Locomotive #1: Homemade electric locomotive

Begun July, 2009

Now that I have a ballast hopper car and several hundred feet of completed track, I'm ready for a locomotive.
Locos for backyard railroads are powered by either electricity (batteries), gasoline (lawnmower engine), or real steam. Steam is the most elegant, but also the most expensive - live steam locos start at $15,000 for a kit! Gasoline power is simplest, but making it reversible is a challenge (requires some sort of transmission), plus it's loud and smelly. So I've opted for making an electric loco.

I'm planning on building something inspired by Rail Rider Supply's Fairmont Speeder... I like the utilitarian design of it.
That loco is gasoline powered, so I'm designing the power chassis based on RideTrains' Mini Motor Car Chassis.

I got some surplus rechargeable batteries:

These are recycled from from computer UPS systems. Each battery is 12V@33Ah.

They connect in series to provide 36 volts:

They'll drive a 1000 watt motor:

The motor is controlled by this board:

It's an OSMC - the Open Source Motor Controller.
I bought a kit from robotpower.com; while I usually design my own circuits and etch my own PC boards, I'm not well versed in MOSFETS and high-power controls, so buying a professionally designed circuit and PCB made a lot of sense.

This current sensor ensures that I won't burn up the controller:

This is a demo board for the Allegro ACS712, a hall effect current sensor chip.
This prebuilt board was only $40, which (again) I figured was worth the extra bucks to have a pre-built module.

Speed is controlled by a small handheld unit:

Press and hold the green button to accelerate forward; press and hold the red button to slow down then accelerate in reverse; click both quickly to coast; hold both to apply the fast-stop brake.
This mimics the elegant simplicity of Linn Westcott's True Action Throttle (TAT), which I built as a teenager from plans published in Model Railroader magazine in the 1970s.
The loco won't run without this small box, so hiding this piece will be a simple way to keep the kids from driving the train without Dad's permission :)

Here's the controller with the cover removed:

The daughterboard is a Teensyduino - a small-footprint, $16 processor module running as an Arduino
It communicates with the master control board via 9600 baud RS232.

The next step is to create the master control board - it'll probably be based on an Arduino Uno - and connect it to the handheld, OSMC, current sensor, and batteries.
The Arduino is a GREAT platform for this sort of application, and someone has already published a project on controlling an OSMC with an Arduino. I'm all for recycling other peoples' successful projects!