Speed Matching Locomotives

 Once the decoder is installed in the locomotive, the job isn’t completely done. To get locomotives so that they can be used in consists (multiple locomotives running together) , they need to be ‘speed matched’. This includes locomotives from the same manufacturer and even the same locomotive model. Depending on the motor, gears, and amount of runtime (drag), most locomotives will run at different speeds. If hooked into a consist, the faster locomotive(s) will attempt to pull the slower locomotive(s) causing wheel slip, decreased pulling effort, overheated motors, and possible decoder failure.

Fortunately, decoders have the ability to speed match locomotives built in. The simple way is to use CVs-2 (starting speed), 5 (top speed), and 6 (mid speed). There are two different methods of speed matching locomotives: either by having a "standard" locomotive and then adjusting the other locomotive speeds to match or by using a standard length of track and figuring out the speed by timing the locomotive. For the club, it just seemed to make more sense to use the timing method. By using Atlas 11 radius snap track, anyone (who wanted to) could build their own speed matching track, although the club also has one for member use.

Using Atlas 11” radius snap track, we have a fixed, consistent diameter loop of track for testing. Next is to determine the circumference of the circle:

11 inch radius circle of track = 69.12 inches (2Rx3.14)

So now we can create a scale speed chart based on the distance: 

                 
Test Track Radius > Module 9 3/4" R 11" R Module 12 3/8" R 13 3/4" R 15" R 19" R
Distance Traveled > 48" 61.7" 69.1" 72" 77.8" 86.4" 94.3" 119.4"
100 4.3 Sec 5.6 Sec 6.3 Sec 6.5 Sec 7.1 Sec 7.9 Sec 8.6 Sec 10.9 Sec
95 4.6 Sec 5.9 Sec 6.6 Sec 6.9 Sec 7.4 Sec 8.3 Sec 9.0 Sec 11.4 Sec
90 4.8 Sec 6.2 Sec 7.0 Sec 7.3 Sec 7.9 Sec 8.7 Sec 9.5 Sec 12.1 Sec
S 85 5.1 Sec 6.6 Sec 7.4 Sec 7.7 Sec 8.3 Sec 9.2 Sec 10.1 Sec 12.8 Sec
C 80 5.5 Sec 7.0 Sec 7.9 Sec 8.2 Sec 8.8 Sec 9.8 Sec 10.7 Sec 13.6 Sec
A 75 5.8 Sec 7.4 Sec 8.4 Sec 8.7 Sec 9.4 Sec 10.5 Sec 11.4 Sec 14.5 Sec
L 70 6.2 Sec 8.0 Sec 9.0 Sec 9.4 Sec 10.1 Sec 11.2 Sec 12.2 Sec 15.5 Sec
E 65 6.7 Sec 8.6 Sec 9.7 Sec 10.1 Sec 10.9 Sec 12.1 Sec 13.2 Sec 16.7 Sec
60 7.3.Sec 9.3 Sec 10.5 Sec 10.9 Sec 11.8 Sec 13.1 Sec 14.3 Sec 18.1 Sec
S 55 7.9 Sec 10.1 Sec 11.4 Sec 11.9 Sec 12.9 Sec 14.3 Sec 15.6 Sec 19.7 Sec
P 50 8.7 Sec 11.1 Sec 12.6 Sec 13.1 Sec 14.1 Sec 15.7 Sec 17.1 Sec 21.7 Sec
E 45 9.7 Sec 12.4 Sec 14.0 Sec 14.5 Sec 15.7 Sec 17.5 Sec 19.0 Sec 24.1 Sec
E 40 10.9 Sec 13.9 Sec 15.7 Sec 16.4 Sec 17.7 Sec 19.6 Sec 21.4 Sec 27.1 Sec
D 35 12.5 Sec 15.9 Sec 18.0 Sec 18.7 Sec 20.2 Sec 22.4 Sec 24.5 Sec 31.0 Sec
30 14.5 Sec 18.6 Sec 20.9 Sec 21.8 Sec 23.6 Sec 26.2 Sec 28.6 Sec 36.2 Sec
25 17.5 Sec 22.3 Sec 25.1 Sec 26.2 Sec 28.3 Sec 31.4 Sec 34.3 Sec 43.4 Sec
20 21.8 Sec 27.8 Sec 31.4 Sec 32.7 Sec 35.3 Sec 39.3 Sec 42.8 Sec 54.3 Sec
15 29.1 Sec 37.1 Sec 41.9 Sec 43.6 Sec 47.1 Sec 52.4 Sec 57.1 Sec 72.4 Sec
10 43.6 Sec 55.7 Sec 62.8 Sec 65.5 Sec 70.7 Sec 78.5 Sec 85.7 Sec 108.5 Sec
5 87.3 Sec 111.4 Sec 125.7 Sec 130.9 Sec 141.4 Sec 157.1 Sec 171.4 Sec 217.1 Sec

Using OPS mode programming and start by setting CVs 2 thru 6 to "0". 

Next get locomotive creeping; read throttle setting (DT throttle reads in %); multiply 255 X throttle reading/100 - use result as starting point for CV2; make fine adjustments to CV2 until you are satisfied with starting speed. Note: 255 will provide the maximum available voltage to the motor, you are determining the percentage of available voltage the will provide the desired result.

Now get locomotive operating at 100 scale miles per hour. Using the same procedure (as above) to calculate a maximum speed starting point and enter it into Vmax CV 5; make fine adjustments until satisfied. If needed, use Vmid (CV 6) to get closer to a linear speed table.

Occasionally you will find a yard switcher or heavy freight steam loco that will not reach 100 smph even when CV5=255. When this happens CV6 set the mid range to be accurate at a more prototypical speed like 60 smph.

In real life passenger trains rarely exceeded 100mph, freights 70mph, and locals or yard switchers 40mph. From looking at the chart, the easiest speed to time and also have a realistic top speed is 70smph (scale miles per hour).

The acceleration rate (CV03) can be set to simulate train weight. Deceleration is the rate at which the decoder decreases speed from one speed step to the next in response to a new decrease speed command. The deceleration rate (CV04) can be used to simulate inertia. Just like the prototype, you can set your locomotives to get off to a slow start because of a heavy load and to take a long time to come to a stop because of the inertia of the train once it is moving. You'll probably also want to set CV's 03 and 04 to a value of 1 so you get some but not too much acceleration and deceleration.

CV54 allows you to use the F6 button to select "switching speed". By setting CV 54 to 1, the decoder will drop the top speed of the locomotive and partially negates acceleration for switching work.

Finally, always remember to Exit from programming mode by pressing the EXIT button.

 

Rev 8