A Pulsed/Feedback DIY model railway controller the finest DC controller ever designed and like the best of everything else unbelievably simple
This is the summing up of a dissertation given by Prof Jonathan Scott;
The large variation between DC controllers and locomotives was frankly surprising. Also surprising was the relative weakness of flagship feedback controllers epitomised by the HM 2000.
The extent to which mainstream controller manufacturers have failed to harness feedback in their designs suggests that they do not take the design of model railway controllers seriously.
The advice would be to employ or contract a professional engineer with experience in feedback control.
My criteria for a DC controller;
1/. It must be very easy to make
2/. The take off from standing must be imperceptibly smooth
3/. The ability to move a loco 1.0 millimetre first time everytime to aid coupling/uncoupling with a 'shunters pole'
4/. Feedback between pulses to enable constant speed slow running.
5/. The controller must make any loco start at exactly the same spot on the control knob.
6/. Short circuit indication by the most simple method
All fulfilled easily by the Pulse/Feedback Gaugemaster UF Style as modernised by Jonathan. This is the circuit
And to prove it a video of extreme slow running;
Please Click the gear symbol and choose 1080p
I do a PDF showing the stripboard layout and detailed instructions so that anyone can build one
The Brian Tilbury pulsed feedback controller 1974
This uses three transistors and gives a square wave output rather than the spikes from the GM style one above. Using the GM one motors make a noise before they start and the spikes cause a high pitched sound, the BT one makes very little noise before starting and the square wave makes a deeper and less noisy output. But; isn't there always one it's more complex to make than the GM.
The output power can be varied this circuit is set to 0.6 Amps by altering some of the components outputs up to 1.5 Amps are attainable.
A PDF is available with the settings for the different outputs please ask.
**The TIP41C output transistor must have a heatsink on it. The circuit will avoid a short circuit by sending the output straight through the output transistor, the output LED will switch off. Once made I use my fingers on a heatsink and register the time it takes to the point where I have to take them off I aim for about 1 minute.
The performance is no different to the GM.
Motor heating
Pulse controllers do heat motors but then so do ramping DC and DCC ones, the nature of the pickup from brush to commutator, from rail to wheel and from wheel to pickup is never a smooth exchange of power.
There is though a lot of nonsense about motor heating, someone makes a statement based on surmising that hot motors burn out, it then passes around the web and becomes gospel. I have yet to see someone post an example of a failed motor due to heating caused by pulses.
In 1980 I made a Manning Wardle 0-6-0 and used a Mashima motor, worst possible scenario for heating a motor, very slow running plus high voltage pulses. It did 9 years at shows and I then packed in model railways until 2009 in 2013 the motor failed, that's 12 years running.
Result
As you can see the brushes are so worn they fell out of their tubes and the commutator is nearly worn through, no sign of motor heating or burn out at all. Sadly the newer Mashima's were not made to this high standard but just a leaf spring with a tiny brush attached.
There we are then, this is what you find, such is life etc :-)