Just had my LHS convert an New Old Stock Atlas GP38 (from out of the box) to DCC with a Tsunami Sound decoder. Electrically all works well, no problems. But the actual motion is jerky at low speed. Tried resetting decoder, cleaned the wheels. All other locos run fine on layout, so not dirty track. Sound and lights stay on fully, just jerky motion. LHS lubricated worm gears, axle ends, motor bearings. So before I tear into it, just looking for suggestions at to whether you think it might might be decoder or drivetrain related. Thanks all.
Really hard here, how did it run on DC? Always try to test a loco before converting to DCC, as if it's not smooth in DC, it will not be smooth in DCC. Try to adjust the BEMF and kick start settings, and try just doing a "break in" run. The settings may help "smoothen" the running of the motor, but if it has a drivetrain issue, or a power issue, no settings will correct it.
My vote, without knowing how it ran on DC, is drivetrain/power issues. As to whether or not it will smooth out over time (break in) or is adjustable via decoder settings....................
How old of old stock are we talking? Did the LHS do a thorough cleaning before the decoder install? It may even be an issue of corroded contacts somewhere inside the unit, poor solder job, etc.... Lights and sound will remain on if it's a power to the motor issue....
Ricky W.
HO scale Proto-freelancer.
My Railroad rules:
1: It's my railroad, my rules.
2: It's for having fun and enjoyment.
3: Any objections, consult above rules.
Download the Tsunami manual from their site. Make sure you get the correct version for the model of decoder you have. Then, look high up in the 190-212 CV range for fine motor control. Read about it, fiddle with it, and see if you can't smoothen out that drive. I had to do this for a DC version of a J Class 4-8-4 from BLI a few years ago.
This is the detailed instruction with the author's signature included at the end. It's a long read, so take your time to figure out what is required, and then begin to experiment with your drive. You can always do a CV8 factory reset if things to turtle on you and start over. Do keep records, though, and do trials so that each set of CV values can be evaluated. Finally, one set will do it for you locomotive:
Tsunami PID/BEMF CV Tuning Concepts
I spent quite some time on the phone with Soundtraxx today. The following is a write up of what I was told. It includes knowledge I have gained recently in researching the PID process in general and the Tsunami decoders in particular. A PID controller is a well-known method of doing “process control”. In our case the “process” is the speed of our Tsunami equipped locomotives. And the task we are working towards is producing a process/procedure that will allow the user to find/discover the best/correct settings for their particular locomotive that will give them the performance they want.
It is also important to understand that the values for a particular locomotive – make and model and scale – may not work for other locomotive … and may not even work for a ‘sister’ locomotive (one that was produced in the same run of the same make and model). And when we are talking about this kind of thing there is an assumption that the decoders are also the same make and model. Yes, certainly if you have two sister locos and you have one of them running the way you like it then you should try the same settings (CVs) for this new one … and at least use them as a starting point. But don’t be surprised if you find you have to change one or more CV values – nor even if the settings for one are significantly different from those that ‘work’ in the other one.
One of the most important aspects of a PID controller is the idea that it is not expected to achieve the “perfect” value on the first pass. It is an iterative process and will reach the targer (in our case target speed) after several successive corrections. And, precisely due to this iterative nature – the formula that is a PID controller uses the history of the past corrections … in addition to the current measurements (in our case the BEMF value that is read during the “off” segments of the PWM. The idea is to “home in” on the correct value for the PWM – and then to keep adjusting the PWM in very tiny adjustments … all with the goal of having the motor turn at a constant RPM for a given speed setting. And also with the goal of changing from any current speed step to a new speed step … smoothly (a nice steady increase or decrease in speed that results in the operator seeing his train moving in a manner that approximates what happens on a real train.
1. CV 209 is the Kp in the PID. It should usually be a low number (25 and below). Kp is the ‘current error’ value. Think of it as the ‘base value’ (size) of the error (difference between the target and the actual). But the value of CV209 is a range from 1 to 255 – so what CV 209 really represents is a “percentage” of the Kp that will be used.
2. CV 210 is the Ki in the PID. It should usually be a low number – and it will usually be a lower number than 209. Ki is the integral error value – that is to say that it is the sum of the past few changes (corrections). Think of it as an ‘adjustment’ to the Kp – based upon what has happened the past few times the PID value has been computed. Again the value of CV210 is not the actual value of the Ki but rather it is the percentage of the computed Ki that will be used to form the actual correction (final PID output calculation) to the PWM.
3. There is a “D” in the Tsunami PID controller. It is not “externalized” and Soundtraxx does not think that we, the users, should be messing with the “D” in the PID formula. The Kd in the PID calculation represents the rate of change, over time, of the PID calculation. Think of it as the slope of the curve of the error. The value for the “D” works the same way as the values for 209 and 210 … it is also a range/percent.
4. Turn off all momentum (CVs 3 and 4) before starting. It is probably even a good idea to just do a decoder reset.
5. It is highly unlikely that you will be successful in tuning the motor performance CVs correctly – if the locomotive wheels or the test track are not clean. Always start all such procedures with cleaning the wheels and track!
6. Use 128 speed step mode for all tuning (and running?). It is very hard for the PID controller to do its job – to provide smooth changes of speed and relatively constant RPM when the speed isn’t changing – if you only provide it with 28 steps (because each individual value represents a much larger percentage of the range of the throttle (think PWM).
7. CV 212 is the “intensity” of the PID calculation that will be used. Think of the PID calculation as a number. That number is actually a ‘correction’ for an error (the result of the PID calculation). If the value of 212 is 255 then 100% of that correction will be used. If the value of 212 is 128 then 50% of the correction will be used. An example will help. Let’s say that the target speed is 100, the current speed is 90. So the “error” is –10. And the PID calculation (for simplicity of this example of how 212 works) is +10. Sooooo, if 212 has a value of 128 then the PID correction, this time around, would be +5. As the value of 212 is reduced the number of iterations of the PID correction process that are required to reach a given target from a given start/error point will take longer and longer. Truly low values of 212 can produce a loco that is very ‘sluggish’ in terms of throttle response.
8. CV 213 is the specification of how often a BEMF measurement is taken. It is a frequency in a number of milliseconds – if the value in 213 is 23 then it takes a measurement every 23 milliseconds. Let’s use an example from real life … this is “how often does the nurse take your temperature?”.
9. CV 214 is the duration of the BEMF ‘window’ (it is NOT the “D” in PID). It is how long the window is open. This is the “how long does the nurse leave the thermometer under your tongue?”.
10. If you set the BEMF cut off level (CV 10) to a small value then the PID controller will be ‘in use’ over less of the entire speed range. This is, in general, a good thing. Values between 20 and 40 are recommended.
11. What does “starts moving” mean? Many of the tuning procedures ask you to do something until the locomotive start to move. There are 3 kinds of ‘movement’. There is the first little bit of movement – it may even be a little lurch – but the loco does not move continuously and will spend more time stopped than moving. The second phase is where the loco is moving but it may not be at a steady rate and it may not be “smooth”. This is not “tie crawling” speed. The third phase is where the loco is definitely moving and is well above “tie crawling”. You would still call it ‘slow’ but you wouldn’t call it very slow. For most PID tuning procedures when it says “until it starts moving” we are talking about the 2nd phase.
12. Locomotives should be tuned “light” (no train cars behind them). You need to know that the loco will perform well on its own. A loco with a train behind it may require more throttle in order to move at the same speed as it does light – and that’s a good thing and is a better simulation of an actual locomotive (and will sound better).
This is all I’m going to write up at this time. I intend to use this information in order to develop a procedure (or small set of procedures) that will allow you to find the best settings for the motor performance CVs - 209, 210, 212, 213, and 214 primarily … but also the BEMF cutoff, the momentum, and the trim CVs.
- Jim Betz (14 June 2010)
Tophias Just had my LHS convert an New Old Stock Atlas GP38 (from out of the box) to DCC with a Tsunami Sound decoder.
Just had my LHS convert an New Old Stock Atlas GP38 (from out of the box) to DCC with a Tsunami Sound decoder.
I had a similar problem with a Atlas GP-35. (Tsunami install I did myself). Turned out there wasn't enough clearence in the shell which was causing the decoder to rub up against the flywheel when I had the shell fully on.
I'll tear apart my GP38 this week and take a peek to see if there could be similar issues (I have to convert it to DCC sound any way)
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
I agree with "Selector's" comments about tweeking the higher end CV's. You might also raise the start voltage CV 2. I did a tsunami install in an Atlas GP38 and found that out of the box the tsunami default for start voltage needed to be increased to get it going. Then changing those high end CV's smoothed out the low speed operation. I use a straight line speed table setting and adjusted the trim settings (CV 66 and 95) to obtain the running characteristics I wanted.
Marty C
Hi,
Sometimes loco problems have pretty basic causes........ You are certain the track is clean and not the source of the difficulty. But how about the loco wheels? Just for grins, put an alcohol soaked paper towel on the track and set one of the trucks on it - the other on bare track. Crank up the throttle for a few seconds, remove the loco, and look at the towel........ That will tell you if the wheels were dirty or got "over lubed" by the shop.
One other thing...... it is possible that the loco ran this way before the decoder was added. Perhaps there is a "rough gear" or something like that. Or, perhaps the loco just needs some serious break in time.
For what its worth...............
ENJOY !
Mobilman44
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
An old Atlas "yellow box" locomotive? I have several and have put TCS T1 decoders in them and have a similar issue. They all have jerky slow speed performance.
They all ran smooth as silk on straight DC. Now, on speed steps 1-5 they creep along just great, but somewhere between 5 and 10, the start to jerk. At 10 and above, they run perfectly well.
I've messed with the BEMF setting some with no real improvment, although I'm not sure I've exhausted all the possibilities yet.
Speed step 10 is really pretty slow. I might just set that to be the minimum.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
[quote user="mobilman44"]
Tophias,
On the Atlas website you can click the support tab and then go to "General Support" and you will get a drop down menu that includes "shell removal" Its a good reference to print out and save.
Thanks Marty, that's something I didn't think to do. With my eyes and hands getting older I can use all the help I can get
UPDATE-finally got the shell off and found nothing to be restricting the drivetrain. Gently, slowly rotated the flywheel and found not feel at binding; no decoder wires getting in the way. All solder joints look solid. Atvfirstvwhen operating loco moves fine, but after a few minutes then the jerking begins. No issues with sound or lights flickering. Could this be something with the motor? Decoder? Would appreciate any advise you can offer. Thanks.
My suspicion would be a flaky or not properly tuned Tsunami decoder motor drive circuitry. That decoder has several CVs that can be set for smoother motor control, but if you don't have any experience with tuning up one of them, you need to take it back to the hobby shop that installed it and see if anyone there knows how.
My first thought is that the BEMF needs to be tuned to the motor. To verify if that is indeed the case, try turning the BEMF off altogether and see if the problem goes away. If it does, you can either leave it off, or turn it back on and fiddle with the BEMF settings to smooth it out.
If the problem persists with the BEMF turned off, no point in wasting time fiddling with the BEMF settings as the problem is elsewhere ....
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Thanks Mark, that seems to have had a positive effect. On JMRI I changed "BEMF CUTOUT" to a value of 1. Now runs smooth, but the prime mover notches up to like three settings before it moves (approx. 15 on my Digitrax throttle). So it now runs smoother, but I don't see how I can put it in a consist. At least it will run by itself. Anyone have advise how to mu it? Thanks.
That is normal when turning the BEMF off, or almost off. To compensate for this, you will need to adjust the starting voltage - CV2. Keep increasing the value in CV2 until the engine just begins to move in speed step one. It should then play reasonably well with your other engines.
THanks Mark, I'll try that tomorrow And report back. And to Selector, if you read this, I also appreciate your input from a few days ago. It just seemed way to involved for my Old, limited capabilities. But I do appreciate the input nevertheless.
Tophias
I'm going to re-suggest what David Bedard suggested. Next time, ask for a Loksound Select decoder. Performance wise, they are so vastly superior to the Tsunami that I wouldn't take a Soundtraxx Tsunami for free if you offered me one. I have purchased just one Tsunami, and I had to go through all the steps that Selector suggested to get it to run even half decently. I will never buy another!
The Loksound Select is also $16.00 less expensive than the Soundtraxx Tsunami (priced at Tony's Train Exchange).
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Mark R. That is normal when turning the BEMF off, or almost off. To compensate for this, you will need to adjust the starting voltage - CV2. Keep increasing the value in CV2 until the engine just begins to move in speed step one. It should then play reasonably well with your other engines. Mark.
thanks Mark, that did it. Spent quite some time fiddling with JMRI settings, ending with BEMF Cutoff at 5, V-Start at 42, and Accel and Decel at 50. It actually plays rather nicely with its mate now. I thank you for helping me salvage this project. And one final question for my general knowledge-I had this loco converted to DCC along with an identical mate. Same locos (both new, old stock, purchased at same time) with same decoder Installed. Why this large discrepancy in performance? Thanks for everyone's input, much appreciated.
Best I can figure is just variations in motor characteristics. These aren't military grade by no means. Just a variation in the spring pressure of the brushes will affect motor performance.
I had six brand new engines that I installed identical decoders in, and he also wanted them speed matched. None of the settings for each engine were the same. I was able to get them to run identical to each other, but there was no way I could use the same settings for each one.
As the engines get a number of miles on them and things begin to get run in, no doubt these settings will have to be tweaked on occasion to keep them all in perfect harmony.
Good to know. Thanks again
hon30critter Tophias I'm going to re-suggest what David Bedard suggested. Next time, ask for a Loksound Select decoder. Performance wise, they are so vastly superior to the Tsunami that I wouldn't take a Soundtraxx Tsunami for free if you offered me one.
I'm going to re-suggest what David Bedard suggested. Next time, ask for a Loksound Select decoder. Performance wise, they are so vastly superior to the Tsunami that I wouldn't take a Soundtraxx Tsunami for free if you offered me one.
I own an 'old' Atlas GP38 that I purchased new in 2004 with the Dual Mode decoder.
I have considered a sound decoder for this loco. Was the OP's problem strictly decoder related? That's not a good endorsement for the Soundtraxx Tsunami.
Rich
Alton Junction
To clarify, mine was also with the dual mode decoder. When I said "converted to DCC" I should have said "converted to sound". sorry for any confusion.
Rich:
richhotrainWas the OP's problem strictly decoder related? That's not a good endorsement for the Soundtraxx Tsunami.
One could say that the decoder was not the cause of the problem. According to the OP all the decoder needed was a little tweaking to get the engine to run properly. You can't expect every decoder to come from the factory perfectly matched to every engine. However, you can get close. The Loksound has a self programming feature that allows the decoder to make its own adjustments to suit each individual motor's charactaristics. All you do is put the loco on a few feet of test track, change CV54 to '0' and then press F1. The loco will take off fast and then quickly slow down to a stop as it measures the motor's operation. Done. Loksound suggests that this method may only give you an approximate match and some further tweaking may be required.
In my own experience every one of the 12 or so Loksounds that I have installed has worked properly right out of the box. Each locomotive started creeping on speed step 1 and responded smoothly throughout the throttle range. That was true even before doing the CV 54 adjustment.
What I have not done yet is speed matching so my experience is a bit limited in that regard.
My point is that you don't have to go through the fiddling with CVs that the Tsunamis seem to require. Loksound Selects are cheaper, easier to use right out of the box, and they run cooler as well. So, Rich, to answer your question, the OP's experience is not a good endorsement for Soundtraxx Tsunami decoders when compared to a Loksound Select.
And, no, I don't work for Loksound.
I haven't done any speed matching yet, because the Loksound locos I have are all single runners, though I did doublehead my T-1s with Loksound 3.5 and did nothing but couple them together. Loksound supports CV2-6-5 for a simple 3 step matching, so any matching that's needed should be easy. With my non-sound locos using TCS which has an automatically adjusting BEMF as well, I doubt I will need to do much unless two locos have vastly different gear ratios.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.