Can Low Speed Control Be Improved In PS2/3 Diesels?

The only thing that comes to mind is to check stuff like the flywheel sensor spacing, I'm assuming you've checked all the possible mechanical issues as you say?

I'd probably try a factory reset and reconfiguration, just to eliminate any configuration issues.

Thanks John. The reader spacing could be an issue with the RS3 as I had to replace it at one time. Will try the factory reset after that.

Scott, the slowest runners on may layout are a pair of Weaver PS2 locos from the early 90's.  They've covered a lot of rail, and I am sure they are mechanically quite limber. Run smoothly at 2mph, and run at 1mph.

PS3 could be setup to crawl very slow via DCC if MTH has opened all the CV's to be tweaked but from what I've read that's not the case. In the DCC world it is not uncommon to have loco's crawl at a rr tie or two per minute.

If I set engine speed to 1 or 2 smph it will move . . . . Occasionally. I did take a tip from RJRs post and run my switcher at 15 smph for a few laps and that seemed to improve things. Maybe that was it, just some gunk in the injectors. 

I don't know if smaller radius curves have an impact or not, maybe 036 is too small or puts more friction on the wheels than say 054 or 072 curves.

I would check the gearing to make sure there's no debris causing the problem.  I have an Atlas GP9 (with PS2 installed) and shortly after putting down ballast I had the engine come to a dead stop, found a very small piece of ballast had gotten between the gearing (it almost caused me to swear off ballasting anymore track).

I would give the trucks a thorough cleaning, then inspect the gears and lube them.

I doubt that full size locos can run at a steady 1 or 2 mph.  Somehow I seem to remember a "rule of 10" that the slowest mspeeds are around 10% of the top speed.

  Also for consideration is whether this will overheat the can motor.

I do see some variation in this.  Some engines do very well at 1-2 SMPH.  Others steady out at 3.  I do think there are a lot of factors involved, most with the motors and gearing condition.

MUs and Slave units can be another area of concern, were performance is better above 3 SMPH.  Again age and condition can have an effect.

Just recently I had to do a repair on an Slave unit were one motor would drag until higher SMPH selected in forward.  If moving in reverse it would start rotating properly.

Moving the motor to a different location did not correct the behavior.  So even can motors can have issues in a specific direction.   G

Most of my MTH engines do not run smoothly at speeds less than 3 smph; however, they all run well at 3 smph.  My new GS 4 runs smoothly at 1 smph in forward and backward at 2 smph.

Thanks to all for the feedback. The 036 curves do seem to be a place where the speed seems to oscillate very slightly. I also have a lot of switch sections in series that could be a contributor. I did add some Labelle heavy oil (can't remember the #) to the gears under the trucks on an S1. Then gave it a good run at 15 smph for a few laps. Low speed control was noticeably improved. Maybe it helps to loosen things up a little.

I have a Lionel Legacy GP9 and it has exceptional low speed control. I seem to remember reading that Lionel speed control technology is different than the tach tape+reader that MTH uses.

Lionel uses a different encoder that has finer steps.  That may be part of the reason that low speed in the 1-2 scale MPH seems better with many Legacy locomotives than with PS2/3 stuff.

My Legacy Genset runs smoothly above speed step 3 (no jerkiness). I run it at speed step 23 which is eqivelant to 3 msph which is the slowest my 4 MU (Heritage, Uboat, GP30 and Tranmaster) Reading will run.

My Legacy genset runs at step 1, you almost need an hourglass to time it's progress!  It's by far the best low speed performer I have.  Interestingly enough, even with just one powered truck, it'll pull 20 cars around, including 2% grades, no sweat at all.

I believe a lot of the low speed performance has to do with the drive method for Lionel engines.  The gearing, and method for motor attachment via the t bone.  Prevents much of the back lash, and thrust changes in the drive train.  G

I'd buy gear ratio differences might help, but I don't see the motor attachment being an issue.  There's still a worm gear as the first stage of the drive in either MTH or Lionel.

Gear ratio, gear teeth cut method (helical cut is better than the straight cut found on most locos), backlash due to tolerance of the machined gears and the precision of the DC motor/s has a lot to do with the slow running of these locos. Of course the electronics and how they measure and correct for speed accuracy also is a major factor.

For smoother running at low speeds, the gear ratio should be such that the DC motor spins fast enough to be in its sweet torque and horse power rating. It is better to have a high gear ratio where the DC motor is spinning faster and hence allows better low speed control.

Having TWO DC motors adds to the problem if they are not 100% matched and synch'd and will cause them to fight each other some what.

Certainly the way two motors are done in our stuff is a factor, since one is not positively controlled, that is less than optimal.

It has nothing to do with the gearing but everything to do with the algorithms that MTH is using in the firmware esp. in the motor drive area. With DCC you can fine tune all the voltages that a motor receives including but not limited to say the kick voltage & time as adjusting these two would eliminate the 1 smph lurching by sending the motor a bit more juice for a millisecond to help "kick" it thru a stall. Motors will "hang" when the armature is rotating in the magnetic field. Skewed armatures are better but they still hang.

I firmly believe that MTH is using a generic algorithm as fine tuning it for every single different loco would be both time & money consuming. That's why MTH advertises slow speed down to 3 smph.

As far as real 1:1 locomotives being able to do the slow speed crawl they do..as in hump service and those pulling the tie replacement, ballast cleaning ribbon rail train. 

Since DCC is so good, why are you wasting your time with DCS?

Gearing, and the truck tolerances and design have a tremendous effect on the cruise performance.  Sure algorithms matter too.  MTH has done work on that also.  You have to remember this PWM powering can have big effects.

Unfortunately, some of the MTH truck drives are lacking in the improvements I have seen in Atlas and Lionel trucks.  If you don't think the precision of the manufacturing process and the design of the gearing doesn't matter, do some comparisons. 

Precision trucks with less friction will prevent the motors from having to hunt to maintain speed and will result in smoother operations at low speeds.  G

Don't try to confuse him with facts GGG.