Mazibug

I saw the schematic for Mazibug on the Bicore-based photopopper page on solarbotics.net, and thought it would make a nice bot to build around my new 200mA jumbo-sized solar cell. For this bot to function properly, its power source at peak power needs to be able to supply the robot and still charge the storage caps. Luckily these N20 gear motors don't draw that much current.

The bot was built around a battery-powered toy car kit off amazon for a measly two bucks, which is a great deal for all the parts you get in this kit. The wooden chassis, wheels and rubber bands were all re-purposed for this build. Initially I had the front wheel stationary in the forward position, but I didn't like the loud scraping noises it made across the desk when moving, so I build this caster using a pinch roller from a cassette player and some spare parts from a plastic gear set. This improved its turning greatly and made the bot much quieter on the kitchen floor.

I finally got around to installing a touch sensor on one of my bots. Due to this bot's high speed and constant movement, a touch sensor and back up feature is necessary to prevent the bot damaging itself by running into walls. I didn't have any click pens to pull springs from, so I got some 0.012" music wire and a long steel screw and turned my own springs using a hand drill, which came out better than I could have hoped for! I will definitely be using this method for future builds. Using a threaded screw allows the turns to be evenly spaced, and create and overall better looking spring.

As seen in the video above, the bot will continually track the light source, rapidly oscillating the motors when trained on the light source. The backup part of the circuit causes it to back up for about five seconds while still orienting itself towards the light. Once the voltage across the caps reaches about 5v, it will switch to photophobic behavior and take off towards darker areas, in my case retreating to underneath the couch. This back and forth feeding and fleeing behavior reminded me of my first robot kit; Cybug Scarab from JCM inventures. I love this circuit and will definitely be revisiting it again.

Specs for my build:
2x N20 600 RPM gear motors
2x 10F 2.7v super capacitors wired in series for 5F @ 5.4v
1x 110 x 69mm 5v 250mA solar cell (more like 190mA)
1x 74HC240N Octal Inverting Buffer