Re: [CAD_CAM_EDM_DRO] Re: stepper vs servo

cadcamcenter@... wrote:

> Hi all,
>
> Jon: No, absolutely wrong! Steppers have discrete steps,....
>
> Does the X and Y axis of a stepper moves in concert or one after
> another? What I am trying to figure out is:
>
> A move from x0 y0 to x7 y7 , is the path like this
>
> _|
> _|
> _|
> _|
> _|
> _|
> _|
>
> or like this:
>
> /
> /
> /
> /
> /
> /
> /

A 45 degree move should be like the 2nd, assuming the computer starts each
axis
stepping about the same time. Even if the steps are pretty discrete, the
fact they
move and stop at the same time makes the path pretty clean. (The spinning
cutter may
leave marks every time the motion stops, however.)

>
> Then how about a move from x0 y0 to x14 y7 ?
>
> Like this
>
> _/
> _/
> _/
> _/
> _/
> _/
> _/
>
> or like this?
>
> __|
> __|
> __|
> __|
> __|
> __|
> __|

Now, here's where the stepper starts to look bad. Assuming you are really
only
moving 7 x 14 steps at a slow rate, the 2nd case is what you get! When you
move fast,
the steppers smooth things out. And, the greater the ratio between the two
speeds,
the worse it looks.

>
> or neither?
>
> Exactly, how are the axes syncronised?

Well, the step pulses are generated by the CNC control, but it can't control
the
RATE at which the motor moves (except with microstepping or servos) so one
motor gets to the terminal point first, and stops. that's the whole
problem!

Jon