Hey, I have been pondering for some time where the boundry is between weight & power of a Scale locomotive. I decided to clean up a 3 foot plank that has Atlas snap track (measures 0.100, but I think it was called Code 83 at order time) the sections are rail soldered & bases glued down to the base plywood plank. I want to do some “Pull” tests on a few of my HO locomotives & see what they do… The track has been polished out to an 800 grit finish, with the rails, (not against, as I am not cheating here) & the plywood plank was clear coated to seal the previous car lengths & weight markings. I plan to use a Micro Mark ‘pull gauge’ to do the tests. On the meter, I have custom soldered loops (hopefully, zero drag) to fit my dead end & into couplers on the loco side.
Do any of you know the correct way to ‘test’ drawbar (coupler) pull on a locomotive? I will be testing HO scale DC locomotives at first, & have to wait a couple days for a custom built panel I built for Amp & Volt meters to dry before I can mount them up & solder up the connections. I know it may be arbitrary to do this, but I feel it would be fun to take such an endevor.
If anyone would like, I could share some of those results here, in future posts, as soon I get to start testing…
Thanks!
Chad:
I recently got one of the MicroMark electronic gauges and have been playing around with it a little. I found that you get more consistent readings in the “push” mode rather than the “pull” mode. If you have this type of gauge I’d like to see if you have the same experience.
Joe
This is a little outside my area, but I would think a controlled or calibrated weight system would be needed to accurately judge the pull or the shove capability of a given locomotive, and it should be on a standardized track, say near-perfectly level, but fixed so that all engines get the same conditions. Then, you would want an indicator of amperage draw by the motor to watch for slippage. The amperage would level out or dip slightly as the wheels began to spin against weights slightly too heavy for the traction of the locomotive.
Crandell
Joe, I wi;ll certainly let you know, as I had not considered that aspect…
Crandell, yeah I agree, & that is why I don’t have any data, as my “Wet Paint” meter addition will take a day or two to dry. I want to use it to see if I can ‘gauge’ the stall & draw points, to focus in & get clean results.
I posted this to see if there was a standard of testing, & I asked the fine folks at the magazine too.
I got what I got, & I will test it. I also have another pull Gauge, one I almost overlooked, it is a Lyman (Firearm) trigger guage, & it is very sensitive (sensed a Nesika 2.48oz trigger brake), it may actually record when a loco ‘brakes’ traction like a gun trigger… May be a good "control’ check…
Honestly, I have a few modern locos, & I am interested in seeing how they 'tow…"
I welcome more opinions & coments!, & Thank you!
I think that you’ll find that the pulling ability (drawbar pull) of a loco is roughly equal to 25% of its weight. This will vary somewhat, I would think, on the number of powered axles, and for steam locomotives it will vary widely based on placement of the weight. For steam locos, the fact that the weight is balanced at the centre point of the driver wheelbase is at least as important as the amount of weight.
A fairly easy way to determine a loco’s drawbar pull is to place it on a straight section of track, one end of which can be elevated. Multiply the percentage of grade which the loco will climb, expressed as a decimal, by the weight of the loco in ounces.
For example, the loco shown below weighs 32 ounces and will climb a 26% grade without slipping. Therefore, the drawbar pull of the loco is .26x32=8.32oz.
I had taken three of these locos to a local railroad club and was hoping they’d run them for me on their layout, but discovered that they had converted to DCC. My DC locos were, of course, not suitable. They did, however, graciously offer to test one on a set-up such as the one I described. I keep meaning to build such a test track for myself, but never seem to have the time. [:-^] This method was discussed in much more detail in an article entitled “How locomotives perform” by Linn Westcott, in the September 1970 issue of Model Railroader, and includes volt- and ammeter useage and a more technical discussion of related issues. (Well-worth getting a reprint if this subject is of interest.)
I do know that most decent-quality locos can handle the addition of much more weight than would be physically possible to cram into the body shell. For instance, this Athearn USRA Mikado could still slip its drivers when restrained from moving, even with a 22oz. “saddle” of sheet lead draped over its boil
Wayne,
Thank you for going into detail, I appreciate that… I am looking over & re-looking at your calculations & am impressed, thank you for giving me some very important insight. I am not going to over look it. I will primarily be testing Diesels on my (now seemingly obscure) test sled. But your insight gives me a much more usable dynamics to apply to a real layout (which of mine, is still unconstucted). I do appreciate your genorus write-up & insight. I am saving it up, (to reference often & apply) & will put it into practice.
Thank you!
An important practical rule is to not overweight any loco to the point where its wheels cannot slip. That can burn out motors if the engine is overloaded with cars on the layout.
It’s also probably obvious that weight balanced over the driving wheels as much as possible will likely have the most benefit.
Good point, as I am still wondering…
At what point will a Kato SD “LET the SMOKE OUT???”
That is the “functional threshold” I have in question, when does tractive power, & mass weight conflict???
Thoughts?
Chad, I can’t answer if you’re referring to decoder smoke, but you shouldn’t see motor smoke as long as the loco can slip its wheels. You can easily test for this: for a steamer, physically restrain the tender (unless it’s a Triplex [(-D]) and apply power. As I noted in my earlier post, I performed this test with a 22oz. saddle of lead draped over an Athearn Mikado’s boiler - the wheels slipped easily. For a diesel (or Triplex), simply add one car and hold the car as the power is applied. While this is a useful safety feature, repeated slipping of drive wheels will wear away the plating from the wheel treads, resulting in poorer electrical pick-up.
As long as the wheels are turning, whether when moving a train or, in the case of a train that’s too heavy to move, merely slipping in place without moving, the motor won’t exceed its rating. If your loco, with added weight or not, won’t slip its wheels when power is applied, then the motor is still attempting to turn, but cannot. In this case, the windings of the motor begin to heat up, eventually melting the insulating varnish on the wire and “releasing smoke”.
Wayne
The monthly product reviews in Model Railroader give the performance ratings for many locomotives, including the number of cars they will pull on straight and level track before slipping and the current draw when running, slipping, and stalled.
Seems like that’s the practical information anyone would need. The point where wheels slip varies based on the power of the motor, efficiency of the mechanism, weight, weight distribution, wheel material, etc.
Every model has a unique combination of these factors and thus performs differently. Even multiple samples of the same model can have differing performance.
Since there’s not much room to add weight in many loco bodies, I’m not sure what a purely theoretical calculation accomplishes or how it would be useful beyond the results that have already been published in the commercial press for many models.
Jeff Johnston wrote about balancing locomotive weight for better performance in MR January 1995 and described his traction test stand based on a dynamometer gauge in MR May 1995.
Thank you, I will have to look into obtaining that 1995 article, as I was not yet a model railroader at that time. Appreciate the input.
As for slippage, with my polished track, & pretty much ‘out of the box’ condition loco’s, I expect they will act like they are on ball bearings, & I will get initally low ‘tow’ reads. I would rather have that than smoke from burnt windings or connections to the PCB… Initially I will be only testing DC units, although some have PCB’s with current limiters, rectifires, & other such things for lights & what not… I mentioned Kato before, cuz if it is direct wired, they are extremely quick & responsive, without any parasitic current draw.
ChadLRyan,
For starters, you should not have a test track that’s different from your typical mainline track if you want the numbers to mean anything in regards to your home layout. For example, you said you polished the rail on your prospective test track with 800 grit abrasive. Unless you also do so for your entire layout, it will skew the readings for all locos tested.
As for a system, take a look at what we do at my club:
It’s a 1 lb capacity hanging spring scale in 1/4 oz. increments. The pulley seen above is made of teflon and mounted on a teflon sleeve, reducing friction to a bare minimum. Add some soft twine and a steel hook made of piano wire, and that’s our drawbar testing machine.
The great thing about the spring scale is that it gives a constant reading. Compared to, say, hanging weights where one has to constantly fiddle with them.
So far, only one engine has ever bottomed out the scale: the BLI Y6b with two traction tires, and even then it needed a running start to do so.
To date, we’ve measured over 1100 locos. After you’ve done a couple hundred or so, you start to see patterns emerge. Namely, that dirty wheels & dirty track can really foul up the readings, giving ones that are too high. Also, that an engine’s vibration will negatively affect it’s performance (another reason why Kato’s pull so well is that they just sit there and spin their wheels at 100% throttle while an Athearn BB or RTR will jump about). As Dr. Wayne & cuyama states, steam loco balance is critical. And adding too much weight can cause a decrease in performance as it overwhelms the motor’s ability to move the engine.
Paul A. Cutler III