Product Reviews

Working Model is an offshoot of the highly-regarded Interactive Physics software. It takes the program's intuitive, inverse-kinematic approach to modelling motion systems and refines it into a full-blown tool for industrial prototyping and analysis in the CAE (computer aided engineering) structural engineering area. The idea is to obviate the need for the production of expensive mechanical models before moving onto the manufacturing or construction stage.

Version 4.0 is broadly similar to 3.0, except that it's Power Mac-native, so it should be up to 10 times as fast as its predecessors. The core simulation engine has also been tweaked to give more accurate results, and there are a few more freebies such as AutoMotion, which integrates the program more closely with native AutoCAD files, and FlexBeam for the analysis of beam flexing under load.

The program's interface should be familiar to anyone who has used a CAD package with the usual collection of tools for refining the parts from which a model is constructed. Once an object is constructed you can alter parameters such as material, density and elastic modulus in the Properties window.

Other objects provided are the actuators - standard parts like springs, motors, dampers, and a series of mechanical joints such as pin, slot, and so on. The program's Smart Editor keeps track of each type of linkage, effector and actuator. And since this is a 2D workspace, individual objects can be assigned as collision detectors. New parametric tracking means the relative positions of joints remain constant, even if the connecting members change in size.

A series of gauges and sliders measure the model's responses and apply variable

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forces, charges, and so on. The response of the gauges (which usually takes the form of graphs of variables plotted against one another) are continually updated throughout the course of the simulation in draggable windows.

Initial set-up takes place in a drawing window known as the Workspace, a blank area in which only one force - gravity - is active. Here you can start drawing your system, adding forces and constraints at will. Working Model's drawing tools are fairly crude, but you can import DXF drawings from other CAD programs to use as parts. Hitting command-r will set the whole thing in motion.

The program's most powerful feature is its ability to link Working Model to other programs via Apple Events, and the built-in scripting language, Working Model Basic. Using the inter-application communication facilities, Working Model can output the data from its gauges to other programs. So, for example, a process being modelled may produce heat, the temperature of which can be calculated from supplied data in Excel. Excel can then take the temperature information, calculate how it affects the properties of materials in the simulation, and feed these new values back into Working Model, which can update the properties of constituent parts on the fly.

For real number-crunching analysis, Working Model can be linked to other dedicated packages such as MathWorks' MATLAB engineering modeller. In this way, the program becomes even more useful in the design of control systems.

The scripting language can be used to control simulations and vary parameters over the course of a simulation. In the simplest case, this could be used to vary the force on a member continually until some known condition is reached. Or it could be used to see how power output from an engine varies with connecting rod length.

The parametrics built into the Smart Editor would assure that all other components would maintain their relative positions and mechanical linkages. However, Working Model Basic is based heavily on Microsoft's Visual Basic, so it's not particularly intuitive.

Working Model is a useful tool, and its relatively high price shouldn't deter its target market. The big disappointment, though, is that there's a 3D version available - but not on the Mac.