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Discussion Starter · #1 ·
Hi,

I have a 2MT which despite my earlier reservations about the wires between loco and tender I very much like.

I've ran in the model for about 45 mins each way, but at slow speeds it remains ever so slightly jerky. You can notice slight variations in speed with every revolution of the wheel sets and from a distance it just does not look nice.

I don't think it's the decoder - just out of interest I tried a few different chips by swapping them round, and also looked at relevant motor CVs. They all appear sensibly set to me.

Does it have to do with tiny can motor that is in the small firebox? Is it just a fact of life and am I expecting too much?

Or is there anything I could do to overcome this? Running in more? Lubricating? CV settings??

Does anyone else have the same experience?

Many thanks,

Walter
 

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Hi Walter
what brand of decoder are you using ? as i have also suffered this probelm with eratic running at slow speeds.
i eventaully managed to figure out that i need to change a cv setting.
If your using a bachmann 3 function decoder try turning off back EMF and this will correct the poor running at slow speed
By default back EMF is enabled on Bachmann 3 function decoder and to turn it off you need to change cv49 and set it to 0 whereas turning it back on would be cv49-1
This definately sounds like a back EMF problem. If you can post and let us know which decoder you are using then we can help you more .
P.S are the track and wheels clean, plus too much lubrication can cause erratic running

hope this helps and good luck
 

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Discussion Starter · #3 ·
QUOTE (hstmad @ 19 Oct 2007, 08:53) <{POST_SNAPBACK}>Hi Walter
what brand of decoder are you using ? as i have also suffered this probelm with eratic running at slow speeds.
i eventaully managed to figure out that i need to change a cv setting.
If your using a bachmann 3 function decoder try turning off back EMF and this will correct the poor running at slow speed
By default back EMF is enabled on Bachmann 3 function decoder and to turn it off you need to change cv49 and set it to 0 whereas turning it back on would be cv49-1
This definately sounds like a back EMF problem. If you can post and let us know which decoder you are using then we can help you more .
P.S are the track and wheels clean, plus too much lubrication can cause erratic running

hope this helps and good luck

Hmm... tried that really. I've got a ZTC 4007 in it at the mo, but have played around with a Bachmann 3-fct and a Lenz Silver. Have tried to switch off Back EMF - doesn't alter things. I've steered away from lubricating so far - thinking that the factory lubrication ought to suffice.

Erratic may not be the best description - the slight jitters are really pretty much in step with the wheel motion. It's like on every 'chuf' (if it would do that!) there is a little bit more torque.

I'm really starting to wonder whether it is the nature of the model - tiny motor in reasonably sized model with no flywheel.... ???
 

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QUOTE (Walter @ 19 Oct 2007, 10:22) <{POST_SNAPBACK}>Hmm... tried that really. I've got a ZTC 4007 in it at the mo, but have played around with a Bachmann 3-fct and a Lenz Silver. Have tried to switch off Back EMF - doesn't alter things. I've steered away from lubricating so far - thinking that the factory lubrication ought to suffice.

Erratic may not be the best description - the slight jitters are really pretty much in step with the wheel motion. It's like on every 'chuf' (if it would do that!) there is a little bit more torque.

I'm really starting to wonder whether it is the nature of the model - tiny motor in reasonably sized model with no flywheel.... ???
have a look at the pick ups and make sure there ok (could be a misaligned wheelset or pick up)
what dcc controller are you using??
 

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Discussion Starter · #5 ·
QUOTE (hstmad @ 19 Oct 2007, 10:27) <{POST_SNAPBACK}>have a look at the pick ups and make sure there ok (could be a misaligned wheelset or pick up)
what dcc controller are you using??

A mere EZ command - I know! Would that play a role?

Has had a good clean just yet.

Misalignment is a thought - dreading it a bit really, especially since it's been weathered and renumbered and warranty would be a bit iffy...
 

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Walter,

Have you tried removing the motor temporarily to check if there is any regular binding when the chassis is pushed? If it isn't free rolling then you have to investigate the numerous possible causes or try a warranty claim. If the chassis is truly free rolling, then it is likely to be down to the motor. Bach have sadly reverted to a three pole motor in most of their recent steam productions, and while not bad, it doesn't offer the smoothness of a five pole skew wound type. As the motor becomes smaller, this lack of refinement really shows up. I have found that Zimo decoders are my friend in this case, offering both very small physical size to fit in confined spaces, and a good range of motor control options to get the best out of a motor. It's that or substitute a Mashima or Buhler dimensionally equivalent motor...
 

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QUOTE (Walter @ 19 Oct 2007, 10:57) <{POST_SNAPBACK}>A mere EZ command - I know! Would that play a role?

Has had a good clean just yet.

Misalignment is a thought - dreading it a bit really, especially since it's been weathered and renumbered and warranty would be a bit iffy...
The bachmann E-Z command is not capable of changing CV values
 

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QUOTE (Walter @ 19 Oct 2007, 10:22) <{POST_SNAPBACK}>Erratic may not be the best description - the slight jitters are really pretty much in step with the wheel motion. It's like on every 'chuf' (if it would do that!) there is a little bit more torque.

We had, and still have, a similar problem on our Bachmann Lilliputt 2-6-0 tank. It is, if i remember correctly a quartering problem which seems to escape rectification.

Regards
 

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Can you unplug the decoder temporarily and try on plain DC?
If it isn't jerky on DC then it may be a motor/decoder problem.
If it is still jerky, then it is a mechanical problem - either a minor bind or as Britho says, a quartering problem.

I've found a rolling road is excellent for picking up problems like this - it's a lot easier to watch the mechanics when the whole loco remains in front of you - or gently chock the front and back up so the wheels rotate off the track to achieve a similar effect.

It would be worth applying minimal lubrication - it takes some time to get from China to the UK and you don't know how long it was sitting around packed at the factory beforehand, so the factory lubrication could have been lost, at least in part.
Hope this helps,
John Webb
 

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QUOTE (BRITHO @ 19 Oct 2007, 13:28) <{POST_SNAPBACK}>We had, and still have, a similar problem on our Bachmann Lilliputt 2-6-0 tank. It is, if i remember correctly a quartering problem which seems to escape rectification.

Regards

I agree with the above.......to be ackward!

I am not familiar with the properties of decoders....but this sounds like a quatering problem....or......an out-of-round wheel[set?]

Also, mention of the possibility of Bachman reverting to a 3 pole motor might also give a clue....3 poles tend to ''cog'' more at low speeds...but have better torque.....the old Triang XO4 was a good example.

I'd put it up aginst some buffers and study the slow speed wheel motion...check for a limp, or binding?

Also possible is a wobbly wheel..which may be 'catching' something at one particular point?

Another issue MIGHT be, of the coupling rods have their holes at different centres to the axle spacing?
If there is 'insufficient' slop, or free play at each crankpin, for example, then the mismatch will cause problems.......maybe it slipped through quality control??

maybe, YOU are the quality control here?????
 

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QUOTE I've found a rolling road is excellent for picking up problems like this - it's a lot easier to watch the mechanics when the whole loco remains in front of you - or gently chock the front and back up so the wheels rotate off the track to achieve a similar effect.

I second that. I bought some Bachrus rolling road stuff about a month ago and have had considerable success in finding out just why my Hornby Fowler 2-6-4T was stalling so much. By only providing one driving axle with power at a time, I discovered that there were pickup "dead spots" on the first and third axles. The rear axle was by far the worst and it has turned out that the back of one of the wheels had something non-conductive for about a quarter of a turn. At medium speed on the rolling road this showed up as variable speed. At low speed the motor would cut out. I am gradually managing to clean off the back of this particular wheel and have high hopes of a good runner when I am finished.

Once a steam loco is running nicely at low speed, I can spend several minutes just watching the pistons "dwell" at each end of the cycle.

David
 

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QUOTE (Walter @ 19 Oct 2007, 10:22) <{POST_SNAPBACK}>Hmm... tried that really. I've got a ZTC 4007 in it at the mo, but have played around with a Bachmann 3-fct and a Lenz Silver. Have tried to switch off Back EMF - doesn't alter things. I've steered away from lubricating so far - thinking that the factory lubrication ought to suffice.

Erratic may not be the best description - the slight jitters are really pretty much in step with the wheel motion. It's like on every 'chuf' (if it would do that!) there is a little bit more torque.

I'm really starting to wonder whether it is the nature of the model - tiny motor in reasonably sized model with no flywheel.... ???

I experienced the same problem with the 9f, but eventually with time and use the jerkyness at slow speed diminished and it is now a good runner at all speeds. Initially I had a lenz silver decoder fitted, this is now changed to the Lenz standard.
 
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