Re: [CAD_CAM_EDM_DRO] microstep accuracy was what comprises as step

Hi Jon,

I just won a bid on a pair of Sanyo Denki "Super R" DC servo motors.
The encoder on them is 2000 cpi, and The motor is rated at 300W, 80V,
4.8A, 2500 RPM (R730-012W). So I *THINK* I've found my servo motors for
my RF-31 mill. Not too much on it on the web. The motor is 3" dia with
a square flange, and the motor is 5" long. Encoder adds another 1.5" to
the length. Encoder pinout printed on the encoder! I plan to drive it
with Gecko 340's.

So is this too much for my RF-31? It might be overkill, but since I
have them, I'll run them! I've been looking for the discussions on
previous servos (I thought I saved a few that I could follow), but I
haven't found them in my saved emails. I'm thinking of 7/8" ball
screws, and a short (1:1?) 3/8" ('L') belt. I'd love a discussion of
the potential of these servos!

This "long term project" just keeps moving along (slightly ahead of my
funds)!

Alan KM6VV


Jon Elson wrote:

>
> Carol & Jerry Jankura wrote:
>
> > What about the controllers that accept microstes but have a real servo on
> > the back end? What kind of accuracy can you attain with these?
> >
>
> It depends on a WHOLE lot of things. There are deadbands inherent in
> closed loop control, but they can be pretty narrow in some systems.
> The encoder resolution is the basic unit here. but, this can get quite
> high at reasonable cost. 1000 cycle/rev encoders are not terribly expensive.
> These give 4000 counts/rev when all encoder transitions are counted.
> If you put this encoder directly on a 5 TPI ballscrew, then you get
> 5 x 4000 or 20,000 counts/inch. So, the unit of resolution is .00005",
> yes that's 50 micro-inches! Now, depending on how flexible your
> machine is, how accurately the screw is ground, how accurately
> the table ways were made, what class of couplings you have between the
> leadscrew and encoder, etc. the accuracy of the machine can be
> low or high. I have such a setup on a VERY old and worn Bridgeport,
> and I can usually hold tolerances of .003" or so on modest sized
> parts. If I need to hold it tighter, I can adjust the program after a
> test part. having a machine with absolutely perfect accuracy still
> won't guarantee accurate parts. You still have to contend with
> thermal expansion of the part, mechanical flexing of the part and
> possibly fixture, and flexing of the tool. These can be considerable.
>
> Jon
>
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