Servos & Simulation's Blog

How to Precisely Control a Motion Base Platforms with Software?

Posted by Rachel Baker on Jan 24, 2017 5:19:07 PM

How does one precisely control a motion base so that the user can know where the motion base is in space and can modify where the centroid of the moving platform coordinate system is in space? Servos and Simulation’s engineers were recently presented with that exact problem. How did we accomplish this? Read below.

Servos and Simulation’s engineers have designed, programmed, and tested precision software to control our motion bases. Since there is no closed form solution to a non-linear Steward Motion Platform such as the ones we design, a specially designed math model was developed to take the commanded roll, pitch, yaw, X (longitude), Y (lateral), and Z (vertical) commands from the host computer and sends control signals to each of the six non-linear actuators on the motion base to instruct the motion base to accurately follow the commands.  The software math model takes care of all the non-linearities of the cranks and pushrods.

In addition, the software allows the center of the moving platform coordinate system to be moved anywhere. For example, the center of the moving platform coordinate system can be moved 20 inches above the center of the moving platform, and roll and pitch will be centered about this new coordinate center in such applications for aircraft pilot feel and realism or off the nose in missile testing scenarios. With customization, the software can determine the location of a point(s) on a Unit Under Test in free space such as in antenna testing.

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As part of the Precision Control Software, Servos and Simulation’s engineers have also developed a Dynamic Software Evaluator package that reads the feedback position sensors from each of the six actuators and calculates the roll, pitch, yaw, X, Y, and Z position of the motion base. The roll, pitch, yaw, X, Y, and Z positions can be sent to the host computer. This allows the host computer to know exactly where the moving platform of the motion base is at any time. The Control Software has an iteration rate of 1KHz, but the host can send data anywhere from 200Hz up to the 1KHz. Typical bandwidth of the Control Software is around 3 to 5Hz.

A separate Server Module handles the exchange of data to and from the Host to the Precision Control Software typically via UDP. Through a special software command set, motion can be started or halted, communications turned off or on, moved to specific locations etc. via the Server Module. The Server Module is also responsible for reporting position data from the Dynamic Evaluator back to the Host.

These two software programs (Precision Controller and Dynamic Evaluator) are independent of each other but, they are memory mapped to work seamlessly between the Server Module, Precision Controller and Dynamic Evaluator.  Either one can be used (with the Server Module) by itself or used together.  As the Server Module is responsible for all communication, both software programs (Precision Controller and Dynamic Evaluator) are completely unaware of user inputs and rely solely on inputs derived from Host communications.

For a video of a motion base running under precision software control, check it out here 

For more information on our entire product and service line, please check out our web site at or email us at

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