I came across this circuit on google. It controls motor speed by simple flip-flop that gives a PWM signal.
The question is can this be used as a servo control ?
first use 5 volts supply instead of 12 volts ...then by replacing the 3RD NPN transistor with a servo. the + goes up, the - goes down and the signal feeds from the flip flop...can we do that ??
Why not, but why?
Adjust a few of the timing values and it should work. But why? An NE555 would give you better stability and linearity with a smaller parts count. Fun circuit, none the less.
Circuit
You might try simulation to evaluate the circuit. Would allow you to play what if with the various components. BTW - analog simulation is not my field of expertise.
yea agree that NE555 works
yea agree that NE555 works good. But the idea is to avoid it by this simpler concept…I will give it a try and see.
Saving yourself hair and trouble
The timing values for an NE555 are easy to calculate. Not so for that flip flop. You are dealing with exponentials and fudgy bits such as where does the transitor turn on at (VBE). Not trivial to do the math as it is with the NE555.
Maybe you could try this?
I don’t know if you could replicate this schema with it but I was very impressed with what you can simulate on this website:
Maybe you could give it a try and let us know how it turns out.
I am quite impressed with
I am quite impressed with the 123d site you suggested. many project I do not have the time to put things together. Now can simulate them before even buying the parts.
I cannot thank you enough.
I was surprized too
My pleasure! 
I was surprized too when I discovered this site. You can even emulate an Arduino in the circuit if you want. I was mind-blown 
