Method to compute relative motor torque

[peteski]

That is an interesting article.  I also learned a new word: recalcitrance. 

It does prove that PWM motor driver is equivalent to a variable regulated DC driver.

As far as using series resistor (rheostat) with the motor to control the motor's speed, model railroaders have known for years that it is a bad idea (since the motor's impedance depends on its load (BEMF).  That is why the better model RR DC throttles are "transistorized".  That provides better voltage regulation independent of the motor's impedance.  And since DCC decoders use PWM to drive the motor, they also provide excellent motor speed control.

[mmagliaro]

With regard to pulses, I got curious, so I did some quick tests on my motor variations.
With my pulsed throttle, all the rebuilt ones can do down to 300 rpm, which is in the 3 mph range for
a RR 4-6-2, and some can get under 200 RPM.  And this is regardless of load.
I can put no load, or up to the 100 ohm load on the generator, and the RPMs hardly blip in the slightest.

This is one thing the Rivarossi stock motor definitely can not even come close to.  So at least I know rebuilding these
motors is definitely worth it, but I don't think rewinding the armatures is.

[peteski]

This is one thing the Rivarossi stock motor definitely can not even come close to.  So at least I know rebuilding these
motors is definitely worth it, but I don't think rewinding the armatures is.

That's what I suspected.   By rewinding the armature you basically increased the motor's working voltage.  That also means that for a given voltage, the rewound motor will use less current (since the winding's  resistance is higher than the original), and I believe it also produces more BEMF voltage (when free running).

[mmagliaro]

That's what I suspected.   By rewinding the armature you basically increased the motor's working voltage.  That also means that for a given voltage, te rewound motor will use less current (since the winding's  resistance is higher than the original, and I believe ti also produces more BEMF voltage (free running).

Yes, I think you are right.  The strong magnet makes these motors extremely powerful (and the torque curves vs the Rivarossi show that).  But it doesn't do anything to make them able to push the engine slower because that is limited by just how slowly the armature can actually turn before it cogs and stops, rather than by how much torque it can produce.   They are nice powerful motors, they don't draw much current, on pulse they can run pretty darn slow, and they won't melt down like the RR motors.  I'm happy with that.

Very soon I'm going to "announce" my offer to sell these to anyone who needs one to revive a dead Rivarossi engine.