Hi, I'm new to this site.

I am building a robotics controller for part of a junior design project at university. I am studying mechanical engineering, and would appreciate any input to this question:

Anyway, my robot has 4 servos. I am using potentiometers from a model airplane controller to adjust pulse width for speed and direction control of modified servos. Anyway, I plan to use one 555 timer in astable mode setting a clock frequency of 50hz, triggering monostable 555's which set the pulse width. I'm sure you are familiar with this type of application. On to the question:

Will it be okay to use a single astable 555 to trigger all 4 monostables, or do I need to set up an astable/monostable combo using a 556 chip for each servo? To reduce parts count and space in the controller, i'd like to use a single astable 555 and combine the 4 monstables on a 558 IC. opinions will be greatly valued.

Thanks!

 

I found a circuit for you that should work well. It's here.

 

We have just had a very long thread in which the OP used that circuit:
http://forum.allaboutcircuits.com/showthread.php?t=47149

1) The 3M3 Ω resistor is too large.
2) The pinouts to the servo are wrong for the vast majority of modern servos -- positive and negative are swapped. The center pin on modern servos is usually positive.
3) That circuit is for manually controlling a servo. It is a little hard to see how that would have much use in a robot.

John

 

It seems to me that you should be able to use a single 555 output (not all things considered), you may need to buffer the 555 output for higher drive currrent or faster edges. But, also consider that a single 555 will provide some synchronicity, whereas multiple sources will be out of sync with each other (if that's important to your design or not).

 

At the point you need 4 circuits may be time to consider a microcontroller, especially at a junior level in a university.