Kato NW2, DCC'd cogs in low speedsteps?

[sizemore]

I picked up a Kato NW-2, threw in a DN123K2 (the plug and pray decoder). It runs as expected, but the slow speed operation stinks in the lower speedsteps. There is no graceful acceleration to desired speed in the single digit SMPH, it cogs, cogs and cogs. My Bachmann 44T with DZ123M0 installed works great and can crawl ties for hours, without cogging and no CV modifications.

I checked the speedsteps, running in A128, checked CV29 - set to 38, verified BEMF was on (006), checked CV55/56 for static/dynamic compensation. Everything looks good. I tinkered with CV's 57/55/56 for about an hour but no real improvement.

Looking for suggestions, should I mess with Vstart or CV65?

Thanks,
The S.

[sizemore]

* crickets, crickets *


The S.

[Ken Rice]

Based on past experiments with various decoder brands my recommendation would be ditch the digitrax and put a zimo in there if you want smooth slow speed.  But that wasn't the question you asked 

[peteski]

Did the model have a very smooth slow speed in DC?

[mmagliaro]

Did the model have a very smooth slow speed in DC?

+1
Until you see how the motor runs on plain DC, you have no way to know where the problem is.
It could have nothing to do with the decoder at all.  Start by disconnecting the decoder and
seeing how it runs on plain DC.

I jumped up when I read this only because I see this a lot on the forums: people having
problems and then asking all sorts of questions about the decoder, its settings, turning BEMF on
or off, and so on, instead of first making sure there are no  mechanical issues
or a motor that just can't cut it very well at low speeds.   PWM and BEMF from a decoder
can work a lot of magic.  But it can only do so much.

[peteski]

Yes, if the mechanism is binding then no amount of fancy BEMF feedback will make it work smoothly. The BEMF circuit will try to compensate for the binding but it has its limitations too.

[victor miranda]

the Kato nw2 has a 3 pole motor.
at the very slowest of speeds you will see a little cogging
once you have eliminated any other sources of cogging.

I can't help with the decoder part because I have not tried to learn the features
... mostly because I don't run DCC.

victor

[peteski]

I thought that NW2 had a standard 5-pole Kato motor. Now I have to look at mine. 

[victor miranda]

it is a smaller motor than the normal Kato motor.

I want to try a 5 pole version of that motor.

... I think Kato went with coreless instead.

victor

[sizemore]

it is a smaller motor than the normal Kato motor.

I want to try a 5 pole version of that motor.

... I think Kato went with coreless instead.

victor

Thats what I thought that it was, a coreless motor, where the cog is strong with that one.

I didn't get a chance to yank it apart and throw the "dumb" board back in it. But I think what I'm seeing is the uber strong cog of the coreless motor in those single digit speed steps. I don't really think its the binding of the chassis given the design. The cogs are too quick, perfectly timed and exact for a bind of sorts. I'll still take it apart, clean and polish what I can.

The S.

[peteski]

Huh?!  Now I'm really confused!  NW2 does not have a coreless motor. Besides, coreless motors do not cog since they don't have iron poles in the rotor.

The first N scale Kato loco to use coreless motor is the FEF-3.

[Mark5]

Yup - NW2 = 3 poles. Kato cheaped out on this one.

[jdcolombo]

I was so unhappy with the performance of my Kato NW2's with the Digitrax decoder that I scrapped it and went with the TCS.  Much better - a hardwired Zimo MX621 would be better yet, but the TCS is quite good and you don't have to hard-wire the lights.   My advice is that if you really want good slow-speed performance from the NW2, scrap the Digitrax and try a TCS.  I don't think you will ever get there with the Digitrax; I tried, failed.

John C.

[peteski]

I took my NW2 apart (it has been a while since I looked inside).

As I was told, the motor is a smaller version of the standard Kato motor.  It has sharply skewed 3-pole motor and the strong rare-earth magnets. I wonder if it is similar motor as the one used in GS-4.  Now I'll have to dismember my GS-4 to compare them.

Anyways. I have not see any cogging running it in DC.  The skewed poles do a good job of minimizing cogging.  It was running at 1.2V (but at that voltage it has no usable torque).  I would have to hook it up a a Digitrax decoder to see how it behaves. I suspect that the perceived coggign is simply the PWM power pulses the decoder is is applying to the motor at slow speed.

[sizemore]

Yup just tore mine apart, 3 pole skew wound armature. And same performance with the "dumb" board. If it truly is the decoder, then are we saying that the larger diesels are truly benefiting from the 5 pole skew wound armatures? My Magic 8 Ball says "Duh".

The S.