multiple 555 servo control question

[jtrout13]

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 2x 556 ICs. opinions will be greatly valued.

Thanks!

 

[MikeMl]

The only problem I see is running all four servos in lockstep (because the beginning of all four PWM pulses start at the same time) will put a big demand on the primary power source. It would be better to start each of the pulses staggered in time. I would be inclined to use a master clock source which runs at 4X 50Hz (200Hz) and then drive a two-bit counter (four states). Use the decoded states of the counter to begin each of the four PWM pulses.