ScaleTrains SD40-2 Pulling Tests

[daniel_leavitt2000]

I'm kinda disappointed. I had hoped these could do about 20 cars on level. It's not a deal breaker for me as conrail used these in sets of 4 on the Boston line, but it's a big step back from the Kato C30-7 which could pull up to 25 on a 1% grade.

[peteski]

https://www.ebay.com/itm/325421017885

Funny thing is that in that listing a listing for an identical scale is shown for $8!
https://www.ebay.com/itm/145640189768

[C855B]

Ha! Hope that extra $2.50 buys 'em a frappuccino at Starbucks!

Nope. It doesn't.

[Rivet Miscounter]

I'm kinda disappointed. I had hoped these could do about 20 cars on level. It's not a deal breaker for me as conrail used these in sets of 4 on the Boston line, but it's a big step back from the Kato C30-7 which could pull up to 25 on a 1% grade.

Do we know it won’t pull 20 on level?

The tests were on 1% and 2%, yes?

The “stump puller”  C30-7’s that were not DCC ready, then the DCC friendly’s were still pretty good.  So yeah if you don’t convert the C30-7’s to sound you still have a “heavy”.   That’s basically what I’m looking at doing.   I actually bought sound decoders for my C30-7’s but I’m rethinking that.

[C855B]

The tests were on 1% and 2%, yes?

Yes. The level stretches on the layout hadn't been cleaned in a while. I was running the track cleaner train on that portion this evening and might have them in reasonable enough shape tomorrow to test with. My SWAG based on testing so far is that 20 if not 25 on the level will be a cakewalk. But we'll see.

[randgust]

Ah yes, it's important to quantify and test.   I got a digital scale (necessary for resin casting mold production) a long time ago, started weighing locomotives in grams, and comparing that to a spring-scale in grams that I modified into an N-scale car with trucks on both ends to measure drawbar pull while in motion (dynamometer car) and static pull to full slip.   Those two measurements also lead to the immediate conclusion that all wheels are not created equal; you'll get anywhere from 10% to 22% adhesion (typically) of pull/weight in the same units.   All wheels, with the best always Kato or old ones that are worn to the point the plating is gone down to brass, worst ones are Atlas a few years back (a little better now).  It's all about the wheel material and metallurgy and total weight on powered axles.   Vibration, yes, out of round will get you.

And it will not make you happy.   If you have to put 3 locomotives on to pull what one used to, the manufacturers might be, but it gets a little absurd after a while.   And it has nothing to do with the number of axles or motor poles or reduction gearing.  Track cleanliness, yes.   And in-motion drag is SIGNIFICANT as wheels 'scuff up' or accumulate dirt, that's the other discovery.   Check the same train on the same track in the same direction after a full wheel cleaning.   Whoa.

EL used to run almost everything through here with 2 3600 hp units, period.  Rarely three, even at track speed.   ATSF assigned 3 3600 six-axles to just about EVERYTHING in my era other than the local and the YK unit coal trains.   PC in my area ran a normal 25-car local with one unit.   G&W runs usual 40 car trains out of here up a 2.2% loaded with four B-B units including one road slug, and does track speed of 40 out of the valley to summit.   

To me, half the fun of N scale is you have actual long trains, my standard 'long road train' is 30 50' carlengths behind three units.   And coming up out of my staging yard is a sustained 2.5% grade around two 13" radius 180-degree curves on a compensated grade.   It was designed and tested in the era of Trix U-boat mechanisms and worked just fine.   Today it's become more and more of a challenge to get power that can still do that.  Original Kato DC six-axles handle it easily today with pull left over.

[C855B]

Today's tests:

A single unmodified ScaleTrains SD40-2 on level track, ESU LokPilot decoder, pulls a 25 car train with manageable wheel slip on start. IOW, don't pour on the coals; throttle-up properly and you will be rewarded with the train moving smartly. NOTE: the first 1/2 of the test train was MTL TSC-equipped, so there was less than usual slack run-out.

The weighted unit? 30 cars, easily. ~20% improvement. I'll be adding the tungsten powder to the remaining three. The full test train was 36 cars, two cars longer than the longest siding on the layout, or roughly 15 feet. It took two units to move it.

Now this is a fun one, in the name of JFRTM - when running the train to the level trackage, I inadvertently left the tail-end cut of eight cars back on the 1%->2% test portion. So instead of backing up the entire train of 28 cars over ~80' and 360+° of curvature - which would be doable, but why court disaster? - I fished a switcher out of the yard to fetch the orphans. The little Bachmann S-4, box-stock, walked the cut up the 2% grade without breaking a sweat. Impressive!

[turbowhiz]

Another data point on these, since I have a force gauge and scale handy….

The ScaleTrains SD-40-2 weighs in at 81 grams and has about ~.14 newtons of tractive force at wheel slip.
(wheel slip or a dead push seems to measure effectively the same value)

My general average larger diesel is ~.19-.20 or so newton of force… Kato ES-44’s, P42’s, ST ET-44’s are in that range. Early Kato F3 is ~.23 newton tractive force. Traction tire equipped Rapido -8’s are monster pullers around ~.39 newtons. These models all weigh in between 105-125 grams, significantly more then the ST SD-40-2.

Smaller 4 axel models on hand I casually tested like the Rapido GMD-1 and a Lifelike GP-38-2 were similar to the ScaleTrains SD-40-2 around ~.14 newtons.

At around 70% of what you might expect from a model of that size these guys aren’t super pullers to be sure. Still a fantastic model though… The fit/finish at least of my example seems to be a notch above the numerous ET-44’s I have. Nary a glue stain or poorly spaced grab to be found, something I can’t say of my ET-44’s.

Another tip regarding the sanding lines: I feel these help make the model. But yeah, they’re maybe pushing that detail vs practical limit alright. I found mine a little wonky in their alignment. So when I had the shell off, I aligned them by heating them with a hair dryer. Carefully… But the heat was the trick to reposition them and they seem to have held their new position well over time. You need to be very careful putting the shell back on… You need to tease the lines over the frame say with a toothpick or somesuch when putting the shell back on otherwise they will get caught up badly and you might damage them.

[C855B]

Sanding lines... on decodering the fourth unit, I thought about "process" for more than two seconds, "There has to be a shortcut at the factory. A jig, maybe?"

Method I concocted? A slip of thin paper on each side of the shell, creating a "funnel" to drop the chassis into. It pushes the sanding lines back perfectly. Pull the slips out, maybe push around the lines at the end sills back in place with a dental explorer, done.

Oh... and I found the one that got away. Now that I have a technique for reassembly, I will attempt to reinstall it.

The monster pullers in my fleet are Con-Cor U50s. One will take 50 cars up that 2% without thinking about it. Weight is everything. I should have my scale by Saturday and can then quantify how much the tungsten added.