Rack loco judder

[scook]

Hi all,

I have two lgb rack locos that judder downhill on a 12% gradient rack section.

One is a schb box cab loco fitted with a lgb 55021 decoder , the other is a lgb dfb steam rack loco fitted with I believe a mfx decoder , they perform like this on both analogue and digital.

Any ideas?

Thanks
Sam

 

[craigwrdouglas2]

Interesting - I have both of those as well on my rack system

It could be a few things -
1. does it do this with loco only?
2. Is it a tension lock issue? that is is the loco taking a hit from the train vehicles going over a tipping point - remember it's doing braking for the train on the downslope and the tension-lock couplers will switch from pulling to holding the train back on the downslope.
3. if it's taking a hit from the train that will impact, load compensation which may take a moment to settle.
4. you could try knuckles instead of tension locks, so the train length doesn't change switching to downhill, or switching stock to plastic wheels to cut down on the weight of the train.
5. you may also want to look at cv 51 - load compensation and setting it to compensate less aggressively might make your judder less harsh.

hope this helps.

 

[scook]

Interesting - I have both of those as well on my rack system

It could be a few things -
1. does it do this with loco only?
2. Is it a tension lock issue? that is is the loco taking a hit from the train vehicles going over a tipping point - remember it's doing braking for the train on the downslope and the tension-lock couplers will switch from pulling to holding the train back on the downslope.
3. if it's taking a hit from the train that will impact, load compensation which may take a moment to settle.
4. you could try knuckles instead of tension locks, so the train length doesn't change switching to downhill, or switching stock to plastic wheels to cut down on the weight of the train.
5. you may also want to look at cv 51 - load compensation and setting it to compensate less aggressively might make your judder less harsh.

hope this helps.

View attachment 355585

Thanks for the info,

Both locos judder without any stock,

Regarding cv51 is there a table for cv values?

Thanks
Sam

 

[playmofire]

Same problem and a possible solution here Rack loco Jerky at Low Speeds

 

[AlanL]

Could it be an effect of backlash in the drive train of the loco?
It is going from drive to overrun repeatedly?
What happens when the loco has a load for a constant pull or a constant push? Simulate a load with your hand to test both conditions.
On your gradient the weight of a train might keep the loco in overrun or it might hold it back so the loco is always driving.

AL

 

[John Randall]

Do they it do it with the loco turned around ? IE gear wear in on direction ?.

 

[dunnyrail]

We found that the Rack locomotive going downhill on the Rack fitted part of the Ruschbahn was very rough running. Ok going uphill. We had at least 3 different Rack locomotives (1 steam 2 electric all LGB) that used the line and they were all the same.

 

[PhilP]

There is a lot of 'slop' in the LGB drive-train.. This adds to its robustness. - A little 'give and take', but does mean you do get a 'judder'.

You won't get rid of this, but can 'tune' the system, a little, to improve it.

PhilP.