DC motor constant speed regardless of load

[David Hess]

Model trains take great advantage of this to operate at very low speeds without stalling.

Have you seen the gearbox on model trains? Not exactly simple. Also, the motors have a 5-pole armature, not just 3-pole.

But you can compare the difference in operation between constant low DC voltage and high voltage with a low duty cycle.  The later can operate at much lower speeds without getting stuck.

A long time ago, model train power supplies used to have a switch to allow half-wave rectification which had a similar advantage at lower speeds.  Low duty cycle PWM is even better.

[Benta]

You keep flogging a dead horse. You cannot ignore commutation cogging at low speeds. Period.

[David Hess]

You keep flogging a dead horse. You cannot ignore commutation cogging at low speeds. Period.

Sure you can.  I gave an example where that is exactly what was done, and the only change was DC to low duty cycle PWM.

[SteveThackery]

Stuck record here:

1/ Don't use a stepper motor.  Too much noise, too much torsional vibration, and it needs a special controller.

2/ Use a brushed DC motor with a gearbox and a straightforward PWM speed controller.

The gearbox is essential - it allows the motor to run at a speed where cogging is irrelevant. Something like the innards of a cheap cordless screwdriver might be ideal. Possibly a bit slow. If so, check out Benta's recommendation for a cheap geared motor. If you've got a variable voltage bench PSU, you can run that motor off that. It's what I do.