Example of a loadout / loadin#

This is an worked example of how to model a loadout from a quay onto a barge using SPMTs. There is a ramp between the quay and the barge.


There are three main parts in this model:

  1. The quay

  2. The barge

  3. The cargo

  4. The ramp


Cargo is a rigid-body with a mass and cog and optionally a visual.

Each group of trailers is modelled using a frame and spmt-wheels. There are rigidly connected to the cargo at the center of the suspension-group.


The barge has a contact-shape (for the SPMTs) on its deck.

There is also a frame located on the deck where the ramp connects to the barge, but more on that later


The quay side is a frame with a contact-shape on its surface.


The ramp is a frame and is connected to the quay. It is allowed to rotate about its y-axis.

The ramp has a contact-shape for the SPMTs.

Connecting the ramp to the barge#

The connection between the ramp and the barge is a connection that can only apply a force in vertical direction. Because the ramp is already connected to the quay-side, we can not mathematically connect it to be barge as well. An option is to connect the barge to the ramp (instead of the ramp to the barge). That would work, but for this example we use a 6D connector.

A 6D connector connects two frames using springs. We can define springs for all six degrees of freedom. In this case we define a stiffness only in vertical direction.

So first we need to create two frames. One on the ramp and one on the barge. The 6D connector will pull these frames towards eachother. We set the frame on the barge as first frame and the one on the ramp as second frame:


For the stiffness only the vertical (Z) component is needed. This can be set to something high. It is important to define the frame on the barge as first frame because this determines the directions of the stiffness springs.

Moving the Cargo#

The easiest way to move the cargo is by settings its x-position. This dof can be left fixed.