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k4kfh / ZephyrCab

Drive a model train with prototypical controls, realistic behavior, and simulated physics; uses JMRI's WebSockets interface for layout connection
http://k4kfh.github.io/ZephyrCab
GNU Affero General Public License v3.0
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Physics of the Westinghouse Brake System #9

Open k4kfh opened 8 years ago

k4kfh commented 8 years ago

Discussion on the physics and math behind the brakes should take place here. Please feel free to comment; there is no wrong way to jump in and talk!

Findings So Far

To keep things organized, discoveries and necessary information for the development of the brake system will be kept in this post.

Useful Papers

Typical Brake Pads have a coefficient of friction of 0.4 and the following dimensions:

The air signal propagates along the train line at ~920fps under ideal circumstances. To account for the imperfections of typical equipment, we will assume 900fps is the standard rate for a change in air pressure to travel along the brake line.

k4kfh commented 8 years ago

http://stoptech.com/docs/media-center-documents/the-physics-of-braking-systems will probably be useful in brake physics math. It explains how to take the linear force on the brake pads and convert it to a torque working to stop the rotation of the axle.

k4kfh commented 8 years ago

One example of brake pad area can be found here:

Product Sale Page Product Data Sheet - Contains Area in cm^2

The brake pads being sold here, according to the data sheet, are available in 175cm^2 and 200cm^2 sizes.

k4kfh commented 8 years ago

Upon further searching, it seems that US railway brakes are more like the ones sold here. Another example can be found at New York Air Brake:

The message I'm getting from this is that the standard width is 3 3/8", the standard thickness is 2", and the length varies between 12" and 16" depending on the company and the applicaiton.

I have updated the standard sizes listed above to reflect these new numbers.

k4kfh commented 8 years ago

I found reservoir sizing info thanks to New York Air Brake.

Additionally, I found an excellent paper from the NMRA explaining several parts of the freight car brake system: http://www.nmra.org/sites/default/files/d9o.pdf

If NYAB's reservoir above (the auxiliary side) is treated as the standard size "main brake reservoir" on a freight car, using Al Krug's 2.5 ratio of brake reservoir to cylinder, the brake cylinder is 1000 cu. in., or 4 gallons.

k4kfh commented 8 years ago

According to Bruce Kingsley, older cast-iron brake shoes lose 10% of their braking power per minute due to heat losses.

k4kfh commented 8 years ago

This could be a useful forum thread: http://www.trainorders.com/discussion/read.php?1,2129770

On the old BN and most likely the new BNSF, the independent brake pressure with steel brake shoes was 45 psi. The composite brake shoes was 72 psi.

k4kfh commented 8 years ago

At least for the time being, most of the brake development is taking place in the psi-simple branch. Following Bruce Kingsley's advice, I am not using Boyle's law and/or actual pneumatic math in the simulation. There's no sense in constantly performing calculations that return virtually identical results, and using Boyle's law creates a need for many more functions and variables to keep track of the additional numbers. So I have opted to simple add and subtract PSI from variables, representing pipes, at a certain rate.