Kato NW2, DCC'd cogs in low speedsteps?

[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

I guess I was thinking in my writing and not being clear.
my apologies... I am not sure how I'll be able to avoid this in future posts...

I'll try again

the newer 3 pole motor is smaller than the normal kato 5 pole motor
It is not a bad motor. If possible, I like to have a five pole version in that frame.
I think that would be a very desirable motor option.

I think that Kato desided that instead of continuing development
of the three pole motor and any possible improvements
that they would start using coreless motors in the next models
and drop the 3 pole.

victor

[victor miranda]

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.

Hi sizemore,
I plead for you to hear this clearly.

the cogging is from the motor.

It is an area where I give no quarter.
Peteski also knows this.
he and I have gone around the subject a few times.

5 poles and a flywheel are a lotta smooth.
when it comes to having small locos like the nw-2,
I will not find fault with the motor Kato used.
there is a limit to how small and how expensive
a model loco motor can be.
from all I have seen, 5 pole and 7mm across is expensive.

.... sadly the danged cogging sticks with us even in tiny 3 pole motors.

victor

[peteski]

I have to disagree on the cogging - I just tried it on DC and I don't feel or see any cogging from the motor (when I put a load on it  by pinching the flywheel). The long skew-wound armature is doing its job quite well.  The only problem I see is that the motor has very low torque at low voltages.  But that is to be expected. 

I guess that next I'll have to reassemble it and try to run it (as so far I've been only playing with the motor itself).  What helps with this type of a loco is a DC throttle capable of pulse power. DCC decoders do the same by using Pulse-Width-Modulated full track voltage to power the motor at low speeds (that is very similar to DC throttles with pulse turned on).

[sizemore]

I'm not stating that the cogging is from the decoder, I know it's from the motor. I'm essentially agreeing with Rice and Columbo (sounds like a law firm), that the Digitrax decoder on the Kato three pole motor stinks. I run Digitrax PnP on the larger locos that all have 5 pole skew wound armatures and have never seen the cogging in the low speed step ranges (steps 1-6 @ 128 step resolution).

I'll grab a TCS decoder this weekend. I had been looking forward to getting the NW2 for a long time and totally bummed by its poor slow speed operation.

The S.

[peteski]

I made some very interesting discoveries.

The engine I was experimenting with is brand new, never ran.  I bough it several years ago and it just sat in the box.

As I mentioned earlier, when I took the motor out and hooked it up to a variable power supply I did not see or feel any appreciable cogging.

I then reassembled the chassis, leaving the trucks out.  I was applying power to the frame halves and/or to the circuit board directly but the motor still ran smoothly. I also noticed that the lower gear was slipping on its shaft (when I was using my fingers to place a load on the universal joint cups).  This is a common issue well documented in these models but has nothing to do with the cogging problem.

I then snapped the trucks back in (loosening the frame halves first) then reassembled the chassis. I left the shell off.  I put the engine on a freshly cleaned test track and took it for a spin. At higher speeds it was running smoothly,  but at slow speed it was running "funny". It sort of looked like what cogging of the motor might look like.  However I also observed an important clue:  the headlight LED was also flickering. That meant that the cogging-like running was not caused by the way the motor runs but by the intermittent electrical connectivity with the track.  Something between the track and the light board was the culprit.

Even thought this was a new loco (the wheels were clean) I tried to clean the wheels first.  I ran it over the MINITRIX brass brush wheel cleaner for a while.  Then I put it on the track and tried running it again.  There was no change in the behavior:  at higher speeds the model ran smoothly, but at slow speed the model was constantly hesitating (cogging-like) and the headlight was still flickering.

However, if I touch the leads of the power supply (still at the same voltage at which the loco runs rough) to the chassis halves, the motor runs smoothly and the headlight glows steadily.

I then looked at the bottom of the trucks and I noticed that the metal bearing-cups/electric pickups in the truck's sideframes are exposed along the truck's bottom.  So, I placed the leads of my power supply (still at the same voltage) on those exposed metal areas of the sideframes. The motor again ran smoothly and the headlight was steadily lit.

This leaves the contact points of the axles and the sideframe cups as a possible culprit. However this is a new locomotive and those should be clean.  I also noticed that the wheel-sets are fairly loose in the truck, so I suppose that the contact in that area might be intermittent.  Then,  even though I cleaned the wheels, I still think that the most likely culprit is a layer of non-conductive blackening on the wheel threads. After having similar bad experience with a similar problem on Kato GS-4, this seems more likely than the bearing cups being the culprit.  On the GS-4, cleaning the wheels also did not fix the problem (the blackening had to be removed using more drastic methods). Right now I don't have time to finish the detective work, but my NW2 definitely has a cogging-like problem at slow speed (but with the headlight flickering).  At least the problem is narrowed down to the wheelsets and possibly the bearing/cups.

I'm betting on the wheel blackening being the problem on my model. Hopefully my findings will help out in troubleshooting this particular model.

BTW, the NW2 motor is identical to the one used in the GS-4.  I checked and verified that.

[victor miranda]

Hi Peteski,
it is the motor.

cheers!
victor



ah I loved that post.

Hi peteski,

I have found a path and it seems everytime I ... improve?...
a loco for better slow speed operation I visit the same problems.

pick a loco (if it runs well you are not doing this) to improve.

Motor, pickups, and re-gearing are about all that can be done.

you decided; 'it stalls so I will visit pick-ups.'

a good choice in my opinion.

clean, polish, tune and get it going so it is electrically un-stallable.

and yet it stalls.

what is the current meter stating?

in my experience with three pole motors...
you just have to add more current and the loco will go.
zoom!

weeeell... you can add a pulse train.
and what happens?
big pulses will jar the motor into action...
and cause noise
lots of little pulses may or may not more the motor when in a powered stall.

lets move on. we know 3 pole motors power stall.

on the assumption (BIG assumption there) that the threepole starts slowly

it will cog because the poles and magnets are place where no matter what
the danged thing will hunt the resting point. (a cog)
if there are 6 cog rest points there are 6 ramps up to the opposite
of a resting point once you get the motor up the ramp
what happens just after that ramp?

get the pickups working perfectly and your reward will be slowspeeds
... with cogging.

victor

[peteski]

Victor,  IT IS NO THE MOTOR!  PERIOD - END OF CONVERSATION.  When I have a spare moment I will clean the trucks to prove it to you.

How can you say it is the motor when the headlight is flickering?!  Add it doesn't flicker when I apply power to an area closer to the motor/light board.  You know better than that.  I didn't not feel the need to measure any voltage/current when I my eyes see very specific symptoms already.

I applied the power supply leads directly to the wheels while holding the model upside down and the symptoms remained (headlight was flickering and the motor was stuttering). Yet when I moved the leads to directly contact the sideframe brass strips the problem was gone.  That clearly shows to me where the problem is.

It is most likely the wheel blackening that is causing the problem.  On my GS-4 that was the problem and I had to use a wire brush in a Dremel tool to remove the blackening layer to the bare metal on the wheel's tire. That solved the pickup problem.  This appears to be similar.

[victor miranda]

ah peteski
why am I laughing?

I am uncertain about the word proof.
This is not a good medium for proving

we will measure the results.

victor

[tehachapifan]

Ha! This goes to show how finicky this hobby is, especially in the scale we have chosen.

Here's a thought that might suggest both of you are right...

I've been noticing that some of my shorter locos do a significant amount of crabbing as they roll along. I assume this happens with longer locos too but the longer length makes it less noticeable. I suspect the crabbing is due to torque from the worm and my hunch is that the axles will push to one side of the truck depending on direction. Perhaps some cogging action from the motor causes as waxing and waning of this axle push that increases and decreases the quality of electrical contact in the axle cups. Perhaps widening the gauge might help (I also have noticed a lot of wheelsets tend to run a little narrow per my MT gauge).

[peteski]

ah peteski
why am I laughing?

I am uncertain about the word proof.
This is not a good medium for proving

we will measure the results.

victor

Victor,  if the headlight flickers like mad while I'm holding the loco upside down and applying power directly to the wheels, how can that be motor cogging?  Then I move the power leads fraction of an inch to touch to the sideframe pickups on the same truck and the headlight stops flickering and the motor smooths out. Kapiche?  There is no need to measure anything.  I KNOW that the current draw would be fluctuating (if viewed on an analog meter as digital meters have too much lag). How do I know? It is called experience - something that you have plenty of.  I will eventually get back to that model to take care of this problem - just not right now.

I will even try to take a video of it before and after the fix. I just don't know if my camera (and Youtube) can capture the flicker and hesitation. In my experience, the videos I post are already a bit choppy and have slow frame rate (I don't have good video taking capabilities)

[sizemore]

I am on WFH status today so I picked up the TCS decoder during lunch. The slow-speed operation has improved dramatically in the low step ranges. Thank you Rich and Columbo on the decoder suggestions.

It now runs smoothly on steps 3-6, however on steps 1-3 it runs but...cogs. No flicker. I'll tweak some of the BEMF settings to see if I can get some improvement, I can compensate with minV and acceleration/deceleration to mask it a bit.

To be honest I think the biggest issue this loco has is the stall torque that the motor needs to overcome based on gearing and drivetrain in those small speed steps. Add to the fact that the three pole motor is more prone to cogging and in Peteski's case stalling its a nice recipe for poor performance.

The S.

[victor miranda]

.... skip steps one to three...
 

I have never tried to find a replacement for that motor and loco.

the gs-4 has a lot more room, so I was planning to use a bigger motor.
.... one day...

victor

[sizemore]

.... skip steps one to three...
 

victor

That's what I'm thinking I'll kick the MinV up a few notches, then add some acc/dec momentum to hide as much as I can. I can live with not crawling ties but smooth starts and stops make trains more beleiveable.

The S.

[victor miranda]

oooof.

..."how can the motor be cogging"...

Hi peteski.

I think we may want to discuss the meaning of the word 'cog.'
my meaning is uneven rotation.

to answer your intended question, for most 3 pole motors
I think one can't discern a cog after about 180 rpm...
and if you can get the motor to swing smoothly at 30 rrm
I'd be very surprised and I would expect you can see cogging at that speed.

not sure how one might do a video...

victor




 

[tehachapifan]

Not even a glance, huh? Silly me.