Re: [CAD_CAM_EDM_DRO] EMC tuning question.

jguenthe wrote:

> I have a question about the relationship between DEFAULT_VELOCITY,
> MAX_VELOCITY, DEFAULT_ACCELERATION and MAX_ACCELEATION. My system is
> currently configured as follows:
>
> DEFAULT_VELOCITY = 0.0167
> MAX_VELOCITY = 0.2000
> DEFAULT_ACCELERATON = 5.0
> MAX_ACCELERATION = 5.0
>
> On my Sherline 5400 mill with 20tpi lead screws this gives me reliable
> rapids of 12ipm. I can increase MAX_VELOCITY up to 0.3000 which should give
> me about 18ipm. This seems to require changes to he ACCELERATION parameters
> but I can't come up with the appropriate numbers to get reliable operation.
> What is the proper relation for the ACCELERATION parameters to the
> MAX_VELOCITY parameter?

There is no standard numerical relationship. As your motors will be
spinning faster, you may need to reduce the acceleration at the higher
end. Since there is only one acceleration used throughout the move,
you may have to reduce it for the whole move. velocity is in user units
(either inches or mm) per second. acceleration is in units of
user units/second^2. Acceleration of 5.0 sounds pretty high. It
may be fine for a Sherline, however. Why do you think it requires
changes? Are you losing steps? If so, then cut it way down, to 2.0 or less,
and then if you want more acceleration, increase it in small amounts
until you again get lost steps. Back it off a good measure to allow
for machining loads, and you should have a good, reliable setting.

If you are not losing steps, what are you worrying about?

Anyway, assuming inches for the user unit, for a 5.0 acceleration but only
.3 IPS velocity, the acceleration all happens in a small fraction of a second.
If you set acceleration for .3, it would take one second to accelerate to
full speed. At 5.0, it would take approximately .3/5.0 = 60 mS to accelerate
to full speed. This is almost certain to require more acceleration than a
small stepper can handle.

Jon