Hi All, I need help with understanding the brakeratio, (in Trainz) and how it xppressed and help with brake force. Is brake force exprresed in kN or PSI Pressure. The Question i have is: braking force?, PSI Pressure or somthing else?. What i undstand so far is: It's total car braking force divided by the total weight of the car on the rails. This is a US Railcar spec. Andrew
This is part of the motor container in the espec and here's what the Trainz Wiki has to say:
brakeratio
Type: Decimal
Desc: Coefficient between the pressure in brake cylinder and the brake force.
A rather confusing definition. From a straight mechanics view point: pressure in cylinder times piston area = force on the piston. That times a lever ratio = force on the brake shoe. That times a friction coefficient times the number of shoes = equivalent brake force applied at the rail head. Further down I indicate there is a limit to that force at which rolling ceases and sliding occurs resulting in a reduction in the braking force on the rail.
N3V typically uses metric units for config inputs - however coefficients in the motor container for resistance force calculations are an exception. But no indication that's the case here. In the espec pressure container pressure in the brake system is specified in grams/m³ (at least they say). That's mass density of the fluid (air) which is a function of temperature and pressure. In the scripting API N3V provide functions to convert this to psi or kiloPascals either gauge or absolute.
The wiki definition above does not sound like a ratio of total breaking force to total car weight to me so how did you determine that? For steel wheels rolling on steel rails the ratio you describe should not exceed 0.3 to 0.4 and that's based on the physics of rolling friction.
If you look at default epsec provided by N3V for locomotives they give the brakeratio tag a value of 55000. BTW that's N3V's default value for any espec that does not specify the brakeratio tag. So something does not look right.
The default cabin scripts have functions to convert this pressure to kPa or psi. I used the following based on them for psi and kPa.
psi abs = 14224.8 x g/m^3
psig = psi abs - 14.7
kPa abs = 98101.7 x g/m^3
kPag = Pa abs - 101.3
I haven't got a satisfactory answer yet as to how the 55000 fits in with the above so maybe I'll learn something new here - thanks for asking the question.
Bob Pearson
