A NEMA 17 stepper is will give ample torque for this application. Better yet, they are available complete with a 23cm threaded rod and lead screw so the motor can provide a liner drive to push/pull an equatorial platform - see for example
https://www.robotgear.com.au/Product...8V-1-7-A-Phase
The matching driver for this is
https://www.robotgear.com.au/Product...igh-Current-V2 or
https://www.robotgear.com.au/Product...urrent-Control
Assuming you will have a nominal 12-15VDC power supply, use resistors in series with the windings to reduce the current to within the motor specs (600mA per phase), or use the MP6500 configured with resistors to control the motor current.
A simple circuit to drive this can be constructed with a couple of chips (7555 and a stepping motor driver to match the motor) and a handful of passive components from Jaycar - you probably won’t find a kit per-se. A few additional things you will need are:
- a push button to rapidly rewind the lead screw back to the start to reset the platform after it reaches its limit;
- potentiometer to provide a modicum of speed adjustment, say +/- 10%
- limit switches to stop the motor when the platform reaches the end of travel in either direction.
If you can say what effective rotational radius of the platform will be, the required step speed can be calculated. The rotational radius of the platform is a function of the length between the pivot and the lead screw, and your latitude.