loco stops then jerks

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Sammo
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loco stops then jerks

Postby Sammo » Sat Mar 10, 2018 10:03 pm

I have set up 2 Bachmann split frame locos with Zimo MX600 decoders
Both are set for speed matching however
One of them, when told to stop, comes to a standstill then jerks forward about 4 inches at quite fast speed. It then comes to rest. The other one which is speed matched to it doesn't do this, even when they are consisted it still does it.
It only started to do this after I set the max speed, if I reset it to its factory defaults it cures it, but then isn't speed matched, which is what I need it to be.

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Peterm
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Re: loco stops then jerks

Postby Peterm » Sat Mar 10, 2018 11:48 pm

The first thing to do is make sure that DC running is turned off.
Pete.

Sammo
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Re: loco stops then jerks

Postby Sammo » Sun Mar 11, 2018 10:45 pm

Thanks I changed CV 29 in a few of the decoders but not sure if I did with this one

Sammo
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Re: loco stops then jerks

Postby Sammo » Tue Mar 13, 2018 10:34 pm

Ive turned off the Analogue in CV 29 Ive tried resetting to CV 8 = 8 and started again
Now it doesn't jerk anymore but its no longer smooth at throttle speeds of 2 to 35 of the 99 throttle settings.

Does anyone know the sequence of what order to do things when I want to. do the following and what the order of CVs to set is

set start speed
set top speed
set med speed
set up the frequency of the back emf
set a limit to the back emf so it cuts off at throttle reading of 25 (which is approx 25% speed.
Set up acceleration and deceleration

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TimberSurf
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Re: loco stops then jerks

Postby TimberSurf » Tue Mar 13, 2018 11:05 pm

I have no clue on decoders, but on industrial inverter drives (from which decoders were based and shrunk), it should be:-

set top speed
set start speed
set med speed
set up the frequency of the back emf
set a limit to the back emf so it cuts off at throttle reading of 25 (which is approx 25% speed.
Set up acceleration and deceleration
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GWR_fan
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Re: loco stops then jerks

Postby GWR_fan » Tue Mar 13, 2018 11:21 pm

Does the faulty loco have any capacitors? Capacitors are known to cause the symptoms you describe. Are both locomotives the same part number or class of loco? Are both chassis the same? Does the faulty one have an additional circuit board?

Bigmet
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Re: loco stops then jerks

Postby Bigmet » Wed Mar 14, 2018 8:46 am

DCC was a factor that hastened the demise of the Bachmann split chassis types I had on the layout, quite apart from the overall rapid wear out when operated intensively. They would run very sweetly indeed when newly set up, and then quite suddenly 'fall off a cliff' in terms of smooth running. The moment any such 'jerk' event was seen (just a stutter when starting or stopping, not running 4"!) it was time to have the keeper plate off, thoroughly clean the axle locations and stub axles and very lightly relubricate. That was the 'charm' to get good smooth running out of them; but it got a little tedious having to do this at an average of about four month intervals.

Some were better than others in this respect, the A4, B1 and J72 mechanisms noticeably superior, the J39 and V2s real trouble, the V1s and Jubilee somewhere between.

ianjeffery
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Re: loco stops then jerks

Postby ianjeffery » Wed Mar 14, 2018 10:52 am

I have found that the Back EMF settings caused all my locos to be jerky.... putting a 0 in the CV for this ( cant remember the cv number - i used JMRI )to stop BEMF removed the jerkiness.

I had horrible jerky/pulsing on my Mallard A4 until i turned this off.

might be worth a try....

Bigmet
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Re: loco stops then jerks

Postby Bigmet » Wed Mar 14, 2018 1:19 pm

ianjeffery wrote:I have found that the Back EMF settings caused all my locos to be jerky...

Good description of a BackEMF set up that is a poor match to the motor. If the decoder offers CV's to alter the BEMF set up, it would be worth your time changing the sampling and feedback values to see if you can make this feature function as it should, because if it can be well matched to a motor the improvement in speed stability and resultant smoothness in operation can be very marked. It is necessary to refer to the decoder instructions to see if such CVs are available, as these are not standardised CV's, every manufacturer has their own choice. (If there is no improvement, nothing is lost over current state, BEMF can still be disabled.)

Sammo
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Re: loco stops then jerks

Postby Sammo » Wed Mar 14, 2018 8:57 pm

Analog is disabled
The loco does have diodes ( I believe them to be diodes as they are used to ensure pure DC ) I can remove them
I do have the facility to alter the frequency of the back emf to supposedly match the motor, I did this when I was first playing around with the settings, I can try and finer tune it though I suppose.

dan8400
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Re: loco stops then jerks

Postby dan8400 » Thu Mar 15, 2018 8:08 am

Hi,

I'm not sure if this helps, but, I have a Hornby Class 153 DMU that did the same thing. I swapped decoders etc but no better. I googled and found out that you need to change CV 54 to 10 and CV 55 to 50.

Mine was a Bachmann decoder and this seems to be a theme with certain loco and decoder combinations.

Worth a try

Thanks
Dan
My Layout Thread: viewtopic.php?f=22&t=30117

Bramshot
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Re: loco stops then jerks

Postby Bramshot » Thu Mar 15, 2018 10:01 am

I would not remove diodes.
Does the loco have a coreless motor? Zimo state that the default value for CV56 is not suitable for these and you should add 100 to the value. Not sure what effect this has, as I used to run my coreless motors with the default value (my decoder is the new 6 pin Bachmann one, which is a Zimo, and has different default values to the Zimo ones), but did not notice any difference when I added the 100, maybe yours is different.

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Peterm
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Re: loco stops then jerks

Postby Peterm » Thu Mar 15, 2018 10:08 pm

Sammo wrote:Analog is disabled
The loco does have diodes ( I believe them to be diodes as they are used to ensure pure DC ) I can remove them
I do have the facility to alter the frequency of the back emf to supposedly match the motor, I did this when I was first playing around with the settings, I can try and finer tune it though I suppose.

The diodes you're talking about are probably capacitors for use on analogue control to prevent interference on tv's, radio's etc. Pretty much obsolete since digital tv came to the fore. They are usually mounted across the motor, not in series. They can be got rid of. They don't normally affect the Zimo's but just in case...

What control system are you using? Some aren't properly compliant and leave dc on the track which could cause this.

No coreless motors in the old Bachmann split frames as far as I know.

CV's 9 & 56 might help, also CV's 10 & 113 for BEMF cut off.

Did you use cv's 66 & 95 for the speed matching? If so, did you restrict the speed of the fastest loco down to the slower one? I've found that this is the best way to do it.

If you haven't already, have a look through the manual: http://www.zimo.at/web2010/documents/MX ... oder_E.pdf

It might help you out of this.
Pete.

Bigmet
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Re: loco stops then jerks

Postby Bigmet » Fri Mar 16, 2018 10:18 am

Sammo wrote:...The loco does have diodes ( I believe them to be diodes as they are used to ensure pure DC ) ...

Puzzled now. Never ever have I seen a Bachmann split chassis mechanism with any visible electronic components fitted to the motor circuit (as supplied new), and I have seen a fair selection of these products over the years. (If there is any suppression on these mechanisms then the components must be inside the motor casing.)

Diodes are not used for suppression in any case. Principal use on a model is for directional lighting control, but I don't recall a split chassis loco with lights. What exactly are these locos?

Sammo
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Re: loco stops then jerks

Postby Sammo » Fri Mar 16, 2018 10:49 pm

Bigmet sorry I didn't mean to confuse you
You are correct in that there are no capacitors / diodes on the split frame Bachmanns
I was referring to the later Hornby Bachmann locos which are not split frame.

I have only had problems with Hornby or Zimo decoders

I have Backmann non sound decoders and ESU Bachmann and Hormby sound locos, all of which have given no trouble up to now

Tonight I used the Hornby Elite controller to see if the problem persisted and it did so that ruled out a controller fault

Recently I had a tank loco which would run slowly and increase slowly its speed, but when it got to 20 it would stop dead the when I increased the speed and it got up to 31 it would go again and almost as if it was carrying on from the 20 speed setting (0 to 99 on the Digitrax throttle)

I reset CV8 to 8 to reset it and started again and each time I altered a CV I ran the loco to observe its reaction to the changes made.
It was OK until I put in a back emf cut off to 25, now according to the manual which I printed out a few months ago the CVs range is as follows
CV #10 is 0 to 252
CV #113 is 0 to 255
So why is it that I need to put a value into these of around 50 to stop this happening?

It now seems that all my problems related to the damn emf cut off which I want to use so that it makes for more realistic double or treble headers.

Back in the days of DC I could put the fastest loco at the front the slightly slower loco in the middle and the slowest loco at the third position and when it pulled the train I had no problems at all, but with DCC we have to speed match or suffer possible derailments which is why I wanted the back emf to cut off before the locos got to the speed that I would be running them at.

Peterm
I used CVs 2 5 and 6 for speed matching, Ive been looking at the manual for about 3 months which is where I got the info.

Bramshot the motors are not coreless

It does say in the Bachmann decoder setup that the diodes can be removed to aid setting of back emf
This is where I got the description as diodes as it says they were used originally to aid pure DC at the motor as well as TV suppression.
Can someone for once and for all please tell me the correct description of these, as Diodes and capacitors are completely different as I was taught that
One is a one way gate and the other is a storage unit.

dan8400
I will have a look at these two CVs and see what it says in the zimo manual

ianjeffery
I may try turning off the back emf completely but I fear I would lose the very smooth slow running

Bigmet
up to now I have never had to clean anything with regard to the backmann split frame locos but I remember when I first got them, I spent hours, I put in half moon phosphor bronze bearings I had made out of tubing and sat the axles in these after filing deeper into the white metal to allow for the thickness of the bearings. I ended up with a lot smoother performance, but I had to smooth the faces off with 1200 wet and dry to ensure not jagged edges.


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