Anybody got ideas about or against using PWM type speed controls on these small brushed DC motors? Someone on YouTube had mentioned that they are too hard on them and shortens the life span. Any ideas? Come to think of it, DCC controllers are not pure DC as far as I know.
Now this is a tough one...
The evolution of model railroad controllers from DC was to increase the start and slow speed motor response. They began primarily trying rectified AC and then moved to PWM. There were a host of other waveforms tried. I believe today that all DCC decoders use PWM to drive the motors. Some DCC decoders are now also using the back-EMF for speed feedback in order to adjust the motor's response.
PWM for motor control can cause excessive heating in the motor coils and increase erosion of the brushes. I remember when PWM first started being used that there was a big concern about overheating the motors. The actual effects of PWM on motors is a mix of many factors. Here are some resources on the theory:
Controlling Brushed DC Motors Using PWMSumida Crossing - DCC Motor Control - PWMMy understanding is that any motor deterioration due to PWM can be reduced by increasing the PWM frequency. I believe the first controllers used a PWM frequency in the 60 Hz range (some tied to mains AC freq). DCC controllers seem to be at 16 KHz (top of human hearing) and maybe higher for the newest using back-EMF sensing.
There doesn't appear to be a definitive answer as to how big the impact is to the motor lifespan. However, PWM with H-bridges is pretty much the accepted way of controlling small motors. The design of PWM for motor control has come a long way.
I keep seeing servo motors popping up in this discussion. Servo motors are a completely different animal. You send a PWM signal to the servo to specify its desired position. But, that is the end of PWM. Servo motors have a angular feedback mechanism from which a comparator drives the motor with a DC voltage in the forward or reverse direction until the angles match.