Chances are that if you’ve been using SOLIDWORKS Motion Analysis with assemblies long enough, you have come across the error of “Fails to Converge.” Generally working with complex assemblies some adjustment to default SOLIDWORKS Motion settings will be required to properly converge your study. Here are a few tips and tricks that will resolve some of the difficulty you may have with setting up your kinematic or dynamic motion analysis. 

Accuracy 

Under the Motion Study Properties, you will find many adjustable options, namely Accuracy. 

This selection provides a trade-off between accuracy and performance of your study. The default numerical value is 0.001. This setting covers most studies, however, in some instances, this may need to be adjusted if sudden changes in force or motor magnitudes exist. 

Advanced Options

At first glance, the advance motion analysis options can look intimidating due to not understanding what these values change or have an impact on inside the study. Let’s break down each advanced setting and talk about their purpose. 

Integrator Type

• GSTIFF: Gear Stiffness integration method is the default selection to use in SOLIDWORKS Motion. Fat and accurate, this method provides the best results for the widest range of studies in SOLIDWORKS.
• WSTIFF: This type of integrator is similar to GSTIFF’s mathematical methods, however, the way that it calculates some coefficients differently. This causes sudden size changes to occur when discontinuous forces, motions or sudden events like contracts exist in the study. 
• S12_GSTIFF or S12: Stabilized Index Two (S12) method is a modified version of Gear Stiffness. This method is more accurate with smaller step sizes but eats up more computational resources due to decreased step sizes.

Maximum Iterations 

This setting controls how many times the SOLIDWORKS Motion solver will attempt to achieve a converged solution at every integrator step. If the value doesn’t converge on the initial step, it will reduce the size of the integrator step down to a smaller size and attempt to solve. The default value is set at 25 and generally doesn’t help resolve a problem you are having if the study does not converge. 

Initial Integrator Step Size

The name is just as it sounds, the first size the solve attempts to solve the solution. 

Minimum Integrator Step Size

This setting I like to consider as my maximum fidelity or resolution of accuracy for a converged solution. If a step in the solution keeps reiterating to a smaller value, the stop point will be this minimum value or the maximum iterations value of 25 we previously mentioned. Generally, another setting that shouldn’t need adjustment.

Maximum Integrator Step Size

Finally, we are in a setting that may be causing you some trouble. This is the most important value inside the advanced options with exception to your integrator type. This value controls the maximum size of each step. If you have seen say a ball or object go through a thin plate or something where the physics didn’t make sense in your study, its because this value is too large.

Jacobian Re-Evaluation 

Similarly viewed as to what the Stiffness Matrix is inside finite element analysis is, this setting checks the Jacobian matrix at every iteration by default. You can adjust this to a smaller value speeding up the studies time to solve, however, note that this could cause the integrator to fail if abrupt changes exist within the study.

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