This is a small vibrobot (based on the awesome bristlebot over at evil mad scientist) that I started work on a couple of months ago but never finished. My initial aim was to make a simple vibrobot that was self-sufficient (BEAM-style) and photo-tropic. This required some sort of directional-control for the bot, a solar engine and light sensors.
I settled on a solar engine from Solarbotics, two Colgate "micro sonic power" toothbrushes and two LDRs that I had laying around. After wiring up the solar engine I wired up the vibrating motor capsules (from the toothbrushes) , the LDRs and a pair of IN4004 diodes as shown below.
The directional-control of the vibrobot is controlled by the two LDRs connected across their respective motors. When the LDR is exposed to sunlight it conducts more current than when it is in the dark. This increased conduction causes the voltage across the motor to drop, slowing down the motor on that side and turning the robot towards the light. The diodes allow the two motor/LDR circuits to act independently.
Now, the important part, does it work? Yes, fantastically well, in fact! Its initial movement is very vigorous and erratic but as the solar engine discharges the bot clearly starts to steer towards the sun. It orientates itself so well at the end of its movement that I will be shortly tilting the solar panel towards the front to speed up the charging time.
Finally, the design of the circuit has resulted in a few interesting benefits that I hadn't realised before which I thought I would list:
- The initial vigorous and erratic behaviour gets the bot out of tight situations, whilst the phototropic behaviour is more evident at the end of the solar-engine's discharge. This gives the bot an "obstacle-avoiding" behaviour that I hadn't planned for.
- The brighter the light, the slower the bot moves and the less distance it covers (due to the LDRs stealing some of the solar-engine's discharge). This has the unexpected benefit of keeping the robot relatively stationary within an area of bright light, whilst making it more active when it is in the dark.
- Finally, as mentioned above, the bot aims its front at the sun almost faultlessly. This will allow me to tilt the solar panel toward the front of the bot (and therefore the sun), increasing its efficiency and reducing the charge time.