Scale Speeds or Just Running Slow?

Model Railroader Layouts and layout building
1

Back in early January, I started a thread about an Intermountain Railway F3AB consist equipped with Digitrax DZ143PS decoders. My observation back then was that this pair of locos seemed to be running awfully slow even at top speeds. I still think that is the case, so yesterday I decided to time these locos.

My HO scale layout has 170 linear feet of track on a continuous loop track plan. That converts to 2.80 miles of scale track to complete the loop. My DCC system puts out 14.8 volts.

At top speed on my throttle, the Intermountain F3AB consist, pulling five Rapido passenger cars, takes 3 minutes, 25 seconds to complete the loop. That translates to 49.2 MPH. Without the 5 cars, the F3AB consist completes the loop in 2 minutes, 50 seconds, or 59.2 MPH. In fact, that is consistent with a prototype F3 loco that was geared for a top speed of 65 MPH. Still, it really looks slow travelling around the layout at top speed.

Thinking that these two HO scale locos might be running slow, I ran another pair of Intermountain Railway F3AA locos, also equipped with Digitrax DZ143PS decoders. Pulling 5 Rapido passenger cars, the average scale speed was 54.5 MPH. Without the 5 cars, the scale speed was 57.6 MPH.

Then, I ran a pair of Athearn Genesis F3A locos equipped with Tsunami decoders. Without any passenger cars in tow, the scale speed of this pair was 69.5 MPH.

My final test was a Proto 2000 E8 loco, equipped with a QSI decoder, pulling 5 Walthers passenger cars. The scale speed was 69.5 MPH. Without the cars, the P2K E8 ran at 84.0 MPH.

So, what should I conclude?

Are the Intermountain locos just geared to run slower? If so, is there any way to speed them up? Is the DZ143PS decoder the problem?

Or, is there no problem? Just leave well enough alone?

Rich

2

Intermountain locomotives are geared to run slower than some other brands, and are actually a more prototypical scale speed.

All decoders that comply with the NMRA DCC Standards and Recommended Practices use CV5 to set the highest speed step (MAX Voltage) to the motor, and if the default is 255 or 0, it can’t be made to go any higher.

3

Are they actually geared to run slower, or is it a limiting voltage causing this. I don’t know the gearing of the IMs. however, I would think that they would be 14:1. Most manufacturerd have set 14:1 as the gearing. Early P2Ks had that gearing of the month issue, not sure if IM would be running 16:1 or 18:1.

4

Bob, can you explain what you mean by “limiting voltage” as a cause?

Rich

5

The higher the number to 1, the slower it will go. Most are 12:1, which will be faster than 14:1. The higher number will pull better, than a lower number but the top speed will be lower.

Frank

6

There may be a way to make the IMs run faster. In the short run, it’s easier to slow the fast locos down I’d think.

I actually went through my fleet’s decoders a couple of weeks ago to limit the speeds on my standard gauge locos. It seemed really slow at first – I called it “ponderous” speed in my crew call talk – but it’s actually more realistic . I didn’t do any speed radar or calcs, but my guess is they average more like 50 mph top speed. There’s the added bonus of more slow speed control, too, by the time I got everything adjusted.

Or you could makes lemonade out of lemons. Call the IMs freight locos, so they’re geared lower than your passenger fleet. The real thing did that, but of course this won’t work so well if they’re steam generator-equipped.

7

One thing is for certain. Your 12v motor is probably already close to it’s max RPM and volts, if you were to give it more volts, it would run faster, BUT, chance’s are you will be maxed out on the motor causing it to overheat and eventally destroy itself. The sure way is to change to gear ratio, on the main drive, which would be at the worm gear and the main drive gear, that would have to be changed to a lower number of teeth on it, thereby reducing the number of revolutions the motor has to turn to complete one full axle revoltuion. That is what the ratio to motor means. for instance: 12:1, the motor turns 12 times to one (1) full revolution of the main gear. You could also add larger diameter drive wheels, which will make it go faster, but not by much.

Frank

8

First clean and lube. Old grease slows down cars.

Second turn off Back EMF (which can really slow things down) (My BackEMF is 0 above 32 speed steps)

Make sure your top voltage is at 255 in the decoder.

If all the above fails, you’ll have to remotor.

You COULD replace the gear tower. But then you are reducing the torque. Torque is what actually what makes your train “go” So it will slow down a lot more when you put a load on the motor. So the best viable solution is to replace the motor to increase the horse power.

Horsepower = (Torque * RPM) / 5252. Since your horsepower is fixed, you end up reducing the torque to increase RPMs.

9

If you are using Digitrax Decoders in a consist try setting CV57 to 102. I had a problem with engines running much slower in a consist. Digitrax recommended the above settting and that seemed to fix the problem.

10

Full throttle voltage may not be getting to the motor due to lighting, circuit board, decoder settings etc. I’m not familiar w/ the IM setup, but would not think it would be a gearing issue. Some early DDC ready boards in P2Ks did this. I also notice this on Stewart/ Kato f units the b unit w/o lighting ran faster than the A w/ the headlight. The decoder may also be doing this, others more knowledgeable w/ this decoder and CVs may be of help.

11

I decided to play with this CV value and it did seem to make some difference. I may call or email Digitrax about this issue.

Rich

12

Bob, thanks for those comments. I took a look at the entire list of CV values, using Decoder Pro. I decided to start a separate thread in the Electronics and DCC Forum, and I included a list of CVs there. Here is a link to that new thread.

http://cs.trains.com/mrr/f/744/t/227366.aspx

Rich