Solved - DCC speed steps for MTH engines

MTH PS-3 DDC speeds steps are in fact smph.  I've done the math and confirmed it with a phone app.  And it is my understanding you can't change the speed, only the rate at which the speed changes (Like Legacy momentum setting.).

DCC decoders if completely compatible work at either 14 or 28/128 speed steps.    Newer decoders default to the 128 speeds steps.     I have heard the MTH decoders do not follow all the NMRA standards.

Another standard is that CV 5 is the maximum speed.   You can limit the top end by setting this CV between 0 adn 255.     CV 6 is the midpoint of the speed range and uses the same settings.    CV 2 is the starting voltage again with the same range.    These settings do use the 20 or speed steps for the curve on the decoder.    They set the speed as 2 intersecting straight lines, one from o to midpoint, and the second from midpoint to max.

I like to set my decoders so about 1/3 of the speed range is on half the throttle.    so if I leave the max at 255, I set the midpoint about 100.     If I reduce the top speed to say 200, I set the midpoint at about 75.     I don't  use the speed tables with all those inputs.     I did reduce the top end on my MTH PAs, and I think on my MG D16.

Perhaps a mystery will be unveiled. That is, how does the MTH tach reader work with DCC? Is this one of the reasons that DCC users do not like MTH DCC?

@prrjim posted:

DCC decoders if completely compatible work at either 14 or 28/128 speed steps.    Newer decoders default to the 128 speeds steps.     I have heard the MTH decoders do not follow all the NMRA standards.

Another standard is that CV 5 is the maximum speed.   You can limit the top end by setting this CV between 0 adn 255.     CV 6 is the midpoint of the speed range and uses the same settings.    CV 2 is the starting voltage again with the same range.    These settings do use the 20 or speed steps for the curve on the decoder.    They set the speed as 2 intersecting straight lines, one from o to midpoint, and the second from midpoint to max.

I like to set my decoders so about 1/3 of the speed range is on half the throttle.    so if I leave the max at 255, I set the midpoint about 100.     If I reduce the top speed to say 200, I set the midpoint at about 75.     I don't  use the speed tables with all those inputs.     I did reduce the top end on my MTH PAs, and I think on my MG D16.

Thanks.   I'll give that a shot.

Ron

@sinclair posted:

MTH PS-3 DDC speeds steps are in fact smph.  I've done the math and confirmed it with a phone app.  And it is my understanding you can't change the speed, only the rate at which the speed changes (Like Legacy momentum setting.).

Can confirm, the speed steps are accurate. Also, I highly recommend setting the "MTH Acceleration" and "MTH Deceleration" in CVs 53 and 54 to values much lower than the default. I use 24 for both, which gives very nice smooth start up and stopping.

https://www.mthtrains.com/site...ction/20dl19404i.pdf

I do not believe there is a way to use a custom speed table, however, without disabling the use of the tach feedback. CV52 must be set to enable "PWM Mode", which as far as I can tell makes the controller run completely open-loop. This is pretty much useless.

Also of interest may be the testing I did in this thread, regarding tach tape spacing. I do this mod on all my diesels, and the transformation in speed control is great. This, combined with the accel/decel tweaks, makes them almost as driveable as a Loksound. 

https://ogrforum.ogaugerr.com/...g-how-low-can-you-go

PERFECTO!!!!

My app says that to change CV5 I must make CV52 =1.  I did that.

Then my choices for CV5 were 1-255.  I changed CV5=150.

The engine speed is much better and I now have a greater range of motion on the throttle to get the engine up to speed.

Running next to a DCS engine, my top throttle is 55 SMPH, my mid throttle is 25 SMPH.  All very slow and smooth from 0 on up.

Interestingly, I do not have a CV6.  CV2 was at 16 and I left it alone.

Thank you for the feedback.

Ron