HO-Scale Model Train Controller

I built this HO-scale model train controller to make “running” the train more realistic, and more fun.

1. The direction of the train is controlled by a double-pole, double-throw switch. I used a big knife switch rated at 63A (purchased on internet) to make changing direction more dramatic. I replaced the switch knob with a lever/knob to make it easier for children to actuate the switch.
2. The throttle is a large knob on a circular turntable, again for a dramatic effect. The turntable is connected to the potentiometer of a 6V-90V 15A DC motor speed control  module (purchased on internet). The potentiometer is connected to the speed controller by wires and a quick disconnect to make construction easier. Because the potentiometer is designed to be mounted through a hole on a thin metal box, it's shaft is too short to use with a plywood box. I also wanted a very robust and smooth rotational throttle action that would not break easily when used by children. These are the reasons why there are Throttle Center and Throttle Ring pieces. 
3. A micro-ammeter (found at my work place) displays the train's relative speed. A 150K 10-turn trim potentiometer is used to adjust the meter reading to 100 for the maximum speed controller output.
4. A 12V (actually 15V) DC power supply provides power.
5. Locomotive Sounds: A DF Player Mini and speaker are used for train sounds. These sounds can also be downloaded from the internet, or recorded from real trains using your phone. The control circuit is very simple, requiring only a momentary switch (https://europe1.discourse-cdn.com/arduino/original/4X/1/9/3/1938bc3998df30a20e701d8fcf47680748b7f524.jpeg). Note, the diagram at this website shows a 4 ohm speaker. You must only use an 8 ohm speaker. If you load multiple sounds on the SD card, each time you press the button the next sound will play. Holding down continuously on the button increases the volume. Power the DF Player Mini from the train power supply using an adjustable 24V DC to 5V DC converter.
6. This is all mounted in/on a ½" plywood box.

Printing Instructions

1. Print the Throttle Shaft Connector with the top (hexagonal) on the print bed and use supports from the bed.

Assembly Instructions 

1. Cut a 2" diameter hole in the plywood top.
2. Mount the potentiometer to the Throttle Center (Potentiometer shaft through the larger hole and the potentiometer key through the smaller hole (the key keeps the potentiometer body from rotating when its shaft is turned). 
3. Put the Throttle Center inside, and on top of, the Throttle Ring. 
4. Use flat-head #6 screws to fasten the Throttle Center to the plywood top, centered on the 2" hole. The chamfered edge will hold the Throttle Ring against the plywood top and allow it to rotate. You will need to put a thin cardboard shim under the Throttle Center to adjust the rotation friction of the Throttle Ring.
5. Push the Throttle Shaft Connector through the hexagonal hole in the Throttle Knob. 
6. Manually turn the potentiometer shaft back and forth to establish its limits. Then push the Throttle Shaft Connector onto the potentiometer shaft, with the desired knob orientation. Align the Throttle Ring with the Throttle Knob and use #4 round-head screws to fasten them together. BE CAREFUL the Throttle Knob has so much torque that you will not be able to sense when the potentiometer shaft has reached its limits. If you turn the Throttle Knob too far it will strip the fins in the Throttle Shaft Connector.
7. Install the Throttle Limiter to avoid turning the Throttle Knob past the potentiometer limits. My potentiometer has 300 degrees of rotation, and the Throttle Limiter is designed to allow 295 degrees (adjust the lower Throttle Limiter to just above the lower potentiometer limit and the 5 degrees of buffer will be at the higher potentiometer limit.
8. The switch knob is pressed fit onto the switch lever, using a ratchet-action woodworkers clamp to supply the pressure.