I've done some work using openSCAD to replicate the gearbox used on the Greenly starter loco.

The initial brief I gave myself is to create a clone of the gearbox, not necessarily identical but close enough that it can be used as a replacement in the loco.

The aim was to allow myself to experiment with different gear profiles and ratios, primarily the use of herringbone gears rather than the straight spur gears used in the original.

As herring bone gears of the same modulus as the original are slightly larger than straight spur gears, the idler gear shaft has to be offset from the line between the crown wheel and the output axle shaft. This is so that the relative position of the motor and axle shaft can be kept the same.

The original gearbox uses modulus 1 gears between the motor and crown gear, and modulus 0.75 between the other gears.

I'm aiming the provide 3 different gearboxes initially:

• A clone of the original
• As the original but using herringbone gears and Zerol gears for the gearbox and crown wheel.
• As above but using mod 0.5 gears for the herringbone gears.

Other's may follow.

All use the same shafts as the original. The original crown wheel called for a rz73 bearing. In many of my implementations I've replaced this with a 3 x 8 x 3.5 thrust bearing. I got these from Amazon:

https://www.amazon.co.uk/dp/B0FD2ZYG3Y 

At first it may seem counter intuitive but the part with the larger hole fits into the crown wheel and the part with the smaller hole bears on the frame which is fixed to the shaft.

Please let me know if there are any problems with the fit of any of the gears.

These are still experimental so are subject to change and I can't guarantee they will work or fit properly.

All were printed on a Qidi Q1 pro using 0.2 layers PETG

Changes:

04/08/2020:

• Replaced the MOD 0.5 herringbone output gear as the original uploaded was MOD 1.0 but incorrectly labelled.