Speed steps

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I am in the early stages of designing a layout in N, based on current British practice and with up to five trains moving at any time. I think DCC is the way to go and will probably buy a Lenz Compact (the European version of the Atlas Commander). It seems to meet my initial needs and is expandable to add more power, more throttles, computer control, etc at a later date (I will never have more than 100 locos).

I would like to add lighting and other functions on some locomotives, so I may need to get decoders from several suppliers to fit the space available. I also plan to model a freight loading bunker so will need reliable operation of heavy (by British standards!) trains at speeds around 1mph, possibly with two locomotives.

I have seen references to the selection of 14, 27, 28 or 128 speed steps but I can't find any explanation of how this works. The Lenz documentation says it is compatible with any of these modes, but recommends the 28 speed setting and suggests that other settings can lead to problems if the settings in the decoder and the main system are different.

Will I need 128 speed steps for realistic slow speeds or will 28 be enough? Does the need for realistic slow operation affect my choice of decoder, and should I also be thinking of something better than the Compact?

-- Edwin Marks (edwinmarks@hotmail.com), November 04, 2004


28 speed steps means that the locomotive's speed is divided into 28 steps from stop to full. The steps are usually equally spaced, but you can reprogram them with some systems to be unequal. This you might want to do if slow speed operation is important to you. I would think that without reprogramming, you will not be happy with 28 equally spaced steps.

As for your choice of systems, I really like systems capable of long addresses so I can use the locomotive's number as its address. Also, make sure it can do all the things you need. Too many people buy the Atlas Commander only to get rid of it because it can't do what they want. It was intended for small layouts.

-- Allan Gartner (wire4dcc_admin@comcast.net), November 07, 2004.

To operate the motor in the loco, the decoder has to provide a varying voltage from min to max value. In 14 speed steps there are only 14 different values of voltage, 28 has 28 values and 128 has 128 values. These values are called speed steps.

Depending on the type of decoder some speed steps can be adjusted to modify a linear speed curve. Options on some decoders for speed step adjustment (speed tables) can be volts Start, volts Mid and volts Max, internal user selectable speed tables, manual adjust of speed steps CV 67 94 for 28 speed steps and external computer adjustment to these CVs to adjust motor performance, to enhance loco especially slow speed operation and to match different mechanisms to have the same performance.

14 speed step decoders are basic early units and may cause jerky motor operation.


-- Marcus Ammann (mammann@optusnet.com.au), November 14, 2004.

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