Terry, back EMF is a function of the motor turning itself. No further equipment is needed. Detecting back EMF does depend upon a PWM throttle to work as the off time of the power is when the voltage is detected. What makes this scheme work nicely is that it provides a good detection time when the need for control is needed most, at low speeds.
-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!
Throttle tables are nice but you have to remember that it is only due to the PWM nature of the output of the decoder that allows the loco to run well at all. Speed under load is still a huge variable and is comparable to the normal PWM throttle with no feedback.
-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!
You cannot detect backEMF directly from a pure DC controller or even one that has a sine wave to it as there is no time in which to do so. You can, however, detect the current of the loco and increase voltage when the current goes up. This sort of detects the backEMF as that voltage impedes the flow of electricity through the motor and thus as the motor slows down, the backEMF goes down and the current, as a result, goes up. This technique is a lot more difficult to implement than actually measuring the backEMF and the voltage increase curve will vary according to the motor type used. I know as I've done both types of systems starting in the '60s when the TAT throttle design first came out. Different motors made a big difference in how much feedback needed to be used in the throttle although multiple motors of the same type didn't make a difference with the current feedback method while the backEMF detection didn't care what the motor was, it just gave the same speed irrevelant.
-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!
The regulated voltage supply type controller is adjusting the current to the motor in order to maintain a constant voltage. It is looking at the average of the signal. The amount of back EMF from the motor changes the overall average current drawn if the controller is to maintain constant voltage. Maintaining constant voltage maintains close to constant speed, depending on the quality of the motor. The same result is achieved by the back EMF PWM controller, which is maintaining a contant average voltage. Same average result, compensating for back EMF, different electric circuit. The voltage regulator type DC controller can be simple compared to the PWM alternatives.
I would imagine a real F7 would not be expected to haul 80 cars on its own. . I would like to know what a prototype F7 could handle up a 2% grade. It is possible to have scale length trains using unmodified RTR locomotives. The trick is to use scale grades with reasonably large curves and not to have wagons to heavy. I do it with both steam and diesel outline locomotives.
SP used single units (GP7 or F7) pulling trains down through the San Jacuian (sp?) valley in the '60s from my train chasing when I was over in that area. It took quite a few locos to take that same train up the hill from there. Nothing like seeing such a train rolling along at some 50mph to amaze me. I don't know if they were empties but I've counted such long trains. On the hill, the locos seemed to be able to handle only about 12 cars or so. I know that model locos can't do anywhere near that well unless they have been well weighted and the cars are very freerolling.
-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!
San Jokin' Valley??? (San Joaquin Valley, central CA)
Most rolling stock available today is free rolling, and I have no trouble getting small quality RTR diesels to haul 12 cars on oily track. If you cannot do this your grades are to steep or your curves are to tight or your carriages are to heavy.
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