A powered chassis for a DIY locomotive.

Pictures

It is designed for a 2-axle locomotive without bogies, e.g. shunter, railbus, railcar, tram or similar vehicle.

The motor used is a 10mm square motor, rated 14700RPM @ 9V, which is relatively low-rpm by micromotor standards. The resulting model can crawl rather well, provided the current pickup is good enough or stay-alive capacitor is installed.

To reduce noise, a rubber O-ring is used to transfer torque from motor to driveshaft (I tried plastic gears, too noisy; but I may use them in future versions), with reduction or around 2:1. Second stage of transmission is a worm gear with 11:1 reduction. There is 1 worm gear set at each wheelpair.

The STL and STEP files provided have wheelbase of 81mm. For other designs Fusion 360 file is provided, so you can change the model according to your needs. There are 2 parameters in the design: wheelbase and motor position along the driveshaft (it can be moved back and forth).

3D-printed parts

  • Motor pulley

  • Driveshaft pulley

  • Chassis middle

  • Chassis upper

  • Wheelset cover x2

  • (optional) Belt cover

All needs to be printed with highest possible resolution, I used 0.08mm layer height and stock 0.4mm nozzle on Creality Ender 3.

Parts to buy

List of parts to buy, with sample products from aliexpress.

Count Component Note Example product

1

DC motor

10mm size

https://www.aliexpress.com/item/32825984761.html

1

Driveshaft

2mm diameter brass axle

https://www.aliexpress.com/item/1005003000715062.html

1

Motor to driveshaft belt

O-ring 13mm OD, 1mm CS

https://www.aliexpress.com/item/4001148792117.html (this is a green FKM one, other types, e.g NBR, should also work)

3 or 4

Driveshaft bearings

bearing 2X5X1.5

https://www.aliexpress.com/item/33007670757.html

2

Worm gear

6x8mm 0.5mm module, 2mm bore

https://www.aliexpress.com/item/32863434323.html

2

Wheelset gear

0.5mm module, 11T teeth, 2mm bore

https://www.aliexpress.com/item/32964343633.html

2

Wheelset

isolated for DC rails

https://aliexpress.com/item/32796356695.html

Current pickups

phosphor bronze wire, 0.4mm diameter, or anything else you can use, the model has no specific details for current pickups

https://www.aliexpress.com/item/1005004251949800.html

Some perfboard to solder the current pickups to, or anything else that can can be glued and soldered

Some thin wires

6

Self-tapping round head screws

1.4x4mm

https://aliexpress.com/item/1005004129037750.html

2

Self-tapping countersunk screws

1.6x6mm (to make top surface flatter, otherwise round-head screws will do)

https://aliexpress.com/item/1005005747913017.html