This is the line following robot which i designed and built for an NCEA electronic design assessment. the idea came to me when playing around with light dependent resistors (LDR's), realising that the motor speed can be varied when wired in series with the LDR and a transistor. I decided to name the robot HEMI, simply because of its hemispherical shape.

Step 1: overview

You will notice that the pictured robot is built to micro dimensions(it measures 45mm in diameter), but this isnt neccesary, and this instructable will explain how to build it according to the parts that you can get hold of. the line follow robot is a great first robotics project, giving you good idea of how to achieve autonomous behaviour using simple electronic components and some mild soldering skills.

parts needed include:

 an NPN transistor
a resistor (the value of which later be determined later)
batteries (between 6 to 12 volts depending on size of robot and motor requirements, I used two 3v button cells).
two motor and gearbox assemblies
a switch
a light dependent resistor (LDR)
and a suitable shell. (mine was the clear case from a toy, it measures 45mm in diameter).
a multimeter or ammeter

note: the picture does not include the transistor because at the time of taking the picture i was still in the process of designing and didnt think that the transistor was neccesary. also, only one resistor was needed.

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