true MUing in HO

Model Railroader General Discussion (Model Railroader)
1

I had an idea last night. I want feedback from those who know, please.

I was trying to speed match my 2 working BLI SD40-2’s last night on my analog layout (I use a Quantum Engineer controller/MRC Railpower 1370) by setting common v-start and v-max values and tweaking the load values on one or the other to try and get them to match. But one still wants to run a little faster than the other resulting in one power truck constantly derailing at the points of my crossovers at mainline speeds when its the last truck through the switch. I know that it’s because it’s loco is pushing a little more than the loco it’s following.

My theory is one decoder, two motors. By cutting off the motor connections on the trailing loco from it’s decoder and connecting the poles on the motors of each locomotive wont they both run at the same speed? I’m thinking 26 or 28 gauge wire fed under the body to a micro connector at the front and rear of each locomotive. A true MU cable if you will. The lead and trailing loco’s decoders will respond with sound but only the lead loco’s decoder sends power to both motors.

I have a lot of time on my hands and my brain just buzzes with these kind of ideas from time to time. Besides, we’re all trying to be as prototypical as we can be. Aren’t we?

2

BTW…I’ve got first dibs on that patent.

3

Sorry, there’s quite a bit of prior art on this idea. Back when command contol systems had few channels, I did this with an F7 A&B set. And later, when DCC decoders were relatively expensive, I did it again with DCC.

Even then, seemingly “identical” units seem to have minor differences in performance due to variations in engine performance, gear friction, etc.

4

If there is a mechanical speed difference, I don’t think this will acomplish what you want. Are you sure the speed difference is causing the truck to derail? I’ve mu’d locos of very different speeds and never had a problem. Did you try checking your wheel gauge? (just a thought)

5

C’mon loath…This ain’t my first rodeo.[C):-)]

6

The decoder is designed to run ONE motor only. If you are running TWO motors, the TWO motors can exceed the amp rating of the decoder, but it might be ok. The other issue is the BEMF (or torque compensation) that is programmed into the decoder. It will probably get really confused with 2 motors.

You can try it, but you know you void your warrenty the moment you cut that first wire…

David B

7

Try putting the faster loco in the lead position. A faster loco pushing a slower unit is more likely to derail.

And even if this isn’t your first rodeo, you might want to double check the swing of all the trucks.

8

Is this why I have more dereilments, when backing units up, when going forward ( in any dirrection ) doesn’t have nary a problem?

9

Ted,You could use a resistor on the faster locomotive…In DCC you can match start voltage and then match the speed steps.

10

Brakie…I wouldnt mention DCC, Ted might go off the handle.

(of course DCC would solve this issue in a second)[8D]

David B