Today sees another leap forward with the W locomotive kit, mating our coreless motor to a new gearbox.
The urge to develop a new box stemmed from my observation a few months ago that many currently available gears were slightly eccentric and that, as a result, any gearbox using them was prone to tight spots. If the gearbox used gears with only equal numbers of teeth, this meant that the gearbox tight spot will occur once for every wheel revolution. As a result problems that I have always ascribed to the mechanism may, in fact, be within the gearbox.
So with that background I specified the ideal box for the W. This would feature:
- A design to put the motor more or less on the boiler centreline
- A low ratio to improve slow speed performance
- Better gears.
- Better bearings
- Compact design
As the kit features ball races on the drivers, I chose to have the gearbox clamp to these rather than fit additional bearings. I had the spur and worm gears cut (not moulded) in the Czech Republic to minimise eccentricity and married these to North Yard worms. The box is 50:1 overall.
In this prototype, the box has been printed on our in-house printer. Production versions may be done in white nylon by others as they are a little time-consuming to produce this way.
The box runs incredibly smoothly and quietly on my trusty old Triang bench test power supply. There are no signs of any tight spots, so to this point the exercise is a success! On DCC it should be even better.
The two stage design allows the use of a 25T 0.3 module final gear that is smaller than the typical 35T or 36T final drive. This allows a much less obtrusive box, and in the W will allow it to traverse a Fell centre rail with room to spare.