Alistair those motors look ok (except read below) and do have some nice gearing ratios...this is exactly what you want...a method to change gearing as you change scopes!
ML steppers are capable of "micro stepping", thus they can get down to 2 microns per step, this system cannot do micro stepping but that's not an issue with the right motor or gearing.
Just look at the specs for the motors as the stepper driver is capable of driving 500mA per coil but...this is de-rated for duty of cycle, thus probably at best 150mA~ 200mA per coil continuous operation. Ok the stepper isn't operating all the time but be aware of trying to drive coils that are too low in ohms, try to limit ~ 15~200mA per coil from motor selection.
I use Hurst which all appear to be ~ 65ohm per coil = 12/65 = 184mA per coil...this is sweet, no heating on package but I wouldn't go too much under this is coil resistance.
The 1st Mclennen motor is almost exact coil Rx as mine,
the P542-M481U is a 5V system, sorry cannot use, but their pdf shows the P542-M482U, a 12V system...this is the one to get. Sadly doesn't show up on RS site!
These McLennen motors are listed (yes I know they are 5V just going into some more details on coil rx for the motors) is 52.2 ohms per coil and this is ~ 230mA...starting to get up a bit in current draw..."but"...since the system has a Schottky diode protection on the PCB, then available voltage is ~ 11.6V thus in reality is ~ 220mA per coil, and should ...mmm just make it ok as it's not being used all the time. Maybe a small heat-sink glued to the driver IC will help alleviate any concerns using these motors. you can also consider that a coil when being driven with current, heats the coils and their actual resistance rises ...meaning you should be ok at this I draw.
IMHO...go for the 12V McLennen system with different gear ratios...looks real nice indeed!
Hope this helps, sorry for the waffle !
