Easements

Previous | Contents | Index | Next

# 2.10.4 Easements

Easements are special sections of gradually curving track used to connect straight and curved tracks (or two curved tracks). Easements reduce the effects of sudden changes in track curves which can cause jerky motion and derailments.

Easements can be created every time you Join (Section 2.2.6) tracks, Extend (Section 2.2.7.4) a track or create a Tangent (Section 2.2.7.2) track.

When using easements, an error message will be generated if tracks have a radius that is too small or are too short for the transition curve.

The Easement dialog is invoked from the Options (Section 2.10) menu.

  Value - allows fine tuning of the easement parameters (restricted to values >= 0.5).

  R - minimum radius of the curved track.

  X - offset between a straight and curved track.

  L - length of the transition track.

  Radio button group with None, Sharp, Normal and Broad. Corresponding Values for these buttons are 0, 0.5, 1.0 and 2.0. Select None to turn easements off.

The values R, X and L are read-only.

These values indicate the worst case of joining a straight track with a curve of radius R. The two tracks are separated by the offset X while the easement curve extends for L/2 inches or centimeters to each side of the endpoints.

The formula used to draw easements is:

             x = l * l * l / (6 * R * L)
             r = L * R/l

where

- l is the distance along the tangent to the easement.
- R is the final radius of the easement.
- L is the total length of the easement along the tangent.
- x is the offset from the tangent at l.
- r is the radius of easement curve at l.

The Easement Button () on the Main Window (Section 3.1) changes its label to indicate the current easement value.

The following diagrams illustrates the R, X and L values and the resulting easement curve.

If curves with a radius larger than R or two curves (that bend in the same direction) are being connecting then the easement curve will be shorter and the offset smaller. If the computed offset is small then no easement is generated.

A curved track that bends in one direction and then bends in the opposite direction is an S-curve. This will generate the worst case easement which is two easement curves placed end to end.

Refer to instruction in section 2.10.4.1 when using sectional track.

- 2.10.4.1 Easements and Sectional Track