RE: [CAD_CAM_EDM_DRO] Gecko Servo Drive Choice

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
>