Note that when using CV’s 2, 5 and 6 you can only speed match at one predetermined throttle setting. You will not be able to match speeds through the whole range of the throttle.
Locomotives should be speed matched when consisted together to avoid possible damage to motors and couplings and to prevent derailments and wheel grinding caused by mismatched speeds. The following describes how to match the speed of the locomotives you regularly use in a consist and/or a helper that may only be used on part of a route, such as up a steep grade. Keep in mind that you don't have to match every locomotive in your stable - just those that will be used in consists or as helpers.
Not that it doesn't exist, but we've yet to find any article on speed matching when only using CV’s 2,5 and 6 that even mentions, never mind explains, why you can only match locomotive speeds at only one throttle setting. That setting can be 20% of full power, 42%, 57%, 70% or whatever but only the one setting and no others. Be aware of this when attempting to speed match using the procedure that follows.
The reasons for this and how to speed match through the whole throttle range using CV’s 67 through 94 are described in ’Speed Matching ‐ Advanced’.
First thing you must do is make yourself comfortable with the process for changing decoder Configurable Variables (CV’s) with your DCC system. Don't be afraid to experiment, you can always reset any locomotive decoder to its factory default if you think you've got it wrong. It’s suggested you start experimenting with CV’s 3 and 4, which vary the acceleration and deceleration of locomotives. The default is zero (instant start and instant stop) but entering values between, say, 3 and 15 for CV’s 3 and 4 will teach you how to change CV’s and how such changes affect performance.
You don't have to use Ops mode programming (a.k.a. Programming on the Main), but you'll find it much more convenient to do so when speed matching. It is possible to reprogram the wrong locomotive when in Ops mode, but you'll be OK so long as you make sure the locomotive you want to change is the one actively displayed on the throttle.
To give yourself a comfort level when first changing CV’s in Ops Mode, take every locomotive but one off your layout and practice changing its speed characteristics "on the fly" with Ops mode programming.
If you use 'Page' mode rather than 'Ops', you'll have to keep transferring the locomotives between the main and programming tracks.
Don't forget to press 'write' when changing the value of a CV, and 'Exit' when you've matched speeds and finished programming.
DECODER SPEED STEPS
It's important to ensure that the decoder speed steps of every locomotive you're going to use in consists should be the same, i.e. 14, 28 or 128. The reason for this is because for 14 speed steps there is an approximately 7% difference between each one (in other words, the speed will jump by 7% each time the throttle is turned to the next step), for 28 the difference between steps is less than 3.6% and for 128 there is only a 0.78% change between each step. If your consist locomotive decoders are using different speed steps then it's highly unlikely they'll run at the same speed at the same throttle settings.
If some of the CV’s beside the address have been changed from the default then it's probably prudent to record them beforehand so you can re-enter them if things go wrong. The most commonly changed CV’s are:
You should also record CV’s 29 (Configuration Register), 56 and 57 (Dither frequency and voltage), 65 (Kick Start Value), and 66 and 95, which are Forward and Reverse Trim respectively.
Keep track of the changes you make to the CV’s on every decoder. Try the sample record we use. DCC Decoder Record
Most decoders can be reset to their defaults by programming in either CV8 to the value of 8 or CV 30 to the value of either 2 or 30, although these values are not cast in stone. Some require the use of a reed switch. See the instructions that came with your decoder for the proper CV and its value. If you don't know the type of decoder in your locomotive you can put it on your programming track and read the value of CV#8. The number that displays is unique to the manufacturer and a complete list can be found at http://www.nmra.org/standards/DCC/mfgnumbers.html
THE THREE-STEP PROCESS
'Speed Matching 101', or the Three Step procedure, uses the following CV’s
Using the three-step method of speed matching will not make every locomotive run exactly the same, but in most cases it will suffice. If you can get the two locomotives' speeds within a percentage point or two of one another at the same throttle setting you can consider it a success. Keep in mind the locomotives will likely work differently under a load, so you may want to consider speed matching all your locomotives with the same load of, say, 10 cars.
For ultra-fine speed matching through all throttle settings use Decoder Pro on the JMRI program (downloadable and it's free).
Estimating Scale Speed
Example: Measured HO track length is 200 inches (0.27462 scale miles) and it takes a locomotive 40 seconds to cover the distance. 60 divided by time = 60 ÷ 40 =1.5 x 0.27462 x 60 = 24.716 scale miles per hour.
|Scale Speed||N. American N-Scale
To calculate the exact scale speed over five feet timed in seconds, use the following:
Time to Travel FIVE (5) Feet at Scale Speed
Note: Only North American N-Scale (1:160) is shown.
|Secs.||N Scale MPH
||HO Scale MPH||O Scale MPH||Secs.||N Scale MPH||HO Scale MPH||O Scale MPH|