Locos "jump" when accelerating...

[Steamfreak]

Hi guys....Got a little time this week to browse the forums. I was reading another thread on DCC which reminded me I have a little "problem" of my own.
I'm using a D'trax Zephyr and all D'trax decoders (123 and 163's). The situation is this....
All of my steamers "jump" speed when accelerating from a stop. The acceleration is not smooth like the deceleration where I'll just turn the control to 0 and the locos come to a smooth stop. When accelerating, if I set the throttle to 2.5 (for example), they'll start accelerating smoothly, but at a certain point, they'll jump to a higher speed. I've monkeyed with CV's 2,3 and 6 'till I'm blue in the face but have not been able to eliminate this jump. It's gotten to the point where I'm considering just resetting these CV's to zero, and accelerate the ol' fashioned way.... Any ideas..??

 

[hamltnblue]

make sure dcc mode is turned off. Doesn't sound like that problem but it could be.

 

[Steamfreak]

Hamltn...Why turn DCC mode off..?? I want to operate on DCC....

 

[hamltnblue]

Oops I meant DC mode. It is new years eve afterall
Also try to switch to 128 speed steps

 

[UP2CSX]

When my engines start behaving "funny", I do a reset and see if it improves. Sometimes fooling with the low number CV's screws up the speed table, which makes the engine jump to a higher speed at a certain point. I also use Decoder Pro to save all my CV changes whn it's running right so I can easily restore the right settings after a reset.

 

[CSX Robert]

Most current Digitrax decoders have Bemf compensation and they default to having it enabled. Digitrax's Bemf compensation does result in a speed jump at a certain point when accelerating. The severity of the jump varies from engine to engine, on some it is barely detectable, and sometimes you can reduce it by adjusting CV55, 56, and 57. You can eliminate it completely by disabling Bemf compensation(by setting CV57 to 0), but then, naturally, you do not get the benefit of the Bemf compensation.

 

[Steamfreak]

CSX Robert....You hit the nail on the head...!!! Last night I spent a couple of hours looking at CV's 55, 56, & 57, they were all off their supposed default values. I don't know why since I never messed with them before, but they were all off, on the high side, particularly CV 56. Its default setting is 48, but they were all set to 80. I reset the value to 48 and the jumping almost dissapeared, so I set it to a lower value (36+/- depending on the loco), and things ran smoothly..!!! Now I got smooth acceleration all through the speed range....!!! Thanks for your input....