Hi,

I am newbie and am looking to build Controllers for a DC Servo on a Bridgeport. I am thinking of using Mach4 and a CNC4PC breakout board.

Can someone point me in the direction of a GOOD reference to understand the various protocols / standards involved?

As far as I can see the Controller inputs, for each axis, are Step and Direction; with a Controller Error line output.

The Step is a set of 5V pulses - what exactly does this represent. Can't quite get my head around it yet.

Presumably Mach4 sends out the pulses to match no. of encoder steps to reach a new position from the current position? But what influences the rate the pulses are sent; is it as fast as possible (and the controller has full velocity control) or does Mach4 control the velocity by the step rate? How does Mach4 decide when to send the next position change; does it depend on the Controller being faster and keeping up using its own velocity profiles to judge when to send the next position? Does Mach4 have some kind of delay to ensure the machine has completed its move or is it the relationship between the Mach4 (slower?) and Controller (faster?) velocity profiles that ensures steps are completed in a timely manner. The Controller profiles are presumably tuned for best machine response. My 'confusion' arises because the encoder feedback goes to the Controller (great for PID control) but not Mach4 which provides the step/position control. Is there a 'danger' of a stop/start path movement if as Mach4 does not know the actual position it must play 'safe'?

Or am I a total idiot and misunderstood!

Thanks in advance for your intelligent replies.

Dick