Re: Servos and Vexta

Alan Marconett KM6VV wrote:

> I'll take your advise on the servos, 2:1. Sounds like good reasoning!
> I certainly don't need/want to go that fast!

One of the problems with servos (doesn't happen all that often if you
build things right) is that a servo runaway WILL go as fast as the
motor/power supply combination CAN go, and that can be pretty
scary. I rarely run my machine over 60 IPM, I'm just not in that
much of a hurry, and if you do it manually, you are likely to have a crash.
When I get a program really working just right, I may turn the feed rates
up a bit.

Since I have only manual tool changes, and sometimes I touch the tools
to the top of the part, and sometimes I rig the program to use length
offsets for different tools, I can get confused, and forget to reset the Z
axis when a tool change requires it. Nothing like plunging a drill bit
into a block of aluminum at 60 IPM to raise your heart rate!

Ahh, but CNC is so nice! I was able to turn the part over (it was designed
to have blind holes exactly opposing each other) and drill extra deep from
the other side, and hit the broken drill bit dead on. It dulled my drill, but
I was then able to drive the broken bit out of the hole and resharpen
the unbroken bit. Saved the part!

> The Super Vexta (I just found out) also has a half/full step switch, and
> I can see a hint at the drive being able to do step/dir as well as
> CW/CCW reading between the Japanese "lines". Possibly if the CCW line
> is held high?

Mine has a 2P / 1P switch that does this, I think. The terminal labels are
"pulse" and "CCW/CW", which gave me a pretty strong indication that
those were really "step" and "dir".

> I can't make it out in diagrams accompanying the Japanese
> text. I didn't find any other switches. There is a T.I.M. signal, and
> an H.off signal out of it, and some diagrams relating them to steps, but
> I've yet to determine their use. One signal would seem to be "tied" to
> "step 0" and every 10 step thereafter. I probably don't need them!
> 1000 spr will be nice!

Some other labels I've figured out is "AWO" = all windings off
and "timing" is an output that becomes active at only one full step
polarity. I guess this is used like the encoder index signal to refine
home position.

Jon