DIY complete Lego 9V compatible railway

[johnnytifosi]

Recently I asked for some advice on how to build my own ghetto 9V railway on the cheap at the help thread. Someone pointed me to an excellent little German youtube channel where the guy did exactly that. I copied most of his techniques, except the power supply, where I found an even cheaper and high-tech solution (described below). I wanted to try the 9V Lego train system but the prices for 9V used sets are at least crazy, and I was not intending to waste so much money on 30 year old used toys. So, loving electrical DIY, I decided to implement my own cheap version with stuff from Aliexpress. What you need to implement this yourself is:

• A USB-C PD trigger board (1 euro): It enables your standard USB-C charger to provide 9V instead of the usual 5V using the Power Delivery standard (you can set it up to get 12V, 15V or 20V for any of your DIY projects).
• A DC/DC buck converter to regulate your voltage from 0V to 9V and act as a speed regulator (a lot more compact and useful than a Lego 9V regulator too).
• A DPDT switch to act a polarity switch.
• A junction box to house the buck converter and switch into a nicer package.
• A Lego Power Functions compatible motor with the decorative side pieces to hold the slot car brushes.
• Lego compatible plastic train tracks (30 curves, 10 straights, 2 switches, 1 crossing)
• 6mm wide double side conductive copper tape.
• Slot car brushes.
• A lot of DIY work, especially laying the copper tape, soldering wires and drilling holes in the tracks to lay wires beneath them.

The total cost of everything above was below 40 euros, but it needed many hours of personal work. The cost-work tradeoff depends on your personal tastes, for me the electrical work was part of the build and equally pleasant to building Lego and the end result provides more satisfaction than an off-the-shelf product. I would say it works quite well, except the switches. The crocodile locomotive is quite useless in taking turns because of the high center of gravity and long wheelbase. It is obvious by the train slowing down due to friction in the curves.I modified it by removing the front wheels which derailed the whole time, maybe I will need to reduce the wheelbase in the center section too to handle turns better. Also I miscalculated and don't have enough straight tracks to incorporate the crossing yet!

Here is a video of the whole railway (subs on):

 

[1963maniac]

5 hours ago, johnnytifosi said:

A DC/DC buck converter to regulate your voltage from 0V to 9V and act as a speed regulator (a lot more compact and useful than a Lego 9V regulator too).

Would you explain a bit more on what this is? Could you show an example of this or share a link. Where can it be bought, etc.?

[johnnytifosi]

@1963maniacSure. It is a power converter that reduces the input voltage of 9V to any voltage at the range 0V-9V by rotating the knob. A DC motor's speed is proportional to its supply voltage, therefore by regulating the buck converter's output voltage we are regulating the motor's speed. It is a switched mode power supply (i.e. it uses a transistor switching at the range of 100kHz) and therefore it is really efficient. You can find such low power modules for literally a couple of bucks all over aliexpress. The particular one I used is linked in the video description too and it is this one: https://www.aliexpress.com/item/4001265705322.html

More info on the operating principle: https://en.wikipedia.org/wiki/Buck_converter

Edited February 26 by johnnytifosi

[XG BC]

nice to see other people also using the diy 9v slot car brush system! i too use it, works very well.

[johnnytifosi]

@XG BCYeap it works really well, and the whole thing costs less than a single 9V motor!

[Jeff B]

I’m really interested on how you installed the slot car brushes on the 9v motor.  Do you have any videos or pictures on how you did that?

[johnnytifosi]

@Jeff B Long story short, you cut out the PF connector, find out which wires power the motor (there might be 2 dummy wires out of 4), trim the wires and solder the slot car brushes to them, mount the slot car brushes on the decorative sides pieces of the motor with duct tape. The process is shown in this video:

This is my own motor:

Edited March 5 by johnnytifosi

[johnnytifosi]

A new video showcasing the DIY 9V crossing, which works brilliantly.

 

[Jon Reynolds]

I do like the crossing and have desires to create a custom 9V compatible one myself, although not a 90 degree version like yours.  Ideally, this would be suitable for a double junction in combination with FX Tracks' P40s.  I haven't seen any plans for FX to make a crossing of any type so I'm hoping we will see a bunch of excellent DIY solutions appear on these pages.