Tuning Gecko 320 drivers with a scope....

I've purchased a small handheld o'scope. I've read a method described
by Dan Mauch that uses 1.5-2 lb handwheels to tune the
motors/drivers. I found it easier to buy a scope than to try and
find/make some flywheels. I don't have a lathe and couldn't find any
sort of substitute item. I've sent the following to support at Gecko,
but I'd like to also ask here. Mariss seems to be here and there, if
he sees both he can maybe answer hear then it will be in
the 'archives' for others.

Hi,
I'm to the point of tuning my Gecko 320 drivers. I have a small
handheld oscilloscope. It has COM and V leads, no Channel 1 or
Channel 2. I've hooked it up to the 2 test points on one driver board
and found one to be + and the other to be -. The illustration in the
manual doesn't match the actual board. I then hooked my V lead to the
+ test point and the COM lead to the DIR input to the driver from the
parallel port.

Here are 3 paragraphs from the manual, in order:

"To see how your servo is compensated it is first necessary to
induce a disturbance. The easiest way is to switch the DIRECTION
input while commanding a constant speed via the STEP input. The
abrupt direction change puts just the momentary load needed on the
motor while you watch how it responds."

"If you are using an oscilloscope, use channel 1 on the test point
and channel 2 on the DIRECTION input. Set the trigger to 'normal',
trigger source to channel 2 and trigger edge to '+'. You should see a
single sweep for every clockwise change in direction."

"Slowly increase STEP speed until you get a picture similar to one of
the three above, and then do the following:"

Am I supposed to be switching the direction, increasing the STEP
speed, or both? If both, is the waveform only supposed to form when
the DIR is switched to one direction, but not the other? Is that a
function of the Trigger? Could this be done via g-code? I would need
an idea of what frequency the STEPS would need to be coming in at so
I could tweak the Feedrate accordingly. Also, can this be done
successfully with the motors de-coupled from the leadscrews? I don't
have any limit switches yet.

I read the cad_cam_edm_dro board on yahoo and have found several
pulse generator ideas. I've also searched back about 30,000 messages.
None seem to do what the Manual says needs to be done, i.e.
adjustable STEP rate input and switchable DIR input. Do you have a
schematic for one that would do that? The schematic has to be pretty
straightforward as I'm not an electrical engineer by any stretch of
the imagination. I can read and follow a schematic.

Regards,
Monte