Can anyone please explain why DCC uses 14 and 28 speed steps? I understand 128 steps - that's straight binary, from the computer basis of DCC. But I'm told most American prototype diesels have an 8-step throttle, so it doesn't seem to be derived from the prototypes. And neither 14 nor 28 is a power of 2. So does anyone know how 14/28 came to be chosen as the standard?
For reference, you can look here:
http://www.nmra.org/standards/DCC/standards_rps/S-92-2004-07.pdf
It looks like originally there were six bits available to control speed, direction, and the headlight. Which left four for speed. Stop, or zero, doesn't count as a speed step, and there is also an emergency stop, which leaves 14 speed steps left. It looks like the next step was to move headlight control out, which increased the available steps to 28.
Jeff But it's a dry heat!
Walleye wrote: But I'm told most American prototype diesels have an 8-step throttle, so it doesn't seem to be derived from the prototypes.
But I'm told most American prototype diesels have an 8-step throttle, so it doesn't seem to be derived from the prototypes.
Most American prototype diesels are also a few thousand times heavier then an HO scale locomotive and can coast under their own momentum many times farther then a scale locomotive. An 8 step throttle in a 1:1 locomotive is constantly switched up and down through the steps as necessary, and sometimes back to "0" so that it coasts.
The difference in how the throttle works is that with the "speed steps" you're choosing how fast you want to go. With a 1:1 throttle you're controlling how much power you generate to send to the traction motors and adjust according to whether or not you need to go faster / slower.
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Sorry, I didn't mean to suggest that DCC should be limited to 8 throttle steps. I was just trying to figure out where the 14/28 step scale came from, since it isn't related to anything on the prototypes. Jeff's explanation of how 3 functions and 16 steps - didn't consider EmStop - got shoehorned into 6 bits is what I was looking for.
Thanks, Jeff!
GraniteRailroader wrote: Most American prototype diesels are also a few thousand times heavier then an HO scale locomotive and can coast under their own momentum many times farther then a scale locomotive. An 8 step throttle in a 1:1 locomotive is constantly switched up and down through the steps as necessary, and sometimes back to "0" so that it coasts.
True, and with the NMRA standard momentum functions, my N scale locomotives can be controlled in a similar fashion, as can your HO locos.
Also remember that DCC is not from America, its European. DCC is invented by Lenz and then given to NMRA to be made to a standard.
/Stefan
- Harry
HarryHotspur wrote:Okay, so how many steps do European prototype locos have?
That depends on age, type, maker, country etc. but as an example the German type 103 electric have 39. A German diesel, BR218, have 15, but both are 40 years old, modern European electrical locos don't really have steps as such.
The physics of the model vs. the prototype are so different, I think that worrying about speed steps with respect to the protoype is an exercise with no point.
Plus KIM not all diesels use 8 throttle notches, Baldwin throttles had a much greater latitude, I don't think they even had notches per se but were more 'continous' like turning the knob of a model RR powerpack or walkaround controller.
Plus not everyone models diesels anyway.
Baldwin used an early 'air' throttle for MU - it did not work very well at altitude. Some of their non-MU switchers had a straight mechanical connection for a throttle. IIRC, FM offered something similar as an option as well.
Most US engines use the standard 8 position throttle controller in the cab. At one time, early GE 'U-Boats' had a 16 position '1/2 notch' throttle(I think it was gone in mid U30 production). It at least was compatible with standard 8 notch throttles.
As far as DCC engines - Some of the above posts should have answered the original question.
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin