Requirements by Geometry | Part 4 – Rhapsody and MagicDraw SysML Models

The emphasis in this blog series has been on “Requirements by Geometry”, the integration of requirements, architecture and 3D mechanical CAD models using MBSE. However, after publication of the first three parts of this series, readers expressed interest in the SysML models used in the example, so we are making them available, along with a brief overview of the key sections. Because we showed diagrams from the MagicDraw version in the previous parts, we will illustrate this part with diagrams created in IBM Rational Rhapsody.  Links to both models are given at the end of this post.

The overall design is for a configurable unmanned ground vehicle (UGV), similar to the designs often used for bomb disposal and other hazardous applications. It consists of an armored body/drive system and two interchangeable payloads, which attach to the top of the body at standard mechanical mounting points and electrical connectors.


Figure 1 Rhapsody SysML Block Definition Diagram, UGV primary systems

A SysML block definition diagram of the main body (Figure 1) contains the batteries, drive and communication systems, and electronics suite, as well as some of the structural elements. There are six independent drive systems, three on each side, connected by two tracks. The communications system allows for direct radio control and monitoring by a remote operator and a body-mounted speaker/microphone for audio communication with humans accompanying the UGV.

The UGV also contains three separate controllers within the body armor. The main Onboard Controller is responsible for movement and payload operation, with capability for some autonomy. The Communication Controller handles communications security and compression for remote operation. There is also an Accessory Controller for other internal systems. All these systems are tied together by data and power distribution busses, which extend out to the payload systems.


Figure 2 Rhapsody SysML Block Definition Diagram, UGV payload systems

Figure 2 describes the payload structure for a particular configuration of the UGV, with a 5-axis manipulator arm in the front position and a combination visual/IR camera array on a 2-axis arm in the rear position. SysML offers multiple ways to model a multi-configuration system, including specializations and product-line variants, but for this example, we are only modeling this specific configuration.

The structural block diagrams in Figure 1 and Figure 2 are only one view of the UGV. In parallel, we have created a series of internal block diagrams (IBDs) modeling the connections between parts and the flows along those connections.  In our example, we have four separate IBDs describing different sections of the top-level UGV block and two more for the individual payloads

  • UGV Electrical and Data Main IBD, covering power sources and controllers
  • UGV Electrical and Data Drive IBD, covering drive assemblies
  • UGV Electrical and Data Accessory IBD, covering communications and other systems
  • UGV Electrical and Data Payload IBD, covering payloads
  • 5Axis Manipulator01 IBD
  • Payload Multicamera01 IBD

The first and sixth of these are shown in Figure 3 and Figure 4, respectively.

Figure 3 Rhapsody SysML Internal Block Diagram, UGV controller and battery systems

Figure 4 Rhapsody SysML Internal Block Diagram, UGV multicamera payload system

An additional feature of this model’s development has been to illustrate the use of Syndeia to transform the SysML model shown above into a Simulink model, which could be used for simulation of the UGV’s operation and performance. The resulting Simulink model for the top-level UGV block is shown in Figure 5, incorporating the contents of the first four SysML IBDs above. Similar models are created for the two payload subsystems in the same transformation. Using Syndeia, all blocks, ports and connectors common to both models may be compared and updated on an ongoing basis to keep the models consistent as system development proceeds.


Figure 5 Simulink model, UGV system schematic (red labels added for clarity)

Download links to the model in both MagicDraw and Rhapsody format are available below. Bot models should open to index diagrams that show available BDD, IBD and REQ diagrams. In MagicDraw, one can double-click the icons to open the diagram. In Rhapsody, right-click the icon and select Hyperlink to go to the diagram directly.

SysML Models:

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Dirk Zwemer

Dr. Dirk Zwemer ( is President of Intercax LLC (Atlanta, GA), a supplier of MBE engineering software platforms like Syndeia and ParaMagic. He is an active teacher and consultant in the field and holds Level 4 Model Builder-Advanced certification as an OMG System Modeling Professional.