The model has been designed in 1:12 scale to represent a NZR motor trolley. The model is intended to capture the essence of a motor trolley and isn’t a rivet counter accurate model of a specific motor trolley.
A motor trolley is a small railcar formerly used by track inspectors and maintenance staff to move quickly to and from work sites. Motor Trolleys were replaced by road vehicles with additional flanged wheels that can be lowered for travelling on rails, these vehicles are called hi-rails.
This project has been a test of Computer Aided Modelling with most of the components being laser cut or 3d printed. The machines I used to manufacture the motor trolley are:
- The Atomstack X7 Pro laser cutter
- The Voxelab Aquila 3D printer
I started designing this around a universal motor gearbox from Jaycar Electronics with version 1 of the motor trolley using this; however while it travels at a reasonable scale speed it takes a long time to travel around the track. To improve this a new drive train was designed using a RF-300CA motor that is designed for CD/DVD players. This motor has increased the top speed however it doesn’t have the torque of the Jaycar gearbox.
Supplies
- Acrylic laser cut parts
- 3PDT center off toggle
- 3mm red LED
- 10mm warm white LED
- 2 x 150 Ohm Resistor
- 2xAAA battery holder
- RF-300CA motor
- SP08-2M sprocket
- SP18-3M sprocket
- 90mm of chain
- 4x 3D printed wheels
- 2x axles 3mm x 102mm
- 4x bearings 683zz
- 2x 8BA x 20mm
- 4x 8BA x 6mm
- 2x M1.7 x 6mm
- 2mm brass rod x 110mm
Chain and sprockets were purchased from MOTIONCO https://www.motionco.co.uk/. All other materials were purchased from AliExpress or any of the model engineering suppliers. CAD file for the laser cutting and STL files for the wheels are available on Thingiverse .
Assembly
You will need to tidy up the laser cut parts to remove burrs with a file or some sandpaper. The holes in the body sides and battery shelf will need to be tapped to 8BA. The brim used by the 3d printer to ensure bed adhesion for the wheels will also need to be removed.
The frame is assembled by first pushing the bearings into the side frames and then, using the axles to ensure alignment, gluing them to the chassis. It’s important to make sure that the shorter end of the side frames faces the front so that the headboard can be installed.
Install the motor mount and support, ensure that these are straight. Once the glue is dry you can install the motor with the two M1.7mm screws. The holes are slotted and it’s best to install in the rearmost position to assist with installing the chain.
Install the smaller sprocket on the motor shaft and align the sprocket on the axle. Install the chain by running around the sprockets and joining it on the large sprocket.
The body work is relatively easy to assemble. I used the headboard to hold it square while the glue dry’s. Leave the headboard to last as the top seat and headlight set’s the position for it. Make sure that the battery shelf is facing the correct way with the two holes towards the front of the motor trolley.
The headboard is glued to the body however make sure that you don’t glue the top seat down. The top seat is held in position with two screws that allows you to remove this to change the batteries.
The seat top has the headlight and back handrail glued to it. The handrail at the back of the motor trolley is bent up out of 2mm brass wire. The handrail should be about 20mm above the seat. The two lifting rails can now be installed on the sides of the body with the 8BA screws.
This is a good point to paint the bodywork. I find that using an etch primer on the acrylic works well. Remove the motor, axles and bearings before painting. NZR motor trollies were traditionally painted in red with a white stripe on the front to improve visibility.
With the bodywork painted it’s time to move onto preparing the electronics. The headlight is a 10mm LED however we don’t want the dome of the LED so this needs to be cut or filed down. You need to be careful trimming the LED as if the internal metal components are exposed the LED may not work.
Glue the battery holder onto the battery shelf with the wires facing forward. The motors I purchased came with a plug on the wire tails, I removed this to solder the wires directly onto the switch. You will need to leave enough slack on the wire connections to allow for the seat to be removed when replacing the batteries.
Wire up as per the above diagram, ensure that you orientate the switch so that pushing it forward makes the motor trolley go forward.
The motor trolley has proven to be fun to run between trains at the track and there are a number of alterations that could be done to this to improve the appearance, and operation.
- I’ve kept the controls simple however it requires you to catch the motor trolley as it comes past, to remove this issue radio control could be fitted.
- The headboard could be replaced with a handrail making it more like a M9 Fairmont speeder from the USA.
- Mudguards could be designed and fitted over the wheels. I’ve left two mounting holes on each side for these if someone want’s to design them.
- While this was designed for laser cutting I’ve added an STL for 3d printing the main components to the Thingiverse and Printables page. This is untested at the moment.
https://www.printables.com/model/1014744-nzr-motor-trolley-35-gauge
Pine Valley Estate Railway 