Help for Junior Project Design Class - Servo Motor & 555 Timer

[hc3]

I'm building a robot for my junior project design class and I'm using a servo motor. I'm using a 555 timer as a variable speed controller. I was wondering how to get a negative signal from the timer. Any ideas?

 

[walshlg]

Ummm, Servos don't have a negative signal, rather the position is maintained relative to the pulse width via the feedback circuit to the position sensor (which is usually a mechanical potentiometer). So you send out pulses at some regular cycle length, eg 50 Hz, and the width of the pulse controls the position -> so a narrow pulse is all the way to CCW and a wider pulse is all the way CW (for example). A 50% of the max pulse length will set it at half way between.