Speed Matching and MU'ing

[Ohio Central]

I am trying to speed match an Intermountain gevo to athearn sd70m-2 with tsunami and I have them pretty closely matched. They still have a little buckling in the couplers but they won't match any better. I am matching them using 28 step speed tables on jmri. My question is how far off can these locomotives be and not cause damage? And how can I get them to match just a little better?

[jrbernier]

  They just need to be 'close' - The real ones are not perfect either.

Jim

[peahrens]

I would expect that when they are pulling a load of cars, usually each will have a share of the load (one is unlikely to take it all, even momentarily, and create coupler slack.  Downhill (cars pushing on the rear loco), there may be more likelihood of some slack occurring between the two as they try to hold speed. 

If you're not satisfied, you might see whether they behave better with BEMF turned off, as folks report this can cause undesired interaction.  On two of my BLIs (SD7 and SD40) I just this week speed matched this week, I tried with BEMF turned off both, but then found that affected one of them significantly at slowest speed (CV2) so I could not get slow speed well matched unless I increased the slowest speed of one significantly, requiring increase of slowest speed for the other as well.  I did not want to give up the default low speed capability.  I also tried with both locos with BEMF on and with only the (normally) lead loco BEMF on (how I left it, I think).  I need to fiddle with this more (just for learning) but when I run them coupled they do just fine, even without a load of cars.  EDIT: I need to re-read the attachments below on momentum, BEMF, etc before fine tuning (or starting over).  Don't think I went about this quite right.

I can't imagine damage occurring, unless the acceleration settings are so mismatched that on rapid acceleration one loco spins its wheels as the other lags in trying to attain a speed.  I forget offhand how the accel / decel settings should be handled to get not just the slowest, top and mid-speeds (when attained) matched but also creating matching (reasonably close) acceleration (momentum) adjustments. 

EDIT: I'll add a link to some Tony's Trains procedures, which addresses the momentum, BEMF, etc:

http://www.tonystrains.com/technews/loconews/loco_speed_matching_easy.htm

http://www.tonystrains.com/technews/consisting-guide.htm

http://www.tonystrains.com/technews/introto_bemf_pid.htm

 

As Jim said, "close" usually works fine, as I'm still learning and the two consists I've done so far are probably only loosely tuned and may bear some tuning.

[duckdogger]

I agree. Close (okay, very close) works. Like many, I put the faster loco first as pulling is less likely to cause a derail than pushing.

[rrinker]

 Close is good enough. I have a pair of P2k Geeps which I MU with an Atlas Trainmaster. The Geeps have TCS T-1 motor decoders, the Atlas Trainmaster has a QSI sound decoder. I didn;t do a darn thing to any of them other then set them all to the same address. These locos run for hours at train shows pulling a fairly heavy train, and they don;t overheat or have any other issues. Uncoupled with no train, the Geeps run pretty close together, since they are identical mechanically and electrically, the Trainmaster has a higher starting speed as well as a bit faster top speed, but all coupled together with the weight of a train behind them they even out and I con;t have issues with one or the other spinning wheels while the rest aren;t moving or anything of the sort.

                --Randy