Tips & Tricks

Driving trailer    Adhesion

Driving trailer.

Many designers guess what power and force is needed for a driving trailer. You don't need to guess, it can be calculated.

In our example we have a pushing loco with  specifications:

Divide power and force by 1951 and the driving trailer forces the loco to do what it has to do. NumWheels is always 1 in a driving trailer.
MaxCurrent remains the same, it is only used for the meter in the cab and has no other effect.
A driving trailer does have pneumatic brakes so give it normal brakeforce.

Engine ( TA1034dt )  driving trailer
Wagon ( TA1034dt )
Type ( Electric )
MaxPower ( 3.28kW )
MaxForce ( 154N#0.15375kN )
MaxContinuousForce ( 154N )
MaxVelocity ( 130mph#220kmh )
MaxCurrent ( 2000A )
WheelRadius ( 0.625m )
Sanding ( 1e9mph )
NumWheels ( 1 )

Since a driving trailer doesn't have a motor it cannot use dynamic brakes, however it can activate the dynamic brakes in the loco (if present).
Add dynamic brakes to the driving trailer and divide DynamicBrakesMaximumForce by 1951. (150kN/1951=77N)

Adhesion

Adhesion is very important for acceleration and braking. The line: Adheasion ( 0.2 0.4 2 0 ) must be present in .eng and .wag files.
It is often said that Adhesion in .wag files is not important. It is not important for acceleration indeed, it is  important for brake effects.
Adhesion for Steamers is different. Adheasion ( 0.15 0.3 2 0 ) is normal for a steamer.
The other important line for adhesion is NumWheels in the engine part of the .eng file (second time in the .eng file).
NumWheels has nothing to do with number of wheels or axels. It is a variable used to define adhesion.

Calculating NumWheels
NumWheels =6.24*weight (imp. tons)/MaxForce (kN)

Example
Locomotive: weight 100t, maxForce 300kN
NumWheels=6.24*100/300=2.08

Increasing NumWheels will result in slipping.