless I used a large panel).

I then tried to use a smaller panel with more current (1.5V) and a AA -> 5V step-up converter (one of these) but the same problem with not enough current from the solar cell to produce 5V from the step-up converter.

The only way I could see this being possible is with a 1.5V rechargable battery installed in the AA -> 5V converter and using a solar cell to trickle-charge the battery. Then you could charge for a day, drive around for a little while (using 5V sensors etc) and then charge again... :)

nice idea . robo - boy i'll try making one .


good to see that people are using solar panels (is it the cheap one? ) keep up the work by the way how did you get the solar panel ????????
Hi, the solar panel was probably the most expensive part, it came as part of a "SCC3733a-MSE Powerful Bundle 2" from Solarbotics - for about $20 USD. I think this panel/bundle is probably the most powerfull (and expensive) Solarbotics has. I used all of the bundle to make the solar engine, except the motor. This solar panel and solar engine combination works fantastically (huge power) but takes about 30 seconds in bright sunlight to charge up.

How about something like these:


for ~$60 for 12 lights - each one comes with a small solar panel, and with a colour-changing LED - also switches and possible plastic chassies for anything you want to use them for later..


I get mine from the local hardware store, they cost about $5 per panel.

Nice robot and cool design!

I like that it's a solarbotic, and the way it turns, with the brighter light in one side :D