1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Horsepower to velocity

  1. Aug 4, 2014 #1
    Hello, I'm building a model train control system, and would like to use real world values and physics to control the trains. I have these specifications about each model of train, and would like to know how I could relate given HP to velocity or Δacceleration.
    Given Values are located here: http://www.thedieselshop.us/Data%20EMD%20GP40.HTML
     
  2. jcsd
  3. Aug 4, 2014 #2

    phinds

    User Avatar
    Gold Member

    HP does not relate directly to velocity. You could put a 1 HP motor on a real train and it would go at approximately zero mph, or you could put one on a roller skate and it would go maybe 50 mph.
     
  4. Aug 4, 2014 #3
    Information

    What information would I need to calculate the velocity of this train?
     
  5. Aug 4, 2014 #4
    In the link to the "Given values" is says the speed is 65 mph, is that not what you want?

    Cheers,
    Terry
     
  6. Aug 4, 2014 #5
    I'm trying to make a momentum control. In a locomotive, there are 9 engine settings (0-8). Each setting is a different percentage of applied power. Under different loads (mass), the train will accelerate faster or slower. I want a way to calculate how much power is being applied to the train (real life), so that I can apply it to the scale model.
     
  7. Aug 4, 2014 #6
    OK. If you ignore rail gradient (a simplification to get started on this) the first thing to account for is rolling resistance. See here <http://en.wikipedia.org/wiki/Rolling_resistance> [Broken] for a coefficient. That will give a (more or less) constant force the engine must provide to maintain any speed. To accelerate you can use F=m.a, i.e for your mass and tractive force/effort you can calculate an acceleration. You will have to guess your tractive effort as a function of engine setting, maybe a simple ratio i.e 8=100%, 4=50% ??
    The other thing that affects all this is aero drag which is a drag force usually proportional to speed squared, and will really only play a part at higher speeds, but is you want to include it you will need to find a suitable drag coefficient for your train.
    The gradient force is the component of the weight (W.cos.theta) where theta is the angle to the horizontal.
    It all gets a bit complicated when you have some of the train on the level, some on the up grade, some on down grade etc!

    Cheers,
    Terry
     
    Last edited by a moderator: May 6, 2017
  8. Aug 4, 2014 #7
    Thank you so much for the starting point! I will continue to work on it!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...