This uses the LM324, a 14-pin DIL IC containing four individual op-amps and running off a single-rail power supply.Two sections of the quad op-amp form a triangle-wave generator, but now the third section is used as a low-gain amplifier, bringing the trough of the wave to just above zero volts and the peak to about 10v.source

Typical remote-control systems and robotics applications use standard R/C servos, which often require a reversal of the direction of rotation. Since varying the input signal’s pulse width between 1 and 2 msec controls the servo’s output position, a circuit that adjusts the pulse width to cause direction reversal can often come in handy. Many such circuits exist that use relatively sophisticated servo-control ICs, but this circuit uses a standard CMOS IC to produce a reliable design at low cost. source

This project has quite a few robotics applications as well.could build a robot with 8 servo motors and control him directly from the Servo Commander software interface, or use the PIC16F84 as the dedicated servo control chip in your Basic Stamp projects. Once you have experimented with the Servo Commander software and the PIC servo controller you will probably come up with hundreds of other applications.source

This circuit takes standard 0-10V control voltage (for example from analogue light controlling desk) and outputs a standard 1-2 ms RC servo motors control pulse. In this circuit NE555 is configured as astable multivibrator. The main timing capacitor (220 nF) is always changed to the voltage level which is determined by the voltage on NE555 pin 5 (in this circuit that voltage is aroun 1.6V). When the timing capacitor is charged only with current coming through 33 kohm resistor, the charging takes around 2 milliseconds. When control voltage is appied to control input, the charging current increased when conrol voltage increases. When th econtrol voltage is 10V, the charging takes around 1 millisecond. source

The program uses two pulsewidth variables, pw1 and pw2; and two sets of routines, left1 and left2, right1 and right2; one for each motor. As you can see in the schematic, the first servo is wired as per the previous circuit. The second servo is now using B3 as it’s pulse out, and B4 and B5 for the SPDT switch.source