This is a 3D printable HO/OO/on30 power bogie chassis that is simple to assemble, inexpensive and can be customised to power a variety of printable model engines.

All parts are sourced from AliExpress:

Worm Gear
66mm 1.5A Worm Gear, 1.45 ID (2 required)
https://s.click.aliexpress.com/e/_dY80FNr
or
68 1.5A Worm Gear
https://www.aliexpress.com/item/32862948918.html?spm=a2g0o.productlist.0.0.3f32314dH1exq0&algo_pvid=9447f319-1e33-4222-8b87-72f7d4b35863&algo_expid=9447f319-1e33-4222-8b87-72f7d4b35863-3&btsid=0be3764515826281277652479e9bda&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

Drive Gear
152A 0.5M Spur Gear, 15 teeth, 2mm ID(2 required)
https://s.click.aliexpress.com/e/_d65sEId

Copper Bushing (4 required)
ID 2mm x OD 5mm x W 4mm
https://s.click.aliexpress.com/e/_dWL9r82
or
https://s.click.aliexpress.com/e/_dWiFp4H

Wheels (2 required)
1:87 Universal Wheel DC
https://s.click.aliexpress.com/e/_dY7Fj3g
or
https://s.click.aliexpress.com/e/_dTAWRJ7

Motor
12V 030 Micro Motor DC, 1.5mm shaft (1 required)
https://s.click.aliexpress.com/e/_dWyx9Cz

Pinion puller (optional)
https://s.click.aliexpress.com/e/_dV4rQ4h

Assembly notes:
a. The motor has a shaft diameter of 1.5mm. The worm gear inner diameter is 1.45mm to ensure it is a tight fit.
b. The wheels have an axle diameter of 2mm. The drive gear has an inner diameter of 1.95mm (tight) and the bushing inner diameter is 2mm.
c. After removing the insulated wheel from the axle, the splines need to be carefully filed off so the bushing can be fitted. A small drop of glue on the insulator when re-assembling prevents it from moving.
d. For simplicity, the power pickup wires are soldered to the copper bushings.
e. The brass worm gear supplied with the motor can be used to avoid having to press it off. (it 'should' be the same size/pitch as the plastic ones on the parts list)

Version notes:
a. Version 2 of the original design has been uploaded. This chassis is symmetrical. The original was designed to have 2mm of extra length at one end to accommodate the longer of the two shafts on the motor, which is not needed.
b. Version 2 includes a minor revision to the bearing retainers.
c. Version 2-2 includes a stronger bearing retainer option.

The loco that the prototype bogie was tested on is located here:
https://www.thingiverse.com/make:766899