Having looked at the photographs I can see the benefit of less visual intrusion of the mechanism, from your choice of gearbox orientation onto the centre axle.Robpulham wrote: ↑Tue Mar 09, 2021 5:05 pm ... my concern is that with the wheels being quite small and the gearbox quite substantial that much of the gearbox will be visible when viewed from the side if fitted to the rear axle.
When fitted to the rear axle the gear box/motor is sat like an 'L' if fitted to the middle axle it's sat like this ¬ so the gearbox is less visible when viewed from the side.
Provided the motor and gearbox assembly can move freely within whatever range the track imposes on the compensation I doubt there will be any problem, since this model is likely going to do its running at low speed. Dynamically, you may see a hint of torque reaction when starting, especially if the motor and gearbox assembly - which does look pretty meaty - comprises about a third of the all up weight of the model. A little more mass in the model would mask that, and more elegant solutions are available, but that's for the small mechanism specialist!