Originally Posted by
kiwibex
I've accepted the fact that off is in the middle, and very sensitive. The only thing that's not great is how small a turn is needed to get the servo on its slowest rotation (a hair's width of a turn, if that).
If you can, reduce the servo's loop gain. That will make the speed easier to adjust with the driver. (I'm not familiar with the particular servo you are using; it's possible that the adjustment could be called EPA, as Dave mentioned. The concepts are related.)
The driver circuit can also be modified to do the same thing (by reducing the variation of its output pulse width), but that will take a certain level of experience with electronics which you might not have. If you have the schematic for the driver available, then we could suggest some changes.
Part of the advantage of digital servos is that the loop gain can be set very high, since, unlike analog servos, it is not dependent on the frame rate. So using an analog servo could make the speed adjustment less critical. But that's probably not an option, given the cost, and your location.