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Original Drive System

The flight sim motion cockpit drive software and control system was always going to be the biggest challenge for me. Proprietary motion cue software for flight simulators is probably available to buy. However the experience of other DIY motion platform builders encourages the view that at least having a go at developing the drive software and control elements myself makes sense as it would substantially reduce the cost of the overall system. So I've had a go at it.....

DIY 3DOF Motion Cockpit Drive System Schematic

So what's in the DIY system? (Schematic above - click for bigger image) - System Now Updated - See HERE

  • At its front end is FS9 and my Motion Drive software application running on the same PC.  The Motion Drive software is written in the AutoHotKey (AHK) scripting language and, with the aid of other free utilities, pulls the detailed aircraft flight motion parameters from FS2004, does the math to determine the appropriate movement cues and sends them down a serial port connection to a micro-controller based Signal Processor unit. The cues are output from the PC in the form of digital position demand signals for each movement DOF.

  • There is a DIY micro-controller based Signal Processor unit which receives the digital position demands sent from the PC. It also receives actual cockpit position feedback data from multi-turn potentiometers on the moving cockpit and using these two sets of data continuously converts the digital position demand data from the PC into analogue speed demand voltages needed to control the drive motors. These are output as three 0 to 5 Volt pulse width modulated (PWM) variable voltage signals which can be read directly by the high current motor speed controllers to drive the motors for each DOF. The Signal Processor unit is in effect a digital position to analogue speed demand converter.

  • There are three proprietary H-Bridge motor speed controllers which do the hard electrical work of driving the electric motors. These control the speed and direction of the motors as directed by the Signal Processor units and handle the full drive currents of the motors.

  • And finally there are multi-turn potentiometers mounted on each drive motor which provide feedback to the Signal Processor Unit, this tells it where each DOF actually is at any moment in time - these are essential because they allow the control system to decide in what direction and how fast to run each motor to get the cockpit to move where the Motion Drive software wants it.

There are other elements to the system too, such as a 9V regulated power supply to power the electronics and a 24V DC supply to power the motors but those listed above are the main working elements.

The drive system has evolved through a few variations in which I've changed or adjusted all the main elements including the software, micro-controller programming and the type of speed controllers used. It now performs well considering it is a DIY build with very little delay between the flight motions occurring in FS9 and the cockpit moving in response.  The Motion Drive software has been structured to allow the programming of the motion cues to be altered and updated - the motion cue programming for each DOF is in the form of a separate AHK script. If you know what you are doing this scripting can be customised in the OpenSource version to give the cues you are looking for if my programming attempts don't suit you.

DIY Motion Cockpit - Drive & Control BoardThe drive system has been relatively easy to build as it uses readily available components and easy to work with bread-boarding methods, electrical connections and wring. The high current side is a 24V DC system so there are no direct mains electricity connections and as such it represents a much reduced electrical hazard.

I've now managed to get the drive system running fairly well. Changes to the motor speed controllers have resulted in an electrically "quieter" system in which the micro-controllers are stable and run fairly reliably. Changes to the way in which data is read from FS9 have resulted in a much faster data transfer rate with new position demand signals now being sent to the drive system every 60ms - about 18 sets per second. And changes to the motion cue programming have given better cues and a better set of programming tools for further development. It is still a low cost DIY system however and will not be as robust as paid-for commercial drives. In particular its high frequency response is limited and demanded oscillations of frequency much above 1 Hz start to be lost - room for development!

Original SPU Design     Original Overall Wiring


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