Sky Adventurer dual axis guiding

The Sky Adventurer features a ST4 style guiding port which allows RA guiding, but that also means it only correct PEC.  The DEC part is manual driven only, so we couldn't guide in a dual axis way.

Motorizing the DEC part is the first step, here we have two approaches:

 

The one on the left is to use an inline shaft coupler, I got one at home which matches quite nicely.  Problem is that, the motor would make the whole thing much more bulky.  The next method is the one on the right, it uses two gears, one on the original manual control knob and another one on the motor, but I got only one such gear ready at home.  I will need to buy one more and the motor could be placed below the DEC body, I will want a smaller motor in that case, and I will also need to find a way to mount the body and mesh the gear correctly.

The following wiring scheme could be used:

Guider -> 

ST4 port of my own, getting the DEC signal to drive the motor -> 

ST4 port of the Sky Adventurer

So no need to modify the Sky Adventurer, just add a "relay box" and steal the unused DEC signal.  A simple geared motor controller could be used to drive the DEC.  Too good to be true?  Best of both worlds?  Let's see... I shall start hunting for suitable parts.  We need gear with 6mm shaft bore.