I have been playing with CV 3 and have tried 60 and 50 as values. (I am new to this so I hope I am using the right terms). I want a slow acceleration rate, problem is the engine sits there still for a few seconds then starts to go. It starts moving just a little to fast, after it starts to move. I like the effect, but I want it to start at a craw, not like I dumped the clutch.
Is there another CV I can change to get it moving quicker but at a slower rate? Engine in question is a HO Athearn RTR SD40-2 with a Digitrax DH 163 pulling 21 cars. I running a Digitrax SEB.
I have finally got my Digitrax PR 3 to night at 9:45 PM so yet to be hooked up.
A possible solution, Ken, would be to kick your starting voltage upstairs, and that would be via CV2, or what we call V-Start. I don’t believe it will get you underway less quickly, but it will get you underway sooner, even immediately. The very slow acceleration from a bare crawl, as I understand it, is controlled through BEMF settiings and maybe ‘dither’, both of which should be covered in the decoder’s manual. But an engine that sits for a couple of seconds after you wind in speed step “30”, say, and then lurches into motion, is not getting the correct start voltage. The decoder is slowly raising the voltage per your CV3 setting, but the engine motor won’t be able to get the axles turning until it can over come all the internal and external resistances and friction in the drive. When the voltage exceeds that necessary to make the engine commence moving, it does it with a jerk. No, not you…I mean the engine…it jerks into…oh, you know what I mean. [:D]
I agree. I would start by putting CV3 (and CV4) back to zero. Then set CV2 so that the engine just barely moves at speed step 1. I find I want a number like 2 to10 for this in most engines. Next, try 10 in CV3. That’s a good starting point. Make it higher if the engine still starts too fast, or lower if it starts too slow. Once you’re happy with CV3, adjust CV4 for deceleration.
A LokSound decoder, by the way, has a built-in “spin up” delay before the engine will start to move. I found I had to set CV3 to zero, or else I needed another beer by the time the engine got moving.
A custom speed table might be the best option. When you get the PR3 hooked up with JMRI you can adjust the sliders for each step exactly how you want them. These are CVs65-95. Check out page 52-56 in the Digitrax decoder manual.
I will try playing CV 2, I was reading about it in the Digitrax book, but want to run it by you folks here first. This morning the SD 40-2 will not move, I have control of the lights and that is it? When I get home tonight I will resit the default and start over.
This is exactly what you should do. And it’s quite easy with the DT400 because it’s obvious when you are on speed step 1. Using Ops Mode programming, you can just keep upping CV2 until the loco moves at the slowest speed it can sustain. You will probably notice this is more reliable on the decoders that have BEMF vs ones that don’t (DH123 series do not). Once you have CV2 buttoned down, now it’s tiem to play with CV3 and 4 and get the momentum set. There’s no ‘best’ value, it really is a personal preference, but you can guide yourself somewhat by the intended function of the loco. Switchers tend to ‘load’ quickly in real life, which is good - switching with a lot of momentum programmed in can be tough! A passenger loco on a short train will take off quickly as well - part of the reason CNJ used big Trainmasters to pull 3 car commuter trains, they could get up and go when leavign a station stop (of which there are many on a local). For freight trains, it’s going to depend on the consist of the train, a heavy ore train will take a lot longer to get up to speed than a train full of empty hoppers going back to the mine. The nice withing with DCC is you have two seperate settings, one for accelertationa nd one for deceleration, so you can have a train that takea a while to get up to speed, but slows down quickly when you shut off to prevent a disaster. This is the fun part where you play, and since you’re only adjusting one CV at a time, you can switch it back
This is beside the point, but a nice thing about QSI decoders is that if you want the engine to stop quickly, but not use the emergency function (you have some time, it isn’t an emergency, but it will soon be an emergency…), you press F7 and the engine brakes hard. If you had CV4 set so that it would have taken, say, 4 feet to come to a halt under momentum, pressing F7 makes the brake squeal sound and it grinds the engine to a halt in about 15-18". A nifty feature.
Crandell, I will have to give that a try, I know F 7 makes the brake squeal, but never held it down long enough to see any braking action.
Randy, this is a dumb question. How can I tell if a decoder has BEMF and what does it stand for and do? I have manily used Digitrax DH 123 and 163. I know the 1 means one amp and 2 or 6 is the number of fuctions. I want to try NCE and Total Train Control (is that the right name) decoders and will still use Digitrax as well.
Thank Folks, you are all great help. Now, are you sorry you got me to finally Digitrax, going to be a lot of CV questions coming! [:D]
Ken, there are some locos that you just can’t make behave using only CV3 and CV4. I call them jackrabbits and they are really noticeable when trying to speed match locos. Even seemingly identical locos may have a jackrabbit in the set.
It is good that you now have the PR3 because you will need to set a custom speed table to slow down a jackrabbit loco that starts too fast even with CV3 set to 0 or 1 (or the Vstart setting at 0 if you are looking at the motor control panel on Decoder Pro…which I imagine you will be using…and man, it is so much easier to play with CV settings using Decoder Pro).
I have at least a half dozen locos that “race off” relative to others even with zero’d acceleration settings.
Learning about speed tables is part of the fun, I think. Some decoders will have preset slow start tables that you can enter in CV25 for example (called exponential curves which is a fancy term for a series of settings of speed CVs that have very low values for the first half of the throttle settings and then rises at an increasingly faster rate to reach the final top speed [sorry to go on if this is all something you perhaps already know].
But with your PR3/Decoder Pro you can just set this curve yourself easily in the graphical speed table panel by pushing the slider buttons to values you want…which for some of my locos is a value of 0 for several of the first half dozen speed steps just to slow them down and extend that beginning crawl to match other locos which don’t need a speed table at all to do this.
There are a couple of ways. The 123 series do not and the 163 and 165 series do have BEMF. This is hidden in the manuals, unless you are looking closely for it. They also call is Scalable Speed Stabilization in some decoder manuals. It is controlled by CV55-57. You’ll note in JMPRI when you are working on a 123 series you won’t see these CVs nor the settings on the Tab.
Here’s what is in the basic decoder manual:
Scaleable Speed Stabilization (Back EMF) intensity, or droop, is controlled by CV57. The factory setting for this feature is 006/x06 which is suitable for most locos. You can adjust this value in the range of 000/x00 for OFF to 015/x0F for the maximum effect. Consult your Digitrax Decoder Manual for info about CVs 55 & 56 and their effects on scaleable speed stabilization. The
Ciso, I seen the speed graph at Simon 1966 house and was sold on the spot. I just got mine this Thursday and have not had the time to hook it up yet. Hope to have it up and running Sunday.
Ok Binkley, that term I have seen listed when reading about the 163’s. Need to look at the NCE decoder site and see which of there decoders have the setting.
Someone else mentioned internal friction. This is often a problem with new or very seldom run engines, including if they have sat on the store shelf for several years, that can be overcome by a few hours of judicious breaking-in at varying speeds both forward and reverse. Some people use Pearl Drops toothpaste in the gear trains as a burnishing/lapping compound to remove any flash or rough spots an polish the gears. Be sure to flush it out and re-lube when finished. John Colley, Port Townsend, WA
Ken, I just realized that I forgot an important element in the F7 braking. You have to reduce the throttle setting, maybe even to zero before you will get the braking. I apologize for that oversight. Also, I do not really know if reducing the speed from, say, 40-30 will have it braking when you press F7 and it will fall to 30 and continue at that new speed…never tested it because I had never wanted to use the feature that way…I have always wanted to get the train to stop, but had some time and didn’t need to use the emergency button.
So, try your engine(s) again. Get them up to a scale speed, quickly zero your DT400 speed on the throttle, and assuming you have a fair bit of momentum in CV4, the engine should make the brake sounds and begin to slow very quickly. It will stop in less than half the distance it normally would for your CV4 setting.
FWIW, I usually set CV4 on my steamers up in the 60-120 range. In that case, pressing F7 any time after I have zeroed the throttle brings my trains to a safe, non-abrupt, halt. I wonder about the effects of repeated emergency stops on the driveshaft and such with a brass weight spinning on it, so I use emergency as seldom as possible.
NCE decoders don’t have Back-EMF at this time. The Digtrax BEMF will have you pulling your hair out trying to get it to work with other engines, lots of adjustments.
The TCS BEMF works great, and can be programmed to turn off at a set speed, or you can use a function button to turn it off (default is F6). At low speeds a P2K GP60 will run with a Genesis MP15AC or an Athearn SD40-2 or an Atlas most anything, as long as they all have TCS BEMF in use. And they all start moving on speed step one, no monking around with CV2.
Yup, none of the NCE decoders has BEMF. ANd I am really digging the implementation in the TCS decoders. None of the ‘jump’ I had to work around that the Digitrax decoders have. And since I’ve found TCS T-1 decoders as low as $17, I haven’t hurt my bottom line too much using them instead of $12 NCE D13SRJ’s.
I set up so that on speed step 1 the loco will move slowly as I almost always stop about 10 feet out, pause, then come up to the cars. I can just bunch or pull out the slack to test control. I have CV3 set at 10 and CV4 set at 5. At a friend’s Operating sessions I have had people ask "what’s up with that? as they didn’t have a clue about momentum so they just cranked up the throttle then were surprised at the runaway. I know my engines and work up through the notches with no problems. My own feeling is that if one is going to the trouble to operate realistically then that should include engine control as well as car card control. John Colley, Port Townsend, WA
Most decoders use only a linear acceleration factor (momentum). That is, the factor remains the same over the whole speed range according to the value you entered in CV #3 and #4. The problem is that when you add a high value in CV #3 to have a nice slow acceleration indicating a heavy train it also takes longer for it to actually start to move from a stand still. Plus the whole acceleration process using CV #3 and #4 as it is, is in most cases not really prototypical either. When you watch a heavy train start up you’ll notice that its acceleration at first is very slow because it has to overcome a lot of friction. Once it reaches a certain minimum speed most trains begin to accelerate faster. Likewise, when decelerating many trains ease up on the brake a little shortly before coming to a full stop; maybe more so on passenger trains to give the passengers a smooth ride.
This is where CV #121 and #122 comes in on ZIMO decoders. These CV’s “stretch” the momentum in the lower speed step range and thereby create a non-linear acceleration/deceleration rate. The two CV’s let you chose the speed step range from 0 up that should be included in that process as well as the “stretch” factor.
I have been playing with CV 3 and have tried 60 and 50 as values. (I am new to this so I hope I am using the right terms). I want a slow acceleration rate, problem is the engine sits there still for a few seconds then starts to go. It starts moving just a little to fast, after it starts to move. I like the effect, but I want it to start at a craw, not like I dumped the clutch.
Back EMF is Back Electro-Motive Force. When an electric motor turns, it generates a small amount of electricity. You can measure this and use it to control the motor’s speed to a very precise measurement. In our trains, if the train starts going up hill and the motor spin rate slows down, the amount of current it produces drops, and a decoder with BEMF detects that and gives more power to the motor so it spins at the rate it was spinning before - to the train goes uphill and downhill the same speed it goes over flat terrain.
CV 3 and CV4 affect the amount of time between speed steps. The amount of time increase for each increase in the CV setting is determined by the manufacturer so it isn’t a set rate, but let’s say on your decoder each number in CV3 adds 1/10th of a second between speed steps. If you have CV3 at 20 and you set your throttle at speed step 10 it will take the decoder 2 seconds to get up to speed step 10 for example.
Some decoders are set so when you turn the throttle up, it first applies enough power to get the engine moving, then applies the momentum to provide a smooth transition to the speed step you set the throttle to. With most of them, it just applies power starting at speed step one and pays no attention to whether that actually makes the engine move or not.
So…let’s say from the above example you have set CV3 to 60. If you set your throttle to speed step 10, it will take the decoder 6 seconds to get to speed step 10. That’s fine, but what if your engine’s motor won’t start turnng until speed step 8 ?? Then your engine is just going to sit there until it gets up to speed step 8, which will take around 4 seconds.
That’s where you can adjust CV2 up a little to get the engine to start moving a little quicker, it increases the power the engine gets at the start.
