Linking/Speed Matching

[drisdon]

I have had some issues linking and operating one pair of locomotives and thought one of you on this group may have experienced something similar. The consist is an Atlas GP40-2 with LM-2S module and Proto 2000 GP30 upgraded with Stewart trucks with LM-2 module.  These will always be ran as a pair so I want them to run well together as a slug and slug mother; CSX GP40-2 and GP30 RDMT. 

Both have same settings for acceleration and deceleration.

Getting the pair to link is not the issue, but the speed matching seems to be the issue.  When linked the GP40-2 will start spinning its wheels several seconds before the GP30 moves. I have tried adjusting the start voltages both ways for each and adjusting the accel. and deccel. one at a time to to troubleshoot, but none resolved the problem.   They will run separately well, but not together.

What am I missing? How would you get these two to work well with each other?

Thanks,
Dan R.

[Alan]

Try resetting the stall current on both. If you repeatedly set the stall current you will notice there is quite a variation in results. Keep setting the stall current until you get it set on the highest or near highest reading you notice.

[Josephbw]

One Question, are you trying to run the engines back to back or nose to tail? If back to back you need to set the direction of the engines before you link them. Otherwise they will be trying to run in opposite directions.

Good luck, Joe

[drisdon]

I will try resetting the motor stall, that is one thing I didn't play with.  I also wonder if it would be helpful to "warm up" the locomotive before setting the stall current? 

Thanks for the suggestion, I will try it and report the results.

As for the suggestion to set the locomotive direction, yes that was set properly. 

[Alan]

I'm not so sure warming up the motor is critical. The issue with stall current setting is when do the wheels slip. As soon as they slip the current falls off. So, anything that changes when the wheels begin to slip, including random chance, will affect the stall rating.

My fleet is exclusively 4 axle Atlas. I own a a few 6 axle Athearns but haven't yet put a module in any of them. The Atlas units at stall are all somewhere between 300 and 350mA. Any one loco can be anywhere in this range each time it is set. I keep setting stall until I get a rating as close to 350mA as possible. I do this to get the truest reading of real stall at maximum wheel traction. My Atlas units run well together.

Shortly after I first got RP, out of curiosity I set the stall current real low by lifting the loco. Sure enough, it ran fine by itself but did not play well at all with the others. That experience is why I immediately recommended you reset stall current.

[William Brillinger]

I will try resetting the motor stall, that is one thing I didn't play with.

The Stall Motor Metric is critical to the locomotives being able to match each others speed. This is the magic number that RP uses to base this function on. Not setting it will result in the locomotives not reacting properly to each other at all.

I look forward to hearing how your results change after this is set.

[nodcc4me]

Drisdon, I have the same Atlas GP40-2 engine. The stall current on it is 320 mA. This seems to be a good setting for it as it speed matches well with other engines.

Joe, if this is any help to you, it is not necessary to set the direction of the locomotives prior to linking them. After you link them just press the MU=2 button and you can easily set the direction of all linked locomotives in that particular consist.

[Antoine L.]

I had similar problems with locomotives from Kato and Athearn when mixed together. Check your installation. For me, a wire was touching a flywheel slightly enough to alter MU operation without me noticing when it was running alone. The "OK" loco was spinning at the "not OK" loco was struggling and feeling heavy.

Problem was immediately solved when I found out and made sure flywheels were free.

Antoine

[Dean]

If your engines are new, some break-in time helps. Reset the current setting after they run for a while.

[drisdon]

Thanks for all of your replies.  I reset the stall motor current in both locomotives.  The Atlas GP40-2 is 380 or 390 mA and the Proto 2000 GP30 was 400 mA.  Also I reset the other settings to default.  I linked the two together and they ran a little better, but the GP40-2 still starts moving (spinning) before the GP30.  The throttle will get to about 20-22% before the GP30 moves.  I then adjusted the starting voltage and that helped, but they still are not a perfect match.  I even tried uncoupling them to see when they would move.  One thought, the GP30 probably weighs almost 25% more than the GP40-2, would that matter?  Also the GP40-2 has sound and the GP30 does not, and with the sound off or on they still perform the same way. 

I've really been wanting to get these two to operate well together, and it's just been much more difficult than I thought it would be.

One other question, unrelated to this topic, how do you do manual notching and still control the train well?

Thanks,
Dan

[Alan]

While, technically speaking, starting voltage should not matter for MUing, it sounds in your case it might. One at a time, not MUed, set the start voltage so each loco begins to move at no more than 5% throttle. It may help your MUing situation. My Atlas units right out of the box were typically 10-15% throttle to achieve movement.

Personally I set start voltages on my steepest downgrade on the layout with a long train behind (lightest possible load on a single loco). This way I know I can get movement with minimal throttle movement and without fear of jack rabbit starts when going downhill. The process can be a bit tedious.

I set all my locos to less than 5% because it makes the throttle response/position more uniform and predictable between different locomotives. My logic is there is no such thing as a powerless notch on a real locomotive running light. Plus, it just doesn't feel right when you nudge the throttle on a loco and nothing happens.

[Alan]

The more I think about this the more it doesn't add up. If the wheels of the GP40 start spinning before the GP30 moves then that means the GP40 has already reached maximum current draw at least once. When the GP40 is at maximum the HC1 would also place the GP30 at maximum. They should both be flying down the track.

This is going to sound like a dumb question but are you certain you have them MUed correctly on the HC1?

Another dumb question... when the GP40 wheels are spinning are they spinning in the right direction? Is it possible the GP30 is dragging the GP40 backwards? Being the GP30 is so much heavier maybe the GP40 can't drag it the other way.

[William Brillinger]

Another thought... Are the modules using the same software version?

If they are not up to date, you might want to update the software on the modules and HC.
Some older versions of the software did not play well with some other versions as I recall.

[Dean]

Try this. Put both locomotives on the same track but do not connect them together, rather leave a gap of at least one locomotive length between them. Then MU them together if they aren't all ready. Remember, the first locomotive you picked for the MU setup is the 'lead' locomotive, and the rest will follow, speed wise. Now try running your MUed locomotives. ( you should be running from the 'lead' locomotive screen ) Do they both go they same direction? If not, press the 'MU=2' button on the HC screen. You can change the direction of the follower locomotive there. Now run your MUed set again, still not connected. Do they start at about the same time? If not, delete the MU setup and work on the locomotive that is not starting properly. I would pull the shell off first and check for mechanical binding. You might want to run it with the shell off so you can see whats happening.
When happy with the mechanicals tune the decoder to the locomotive.  If is a new locomotive, you might want to run it singly for 30 minutes in each direction. This will break in the locomotive and make the tuning easier.
Remember, the locomotives in a MU consist 'learn' to run together and follow the lead locomotive, but it does take a little time.
The great MU capabilities are the reason I started using RailPro.

[Homeless by Choice]

Guys,

This is a very interesting problem solving discussion.  Thank you for the very informative step by step debugging process.  Please continue the discussion and be sure to post the final resolution in detail.  I was under the simplistic belief that you basically determine the max current, MUed the engines, and bingo you were done.

I am not one bit faulting the design or questioning my decision to invest in the RailPro system.  I just want to understand/learn all the logic and setup requirements so I can stay on top of any possible issues.  I am sure that this is MUCH MUCH easier than using a DCC system.

Thanks for the information,
LeRoy