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Measuring RPM via Photo reflector
Computer
Interface
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Stepbots by: Wouter van Ooijen I have build a number of stepbots: small PIC-controlled robot vehicles using stepper motors. The basic idea is to use two steppers which are directly connected to the front wheels, and a real wheel which can turn freely. The two steppers take care of the propulsion and steering. The steppers from old 5.25 disk drives are very practical, requiring 100 mA (per coil) at 12 Volt, which can be provided by 10 penlight NiCads. A 7805 regulator provides the 5 Volt required for the PIC 16f84 brain. A single ULN2803 interfaces the brain to the two stepper motors. I use either a 24 Volt wall wart to charge the NiCads and series resistor in the robot that selects the appropriate charge current, or a removeable NiCad pack. 5.25 inch diskdrives contain a number of different stepper motor types. You can find steppers with 4, 5 and 6 wires. The 4 wire types (often found in the more recent 5.25 drives) are bipolar and can not be used with the circuit described here. The 5 and 6 wire types are essentially the same. Use an multimeter to find the one (5 wire steppers) or two (6 wire steppers) common wire(s) that have a low resistance to other wires. For a 6 wire stepper connect the two commons together and you have a 5 wire stepper. Now you must find out the stepping sequence. You can do this by hand, using a 12 V power supply (watch out for the spikes when you remove the power from a coil!), or by connecting the stepper to the robot circuit programmed for continous motion. In both cases you must find the correct sequence by trial and error, but you can keep one coil fixed, and from the remaining 8 possibilities two are OK (one for forward and one for backward motion). |
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