PWM controllers can be a real problem where you have a mix of old style iron core motors and bell armature (coreless) motors.

Coreless motors require a high frequency, typically in the 20kHz to 50kHz range, while iron cored armatures require typically less than 5kHz.

The problem is that when you operate a coreless motor on the lower frequecy you can literally shake the rotor winding apart as it has so little mass it can oscillate at the drive frequency, eventually shaking the winding apart.

But if you operate an iron cored armature with high frequency PWM you get heating problems in the iron core due to losses in the iron at the high frequency, and if left driven like this will eventually overheat.

The end problem is that there is no one PWM frequency which is satisfactory for both motor types. We have DC controllers at our club that have a switch on them for switching between the motor types - but this relies on the operator knowing what sort of motor is fitted.

I tried a custom built PWM controller with the old motors (that's all I have). Absolutely fantastic at ultra slow speed. But as soon as you turned the speed up a bit, the motor sounded absolutely dreadful. I thought it was being ripped apart. Stopped using it.

Very interesting information, I have been playing a bit with making my own PWM controller, combined with a camera to detect position and speed on the layout, do you know if it is possible to "auto detect" the type of motor? - I'll try to do some measurements, but I would guess that you could make a sweep of frequencies, and for the iron cored motors, would see a higher efficiency at the low frequencies (i.e. more speed for a given % of "on" time for the different frequencies)? - maybe some signal analysis could do it too?

How do I tell what kind of motor is in a given loco (like from the model number or by taking it apart) so I know what I'm measuring on?

Newer coreless motors will have lower inductance than the old style motor, so if you were to measure the current with a high-ish frequency signal you could use this to detect which is which. I imagine you could use the PWM itself for this - start with a high frequency PWM and low duty cycle and if the current is below a certain threshold switch to a lower frequency.

Cheers


Chris

What is the gaugemaster design?

That YouTube video is very good. I had thought that the Gaugemaster controllers were PWM, but it seems I was wrong. Gaugemaster's website is somewhat inscrutable regarding how their products work.

To the OP I would recommend one Rokuhan controller (buy or borrow) to test first. With my collection of Marklin locos I found the Rokuhan controllers to be "difficult". With some older engines the controller safety would trip and shutdown, other newer ones would not stop running at low throttle due to Rokuhan's ingenious system that keeps the lights of their locos on at the throttle stop. And a lot ran just fine. I used PWM controllers by Snailspeed too. In the end I settled on the older Marklin white controllers that are hard wired because they just work, but with those big speed steps that we all dislike. Regarding AZL I converted all of mine to DCC and use an NCE Powercab. But I never had a problem running AZL or MTL locos with Rokuhan. My Marklin European trains remain DC.