Speed control is driving me crazy! - Final(?) comments

Hi Walt,

Sorry to hear this is still causing angst.  If it were me, I would install the tach strips.  Be sure to use ones that match the dimension of the stock painted stripes.  Once installed, pace both RS3's against another PS2 engine to confirm that they are working properly.  Then you should be good to go next Christmas.

Walt, just for kicks, measure the sensor-tape gaps.  Also, if you have an AC ammeter, try checking each loco separately to see if the amperage draw is identical.  If not, one could be "tighter" than the other.

Walt, I once had two identical SKU engines that had a speed differential closer to 10 smph.  One had some miles on it and one was new out of the box.  I thought one might need to be broken in, but the new one was the fastest.  I checked tach strips, sensor spacing and downloaded personality files into both.  No change.  Finally, I put both on the bench and pulled off the trucks, cleaned out the old lube, applied the Red 'n' Tacky and oiled all axles.  They've been perfectly matched ever since.

I'm not sure why some forumites don't like posting their thoughts straight in a thread, but I got a few emails on this.  One thought that I kinda like suggested waiting until I get my layout up again and see then how things run.  If need be apply the new strips then but the approach suggested is the familiar "if it ain't broke don't fix it" theory.

Gary: I maintain my engines VERY well.  Each year every engine gets a good cleaning and lubing.  But your idea was also one of the ones that was emailed to me so apparently it is a somewhat common reason.

RJR: I did measure that gap with my old auto (can't think of what the tool is called - it is used to set gaps in spark plugs).  Both matched.  Also, my MRC dual 270 has ammeters on it so I will write your suggestion down and try it when I get things out for Christmas.

Dave: I hope the diameter of my fly-wheel isn't one of the 2 smallest ones!!!!  The 2 smallest ones are only 0.7mm apart!!!!!   That's some awful accurate measuring!  Also Dave on you last suggestion, I did do that to the UNALTERED engines when I tested 2 nights ago.   I honestly don't care too much how they compare to other engines, as long as they mate up to themselves.

I did get an offer from someone at York to send both of the engines to him and he would make sure that they run the same.  I'll exhaust my options first but I sure am not going to forget that offer!!!!!

As always, thanks - walt

Hi Walt,

If you're nervous about the details of doing this, bring the engines to October York.  I can install the tach strips for you and make sure you get the right ones to maintain factory speed.  Bring your DCS remote and we can test run the engines together on the MTH display layout.  That will get you ready for next Christmas.

I appreciate the practicality of this sentiment but I think it's asking for trouble.  While both engines may run at the same speed today, if it is the incorrect commanded speed due to dirty tapes, incorrect gaps, sticky transmissions, whatever, the two engines will surely diverge over time.  Better to make them both run at the correct scale speed by changing the tape, touching up the stripes, whatever.

So I suggest you fix the speed on any engine that is not running at the correct absolute speed.  As you've done, you can compare them to other known-good engines.  Or it may be simpler to measure the speed (1 sMPH = 0.367 inches/sec) with a stopwatch and tape measure.  For example, command each engine to 40 sMPH and they should run 14.7 inches per sec, or 147 inches in 10 sec, etc.

Walt,  Stan make a very good point.  You need to find out which one is the problem engine, let's hope not both.  Once you find which one won't maintain speed, then you can work for the solution.  G

Dave: thank you for that offer.  Are you talking about Barry's Wednesday night dinner or regular York days?  I'm not overly concerned about not being able to do it, heck it's glueing a piece of material on that is already self-adhesive. 

Stan: good point.  I believe it's the "faster" one.  While my 2011 layout was still up, I ran comparisons between 4 other PS2 engines and these 2.  The problem is that NONE of my 9 PS2 engines run the same speed!!!  Some are pretty close but if I run them say 4" apart, it takes maybe 3 or 4 minutes of running at 40SMPH for them to be a foot or 2 apart, or have one overtake the other.

I sometimes get very frustrated because I try really hard to do all of the correct things - I keep my track clean, I keep my engines and their wheels clean and lubed, I wire my layout according to "the book", etc.

You guys are the best - I ask some pretty basic questions here at times and typically I get non-abusive, helpful, and sane answers!

- walt

Walt, what voltage do you run at?  A full 18-20V?  It's hard to imagine that any sort of binding could be the issue since binding would imply that the engine can not even make whatever speed you are trying to go.  That is, if DCS says go 40, and the engine does not, and the tach strips are correct, then that means the engine is going flat out and not even making 40.  Considering how fast these things can go, that's a lot of binding.

So: if you run the slower engine by itself, and if it can go faster than your target speed (can it hit 70 smph?), then I would look to the tach tapes, sensors, or perhaps a slipping/loose flywheel.

A slipping/loose, but sometimes sticking flywheel would explain why it works sometimes and not others.  So would dirt in and around the sensor, or perhaps a flaky sensor.  The common electrical faults in this area is not something I know much about.

Mike

Thanks for jumping into the fray Mike!

The engines run fine at ALL speeds.  With 42" curves I can't go wild on the speed but I've run them at least 90 SMPH (I know because I was charting things and topped out at 90).  They seem to run perfectly.

Yeah, the fact that when I pulled them out of storage Saturday and they ran exactly the same speed, and matched my GP20 too, had me scratching my head.

Unfortunately due to some company coming I had to tear down the temp track so I won't be testing again for a while.

I'm still stuck, in a way, on that "if it ain't broke don't fix it", but I won't be able to tolerate inconsistent performance.

thanks again - walt

Walt,

if I run them say 4" apart, it takes maybe 3 or 4 minutes of running at 40SMPH for them to be a foot or 2 apart, or have one overtake the other.

That's well within the tolerances necessary for running a lashup.

Walt, a simple question:  Does it happen regardless of whether locos are in forward or reverse, and if the locos are pointed in opposite directions but heading in same direction?  This would be an indication of "one-way" binding.

I'm not so sure that speed control is capable of keeping speeds the same if load (binding) differs.  Might well be that a slight drop in speed is necessary to indice the circuitry to incerase power to the motors.

I would not have believed what Barry said (but I do) after reading how many people say that they can run two engines for a LONG time and have them the same distance apart all of the time.  I remember Barry came up with some percentage that was acceptable.  I bet if I look in my notes I will find it.

Should the faster or slower engine take the lead.  I would think that the slower engine should be on the lead - I think I read that somewhere.

RJR: interesting suggestion!  I do know that speed does matter.  Call them front and rear engines for simplicity here.  Anything slower than 18 sMPH and the rear engine will overtake the front engine.  The slower they go the faster that happens.  Between 18 and 20 sMPH and they run pretty darn close to the same speed.  The higher the sMPH results in the front engine pulling away at a faster rate - the one that I mentioned above.

I am going to get my track back out now that my company has left and try that reverse running that RJR mentions.

I also am going to just bite the bullet and apply the tach strips.  I'll make sure that gears are clean and lubed and that there's nothing inhibiting movement.

- walt

A WHAT? 

How about this...That's well within the tolerances necessary for running a MULTIPLE UNIT CONSIST.

LASHUP...what a horrible word.

Rich,

How about this...That's well within the tolerances necessary for running a MULTIPLE UNIT CONSIST. 

Just using the vernacular.  

Hi Walt,

The problem is that NONE of my 9 PS2 engines run the same speed!!!  Some are pretty close but if I run them say 4" apart, it takes maybe 3 or 4 minutes of running at 40SMPH for them to be a foot or 2 apart, or have one overtake the other.

If you run your engines at 40 smph for 4 minutes they should travel a little over 293 feet.  If they drift from being 4 inches apart to 12 inches apart in that distance, that means they are accurate to within 0.23%.  That's just fine.  In the HO world where BEMF is commonly used for speed control, most engines are only accurate to within 10%.  That's part of the reason MTH is having some success in HO.

A more effective test to differentiate between an engine that is working correctly and one that's not is to run them back and forth (both ways is important) at 10 to 15 smph on a straight length of track.  If a tach reader isn't working properly the gain or loss between engines will still be noticeable.  By running both ways you detect most mechanical problems like a loose truck mounting screw or debris in a gear.

Anything slower than 18 sMPH and the rear engine will overtake the front engine.  The slower they go the faster that happens.  Between 18 and 20 sMPH and they run pretty darn close to the same speed.  The higher the sMPH results in the front engine pulling away at a faster rate - the one that I mentioned above.

That's a REALLY important piece of info Walt.  When a tach system fails the damaged engine will run faster than normal.  The statement above indicates that you may have different problems with each engine.  To perform a proper diagnosis each engine will need to be paced against a know good engine.  We could do that a York during the show.  I'm sure we can borrow a track on the MTH display for a few minutes of testing.

How about this...That's well within the tolerances necessary for running a MULTIPLE UNIT CONSIST.

Rich, when you get MTH and Lionel to change the terminology in their menus I'll happily change mine.  Until then...  LUMP IT!   It's hard enough explaining the systems in text over a web forum, let alone translating.

LASH-UP, LASH-UP, LAAASH-UP!!

I can't see how it woould make a difference whether slower or faster is in the lead, since they are going to go the same speed as long as coupler holds together.  UNLESS, you have an issue where one keeps getting derailed or, UNLESS your lashup is with a loco at each end of the train, where there will be a tendency for cars to derail.

I did 2 things since last checking in on this post:

1. I ran a bunch on comparisons using sMPH, engine orientation, and distances.  Summary below.

2. I replaced the tach strip in both engines.

The 3 tests were prior to putting on the new tach tape.

TEST ONE: I ran the faster engine short hood forward and kept the slower one long hood forward.  I ran them in a lashup simulation but started them off 4" apart.  I ran them at 10, 25, and 40 sMPH for 3 minutes and then measured how far apart they were after that.  After 3 minutes at 40 sMPH they were 4' 6" apart!

TEST TWO:  Both had long hood forward in a lashup simulation.  Again I ran them for 3 minutes.  For some odd reason the "slower one" did NOT overtake the "faster one" running at 10 sMPH as I was expecting and the faster one was 1' 3" ahead.  At 40 sMPH the faster one was 2' 9" apart.

TEST THREE: faster engine long hood forward, slower engine short hood forward (reverse of test one).  I only ran them at 40 sMPH for 3 minutes and the distance gained was only 11".

After replacing, cleaning, lubing, and checking for any kind on bind issues (for which I did not find anything) I ran them as separate engines long hood forward for 3 minutes at 40sMPH and they were still 1' 6" apart after that amount of time.

I also found a printout I was looking for: it was a thread on this forum from back when and it suggested running the slower engine as the lead engine.

Dave H. has me convinced that what I have is OK to run as a lashup.  Dave: I think I'll still try to remember to bring them to York though since you made a really nice gesture in an attempt to help out.  Someone else on this thread also made a really nice off in person at York so I don't want to ignore that offer in respect to that person.

- walt

You know what..I'd run them in a lashup for awhile and monitor the amp draw. If the amps start climbing after say 10-15 minutes then I'd start worrying..that is if you have a transformer with a ammeter.

Under a load these DC can motors behave different.

CRH: yes, I do have a transformer with built in ammeters - it's the MRC dual 270.  I'm guessing by you making your comment that over time the motors that's faster will start straining and the AMPERAGE draw will go up????

- walt

What could happen as time goes by is that the faster motors will get hotter, which can weaken the brush springs.

I did the meticulous task of charting timings last night using the 2 original culprit engines and later on a (relatively) newer GP20.

I'm going nuts!

I used a formula that was in CTT in the January, 2012 issue.    The formula was "Measure in inches a stretch of track and time how long in seconds it takes a train to go from one end to the other.  Take the inches times 2.72727 and then divide that by the time in seconds."

All tests were at 20sMPH running 1,392".  I recorded the time in seconds.

My 1st test had both long hoods forward.  I got calculations of 17.3sMPH and 17.4sMPH.  I was really happy - I didn't really care that according to the formula they didn't run at  20sMPH - the ran almost identical times and that's what I'm shooting for.

My 2nd test had both short hoods forward.  I got calcs of 20.08sMPH and 20.1 sMPH!!!!

I then did the GP20 by itself doing both orientations and got identical 20.03sMPH calcs!!!!

Then I put the 2 RS3's back on with the GP 20, putting them behind it (not coupled together, but spaced a few inches apart) since my first test showed them running slower.  To my surprise, or was it more confusion and frustration, all 3 ran darn near the same sMPH and only changed relative distance from each other by maybe an inch or 2.

But the frustration is found in that my last test results showed the RS3s running at 20sMPH instead of the original 17.3sMPH.  How did they change the way that they run?  This has been happening every time that I try to chart things - results keep changing.

I'm done and am going to run the 2 RS3s as a lashup with short hood forward.  Thanks for you patience and advice!!!

- walt