# DCC - Speed Matching, Probably a dumb question but..



## Peter Osborne (Jan 5, 2008)

So I have two Bachmann Shays. One a 3 truck with the Soundtraxx "Quasami" sound decoder as delivered and a 2 truck with a LoksoundXL decoder installed. I'd like to double head (advance consist) these on occasion, and I'm thinking that since the mechanisms and power to the track will be the same, that if I adjust the three CV's for start, mid and max voltage to be the same, that if the decoders are reasonably accurate in how they work, that I should be off to a good start. 

Anyone see a problem with this idea?

Peter,


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## Greg Elmassian (Jan 3, 2008)

nope 

Greg


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## lownote (Jan 3, 2008)

That's what I do--set those three parameters so they match and you're all set. I do it on the mailine, with one loco following and one trailing, till at each speed setting they say the same distance apart


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## Axel Tillmann (Jan 10, 2008)

Potential problems include:
- Different treatment of those values by the two different manufacturers. E.g. I tried to match up an LGB decoder with a Zimo decoder. Endresult I ripped out the LGB decoder and the problem was solved 1,2,3
- different motor behavior. If the problem is minimal paly with the backEMF or turn backEMF off, if it is more severe use Shottky diodes to offset different startin voltage behavior.


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## Greg Elmassian (Jan 3, 2008)

When I get that problem (and I rarely do), then I resort to individual custom speed tables. 

I did that for fun on 2 USAT locos, just to see how close I could get them... I can keep them running 2 feet apart for about 6 hours! 

I agree with Axel on the BEMF, that it can be a problem, and many decoder manufacturers tell you to disable BEMF when consisting. 

Funny thing, I have left it on for all my decoders, and no problems... most decoders are QSI and Zimo... 

I guess I can leave that "trick" up my sleeve later if I encounter problems. I've found that many times when I thought my speed matching was not right, I actually had erratic operation of the loco, last time I found one of my GP7's had stripped gears on one motor truck! (My fault too, misassembly). 

Regards, Greg


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## Peter Osborne (Jan 5, 2008)

Good observations. Thanks. 

I already found one glitch. The Quasami does not seem to support mid and max, but both support speed tables, so that would seem to be the way to go. 
Time to crank up Decoder Pro and start poking around in these decoders. 

Peter.


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## Greg Elmassian (Jan 3, 2008)

Yep, on the Quasinami, you must do a bit of experimentation. Did you get any documentation on CVs for that decoder? 

I've never seen them documented. 

Regards, Greg


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## Peter Osborne (Jan 5, 2008)

I downloaded the sound decoder CV list from the Bachmann site, but who knows if it matches the Q. 

When I use Decoder Pro and ask it to read the decoder type and match it to a defn file, it picked the Soundtraxx Bachmann OEM template without hesitation. I then asked it to read all the CV's which took about 5 mins but worked. I've not had a chance to compare the actuals found by DP vs the documentation, but its working or my purposes. 

Peter.


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## Greg Elmassian (Jan 3, 2008)

The def file in decoder pro is probably the most accurate documentation you can find. 

Was the decoder cv list you downloaded specifically for the Q? 

Regards, Greg


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