Science Buddies: "Ask an Expert"

Dear Experts,
One of my 6th grade students has bought the kit and assembled the light tracking bristle bot. The bot worked with a 25 watt bulb leading the way. When he tried to lead his bot through a maze with a 100W bulb, it began going in circles. When he tried the 200W bulb, it died. He has tried to revive it several times, including detaching and reattaching connections, making sure all connections are tight, sending you a picture (and securing connections again).
My question is if the increase in wattage may have caused the problem? Is it possible there was confusion to the sensor because the higher watt bulb reflected off of other surfaces? We had him try again without competing light and black paper surrounding the maze, but it still did not work at all.
It seems as if something is broken, so he is testing the motors tonight. Unfortunately, time is running short for his project and we are hoping the problem is not with one of the parts we would have to order to replace. I am hoping you can offer some insight.
Thank you,
Nicola Cleveland

Hi Nicola,

To clarify, was your student using regular light bulbs for this project? If so, was he doing anything to direct the light, like rolling a black piece of construction paper into a cylinder and putting it around the bulb? In general, this project will work better with a directional beam of light from a flashlight, than a lightbulb which sends light out in all directions. That makes it easier to hit just one sensor at a time to steer the robot left and right. It is possible that increasing the wattage could make it difficult to only hit one sensor at a time because there's so much light going in all directions, but it shouldn't cause the robot to break or stop working (it would just keep going straight or, if something is lopsided - like one of the toothbrushes being crooked, or the potentiometers not being adjusted equally - going in circles). So if the robot stopped working altogether, then something else is wrong and your student is taking the right steps by re-checking the circuit and testing the motors individually etc.

Hope that helps, please write back if you have more questions.

-Ben