I am trying to get a locomotive to accelerate very slowly. I need to have it accelerate from a dead stop to top speed in 2 minutes. The best that I have managed is 1 minute 25 seconds. I have CV3 set at 255. Is there anything else I can do to get this thing to accelerate more slowly? The only idea other than adding more weight to the load of cars the loco is pulling that I have had is to use a 2nd loco. I would have the first loco accelerate to the mid point of speed (60 seconds), then have the 2nd loco accelerate from mid speed to top speed in the remaining 60 seconds. Does anybody think that this is a viable option? Any ideas or suggestions would be greatly appreciated.
I'm not sure if CV3 works the same on all decoders, so I'm not sure this is accurate, but I believe it is. The information I used is from the Digitrax decoder manual. It sounds like you are using 28 speed steps. I don't think you can get your acceleration rate that slow with 28 speed steps. The valid values for CV3 are 0-31 (anything above 31 probably gives the same result as 31). The acceleration rate = CV3/10 per speed step(this isn't how they spell it out in the manual, but this is how I intrepret it). With 28 speed steps and CV3=31, rate = 31/10=3.1. 3.1 * 28 speed steps = 86.8 seconds = 1 minutes, 26.8 seconds. Pretty close to what you are getting. If you can use 128 speed steps then programming CV3 to 10 shoould give you 128 seconds (10/10 * 128) or CV=9 should give you 115.2 seconds. Disclaimer: I have not tried this. I have played with acceleration and deceleration rates, but have not timed any of them.
I am using a nce d13srp decoder on 128 step mode. I played with all different settings for the mometum. 255 gives the slowest acceleration. I'm starting to think I exceded the limits that can be done with it. What if I were to use a second decoder on the same engine? Have the first working the first 60 seconds where it only goes to half speed. Then on the second decoder it gets started on the 60-120 second time frame. Just have the programing on it duplicate the first but don't activate until the first gets to it's top speed. My thinking is that it shouldn't overload anything because the total top speed is only 25 percent of the total track power. Th only problem that I am forseeing is programing it. I will put in update tonight how this works.
OK, so the acceleration does not work the same between different brands of decoders. According to the d13sr manual , you should be able to do it. When you say "top speed" are you refering to speed step 128, or are you setting it to some speed below that. If you are not using the full speed range then you need to adjust Vmid and Vmax. According to the manual, each unit in CV3 equals 7mS. If this is correct, then with a value of 255 it would take 2 minutes to reach speed step 67. (255 * 7mS * 67 steps = 119.595 sec).
Top speed as in scale 7.7 mph at speed step 128. I am using the alternate speed table. Vmax is set to 60 which equals a scale 7.7 mph at least for this loco. I tried using the factory table with adjusting the Vmid and Vmax but the loco would drive crazy like.
Well, I was looking through the d13sr manual and it has CV23 listed as "acceleration adjust" but gives no information on what it does. It might be worth trying diffirent values for it. Other than that, I am stumped.
I think that CV23 has something to do with consist mometum settings. Update on this. Talked to the factory yesterday. The guy there said that the decoder is supposed to take 240 seconds to get up to top speed with cv3 set at 255. He suggested resetting the decoder. He said that he was going to try the values that I put in the decoder and see if they work for him. After that I decided to do some more testing on it. I did get the 240 seconds of acceleration when the Vmax was set at 255. Then I tried with the Vmax set at 128. It took 120 seconds. With Vmax at 60, it took 60 seconds to get to top speed. My guess is that acceleration time is tied to overall percentage of total track rail power. If that's the case my second decoder idea isn't going to work. But using some resisters between the motor and decoder should.
I have been watching this thread and I had a feeling this is the case but wasn't sure enough to jump in. I think the momentum CVs are effectively the rate of acceleration/deceleration, so if Vmax is lower than maximum then it will reach that speed sooner. I'm afraid I can't see how your ideas for using two decoders would ever have hung together. The resistor idea might work, but it will depend a bit on how constant the load on the motor (loco?) will be. Ideally you'd either regear the drive train so at full volts the speed was only what you need, or maybe put a higher voltage motor in (24 or 30V perhaps), so it never got above half speed or whatever, but I think those two ideas may be going a bit over the edge for the real world. But then again, is a model railroad 'real world'?
I found some additional information on CV23 here: http://www.tonystrains.com/technews/consisting-guide.htm He talks about CV23 about half way down the page. CV23 is for adjusting the acceleration for advanced consists, but some decoders continue to use it when not consisted. Even if it only works when consisted, you could use the consist address even though it is just the one locomotive. If you use CV23 it is important to note that values above 127 are considered negative (128=0[I think], 129=-1, 130=-2,...). Again, CV23 is different among decoders and I could not find anything specific about it for your decoder, but it may be worth a try.
Well the resisters didn't work but I'm not surprised. What I eneded up doing was lowering the track voltage. It's not perfect but it works ok. After going through everything I think they only correct solution is to gear down the locomotive more and possibly have a motor that runs less rpms. Thanks for all of the suggestions and ideas.
