Speed Matching the same decoders

[southernalco]

I have a problem with my two HO DCC units.  I have two Atlas locos, both with Digitrax DP125PS decoders.  Both decoders were set at CV2=2, CV5=40, and CV6=26.  Both start at SS one, unit #1 at 0.80 SMPH and unit #2 at 1.40 SMPH.  I reversed the decoders and the starting speed of unit #2  dropped to  0.80 (the starting speeds were reversed too), apparently the slow speed follows the decoders.  On  DC, both locos will start and run at approx.  a slow and steady 0.50  SMPH.  So it's got to be in the decoders.

Now, how do you adjust the speeds so the faster unit will run slower?? Has anyone noticed a difference from decoder to decoder in the same make and model??

Your kind assistance will be appreciated.

Gene

[Rangerover]

I'm rather new at all this consisting and speed matching using the cv's. I can only tell you how I accomplish this using JMRI Decoder Pro with a Digitrax PR3 interface. It's quite simple using these programs instead of me tring to put it in words, take a look at this vid clip from their program.

http://macrodyn.com/assets/video/mrh/JMRI/DecoderPro3_player.swf

Aw, the simplicity!

[cmarchan]

southernalco

I have a problem with my two HO DCC units.  I have two Atlas locos, both with Digitrax DP125PS decoders.  Both decoders were set at CV2=2, CV5=40, and CV6=26.  Both start at SS one, unit #1 at 0.80 SMPH and unit #2 at 1.40 SMPH.  I reversed the decoders and the starting speed of unit #2  dropped to  0.80 (the starting speeds were reversed too), apparently the slow speed follows the decoders.  On  DC, both locos will start and run at approx.  a slow and steady 0.50  SMPH.  So it's got to be in the decoders.

Now, how do you adjust the speeds so the faster unit will run slower?? Has anyone noticed a difference from decoder to decoder in the same make and model??

Your kind assistance will be appreciated.

Gene

DP125PS? Do you mean DZ125PS?

[southernalco]

Yes, it's a  DZ125PS..............

[cmarchan]

Try setting CV57 in each decoder to 0 and check the speed of each unit.

Another option is to record the CV values that were changed from their defaults, reset each decoder and set CV57 to 0 in each decoder. Check the results. If the speed between them is closer, try changing the  BEMF settings (CV55, 56, 57)  after setting start voltage, mid voltage and max voltage.

 

Gross differences between decoders could represent a flawed unit; I would try making the adjustments described above before going that far. In normal circumstances, it is not uncommon to find differences between decoders of the same model as there are tolerance specifications in solid state electronics and values can vary 5% - 20% in some cases.

[wjstix]

One thing to understand is what you're doing is speed-matching two engines, not two decoders. Setting the CV's the same on the two decoders doesn't make the engines run at the same speed.

Think of it this way, by setting CV 5 at 40 you're telling the decoder that when you turn your throttle all the way up, you want 40/256 of the available power transmitted to the motor. If both decoders are set the same, both are getting the same pct. of available power, so if one engine runs faster than the other it's going to still run faster.

What you need to do is increase the CV amts for the slower engine, or reduce the CV setting on the fast one. As it is, you have them set very very low...I'd maybe try setting CV 2 at 0, CV 5 at 100 and CV 6 at 50. Then take the faster engine and reduce the CV's proportionally - i.e. change CV 5 to 90 and CV 6 to 45 and see how that works. It may take time to get it just right, but eventually they'll run at the same speeds throughout the throttel range.

Don't forget you can use CV 3 and 4 - starting and stopping momentum - to help the engines start and stop together too.