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...My question is; how does the servo selfcenter and how is this system constructed?
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Hi Edblad,
servos use a feedback mechanism, comparing the desired position (usually derived from a PWM signal [1-2ms pulses every 20ms]) with the actual position. In most standard RC servos, a potentiometer connected to the drive shaft senses the actual position. Some of the basics are explained here:
http://www.geocities.com/bourbonstre...rvobasics.html
Instead of a pot for position sensing, many alternatives are possible: Hall sensors (linear sensors or digital ones [together with a magnet on one of the shafts driving the gear; the microcontroller calculates the actual position by taking the gear ratio into account]), optical sensors, etc.
I have built my own (digital) servos (using optical and Hall sensors) for special applications. In many cases, you can trim down the case of a commercial microservo so that it fits into a 1/87 scale model.
Another very helpful source of information is the open servo project:
http://www.openservo.com/
All the best,
Fred