Re: Gecko Servo Drive Choice

Tim,
I don't care if you aren't Mariss, I'll take help from anybody 8>)

The computer I'm planning to use is a 266Mhz Pent MMX (same one you
helped me set up with Linux/EMC). High speed isn't a big issue with
me, just want it to go to the right place reasonably quickly. My
ballscrews are 5 tpi, I was thinking 2:1 reduction, but only for the
sprocket size, I'm not wedded to it.

Sounds like with the slower computer I might be better off using the
G340's, although you seemed to think it wouldn't matter much when you
assumed a faster computer?? On the other hand, the encoder count is
200/800, which is less counts than you were thinking with your
example calculation.
Terry

--- In CAD_CAM_EDM_DRO@egroups.com, "Tim Goldstein" <timg@k...> wrote:
> OK, so I am not Mariss. I was involved in quite a bit of discussion
that
> lead to the creation of the G340 product though.
>
> First the from the field answer to your question. If you are
running EMC on
> a AMD K6 500 or faster computer and have a 3:1 reduction and a 5
tpi screw
> you will get 135 ipm from the setup at 24 v. What happens if you
try to go
> faster at this voltage is the motor hits its maximum RPM at about
2100 rpm.
> If you alter the effective reduction (screw and reduction ratio)
you can get
> faster movement (motor will still only go so fast, but the table
will move
> farther). At the above step rate EMC has no problem and the GUI
remains
> responsive if you are using steppermot.
>
> There primary reason for the G340 is that you are using a
combination of
> high encoder count, large reduction ratio (actual reduction +
effect of
> screw pitch), and a step and direction program on a computer that
has a
> limited step rate. Here is an example.
> Encoder 1000 slot = 4000 steps per motor revolution
> 2:1 belt reduction and 10 tpi screws = 20 motor turns per 1" table
movement
> 20 revolutions X 4000 steps per rev = 80,000 steps per inch
> 180 ipm then requires 80,000 steps X 200 = 14,400,000 steps per
minute or
> just over 240,000 steps per second. That is a pretty tall order for
most
> step and direction programs. If you use the G340 in 10X mode it
will allow
> you to run the program to generate 24,000 steps per second (a far
more
> realistic rate) and the electronics will multiply the steps to
drive the
> motor. The only advantage of using this high encoder count setup
over with
> the driver multiplying the step rate over a 100 line encoder in the
same
> setup with no pulse multiplication is that the dither of the servos
at rest
> will be 1/10 the amount. Does this make any difference in the real
world,
> probably not as I am convinced that dithering .000125" or 0000125"
will not
> actually move the table anyways.
>
> So, the main advantage to the G340 is it allows you to use a greater
> combination of encoder counts and reduction ratios. For your case
this make
> no difference as you are in a range that would be handled with no
pulse
> multiplication. The other advantage to the G340 is it allows you to
use the
> gnd from the parallel port or a 5V line as the common for the step
and
> direction signals while the G320 must have a 5V common.
>
> Tim
> [Denver, CO]
>
>
> > This is a question for Mariss at Gecko, which may be of interest
to
> > other folks on the list.
> >
> > I would like to know if a G320 or G340 drive would be more
> > appropriate for the machine I'm working on. It's a Rong Fu RF-45.
> >
> > I am going to use the servo motors Dan Mauch has started to
supply,
> > they are ballbearing, DC Brush type motors that have an optical
200
> > CPR HP optical encoder (800 Counts in quadrature) The motor is a
> > 24VDC brush type, approximate torque is 420 oz in.
> >
> > One caviat, I may end up using a different motor for the Z axis if
> > the ones discribed are not suitable for that axis.
> >
> > I plan to use EMC for the system control software, and I don't
know
> > if I can take advantage of the micro-stepping feature of the
G340's
> > or if it is an advantage to do so in any case.
> >
> > I would appreciate your thoughts on the best way to go for this
setup.
> > Terry May
> >