Re: [CAD_CAM_EDM_DRO] what is a Gecko ?

info_cynic wrote:

>Hi. Can anyone tell me the difference between the two servo drivers
>that Geckodrive sells? Thanks.
>
>

I assume you mean the 320 and 340. The 340 is a 320 with one affed
function.
This is that one step pulse sent to the driver causes it to move 1, 2 5
or 10 encoder
counts. The 320 always moves one encoder count for every step pulse
received.
The only reason for using the 340 is to accomodate software that has a
very limited
rate of step pulses. You can calculate the rate of encoder
counts/second that you
will need on any particular system, and then see if the software can
generate
step pulses that fast. Assuming you want to move at X inches per minute,
divide by 60 to get inches per second. Multiply by leadscrew pitch in TPI,
multiply by belt reduction ratio, if any, multiply by encoder count in
cycles per rev * 4 (or by encoder counts per rev without the *4). So, for
120 IPM, that is 2 IPS. With a 5 TPI screw, 4:1 reduction and 1000
cycles/rev
encoder, you get 2 * 5 * 4 * 4000 = 160,000 steps/second. This would tax
any software step generation scheme. With the Gecko 340 set to x10, you
would need only 16,000 steps/second to drive it at the same rate. The
downside
is that the positional resolution is ALSO reduced by a factor of 10.
With the Gecko 320 (or 340 set to x1) you would get 4000 * 4 *5 discrete
positions per inch, or .0000125" per step. With the Gecko 340 set to x10,
resolution would be .000125", which is still not terribly coarse. However,
when moving slowly, as in interpolating around a large circle, the Gecko 340
on x10 would be moving in jumps of 10 encoder counts, or .000125", while
the x1 drive would be moving in increments 1/10th that size. This could
be a concern for precise milling. There are systems that generate step
pulses
in hardware, thereby removing the speed limits of software step generation.

Jon