Re: [CAD_CAM_EDM_DRO] Re: breakout boards plus - hard choice

R Rogers wrote:

> Peter,
>
> Yeah I do think the unstallable stepper is being developed for the G100. Sounds like a good system. Personally, I'm not sure it's the direction to go though.
>
> If I understand it correctly, current stepper and servo drives are all unstallable in a sense, that they allow a certain following error.

This is not true for steppers. Any lag greater than 2 full
steps guarantees at least a loss of one full cycle=4 steps, and
unless it happens at dead slow speed it will cause the motor to
stall completely. Servos always have feedback, by definition,
and so will tolerate some amount of follwoing error, and will
then correct position when the overload is relieved.
The ability of the motors to lag behind the commanded position
and not lose position ultimately.

>
> A properly setup and operated system is very reliable in regards to positional accuracy.

I believe steppers can be quite reliable if the total operating
envelope of the machine is completely known. If you are trying
different things every day, then to total envelope of possible
conditions can't be known, that's when I get a little uneasy.
The only time this is an issue is when some unusual event
takes place thereby restricting an axis for whatever reason.
Yes, such as a chip on the ways or screw, bumping into a clamp
or the vise, etc. You won't always be aware of this happening,
and so you could have the position knocked off without even
knowing it. Of course, you can also exceed the grip of your
work fixture and cause the workpiece to slip and not know it, so
losing steps isn't the only way to mess up a workpiece.

Jon