[merkit the grof]

- If you have anything less than infinite resistance between the rails "all the time",  this is a short circuit  and the track won't be able to power the cars.
-When a dc motor is open circuit, no current can flow in the coil., If no current flows, no backEMF can be produced
-When a dc motor is closed circuit (shorted across the contacts) current flows through the coil producing a backEMF causing the motor to resist being turned.

I think there a little bit of a misunderstanding.
I didn't say the 2 rails were shorted together, simply that when we apply the brakes, each side of the motor is still connected via the track rails/wiring. The diagram probably explains it better.
   

This wiring has a resistance which changes all the time depending on how far or near the car is to the controller.
The negative side of the motor is always connected to ground via the track wiring, the motor is never ""open circuit"
There is another situation where current will not flow across the motor, that is when both side are connected to the same voltage, important point because this is what helps us get the same braking effect all the way round the track.

Between the 2 extremes, the level of backEMF can be controlled by introducing a resistance between the motor contacts.
The resistance allows some current to flow. A variable resistance can produce various amounts of backEMF.

"In practical terms what is different about the brake behaviour between the 2 methods?
- diodes drop a fixed voltage 
- resistors drop voltage dependant on the amount of current flowing. 

In practical terms, control of diode based braking should be less impacted by the motor being used.

Alan

OK, so it seems that a resistance brake adjuster might need to be turned further than a diode one to get the same breaking effect, but no drastic change like some sort of sweep braking or worst still, reverse sweep braking.


Joel