From what I hear most people have tuned the Geckos without the use of a scope, for my drives the config software has a built in scope. On the axis motors I just tuned them by ear and have since looked at the software scope and they are good. The spindle motor was a different story, it was extremely hard to tune and I needed to use the scope in the software to get it right, the reason was probably due to the size of the motor combined with the backlash in the gearing in the headstock and 30Kg of chuck being spun but now its tuned it works well
RE tuning and sizing, afraid if you dont have these two done properly then you will never get it to work no matter if it is the control or the drive that the loop is closed to. Unless of course you have the CNC Brain which supposedly can do this although I have not seen anyone reporting one working for any more than basic open loop movements yet let alone the advanced compensation and double closed loop it is meant to be capable of.
128 counts seems quite a large amount, especially with a 300 line encoder (1200 count), on my setup that would be 0.5333333......mm, not good
I am thinking with motors tuned/sized (yes these chicken words again
) properly then it is likely you will never see that large an error. Not sure if you can in any way monitor the following error with the Geckos, with mine the drive config software can monitor it and also gives the max and min errors
Hood