I've only today come across this forum, so apologies if I am repeating what others have already done or said. I have only returned to the hobby in the last couple of years, so things like DCC are new to me. I do remember Hornby's Zero 1 coming out! I've been experimenting with battery powered/radio control over the last few months and have recently got a prototype running in a OO Lima class 47 bought from ebay. My system has a controller PCB of my own design with a a PIC micro, a miniature 2.4GHz radio tranceiver module, some LED outputs for head/tail lights, and a H-bridge motor IC driven by a PWM output from the PIC to drive the motor. An on-board battery overcomes any problems with intermittent track power. The steel weight has been replaced with a few strips of lead as this takes up less space.
Rather than using a back emf technique, the motor speed is measured digitally. The motor has been modified so that a LED shines through the armature and a phototransistor produces a signal which is modulated by the rotation of the motor.
This pulse train is fed back to the PIC which measures the motor speed and adjusts the PWM drive according to the speed demanded over the radio link.
THEREFORE, the loco goes (within the limits of the motor power) at the speed you demand, whatever the load behind it or the gradient or curve of the track. This allows for a high degree of control even at slow speeds. In theory, the battery is large enough to run the loco on its own for the best part of an hour, and it is trickle charged from the track, when available. Power is sent via a DCDC converter to the motor via the controller PCB.
The reason for the DCDC converter is that the track voltage is higher than the battery voltage so that the battery can be charged. Without the DCDC converter, any sudden changes between the battery/track voltage on the motor as the wheels turn will cause the loco to judder as the PIC adjusts the PWM drive to achieve the demanded speed. The DCDC converter is very quick to correct for changes to its input voltage, so it provides a stable output voltage for the motor. Aditionally, Since it has a wide input range, it allows the battery to discharge right down to a voltage where without it, the motor would probably stall, extending the operating time in the absence of track power. Commands are currently sent via another radio module from a PC to set direction, speed, which end the driver is sitting (ie define which is forwards and backwards), and day/night headlight and tail light controls.
Since the radio module is bidirectional, the loco can also report data back to the PC, eg battery level ie "fuel", or even "amps" as on a real diesel electric loco to show how hard it is working. As you can imagine, the electronics and batteries take up quite a bit of room, so while it fits (just) inside OO gauge diesel locos, it is probably not suitable for shunters or OO steam locos. It is still very much work-in-progress, when my very limited spare time permits. There is still lots to do, and while the system works OK with my Lima "Duff", I do need to see if it still fits in other classes of locos with similar motors. There may be more design work to get it to work in locos from other manufacturers which may not allow the same optical technique for measuring the motor speed, or where space is more limited.
I also want to use a Rasbperry Pi instead of a PC to control everything, including points and signals, making it possible in theory to handle everything on a layout with just two wires (eg the rails).
Any feedback would be appreciated!
David.