Servomotor Control Program

  
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In our first program, we will simply sweep the servomotor from CCW to CW and then sweep back. The program will be kept simple as to demonstrate the priniciples of controlling a servo with a the PIC Basic language. The schematic can be seen in figure 2 (below). The variable pw controls the pulsewidth, and is started at 100 (extreme left, -45 degrees). The program sends the pulse out to
Servomotor Control Program - schematic

the servo, and then is increased by a value of 1 until it reaches 200 (extreme right, 45 degrees), at which point it will reverese the rotation. If desired, we could extend the rotation of the servomotor to a full 180 degrees (-90 to 90 degrees) rotation by decreasing the minimum pulsewidth to below 1 ms and increasing the maximum pulsewidth to over 2 ms. This can be accomplished with our previous program by modifying the occurances of 100 and 200 to your desired minimum and maximum pulsewidths, respectivly. However, a note of caution: the pulsewidth required for servos varies from brand to brand. One motor may require a 2. 8 ms pulsewidth for maximum rotation, while another may only need 2. 4 ms. Furthermore, servomotors have end stops that limit its rotation. If you send the motor a pulsewidth that is beyond the end stops, the motor will keep trying to turn. A motor in this stalled condition not only draws more current, but also puts wear on the internal gears, shortening the lifespan of the motor.



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