jerky Bachmann MPV

[Gt.Shefford]

I have a P4 Bachmann MVP which is noticeably jerky when running at slow speed. it was run in prior to converting to P4 and then tested on DC afterwards. It was originally fitted it with a lenz standard and it ran smoothly. Lately i fitted a sound decoder (loksound v4 from Legomanbiffo) and now its noticeably jerky until speedstep 24.

 

I'm at a loss for a diagnosis as it worked fine on DC, then with a lenz and even a Bachmann decoder, but when the loksound is fitted the jerkiness is back. I've gone through the cv54 to zero autotune but that made no difference. All the pickups are adjusted with light pressure on the wheel backs and the plastic crimps that Bachmann use for anchoring the wires have been removed and the wires soldered.

 

Any suggestions for what to try next?

 

Jonathan

[geoff]

I have a P4 Bachmann MVP which is noticeably jerky when running at slow speed. it was run in prior to converting to P4 and then tested on DC afterwards. It was originally fitted it with a lenz standard and it ran smoothly. Lately i fitted a sound decoder (loksound v4 from Legomanbiffo) and now its noticeably jerky until speedstep 24.

 

I'm at a loss for a diagnosis as it worked fine on DC, then with a lenz and even a Bachmann decoder, but when the loksound is fitted the jerkiness is back. I've gone through the cv54 to zero autotune but that made no difference. All the pickups are adjusted with light pressure on the wheel backs and the plastic crimps that Bachmann use for anchoring the wires have been removed and the wires soldered.

 

Any suggestions for what to try next?

 

Jonathan

 

Jonathan, if you are sure ALL the pick ups are working ALL of the time and the wheels and track are really clean you may find it helps to repeat the auto tune process, possibly more than once. If this fails to reach a more suitable set up you will have to set about manually tuning the BEMF. It may also help to run the machine for a while to ensure that the motor and transmission are warmed up before tuning the BEMF. You could also try turning off the BEMF but this usually affects the sound performance or even prevent it from working properly at all. 

 

Geoff

[Gt.Shefford]

Thanks for the suggestion Geoff. I'll have a look at manually tweaking the BEMF and see that improved things.

 

Jonathan

[10000]

After a complaint by a customer about jerky running on a Bachmann loco that we had fitted a Bachmann decoder into the owner of the shop rang Bachmann support. Eventually he managed to get out of them that with all small motor Bachmanns it is best to turn off BEMF

[geoff]

Thanks for the suggestion Geoff. I'll have a look at manually tweaking the BEMF and see that improved things.

 

Jonathan

 

Jonathan, the quote below is taken from a posting made today on the Loksound Yahoo group. There are others supporting that approach.

 

"I get it about "if it ain't broke - don't fix it". Having said that

I've actually tested Auto Tune and found that doing it more

than just once results in different values for the BEMF CVs.

 

My method is to "keep doing it until the loco runs correctly".

Seems to work. Just for me? I think others report the same

thing.

I can say that I have not found that the loco gets "incrementally

better" each time you Auto Tune it - it seems to "bounce around"

rather than hone in on the target.

 

===> But I have -ALWAYS- been able to get the loco running

perfectly using Auto Tune. (Just not always the 1st time.)

 

And I consider the Auto Tune to be sheer magic and an

amazing tool that I rely upon. Heavily."

 

Geoff

[Gt.Shefford]

Thanks for looking out that passage on auto tune. I ran it a couple of times and made a note of the resultant cv 5 and cv 6 values. On each occasion the values were 190 and 95 respectively.

 

After bench testing this afternoon I'm now fairly sure the problem is mechanical. Removing the leading axle and testing the unit on a rolling road succeeded in eliminating the jerkyness. My next job will be to replace the axle and re-test.

 

Jonathan

[geoff]

Thanks for looking out that passage on auto tune. I ran it a couple of times and made a note of the resultant cv 5 and cv 6 values. On each occasion the values were 190 and 95 respectively.

 

After bench testing this afternoon I'm now fairly sure the problem is mechanical. Removing the leading axle and testing the unit on a rolling road succeeded in eliminating the jerkyness. My next job will be to replace the axle and re-test.

 

Jonathan

 

CV 5 and CV6 are the max and mid speed step settings respectively, they are nothing to do with the BEMF. You use those two cvs to set the top speed and mid speed of your locomotive. They, along with cv2, form the basic speed curve, cv2 being the start voltage. The Loksound v4 has a complicated speed curve arrangement and I strongly advise you to join the Loksound Yahoo group where you can get some really informed assistance from some very talented guys. Where about in the UK are you Jonathan?

 

Geoff

[Gt.Shefford]

That would explain why those cv values remained unchanged. Legomanbiffo's notes supplied with the decoder describe how to perform the autotune but then conflate that with reference to adjusting cv 5/6. I've got a copy of the south west digital "how to set up BEMF" so I'll work through that and see what happens.

 

Jonathan