HO scale horsepower measurements
Measuring scale horsepower for real
or what we really want to do
So how much pulling power do your locomotives really have? How much more do you get when you add locomotives to get a consist? Are newer locomotives better at pulling?
First things first: why do you want to know? I can answer that for myself and that answer is because no one else is doing it or talking about it.
Practical answer is that when you are planning a steep grade, can you pull your train up that grade? How can you keep statistics that will help you figure out that problem and record the information.
There is a simple tool called a Newton Spring Scale. It's a tube with a spring and a hook that is used in physics to find out how much force is needed to drag objects across a surface or up an incline.
If you're looking at the various scales you buy for a couple bucks, the one you will want to have first is the 5 Newton scale, usually the green one. The next one you want is the 30 Newton scale - you won't use that one a long until you have long trains to test.
In physics you generally hook on to something a drag is across a surface or up an incline and your partner reads the scale and you get a number in Newtons or grams.
On the model railroad, you use a twist tie and attach a dummy coupler to the hook. Then you put a nail or screw in your test track and put the loop at the top of the scale over it so it's laying on the track with the scale visible and the dummy coupler available to attach to a locomotive.
Next, hook on a locomotive and give it some power so it can stretch the scale until it's wheels slip and that will give you a reading you can record. Add more locomotives and start a horsepower chart. Measure them separately and in groups or consists. Reverse their directions and measure again. Rearrange your consists and make more measurements.
You should find that an average locomotive pulls around 1 Newton and more powerful locomotives pull almost 1.5 Newtons. Consider that 1.5 is 50% more power than 1 Newton.
Hook up a train of cars and use the scale to drag them. This tells you how many Newtons are needed to pull that train. Try it again on some grades and watch how much even a light weight train increases the force required dramatically.
We'll get into the conversions to change Newtons to torque and horsepower later. But for your own use, I suggest using and recording the Newton reading directly because it makes things super easy. Just so you know 1 Newton is about .22 pounds.
I made a video demonstrating an Athearn SDP40, GP50 and GP60 on the bench: