Is this something we are not really aware of?
About 128 speed step mode.
128 speeds are from 0127. We think of how many speeds, so Zero is the first one, so the 128 is really a speeds of 127 to us.
Speed of 1 sent to a decoder is special. That tells the decoder to do an “Emergency stop”. So that to our mind that leaves 126 speeds that we can tell the decoder to do.
We have 28 steps in the speed table that define different points in the 126 speeds. Divide 126 by 28 and you get 4.5. So speed table step 14 should have maximum affect on throttle setting of 63, but what throttle setting do step 13 and step 15 affect? For 13 there is no throttle of 58.5 so its assigned to either 58 or 59. The same for step 15, its either in full affect for 67 or 68 speed on the throttle.
The designer of the decoder now has to make a choice, How do I handle the odd number speed table CVs? They have to have a whole number that is either 4 or 5 greater than the preceding number in the throttle speed.
Manufactures handle this dilemma in different ways!
Digitrax increase the throttle steps by 4 as the speed steps increase, Speed step 1 affect throttle speed of 1, step 2 affects speed of 5, step 3 affects 9 and so on until step 27 affects throttle setting of speed 105. That leaves Throttle speed of 109127 to be affected by step 28. Step 14 (often thought of as mid point) affects throttle setting of 52. Throttle mid point of 64 is most affected by step 17
Soundtraxx took a different approach they increase the throttle speed affected by 4 and then the next step affects the throttle speed by 5, that way Throttle mid point of 64 is affected by Step 14.
NCE and QSI are also different than other Manufactures.
This means that when JMRI plots a straight line speed curve the Loco is not going to always respond with nice smooth speed changes as the throttle is changed from speed to speed.
Walt Thompson
1405 Portland Ave
Saint Paul, MN
55104
Ph 6516448673
Moderator, Yahoo JMRIusers group
NMRA, TLR, TCD
NRMA #136859
