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Measuring RPM via Photo reflector
Computer
Interface
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The front wheels are taken from broken office chairs. These wheels are a bit difficult to take apart, but a combination of patience and some brute force will do the job. I drill a hole through the center of each half wheel which is a little bit smaller than the metal cylinder on the steppers' shaft and use some force to push it onto the shaft. A strip of self adhesive staircase grip paper around the wheels improves the grip on smooth undergrounds. The real wheel is a swivel wheel, the kind used under office chairs and TV trolleys. It is important that the real wheel turns easily, which requires that it has a very small area of contact with the underground, and that this area is only a tiny bit (a few mm) behind its vertical axis. The wheel on the left picture is much better than the one on the right. An alternative real 'wheel' is a smooth sphere that simply sits beneath the real of the stepbot. The brain of the robot is a Microchip PIC 16f84 microcontroller. This chip not very expensive, has enough horsepower for this simple control task and can be programmed quickly without removing it from its circuit. I use either a test clip directly on the chip, 2x3 pin header (one pin cut off as key) or a D15M connector as in-circuit programming interface. The electronics (16f84, crystal, 7805, ULN2803 and a few pin header connectors) can be build on a 2 x 3 cm breadboard.
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