# What causes the "lurch?"



## gimme30 (Jul 26, 2018)

I have a couple of diesel engines that when new would lurch at low speeds, and even after being broken in, will still sometimes come to a complete stop at low throttle. Give a little more gas and they'll take right off again, but I don't like to run them that fast. I've cleaned the wheels and track, and while lubing the gears noticed there's a small amount of side-to-side play along the axles. I don't know if it's even possible, but I've considered shimming the gears to see if that will help.

Thing is....they're SO tiny! And as I've never disassembled the trucks on a diesel I don't know if it's even possible or if shims would help.

It's not just the diesels either. I have a Bachmann 0-6-0 that ran horribly at first, much better after a few hours being run-in, but now will come to a grinding halt even at full throttle!

Is there anything I can do to correct this?


----------



## wvgca (Jan 21, 2013)

nope ...
cogging is merely the effect of when the motor rotor and stators are aligned, in that a motor with fewer poles [as in a 3 pole motor] would tend to align in only three positions as opposed to a larger number of poles ..
by the way 'grinding' has nothing to do with cogging...


----------



## MichaelE (Mar 7, 2018)

That side to side play is what allows model railroad equipment to negotiate the curves we have to use on our model railroads. I'd be careful about removing it.


----------



## gimme30 (Jul 26, 2018)

Thanks gents. 
I suspected that play might be necessary but wasn't sure. 

You'll have to excuse my brain fart when writing the title to this thread. At the time I was pondering this little problem, thinking it may be improperly meshed gearing, with the appearance of an electric motor cogging under low current. So...the title didn't come out exactly as I had intended. My apologies.

Apparently most of my brain leaked out of my ears overnight.

I should tell you that, when sped up, the problem _appears_ to go away, but I can hear it, and if I watch closely I can see it happening, although not to the extent that the engine stops.

It seems unlikely to me that it would be out-of-round gears, although as it turns out this only happens with the Bachmanns so....

I'm at a loss fellas!


----------



## Big Ed (Jun 16, 2009)

You can edit the title, go to the first post click edit then click go advanced edit. There you can change the title if you want.


----------



## CTValleyRR (Jul 26, 2014)

How old are the locos? Older pancake motors do not perform very well at low speeds, especially compared to newer, multi-pole motors with flywheels. Remotoring is kind of a drastic solution, but it might work.

Also, is everything clean and properly lubbed? Poor electrical contact due to corrosion and chunk of congealed lubricants can also cause the behaviors you're describing.


----------



## gimme30 (Jul 26, 2018)

Sorry about the late response, work sure has been keeping me busy lately.

Ct the oldest is the 0-6-0, and last night I figured out why it was having issues. The first 2 or 3 minutes on the track it actually ran fine. Or at least, as well as it used to after being broken in. Then nada. Looks like an axle broke or the wheels slipped off the ends, but either way, in this case, mystery solved. 

The diesels are another story. I took 2 of the worst offenders apart this morning and can't find anything obviously wrong-there's no congealed or excess lube, in fact the gears in the trucks were definitely on the dry side but there is no sign of uneven wear. 
Both engines are less than a year old and neither have more than 5-10 hours on them. 

Just in case, I cleaned the track AGAIN and went over it with my volt meter and saw no variation or drop out along the entire length, but it got me thinking.....
I've read plenty here about people fixing their surging or starting issues by programming a higher start voltage. Both of my engines are dcc equipped... but I'm not.

I can still hear the "unevenness" at speed so maybe it has nothing to do with the dcc at all, just a thought.


----------



## traction fan (Oct 5, 2014)

*DCC and smooth slow speed running*



gimme30 said:


> Sorry about the late response, work sure has been keeping me busy lately.
> 
> Ct the oldest is the 0-6-0, and last night I figured out why it was having issues. The first 2 or 3 minutes on the track it actually ran fine. Or at least, as well as it used to after being broken in. Then nada. Looks like an axle broke or the wheels slipped off the ends, but either way, in this case, mystery solved.
> 
> ...



gimme30;

One of the many benefits of DCC is smooth operation at slow speeds. Usually, a good deal slower, and smoother, than with DC.
For you to have the slow speed starting, and running, problems you describe, on a DCC locomotive, is weird. Especially since the same problem exists on two locomotives. 
Whether programing the starting speed will help, or not, I'll leave to the DCC "digital divas" one of which I definitely ain't!
I spent a lifetime troubleshooting electro-mechanical stuff for a living, and model trains as part of my hobby. But I retired before much of today's computerized equipment had been invented.
Now I like DCC, and I use DCC. But beyond understanding the general theory, what goes on inside my NCE Procab is largely a mystery to me. :smilie_auslachen:
You might post your question about reprogramming the starting speed on the "Technical Forum" section here. They have lots of digitally savvy folks there who should be able to answer it for you. 

In terms of general troubleshooting, your "The DCC system might be causing this problem." theory makes sense. Either both your diesels have the same problem, or some common factor is affecting both of them. The DCC system, and track, are two common factors; and you've already checked the track pretty thoroughly.

Both locos having the same problem is possible, if somewhat unlikely. The likelihood factor would go up exponentially if both locos are older designs with three-pole motors, no flywheels, and too-high gear ratios. I go back in N-scale to the jurassic era, when such lousy runners were all that was available. Back then, we had "two-speed locomotives." (The two speeds were 120mph, and stop!  ) Those old dogs jumped instantly from stop to full speed whenever you tried to run them. 

Yet you say your diesel locos are quite new. Does that mean newly manufactured, or "new to you?" (a.k.a. used, e-bay wonders) 
What brand are they? Do they have flywheels? What is the electrical path from the wheels up to the DCC decoder? Are there any metal contacts that might be dirty, or is the wheels-to-decoder connection hard-wired? How many poles do the motors have? You can determine the number of poles by looking at the "rotor," the spinning part of the motor. It should have groups of laminated metal plates separated by gaps, that all rotate around the motor shaft. Mark one of these metal plate groups and then slowly hand-turn the rotor. As you turn the rotor, first, it should turn easily with no binding. Second, count the number of plate groups. You should find either five, (good) or three,(bad). The plates may also be "skewed" where the individual plates in a given group are not aligned exactly with each other. Rather, they form a sort of "stair step" pattern with each plate slightly ahead of its neighbor. This "skewed armature" feature, is also a good thing.

NOTE: Clear, close-up, photos of the locomotives, with the body shells off, would be a great help in diagnosing the problem.

While your looking at the motor, check out the "commutator." This is a group of three, or five, copper plates with little gaps between them. Its mounted on one end of the shaft, within the motor. The two motor brushes rub on these plates. Are the copper plates clean and shiny? If not, use a pencil eraser to rub off any dirt. Be very careful in this area. There are some very, very, tiny wires soldered to tabs on each plate. You don't want to break one. Were any of these wires already broken? If so, the motr is basically toast, unless you can do some serious micro-surgery by soldering the broken wire back on. (Yeah right! hwell

Finally, if you find you can't fix the problem, you might consider replacing the loco with a Kato brand diesel. They are excellent, super-smooth, runners, and have five-pole motors, dual flywheels, and sensible gearing. In my opinion, they are the best N-scale locos available.

Good luck;

Traction Fan :smilie_daumenpos:


----------



## Dennis461 (Jan 5, 2018)

Did anyone suggest a PWM throttle if you are running DC? The reason DCC is good is partly due to its PWM built in throttle.


----------



## GNfan (Jun 3, 2016)

Back when Bachmann had a forum of their own, it was common knowledge there that the white plastic Bachmann once used for gears would turn brittle over time and crack or lose teeth. If your 0-6-0 is quite old (like stamped "Made in Hong Kong"), check the gears for missing teeth.


----------



## gimme30 (Jul 26, 2018)

Well GNfan you nailed it! Since the 0-6-0 has been relegated to shelf duty I decided to go ahead and take it apart and sure enough a tiny chunk of white plastic fell out when I took off the shell. 
I really liked that little engine, even though it couldn't pull more than 2 or 3 cars downhill with a tailwind. I don't know that I'll repair it though...all those tiny little parts! They're cheap enough that if I decide I can't live without it I'll just buy another one. 

TF I tried getting pics but my little point-and-shoot can't focus well up close. I'll try again under better lighting this weekend, or use the cell phone camera. Boy do I regret selling off all my 35mm gear now! 

In the meantime I'll try to be more specific. Both engines are made by Bachmann, one is an RS3 and the other a GP7. Both are dcc equipped purchased new from Trainworld, and look identical to me under the shell although they're geared differently as the GP7 is much slower. They both have what look like closed end bell motors so I'll have to dig those out to see how many poles they have. There are flywheels at either end. Power is transferred via copper (?) wipers which look clean to me, but then again my eyesight isn't what it used to be. 

They both have PCB's mounted on the top of the frames but I have no idea where/how power is received. 

Ok don't laugh, but I'm using a Bachmann transformer that came with a Dewitt-Clinton. ( I couldn't resist!) My guess would be it is not PWM?


----------



## traction fan (Oct 5, 2014)

*DCC equipped loco running on a poor quality DC pack?*



gimme30 said:


> Well GNfan you nailed it! Since the 0-6-0 has been relegated to shelf duty I decided to go ahead and take it apart and sure enough a tiny chunk of white plastic fell out when I took off the shell.
> I really liked that little engine, even though it couldn't pull more than 2 or 3 cars downhill with a tailwind. I don't know that I'll repair it though...all those tiny little parts! They're cheap enough that if I decide I can't live without it I'll just buy another one.
> 
> TF I tried getting pics but my little point-and-shoot can't focus well up close. I'll try again under better lighting this weekend, or use the cell phone camera. Boy do I regret selling off all my 35mm gear now!
> ...


 gimme30;

If the Bachmann RS3 and GP7 are DCC equipped, that explains the circuit board inside, it's likely the DCC decoder. That brings up another possibility, are theses DCC decoders of the dual-mode type, that are designed to operate on either DCC, or old fashioned DC. It also raises a couple more questions. Do you own a DCC controller? (i.e. NCE powercab, Digitrax zephyr, etc.) If you do own one, why are you using a cheap DC power pack, rather than running your DCC equipped locomotives on DCC? 

I got the impression, from your first post, that you were experiencing the "lurch then stop" behavior, while running these locos with DCC. That's one thing that puzzled me, since DCC is usually very smooth running, with excellent speed control. I'm now wondering if the problem may be in that super-low-end-toy(p.o.c.) power pack from the DeWitt-Clinton set. Is that what you have been running these trains with all along, or was something else used?

The "bell" motors you saw are probably a type commonly called "can" motors, since they a fully enclosed in a metal can-shaped housing. No need to open it. If your locos have can motors and flywheels, then they are not the old three-pole motors/no flywheels/high gear ratio, duds, I was concerned about. Your locos should be capable of smooth running at slow speed.

Traction Fan :smilie_daumenpos:


----------



## gimme30 (Jul 26, 2018)

Hiya TF!

In my first post I wrote that these loco's were dcc equipped, but that I'm not. I didn't elaborate much so I see how that'd be easy to miss! 
Being a gadget freak dcc greatly appeals to me and when I can move on to a HO layout that's definitely the route I'll be taking, but I don't need it, (or the additional expense!) for my little N scale track. 

Anyway to clarify both engines are dual mode but you and Dennis may be on to something here. I do own a few Kato models and they don't exhibit this behavior at all, but they are DC only. Could it be that my cheapo transformer's lack of PWM is causing the problem?

Does anyone make a conventional DC transformer with PWM?

I know I need to upgrade, but I gotta tell ya, that lightweight cheap feeling Bachmann unit sure works a lot better than the metal brick I initially started with! It was one of those gold-cased MRC throttles that IIRC came with an Atlas set. All of 3 speeds....move the lever until the engine started moving, get a small increase at mid range, then no change until you were at WOT! If it ever conks out I'll use it to anchor my fishing boat.

Any advice on a suitable replacement? Current MRC models don't get the greatest reviews, and I'm not sure I'd like the knob-on-a-lever arrangement Kato uses.

Please disregard the "closed endbell" terminology...that's a throwback to my R/C days that sticks with me whenever I see a fully encased motor. When open cans were introduced we were thrilled-We could change our own brushes! True our own comms!


----------



## sid (Mar 26, 2018)

you really should go to dcc it is much better and if your gunna move to that any way with ho ya might as well get dcc then you will have it. i use NCE witch is great , very easy to use. it has every thing you need to go right out of the box and not bad on price if you shop around a bit.


----------



## gimme30 (Jul 26, 2018)

Don't tempt me Sid, you're gonna drive me straight to the poorhouse!

Anyway I don't think I wired my track correctly for DCC. hwell:


----------



## traction fan (Oct 5, 2014)

*DCC or DC*



gimme30 said:


> Hiya TF!
> 
> In my first post I wrote that these loco's were dcc equipped, but that I'm not. I didn't elaborate much so I see how that'd be easy to miss!
> Being a gadget freak dcc greatly appeals to me and when I can move on to a HO layout that's definitely the route I'll be taking, but I don't need it, (or the additional expense!) for my little N scale track.
> ...


gimme30;

I can't advise you on a DC power pack with pulse wave modulation. I think that's what PWM stands for.
However, a good quality, new, DC power pack won't be all that much cheaper than a DCC controller.
I use, and like, the NCE Powercab. It costs about $200 new retail. On sale, or used, you could probably get one for less. It has everything in one small hand-held unit. You hook it up just like a DC power pack; two wires from the controller to the track, that's it. It's easy to operate, and easy to program, and it will work with N-scale, or HO-scale. I think you will be very pleased with how slowly, and smoothly, it will run those same two locomotives; and with no lurch. 

Here's an experiment you can try, before buying anything.
Test run the locomotives on battery power.
Flashlight type batteries put out pure, simple, steady, reliable DC power. If you have one of those mini 9 LED flashlights that run on three AAA cells, that will work. Pull the battery holder out of the flashlight and hook it up to a loop of track. Run one of the suspect locomotives around several times and see if there is any lurch, or other problem. If all is well with battery power, then I would be very suspicious of that Dewitt-Clinton power pack. Conversely, if the locos still behave badly on battery power, then I think those locos don't like DC power very much.
If your straight DC, Kato, units work well on both battery power, and also on the Dewhitt power pack, then your Bachmann RS-3 and GP-7 are the problem; at least when they are run on DC.
I would then suggest you try them on an NCE Powercab, or the DCC controller of your choice.

Good luck;

Traction Fan :smilie_daumenpos:


----------



## gimme30 (Jul 26, 2018)

Batteries! Why didn't I think of that? 
Chalk it up to another dumb blonde moment...

I'll give that a shot when I get home tonight!

After a quick look at what's available on the transformer market, it looks like I may have to make the leap to DCC afterall-one high end (IE more expensive) MRC unit I ran across is $150, which doesn't make sense as the Powercab will do so much more for only a few more dollars. 

Better go count those pennies...


----------



## sid (Mar 26, 2018)

you wont regret the NCE power cab work fantastic and is easy to use. im a complete knuckle head and i can use it pretty good, but im stil learning . (im stuck in kindergarten) hahahaha


----------



## traction fan (Oct 5, 2014)

*NCE powercab on sale*



gimme30 said:


> Batteries! Why didn't I think of that?
> Chalk it up to another dumb blonde moment...
> 
> I'll give that a shot when I get home tonight!
> ...


gimme30;

If you can rustle up $189.36 in pennies, or other coin of the realm, www.modeltrainstuff.com is selling a brand new NCE powercab starter set for that price.  I've ordered from them, and they are a good, reliable, online dealer. When you get around to building your HO dream layout, the Powercab will work fine for that too. You can also add sound decoders in future, if you want. The powercab can operate all the lights, loco sounds,(steam chuff, diesel prime mover, coupler clash, air brake sounds, and of course, the ever popular, whistles and bells your heart desires!

Traction Fan :smilie_daumenpos:


----------



## gimme30 (Jul 26, 2018)

Ok I was able to try the battery trick with limited success. I tried 3 cells at first and one of the engines wouldn't move at all, so I tried a 9 volt, which conveniently fits across the rails but turns out is a wee bit much-that little RS3 shot off like a rocket! Both Bachmanns continued to lurch, while the Katos ran flawlessly as usual.

That rules out my cheapo transformer, so it looks like until I can pick up a Powercab this will remain a mystery. 

As you know from my other thread I'm looking for more pulling power, and I went ahead and pulled the trigger on that pair of C420's I was looking at. 

I'll know soon how Atlas compares!


----------



## gimme30 (Jul 26, 2018)

I don't think there's much I can do to remedy the situation. Over the weekend I pulled both engines apart down to their basic components. With the motors out of the frames I built a simple jig to measure runout at the worms and found some very slight vertical variance at the aft end of the GP7 motor-the RS3 worms are fine. The O.D. of the offending worm measured fine so my guess is the shaft running through the motor is ever so slightly out of true.

For the RS3, it looks like it's an issue with the gears in the front truck. Although what that may be I couldn't tell you! I CAN tell you it's a major PITA getting all those little gears back in place. Anyway, according to my calipers none of the gears were out of round but I suspect the mesh is tighter on the front truck than it is on the rear-spun by hand the difference in resistance is noticeable. Again, I don't know that that _is_ the trouble but I can't find anything else wrong with it!


----------



## traction fan (Oct 5, 2014)

*"Spun"? or turned?*



gimme30 said:


> I don't think there's much I can do to remedy the situation. Over the weekend I pulled both engines apart down to their basic components. With the motors out of the frames I built a simple jig to measure runout at the worms and found some very slight vertical variance at the aft end of the GP7 motor-the RS3 worms are fine. The O.D. of the offending worm measured fine so my guess is the shaft running through the motor is ever so slightly out of true.
> 
> For the RS3, it looks like it's an issue with the gears in the front truck. Although what that may be I couldn't tell you! I CAN tell you it's a major PITA getting all those little gears back in place. Anyway, according to my calipers none of the gears were out of round but I suspect the mesh is tighter on the front truck than it is on the rear-spun by hand the difference in resistance is noticeable. Again, I don't know that that _is_ the trouble but I can't find anything else wrong with it!


gimme30;

If you're talking about spinning the wheels when the worm gear is removed from the truck, that's one set of problems.
I'm assuming though that your talking about turning the worm by hand and also driving the rest of the truck's gears & wheels in the process. Is that correct?
There shouldn't be a noticeable difference in the effort needed to hand-turn the worm in one truck vs. the worm in the other truck. It's possible that the worm that needs more effort is too close to the spur gear that it meshes with. Depending on how they're mounted, you may be able to get a looser fit by filing a tiny amount of the worm's bearings away. Or you could let the worm spin on the motor while its out of the loco and powered up. Then hold a file, or fine-grit sandpaper, against the worm's outer surface to turn it down a tiny bit. Do you think the problem might be that the worm bearings themselves are too tight on the shaft that rotates inside them?

Yes, model locomotive parts are small. The smaller the scale, the smaller the parts. If you don't have an Optivisor, a locomotive cradle, (see photo) and a towel over your workbench, when you take one of these little beasts apart, well good luck, you'll need it! The towel is to help keep little tiny, (but essential) parts from flying off to "never never land" (Where you'll never, never, find the @$^^&*&% thing! 

If all else fails, Kato makes RS-3s that run like the proverbial Swiss watch.


good luck, have fun?

Traction Fan :smilie_daumenpos:


----------

